Author(s): Wu, SZ; Wu, YF; Zeng, F; Tong, Z; Zhao, JQ
Title: Tunability of fluorescence property of a terbium-complex-containing polymer via incorporation of a transition-metal complex
Source: MACROMOLECULAR RAPID COMMUNICATIONS, 27 (12): 937-942 JUN 24 2006
Abstract: In this study, a terbium-complex monomer and transition-metal-complex monomers (Fe-III, Mn-II, and Ni-II complex monomers) are synthesized, and novel acrylate copolymers are then obtained through covalent attachment of the terbium complex and the transition-metal complex onto the macromolecular chain simultaneously. The copolymers developed herein present the characteristic fluorescence properties of the terbium(III) ion. The incorporation of an MnII complex into a Tb-III-containing polymer leads to greater fluorescence enhancement compared with the NiII complex, while the incorporation of the FeIII complex results in fluorescence quenching, thus the incorporation of different transition-metal complexes into the copolymers ensures tunability of the copolymer's fluorescence property.
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Record 2 of 70
Author(s): Ye, SQ; Wang, CY; Liu, XX; Tong, Z; Ren, B; Zeng, F
Title: New loading process and release properties of insulin from polysaccharide microcapsules fabricated through layer-by-layer assembly
Source: JOURNAL OF CONTROLLED RELEASE, 112 (1): 79-87 MAY 1 2006
Abstract: Polysaccharide multilayer rnicrocapsules were fabricated in aqueous media by the layer-by-layer self-assembly of chitosan (CHI) and sodium alginate (ALG) on melamine formaldehyde (MF) microparticles of 2.1 mu m diameter as templates, followed by removal of the templates through dissolving at low pH. The loading process was observed with the confocal laser scattering rnicroscope (CLSM) using fluorescence labeled insulin. Insulin was spontaneously loaded into the ALG/CHI microcapsules at pH below its isoelectric point of 5.5 where insulin was positively charged and the loading capacity increased with pH decreasing from 4.0 to 1.0. Because there exited a negatively charged complex of ALG/MF residues inside the microcapsules formed during the MF particle dissolution. A novel two-temperature loading procedure was proposed as loading at 20 degrees C for the first hour and at a higher loading temperature for the second hour. This procedure was very significant that increasing the second loading temperature from 20 to 60 degrees C not only increased the insulin loading capacity, but also slowed down its release rate. The release rate of insulin at pH 7.4 was found much faster than that at pH 1.4 due to the positive charges on the insulin. Cross-linking the ALG in the microcapsule shell with calcium ions (Ca2+) or re-sealing the microcapsules with additional layers also remarkably decreased the insulin release rate. The results provide a simple method to control the loading and release of protein molecules within these polysaccharide microcapsules. (c) 2006 Elsevier B.V. All rights reserved.
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Record 3 of 70
Author(s): Wu, SZ; Zeng, F; Zhu, HP; Tong, Z
Title: Formation of microscopic ordering and macroscopic patterns in solid polyacrylate-tetraoctylammonium bromide films
Source: MACROMOLECULES, 39 (7): 2606-2613 APR 4 2006
Abstract: Previously, we observed the rather unusual macroscopic patterns that formed in the solid films cast from organic solutions containing a surfactant tetraoctylammonium bromide (TOAB) and a chromophorecontaining polymer, and we proposed that the patterns resulted from the phase separation between the polymer-rich amorphous structures and the surfactant-rich mesomorphous structures (Macromolecules 2005, 38, 9266). In this study, it was found that the mesomorphous structure and macroscopic patterns could also form in the solid films cast from a mixture of toluene, TOAB, and polyacrylates with common polar groups like hydroxyl or carboxyl. It was also found that the higher polymer chain mobility as well as the balanced interactions between the three components in the system are crucial to the formation of mesomorphous structure and the macroscopic patterns. The patterns and the ordered mesomorphous structures were found to be destroyed at the elevated temperatures, further proving that the pattern formation needs the participation of solvent. The small-angle X-ray scattering (SAXS) investigations shows that different polar groups in the polymer chains cannot make any difference in SAXS profile in terms of peak position ratios, suggesting that the resultant mesomorphous structures do not change with the type of the polar groups in the polymer chains. These results prove that the ordered supramolecular structures can also be formed in the polymer-surfactant-organic solvent system, and the weak van der Waals interactions can lead to the formation of mesomorphous structures and macroscopic patterns.
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Record 4 of 70
Author(s): Zhao, DL; Ren, BY; Liu, SS; Liu, XX; Tong, Z
Title: A novel photoreversible poly(ferrocenylsilane) with coumarin side group: synthesis, characterization, and electrochemical activities
Source: CHEMICAL COMMUNICATIONS, (7): 779-781 FEB 21 2006
Abstract: A novel poly(ferrocenylsflane) with a coumarin side group was synthesized. This photoreversible polymer exhibits interesting electrochemical activities, which change with photodimerization and photoscission reactions of the coumarin moieties.
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Record 5 of 70
Author(s): Wang, CY; He, CY; Tong, Z; Liu, XX; Ren, BY; Zeng, F
Title: Combination of adsorption by porous CaCO3 microparticles and encapsulation by polyelectrolyte multilayer films for sustained drug delivery
Source: INTERNATIONAL JOURNAL OF PHARMACEUTICS, 308 (1-2): 160-167 FEB 3 2006
Abstract: Combination of adsorption by porous CaCO3 microparticles and encapsulation by polyelectrolyte multilayers via the layer-by-layer (LbL) self-assembly was proposed for sustained drug release. Firstly, porous calcium carbonate microparticles with an average diameter of 5 mu m were prepared for loading a model drug, ibuprofen (IBU). Adsorption of IBU into the pores was characterized by ultraviolet (UV), infrared (IR), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) experiment and X-ray diffraction (XRD). The adsorbed IBU amount Gamma was 45.1 mg/g for one-time adsorption and increased with increasing adsorption times. Finally, multilayer films of prolamine sulfate (PRO) and sodium poly(styrene sulfonate) (PSS) were formed on the IBU-loaded CaCO3 n-ftroparticles by the layer-by-layer self-assembly. Amorphous IBU loaded in the pores of the CaCO3 microparticles had a rapider release in the gastric fluid and a slower release in the intestinal fluid, compared with the bare IBU crystals. Polyelectrolyte multilayers assembled on the drug-loaded particles by the LbL reduced the release rate in both fluids. In this work, polymer/inorganic hybrid core-shell microcapsules were fabricated for controlled release of poorly water-soluble drugs. The porous inorganic particles are useful to load drugs in amorphous state and the polyelectrolyte multilayer films coated on the particle assuage the initial burst release. (c) 2005 Elsevier B.V. All rights reserved.
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Record 6 of 70
Author(s): Liu, SS; Wang, CY; Liu, XX; Tong, Z; Ren, BY; Zeng, F
Title: NRET from naphthalene labels in multilayer shell wall on melamine formaldehyde microparticles fabricated with layer-by-layer self-assembly to pyrene-labeled polyelectrolyte in solution
Source: EUROPEAN POLYMER JOURNAL, 42 (1): 161-166 JAN 2006
Abstract: Core-shell colloidal particles were prepared with the core of monodisperse melamine formaldehyde particles (MF) with a diameter of 3.5 mu m. The shell deposited on the core by the layer-by-layer (LbL) self-assembly was made with a copolymer ANp3 of 2-acrylamido-2-methylpropanesulfonate sodium (AMPS) and 3 mol% naphthalene label monomer and poly(diallyldimethylammonium chloride) (PD). Nonradiative energy transfer (NRET) from the naphthalene labels deposited on the MF particles to pyrene labels at a polyelectrolyte APy3, a copolymer of AMPS and 3 mol% pyrene label monomer, or to an ionic pyrene probe 1-pyrenemethylamine hydrochloride (PyMeA (.) HCl) in water was observed. The NRET efficiency was expressed as the emission intensity ratio I/I-0 of naphthalene with and without existence of pyrene in the surrounding solution. With increasing pyrene concentration, I/I-0 decreased down to about 0.2 and the mechanism for this NRET from the inner naphthalene label to the pyrene labels in solution is still ambiguous. (c) 2005 Elsevier Ltd. All rights reserved.
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Record 7 of 70
Author(s): Wu, SZ; Zeng, F; Zhu, HP; Luo, SJ; Ren, BY; Tong, Z
Title: Mesomorphous structure and macroscopic patterns formed by polymer and surfactant from organic solutions
Source: MACROMOLECULES, 38 (22): 9266-9274 NOV 1 2005
Abstract: Ordered mesomorphous structures were obtained from the ternary system of organic solvent, polymer, and surfactant, and this microscopic ordering could lead to unique water-wave-like macroscopic patterns in solid polymer-surfactant film. The mesomorphous structures and macroscopic patterns were obtained by dissolving a nonpolyelectrolyte polymer and cationic surfactant in organic solvents and casting the solutions on glass substrates. The patterns thus obtained are composed of concentric rings, and these concentric rings, with their diameters up to centimeters, alternatively consist of macroscopic convex ridges and concave valleys, with the former being amphormous phase and the latter being ordered mesomorphous one. This macroscopic patterning in a solid polymer-surfactant system could offer a new way for fabricating ordered supramolecular structure in macroscopic dimensions.
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Record 8 of 70
Author(s): Ye, SQ; Wang, CY; Liu, XX; Tong, Z
Title: Deposition temperature effect on release rate of indomethacin microcrystals from microcapsules of layer-by-layer assembled chitosan and alginate multilayer films
Source: JOURNAL OF CONTROLLED RELEASE, 106 (3): 319-328 SEP 2 2005
Abstract: Indomethacin (IDM) microcrystals sized 5 similar to 10 mu m were directly encapsulated with nature polysaccharides chitosan (CHI) and sodium alginate (ALG) through layer-by-layer (LbL) self-assembly. Due to partial dissolution of IDM in the deposition solution, the retention of the IDM microcrystals gradually decreased with increasing deposition times and became 47.7% as 10 layers of polysaccharides formed. The release rate of the IDM from the microcapsules was monitored with UV absorbance. The half release time t(1/2) of IDM in the microcapsule increased with the layer number and the initial burst phenomenon was relieved after encapsulation. It was found that added NaCl did not affect the release rate even up to 0.5 M of its concentration, while increasing the release temperature remarkably speeded up the release process. The prolonged release of the encapsulated IDM was still observed when the aqueous release solution containing 20 vol.% ethanol. It was very significant that increasing deposition temperature from 20 to 60 degrees C reduced the release rate efficiently, owing to the increase in multilayer thickness and formation of a more perfect multilayer film. This finding provides a new and simple method to control the permeability of the LbL assembled multilayer films. Because of the biodegradability of CHI and ALG and various methods to tune the release rate, the LbL self-assembly on drug microcrystals promises high potential for encapsulation used in controlled release. (c) 2005 Elsevier B.V. All rights reserved.
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Record 9 of 70
Author(s): Ye, SQ; Wang, CY; Liu, XX; Tong, Z
Title: Multilayer nanocapsules of polysaccharide chitosan and alginate through layer-by-layer assembly directly on PS nanoparticles for release
Source: JOURNAL OF BIOMATERIALS SCIENCE-POLYMER EDITION, 16 (7): 909-923 2005
Abstract: Polysaccharide multilayer nanocapsules have been fabricated in aqueous media by the layer-by-layer self-assembly of chitosan (CHI) and sodium alginate (ALG) on monodisperse polystyrene (PS) nanoparticles with a diameter of 180 nm as template, followed by removal of the templates through dissolving in THE The pH and added salt concentration of the polyelectrolyte deposition solutions were optimized to ensure the alternating deposition. Consequently, the most suitable pH values were found to be 6.0-8.0 for ALG and 3.5 for CHI and were used in the deposition. The concentration of added NaCl used in the adsorption solutions was 0.5 M, which led to an average thickness of about 13 nm for 5 bilayers of CHI/ALG shell-wall zeta-potential indicated the stepwise and alternating adsorption of CHI and ALG to form multilayer film on the PS nanoparticles. The characteristic bands of PS residue almost disappeared in the IR spectrum of the nanocapsule after dipped in THF, confirming thorough removal of PS templates from the core-shell particles. TEM, SEM and AFM were utilized to observe the nanocapsules of about 225 nm in diameter (by TEM). A hydrophilic drug model, acridine hydrochloride (AH), was chosen to investigate the loading and release properties of the nanocapsules. The positively charged AH spontaneously deposited into the capsule due to the electrostatic interaction with the negatively charged styrene sulfonate residues from the PS template inside the capsule. The rate of AH release became slightly slower when the capsule wall was cross-linked with glutaraldehyde, but the accumulative released amount for the crosslinked capsule was obviously reduced. These nanocapsules made from nature polysaccharides have a potential application in controlled drug release.
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Record 10 of 70
Author(s): Lu, L; Liu, XX; Dai, L; Tong, Z
Title: Difference in concentration dependence of relaxation critical exponent n for alginate solutions at sol-gel transition induced by calcium cations
Source: BIOMACROMOLECULES, 6 (4): 2150-2156 JUL-AUG 2005
Abstract: The sol-gel transition in aqueous alginate solutions induced by chelation with calcium cations from in situ release has been investigated with viscoelastic methods. Two alginate samples having different molecular weights (MW) were used over the concentration C-Alg of 2 similar to 6 wt % with different mole ratio f of Ca2+ to the alginate repeat unit. The gel pointf(gel) and relaxation critical exponent n were determined according to Winter's criterion, the later agrees well with that obtained from the relaxation modulus. The results indicate that the power law is valid for the dynamic relaxation at the gel point and the critical gel possesses the self-similarity in structure. With increasing C-Alg, f(gel) for the alginate with lower MW decreases dramatically and n is almost constant of about 0.71. In contrast, f(gel) for the higher MW alginate with is almost a constant and n decreases from 0.72 then levels off at 0.37 with increasing C-Alg, indicating that the concentration dependence of n varies with MW of alginate in the starting solution. The fractal dimension d(f) estimated from n suggests a denser structure in the critical gel of higher MW alginate. Either n or df has been found to follow one curve for the two samples if plotted against the number of cross-link junctions per polymer chain, which is proportional to the alginate MW.
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Record 11 of 70
Author(s): Ren, BY; Cheng, ZY; Tong, Z; Liu, XX; Wang, CY; Zeng, F
Title: Novel structure change in nonequimolar complexes of linear poly(ethylenimine) and octadecanoic acid: Effects of composition
Source: MACROMOLECULES, 38 (13): 5675-5680 JUN 28 2005
Abstract: Polymer-amphiphile complexes based on specific noncovalent interactions have received considerable attention in recent years due to its simple preparation and interesting properties. However, little attention has been paid to the complex composition effect on the crystal and mesomorphous structure of amphiphile side chains in nonequimolar polymer-amphiphile complexes. The structure of a series of nonequimolar linear poly(ethylenimine)-octadecanoic acid complexes, lPEI-OA-x, with the molar ratio x of OA to the lPEI amino group ranging from 0.66 to 1.45, was investigated with WAXD, SAXS, FTIR, DSC, fluorescence spectrum, and polarized optical microscope. Two crystalline modifications beta(O) (beta-orthorhombic) and beta(T) (beta-triclinic) of OA side chains have been found to coexist in the complexes varying with x, and only 8-10 CH2 groups in an OA molecule participate in the crystallization. The crystalline OA tails with amorphous lPEI form the lamella stacking structure. The complexes of x > 1.0 are predominant with beta(O) form and stacked into an end-to-end bilayer lamella with the long period of similar to 5.6 nm. While for the complexes of x < 1.0, the PT form is dominantly stacked in the interdigitating monolayer structure with the long period of similar to 2.8 nm. The fluorescence emission from pyrene-doped complexes indicates a decrease in the microenvironment polarity with increasing x. The thermotropic liquid crystal state has been observed from the complexes of x < 1.0 at temperatures above the melting point of the OA tail crystal. This study demonstrates that the crystalline and mesomorphous structures of polyelectrolyte-amphiphile complexes can be effectively tuned by changing the relative amount of bound amphiphiles. In other words, the stacking structure of amphiphile molecules depends on the amount of added binding polyelectrolytes.
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Record 12 of 70
Author(s): Sun, QL; Tong, Z; Wang, CY; Ren, BY; Liu, XX; Zeng, F
Title: Charge density threshold for LbL self-assembly and small molecule diffusion in polyelectrolyte multilayer films
Source: POLYMER, 46 (13): 4958-4966 JUN 17 2005
Abstract: Polyelectrolyte multilayer films were prepared via the layer-by-layer self-assembly using poly(diallydimethylammonium chloride) (PDADMAC) and pyrene labeled polyanions of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and N,N-dimethylacrylamide copolymers with different charge densities (AMPS mole fraction) F-AMPS = 0.20-0.999. Multilayer growth with alternating deposition from salt-free polyelectrolyte solutions was monitored by fluorescence intensity and film thickness, showing a charge density threshold between 0.574 and 0.711 for our polyanions, below which the multilayer cannot be formed due to desorption in the following depositions. For the fully charged polyanion, thickness of the multilayer film increased with increasing NaCl concentration in the deposition solution; while for other polyanions with lower F-AMPS, little growth in multilayer films was found when NaCl concentration was 0.02 mol/L or higher. The quenching rate of nitromethane to the pyrene label in the multilayer film was adopted to detect the chain density and permeability of these films. Decreasing the charge density, increasing the salt concentration and reducing the layer number will accelerate the quenching rate. The former two is due to the formation of a looser structure in the multilayer films at low charge density of the polyelectrolytes or high salt concentration in the deposition solutions, while the last one is mainly due to the reduction of diffusion distance. (c) 2005 Elsevier Ltd. All rights reserved.
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Record 13 of 70
Author(s): Liang, ZP; Wang, CY; Tong, Z; Ye, WH; Ye, SQ
Title: Bio-catalytic nanoparticles in multilayer assembled throt with urease immobilized gh layer-by-layer technique
Source: REACTIVE & FUNCTIONAL POLYMERS, 63 (1): 85-94 2005
Abstract: A novel core-shell colloid with multilayer for biocatalysis was elaborated by the layer-by-layer assembly technique. Urease was adsorbed in alternation with the oppositely charged polyelectrolytes onto polystyrene (PS) colloid nanoparticles as either polycation or polyanion switched by the solution pH. Microclectrophoresis, transmission electron microscopy (TEM) and UV-vis spectrum absorbance were employed to monitor the regular and stepwise growth of the multilayer films with the enzyme and counterpart polyclectrolytes. The colloid nanoparticles coated with negatively charged urease were found to be more stable than those coated with positively charged urease. The catalytic activity of the urease immobilized on the PS nanoparticles, having higher storage stability, was 23.67% of that for the free urease in aqueous solution. Addition of 0.05 M NaCl increased the activity of the immobilized urease by 65%. Coverage of synthetic polyelectrolyte layers on the urease layer reduced the activity of the immobilized urease. Therefore, by adding salts or covering with polyclectrolytes, we have achieved an enhancement or restraint of the bioactivity of immobilized enzyme, indicating a novel method for biotechnology. (c) 2005 Elsevier B.V. All rights reserved.
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Record 14 of 70
Author(s): Wu, SZ; Zeng, F; Zhu, HP; Tong, Z
Title: Energy and electron transfers in photosensitive chitosan
Source: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 127 (7): 2048-2049 FEB 23 2005
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Record 15 of 70
Author(s): He, CY; Liang, ZP; Wang, CY; Liu, XX; Tong, Z
Title: Immobilization of superoxide dismutase by layer-by-layer assembly on surface of PS colloid particles and their bioactivity
Source: CHEMICAL JOURNAL OF CHINESE UNIVERSITIES-CHINESE, 26 (1): 88-92 JAN 2005
Abstract: Novel enzyme multilayer films on the surface of polystyrene(PS) colloid particles was fabricated by layer-by-layer (LbL) self-assembly. Superoxide dismutase(SOD) was adsorbed on the PS particles as either polycation or polyanion switched by adjusting pH alternatingly with the oppositely charged polyelectrolytes. zeta-Potential and TEM results indicated the regular and stepwise growth of the multilayer structure. The amount of the immobilized SOD was estimated from the difference in SOD bioactivity of the supernatant after adsorption and SOD solution before adsorption by using the pyrogallol oxidation method. The immobilization amount of SOD was 12 and 51 IU when adsorbed in pH = 8.0 as a polyanion and in pH = 4.3 as a polycation, respectively. However, the relative activity of the former was 23.4% while that of the latter was 2.9%, compared to that of free SOD in aqueous solution. Anionic SOD was found to form more regular and smooth layers on the PS particle surface and cationic SOD to aggregate. By adjusting pH of the adsorption solution we can optimize the assembled status and bioactivity of particle-immobilized enzyme.
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Record 16 of 70
Author(s): Wang, CY; Ren, BY; Tong, Z; Zeng, F; Liu, XX; Wu, SZ; Liu, P
Title: Fluorescence observations on complex formation between linear and hyperbranched polyelectrolytes in dilute aqueous solutions
Source: EUROPEAN POLYMER JOURNAL, 41 (1): 185-191 JAN 2005
Abstract: The complexation between poly(ethylene imine) (PEI) and poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) or AMPS copolymers was investigated with the relative excimer emission intensity I-E/I-M of a cationic probe 1-pyrenemethylamine hydrochloride (PyMeA . HCl), fluorescence nonradiative energy transfer (NRET) I-Py/I-Np of naphthalene to pyrene labels, the fluorescence anisotropy r and I-E/I-M of pyrene labels. PEI was a hyperbranched weak polycation in acid solution, which formed complex with anionic polyelectrolytes due to the electrostatic attraction. The I-E/I-M of PyMeA . HCl probe decreased to zero, the intra-, intermolecular NRET I-Py/I-Np and I-E/I-M of pyrene labels on the AMPS copolymers reached their maxima when 7 was increased from 0 to 2.4, which was defined as the mole ratio of the amino group in PEI to the AMPS group in the polyanion. These facts indicated the formation of nonstoichiometric complex of the oppositely charged polyelectrolytes when chi = 2.4 at the concentration much lower than their overlap concentrations. The intermolecular aggregate appeared as indicated by an increase in the intermolecular I-Py/I-Np and r with chi up to 2.4 due to neutralizing and hydrophobizing the polyelectrolytes and the bridging effect of the PEI chain bound on different polyanion chains. At high pH, PEI became a neutral polymer and did not bind with the AMPS anion to form the complex as illustrated by the constant value of r for the pyrene labels attached to the AMPS polyanion as that without addition of PEI. The amino group in PEI quenched pyrene and naphthalene emission, resulting a decrease in both I-Np and I-Py. (C) 2004 Elsevier Ltd. All rights reserved.
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Record 17 of 70
Author(s): Tang, T; Zeng, F; Wu, SZ; Tong, Z; Luo, DB; She, WL
Title: Photo-induced birefringence and all-optical switching effect in azobenzene-grafted polyurethanes
Source: OPTICAL MATERIALS, 27 (3): 585-590 DEC 2004
Abstract: In this study, azobenzene-containing chromophore 4-N,N'-bis-(2-hydroxyethyl)amino-4'-nitro-azobenzene were synthesized by using 4-nitroaniline and m-tolyldiethanoamine. Then they were polymerized with toluene 2,4-di-isocyanate (TDI) and polyethylene glycol (PEG) in N,N'-dimethylformamide (DMF) to obtain novel polyurethanes which exhibit photo-induced birefringence properties. Polyols such as 1,4-dibutanol or tri-hydroxyl propane were introduced into the polyurethane structure to adjust the flexibility of the polymer chain segments. An experimental setup, in which the He-Ne lasers produced signal beams and Ar+ lasers the pump beams, was employed to investigate the photo-induced birefringence and optic-optic switching properties of these polyurethane materials. It is found that, with increasing pump beam power, the extent of both birefringence and optic switching response first slightly increased due to reorientation mechanism, and then decreased due to thermal effects. And the flexibility for the chain segment also has remarkable effects on birefringence extents and optic switching modulations. (C) 2004 Elsevier B.V. All rights reserved.
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Record 18 of 70
Author(s): Ren, BY; Tong, Z; Liu, XX; Wang, CY; Zeng, F
Title: Mesomorphous structure and properties of non-equimolar complexes of poly (ethylenimine) and perfluorooctanoic acid
Source: LANGMUIR, 20 (24): 10737-10743 NOV 23 2004
Abstract: A series of solid complexes, PEI-PFAO, made of poly(ethylenimine) (PEI) and perfluorooctanoic acid (PFOA) with different compositions were prepared through a "starving addition" method, where PFOA was fed into PEI solution at the molar ratio, phi(feed), of acid group to the amino group of PEI, never beyond unity. Wide-angle X-ray diffraction diagrams confirmed amorphous structure of these complexes. Small-angle X-ray scattering indicated two ordered mesomorphous structures of alpha and beta lamellar phases, with respective long periods of 2.29 and 1.15 nm in the complexes. By increasing the actual molar ratio, phi, of PFOA to the amino group of PEI, the complex structure was altered from alpha-phase dominant to beta-phase dominant. All complexes exhibited two thermal degradation processes induced by decomposition of the bound PFOA below 230 degreesC and PEI backbone at about 350 degreesC. The initiating degradation temperature, T-id, decreases with increasing phi due to the preferential degradation of the PFOA chain bound to the tertiary amino groups. The glass transition temperature, T-g, of the complex increases with phi up to the degradation of the complex of phi = 1. This increase in T-g with phi also supports an ordered alignment of the bound PFOA chains, which greatly restricts the PEI mobility. The solid surface tension, gamma(S), and critical surface tension, gamma(C), of the complex are between 15.4 and 16.8 mN/m and between 13.5 and 15.4 mN/m, respectively. The latter is very close to or even smaller than gamma(C) of PTFE (15 mN/m), suggesting the enrichment of CF2 and CF3 groups at the complex surfaces. The fact that the PEI-POFA complex combines high hydrophobicity with selective thermal degradation of bound fluorinated chains promises a potential of selective change and local functionalization of the surface in a well-controlled manner.
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Record 19 of 70
Author(s): Liang, ZP; Wang, CY; Sun, QL; Tong, Z
Title: Novel microcapsule fabricated by LbL nano self-assembly
Source: PROGRESS IN CHEMISTRY, 16 (4): 485-491 JUL 2004
Abstract: The article focuses on a novel and versatile technique of layer-by-layer deposition(LbL), developed for preparing nano- or micro- capsules. The strategy outlined readily affords precise control over the size, composition, construction, shape and wall thickness of the hollow capsules. Consequently these capsules have potential applications in biochemistry, pharmacy, controlled- release, cosmetic and catalyst.
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Record 20 of 70
Author(s): Liu, P; Zhang, YM; Feng, GJ; Hu, JH; Zhou, XP; Zhao, QH; Xu, YH; Tong, Z; Deng, WJ
Title: Synthesis and liquid crystal properties of a novel family of oligothiophene derivatives
Source: TETRAHEDRON, 60 (24): 5259-5264 JUN 7 2004
Abstract: In order to develop novel oligothiophene-based liquid crystals capable of hydrogen bonding, new terthiophene derivatives containing an alkylamide group, N,N'-dialkyl-5,5"-dichloro-2,2:5',2"-terthiophene-4,4"-dicarboxamide (DNC(n)DCl3T, n=8, 18), N,N"-dialkyl-5,5"-dibromo-2,2':5',2"-terthiophene-4,4"-dicarboxamide (DNC(n)DBr3T, n=5, 8, 16, 18), or N,N'-dialkyl-5,5"-diiodo-2,2:5',2"-terthiophene-4,4"-dica-rboxamide (DNC(n)DI3T, n=8, 18), were designed and synthesized, and their thermal behaviour was examined. It was found that DNC(18)DC13T, DNC(n)DBr3T and DNC(n)DBr3T (n=8, 16, 18) form a smectic A phase and that the alkyl chain length greatly affects liquid crystal phase formation. The absence of liquid crystallinity in the corresponding ester derivatives suggests that intermolecular hydrogen bonding also plays a role in the formation of a liquid crystal phases in the DNC(n)DBr3T system. (C) 2004 Elsevier Ltd. All rights reserved.
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Record 21 of 70
Author(s): Zeng, F; Wu, SZ; Tang, T; Sun, ZW; Wang, CY; Liu, XX; Tong, Z
Title: Preparation of colloidal crystals with polyhedral building blocks through post-polymerization
Source: COLLOID AND POLYMER SCIENCE, 282 (6): 651-655 APR 2004
Abstract: An alternative approach was adopted to prepare colloidal crystal with polyhedral building blocks. First, monodisperse polystyrene particles that contained about 30% wt of monomer were obtained by emulsifier-free emulsion polymerization at 38 degreesC. These monomer-containing particles were used to prepare colloidal crystal on the surface of dispersion, before the spherical particles in the colloidal crystals underwent deformation between two quartz plates at 75 degreesC for 40 min by interfacial tensions, and finally the deformed particles were "frozen" through post-polymerization.
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Record 22 of 70
Author(s): Tong, Z; Wang, CY; Ren, BY; Liu, XX; Zeng, F
Title: Binding of ionic surfactants on oppositely charged polyelectrolytes observed by fluorescence methods
Source: CHINESE JOURNAL OF POLYMER SCIENCE, 21 (6): 609-620 NOV 2003
Abstract: Our recent studies concerning the binding of ionic surfactants on oppositely charged polyelectrolytes observed with fluorescence techniques are reviewed. The cationic surfactants cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium chloride (DTAC), and nonionic surfactant octaethylene glycol monododecyl ether (C12E8) were allowed to bind on anionic poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and its pyrene and/or naphthalene labeled copolymers. The relative excimer emission intensity I-E/I-M of a cationic probe 1-pyrenemethylamine hydrochloride (PyMeA(.)HCl) and the non-radiative energy transfer (NRET) I-Pv/INp of naphthalene to pyrene for labeled polyelectrolytes were chosen to monitor the binding process and the conformation change of surfactant-bound polyelectrolytes. The 1:1 aggregation of polyelectrolyte-CTAB with respect to the charge was found as long as the CTAB concentration was slightly higher than its critical aggregation concentration (CAC). The intermolecular NRET indicated that the CTAB-bound polyelectrolytes aggregated together through the hydrophobic interaction between the CTAB tails. However, neither 1:1 polyelectrolyte-DTAC aggregation nor intermolecular aggregation of DTAC-bound polyelectrolyte was observed owing to its weaker hydrophobicity of 12 carbon atoms in the tail, which is shorter than that of CTAB. As known from the fluorescence results, nonionic surfactant C12E8 did not bind on the anionic polyelectrolytes, but the presence of PAMPS promoted the micelle formation for C12E8 at the CAC slightly below its critical micelle concentration (CMC). The solid complex of dansyl labeled AMPS copolymer-surfactant exhibited a decrease in local polarity with increasing charge density of the polyelectrolyte or with alkane tail length of the surfactant. SAXS suggested a lamella structure for the AMPS copolymer-surfactant solid complexes with a long period of 3.87 nm for CTAB and 3.04 nm for DTAC, respectively.
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Record 23 of 70
Author(s): Wu, SZ; Zeng, F; Yao, SL; Tong, Z; She, WL; Luo, DB
Title: All-optical switching effect in novel chiral biazobenzene polymer films
Source: MACROMOLECULES, 36 (25): 9292-9294 DEC 16 2003
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Record 24 of 70
Author(s): Wang, CY; Tong, Z; Zeng, F; Ren, BY; Liu, XX
Title: Binding on strong polyelectrolytes of mixed ionic and nonionic surfactants below their critical micelle concentration observed by fluorescence
Source: COLLOID AND POLYMER SCIENCE, 282 (2): 141-148 DEC 2003
Abstract: The binding of mixed surfactants of cationic cetyltrimethylammonium bromide (CTAB) and nonionic octaethylene glycol monododecyl ether (C12E8) on anionic polyelectrolyte poly[2-acrylamido-2-methylpropanesulfonic acid (PAMPS)] and fluorophore-labeled copolymers containing about 40 mol% of AMPS was investigated at different mole fractions, Y , of CTAB in the surfactant mixture. The excimer emission of the cationic probe 1-pyrenemethylamine hydrochloride (PyMeA.HCl), nonradiative energy transfer (NRET) between pyrene and naphthalene labels and I-1/ I-3 of the pyrene label were determined by varying the total surfactant concentration, c(Surf). The I-E/ I-M value of PyMeA.HCl firstly increases and then decreases to 0 with c(Surf), showing a maximum on every curve. The critical aggregation concentration of the mixed surfactants determined from the I-E/ I-M maximum decreased from 5x10(-5) to 1x10(-5) mol/l as Y increased from 0.1 to 0.50, and then leveled off as Y increased up to unity. And at least 5x10(-6) mol/l CTAB was required for the mixed surfactants to bind on the PAMPS cooperatively. Equimolar binding of CTAB on AMPS was formed at I-E/ I-M=0 when Y greater than or equal to0.25, while at Y =0.1 some CTAB molecules in the mixed micelle were directed to the water phase without binding with AMPS. Both the intramolecular and the intermolecular NRET increased and then decreased with c(Surf), having a maximum on each curve corresponding to the equimolar binding of CTAB and AMPS so long as Y >0, indicating the coiling of the chain and interchain aggregation upon bound surfactants. The I-Py/ I-Np value at the maximum decreased with decreasing Y because more nonionic surfactant C12E8 participated into the polyelectrolyte-mixed surfactant complexes together with bound CTAB.
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Record 25 of 70
Author(s): Lu, L; Liu, XX; Qian, LY; Tong, Z
Title: Sol-gel transition in aqueous alginate solutions induced by cupric cations observed with viscoelasticity
Source: POLYMER JOURNAL, 35 (10): 804-809 2003
Abstract: Sol-Gel transition was occurred in 2 wt% aqueous solutions of four alginate samples with different molecular weight M-w and the ratio M/G of repeat unit mannuronate (M) to guluronate (G) induced by adding cupric ions. The transition was monitored with dynamic moduli G' and G" in the linear region of viscoelasticity and the gel point was determined according to the Winter's criterion where the loss angle tan (5 became independent of frequency omega. The mole ratio of Cu2+ to the carboxyl group in alginate at gel point, f(gel), was higher for the samples with lower molecular weight than those with higher molecular weight without obvious M/G dependence. This suggested there was no M/G selection of Cu2+ complex formation with alginate. The relaxation critical exponent n for alginate samples with higher G content was lower than 0.5, meaning G' > G" for the critical gels with a denser network. The cupric ion number relevant to one alginate chain at the gel point, N-gel, was estimated from f(gel) M-n/M-0 and reflected the gel elasticity.
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Record 26 of 70
Author(s): Sun, QL; Wang, CY; Ren, BY; Liu, XX; Zeng, F; Liu, P; Tong, Z
Title: Effects of added salts on intra- and inter-molecular fluorescence NRET of sulfonate polyelectrolytes
Source: CHEMICAL JOURNAL OF CHINESE UNIVERSITIES-CHINESE, 24 (9): 1695-1699 SEP 10 2003
Abstract: Naphthalene and pyrene singly and doubly labeled polyelectrolytes were prepared by radical copolymerization of 2-acrylamido-2-methylpropane sulfonic acid(AMPS) from 5% to 99% (molar fraction) and N, N-dimethylacrylamide with the label monomers. Fluorescence nonradiative energy transfer (NRET) was measured in NaCl and CaCl2 aqueous solutions up to the concentration of 6 X 10(-3) mol/L. Intra- and inter-molecular NRET determined with doubly labeled samples and mixtures of singly labeled samples indicated that owing to the salt screening effect, increasing salt concentration enhanced the NRET and the enhancement of calcium cation was stronger than that of sodium cation. The normalized NRET E-n, defined as the NRET in salt solution relative to that in water for a given sample, showed that intramolecular E-n decreased with the increase of charge density F-AMPS in the samples with a maximum at F-AMPS approximate to 0.45. In contrast, the intermolecular E-n increased with the increase of F-AMPS, suggesting that there were inhomogeneous intermolecular aggregates in polyelectrolyte solutions due to the condensed counterions even at a concentrations lower than the overlap threshold c*.
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Record 27 of 70
Author(s): Liu, XX; Qian, LY; Shu, T; Lu, L; Tong, Z
Title: Sol-gel transition and gel point determination for aqueous solutions of sodium alginate
Source: ACTA POLYMERICA SINICA, (4): 484-488 AUG 2003
Abstract: The aqueous solutions of 4 sodium alginate samples with different molecular weights, molecular weight distributions and M/G ratios were characterized with GPC, elemental analysis, and H-1-NMR. The sol-gel transition was determined by monitoring the dynamic moduli of these solutions with increasing their concentration within the linear viscoelasticity region at 25 degreesC. This transition was found to obey the Winter and Chambon's relaxation modulus equation G(t). From the independency of tandelta on frequency omega, the concentration of the gel point c(gel) and the critical exponent for the sol-gel transition n were estimated. For all samples c(gel) is 7.6wt% similar to 8.0wt%, almost independent of molecular weight M-w, and n equals 0.32 similar to 0.38 for three samples with higher M-w and 0.61 for the sample with lower M-w. This finding indicates that physical gelation in aqueous solutions of sodium alginate is mainly induced by the interaction between repeat units of the macromolecules, and that the longer chains contribute more perfect crosslinking structure at the gel point.
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Record 28 of 70
Author(s): Sun, QL; Wang, CY; Ren, BY; Tong, Z; Liu, XX; Zeng, F; Liu, P
Title: Conformation of polyelectrolyte chains with sulfonate groups observed with fluorescent nonradiative energy transfer
Source: CHEMICAL JOURNAL OF CHINESE UNIVERSITIES-CHINESE, 24 (7): 1302-1306 JUL 2003
Abstract: Strong polyelectrolytes were prepared by copolymerization of 2-acrylamido-2-methylpropane sulfonic acid(AMPS) from 5% to 99%(charge densities) with N,N-dimethylacrylamide and lightly labeled by naphthalene and pyrene, respectively. The overlap mass concentration p* determined by intermolecular nonradiative energy transfer(NRET) decreased from 0.55 to 0.25 g/L with increasing the charge density of the samples and was about one order of magnitude smaller than that determined from the relative excimer emission. With increasing the charge density in dilute aqueous solution, the intermolecular NRET was first weakened till the charge density of about 30% and then enhanced. This phenomenon can be qualitatively interpreted in the framework of Manning's theory for counterion. condensation and tion of highly charged polyelectrolytes.
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Record 29 of 70
Author(s): Liu, P; Zhou, XP; Hu, JH; Zhao, QZ; Deng, WJ; Tong, Z; Xu, YH; Wan, MX
Title: Synthesis and liquid crystal properties of a novel class of oligothiophene derivatives
Source: ACTA CHIMICA SINICA, 61 (5): 774-779 MAY 2003
Abstract: With the aim of developing new oligothiophene-based liquid crystals involving hydrogen bonding, new terthiophene derivative's containing an alkylamide group, N,N'-dialkyl-5,5"-dibromo-2,2': 5', 2"-terthiophene-4,4"-dicarboxamide (DNC(n)DBr3T, n = 5, 8, 16, 18), were designed and synthesized, and their thermal behaviors were examined. While DNC(n)DBr3T compounds with n 16, 18 were found to form smectic A phase, DNC(5)DBr3T did not form liquid crystal phase. In addition to liquid crystal behavior, crystal polymorphism was also observed for DNC(16)DBr3T. It is shown that the alkyl chain length greatly affects liquid crystal phase formation. The absence of liquid crystallinity in the corresponding ester derivatives suggests that intermolecular hydrogen bonding plays a role in the formation of liquid crystal phase in the DNC(n)DBr3T system.
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Record 30 of 70
Author(s): Sun, QL; Ren, BY; Liu, XX; Zeng, F; Liu, P; Tong, Z
Title: Fluorescence study for the electrostatic interaction and aggregation in dilute polar solution of polyelectrolytes
Source: MACROMOLECULAR SYMPOSIA, 192: 251-264 MAR 2003
Abstract: Fluorescence decay and quenching of pyrene labels on copolymers of 2-acrylamido-2-methylpropanesulphonic acid (AMPS) and N,N-dimethylacryl-amide (DMAA) were observed in dilute salt-free aqueous solutions as a function of the mole fraction F-AMPS of AMPS from 0 to 0.896. Monoexponential and biexponential decays were found for the samples of F-AMPS < 0.35 and samples of F-AMPS > 0.35, respectively. The fast decay component is 80% and the averaged lifetime
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Record 31 of 70
Author(s): Sun, QL; Tong, Z; Wang, CY; Liu, XX; Zeng, F
Title: Fluorescence decay and quenching of pyrene labeled on sulfonate polyelectrolytes in salt-free aqueous solutions
Source: EUROPEAN POLYMER JOURNAL, 39 (4): 697-703 APR 2003
Abstract: Fluorescence decay and quenching of pyrene labels on copolymers of 2-acrylamido-2-methylpropanesulphonic acid (AMPS) and N, N-dimethylacrylamide were observed in dilute salt-free aqueous solutions as a function of the mole fraction F-AMPS of AMPS from 0 to 0.896. Monoexponential decay was found for the samples of FAmps < 0.35 and biexponential decay for the samples of F-AMPS > 0.35. The fast decay component is 80%, and the averaged lifetime (T) and lifetime T, of the fast decay is decreased with increasing FAmps. Quenching efficiency of Cu2+, I-, CH3NO2, and dinitrobenzene to the pyrene label was investigated in the framework of Stern-Volmer plot. With increasing FAmps the quenching efficiency of Cu2+ is increased while that of I- decreased. For the neutral quenchers, the quenching rate constant k(q) increases when F-AMPS < 0.449 then decreases, showing a decline of accessibility to the pyrene label. These results were interpreted consistently with the counterion condensation concept, where condensed counterions caused the polyelectrolyte chains to aggregate. The existence of less-polar "temporal aggregated domain" in highly charged polyelectrolytes appears to lead to the slower decay and lower accessibility of the pyrene labels. (C) 2002 Elsevier Science Ltd. All rights reserved.
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Record 32 of 70
Author(s): Guo, YQ; Tong, Z; Chen, MC; Liang, XH
Title: Solution miscibility and phase-change behavior of a polyethylene glycol-diacetate cellulose composite
Source: JOURNAL OF APPLIED POLYMER SCIENCE, 88 (3): 652-658 APR 18 2003
Abstract: Polyethylene glycol (PEG) and diacetate cellulose (CDA) exhibit good miscibility in acetone solution. The miscibility is related to the molecular weight of PEG, which increases as miscibility decreases. The phase-change behavior of PEG in composite with CDA prepared from the miscible solution was found to be completely different from that of pure PEG. When the PEG fraction in the composites was less than 85%, PEG within the composite did not melt into liquid; even when the temperature was 40degreesC higher than the melting point of PEG, the PEG-CDA composite exhibited solid-solid phase-change behavior. Thermal analysis indicated that the PEG-CDA composite had greater enthalpy and exhibited good thermal stability. The PEG-CDA composite that exhibited solid-solid phase-change behavior can be used as a new kind of phase-change material for thermal energy storage and temperature control. (C) 2003 Wiley Periodicals, Inc.
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Record 33 of 70
Author(s): Liu, XX; Qian, LY; Shu, T; Tong, Z
Title: Rheology characterization of sol-gel transition in aqueous alginate solutions induced by calcium cations through in situ release
Source: POLYMER, 44 (2): 407-412 JAN 2003
Abstract: Four alginate gels were prepared by in situ release of calcium cations from Ca-EDTA with gradual hydrolysis Of D-glucono-delta-lactone (GDL) in 3 wt% of aqueous solutions of four alginate samples with different M/G compositions, molecular weights, and molecular weight distributions. The sol-gel transition was monitored by measuring the dynamic mechanical spectroscopy in the linear region with variation in the mole ratio f of Ca2+ to the carboxyl group in the alginate. f(gel), the critical value off at the gel point, was determined according to the appearance of power law relaxation for the storage and loss moduli as proposed by Winter and Chambon. The critical exponent of relaxation moduli n for the power law was estimated from the loss tangent tan delta = G(II)/G(I) at the gel point which is independent of angular frequency. f(gel) for the two samples with higher M/G ratio is about 0.037 while that for the other two samples with lower M/G ratio is 0.049 and 0.060, suggesting that more Ca2+ cations are chelated into the 'egg-box' cavities formed by the G sequence to cross-link alginate chains with higher G content. The n value is higher than 0.5, showing that the Ca2+ induced alginate network is not perfect due to its low concentration. (C) 2002 Elsevier Science Ltd. All rights reserved.
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Record 34 of 70
Author(s): Wang, CY; Tong, Z; Zeng, F; Ren, BY; Liu, XX
Title: Simulation for binding equilibrium of ionic derivative of pyrene with polyelectrolyte
Source: ACTA POLYMERICA SINICA, (6): 729-733 DEC 2002
Abstract: Binding of cationic derivative of pyrene, pyrenemethylamine hydrochloride (PyMeA.HCl) to a polyanion, poly (2-(acrylamido)-2-methylpropanesulfonic acid) (PAMPS) in aqueous solutions was probed by the excimer fluorescence and simulated with a competitive binding equilibrium model. The relative emission intensity I-E/I-M of excimer to monomer displays a maximum with increasing PyMeA.HCl concentration and the binding stoichiometry for saturation binding is determined from the concentrations of PAMPS and PyMeA.HCl at the maximum. I-E/I-M obviously decreases with adding sodium chloride of about 10(-4) mol/L into the solution due to the. competitive binding of sodium and probe cations. In our binding equilibrium model; the binding of different cations on anionic polymer is considered as an equilibrated reversible process governed by the equilibrium constant. I-E and I-M are assumed to be proportional to the probe concentrations forming excimer and remaining individually, respectively. Calculated bound probe concentration c(DL) increases with total probe concentration c(DO) before binding saturation and the increasing rate becomes higher with higher value of the equilibrium constant. The simulated I-E/I-M as the above probe concentration ratio, also shows a maximum with increasing c(DO) at the same position as experimentally observed. By assuming. a comparable binding equilibrium constant for the cation of added salt, the, abrupt decrease in I-E/I-M observed with adding salt is reproduced by the simulation.. These results, indicate that the competitive binding of ionic pyrene probe on polyelectrolyte can be reasonably described by the binding equilibrium model.
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Record 35 of 70
Author(s): Zeng, F; Sun, ZW; Wang, CY; Ren, BY; Liu, XX; Tong, Z
Title: Fabrication of inverse opal via ordered highly charged colloidal spheres
Source: LANGMUIR, 18 (24): 9116-9120 NOV 26 2002
Abstract: A new and simple procedure for producing highly ordered three-dimensional colloidal crystalline template was developed, which employs latexes containing highly charged polystyrene spheres. The water on the surface of the latex was evaporated, causing the formation of close-packed colloidal crystals on the surface. The driving forces for the formation of close-packed crystal involve electrostatic interaction and lateral capillary force, and the ion diffusion during the evaporation is considered to be an important factor for the successful assembly of ordered structure on the latex surface. Then the sol-gel solution was infiltrated into the interstitial space of the prepared colloidal crystals through capillary effect, and ordered inverse opals were obtained by calcining the polystyrene beads. The inverse opal thus prepared has long-range ordering with its defect-free area extending to over 10 micrometers and covering thousands of pores.
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Record 36 of 70
Author(s): Wang, CY; Tong, Z; Zeng, F; Ren, BY; Liu, XX
Title: Fluorescence study of chromophore labeled strong polyelectrolyte bound with oppositely charged surfactant
Source: COLLOID AND POLYMER SCIENCE, 280 (9): 814-821 SEP 2002
Abstract: Four strong polyelectrolyte samples of 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS) and N,N-dimethylacrylamide (DMAA) were radically copolymerized with a single label of naphthalene or pyrene, with both labels and without label. containing, about 40 mol % AMPS. Fluorescence nonradiative energy transfer (NRET) IPy/INp, anisotropy r, I-1/I-3 and excimer emission I-E/I-M, of pyrene labels were observed in dilute aqueous solutions with and without cationic surfactant of cetyltrimethylammonium bromide (CTAB). The overlap concentration as determined as 3 g L from the appearance of intermolecular excimer. The variation of intra- and intermolecular NRET with total polyelectrolyte concentration showed that the charged chains preferentially interpenetrated each other rather than reduce their coil volume as their concentration beyond the overlap threshold. By binding with CTAB, the polyelectrolyte chain became more coiled as known from the reduced viscosity. The intramolecular NRET was dominant when [CTAB] less than or equal to 4x10(5) M and then the intermolecular NRET occurred at higher CTAB concentrations with hydrophobic aggregation between CTAB tails bound on different polyelectrolyte chains. The CTAB concentration corresponding to the maxima of I-Py/I-Np just is equal to the AMPS monomer concentration, indicating, the formation of 1:1 binding between surfactant and polyelectrolyte in very dilute solutions. Added salt of NaCl up to 0.1 M hardly affected the intramolecular NRET but affected the I-Py/I-Np value for the intermolecular NRET.
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Record 37 of 70
Author(s): Liu, P; Tong, Z; Deng, WJ
Title: Synthesis and gel-forming properties of a novel class or oligothiophene derivatives
Source: CHEMICAL JOURNAL OF CHINESE UNIVERSITIES-CHINESE, 23 (8): 1632-1637 AUG 2002
Abstract: In order to develop a novel class of low molecular-weight organic gels and to gain an insight into the relationship between molecular structure of gel-forming compounds and gel-forming properties, a novel family of low molecular-weight organic compounds containing terthiophene and tetrathiophene, N,N'-distearyl-5,5"-(2,2' : 5' 2"-torthiophene)dicarboxamide(DNC(n)DOc3T), N,N'-dialkyl-5,5"-(3,3"-dioctyl-2, 2' : 5' 2"-terthiophene) dicarboxamidc (DNC(n)DOc3T, n = 5, 8, 16, 18) and N, N'-distearyl-5, 5"-(3, 3"-dioctyl-2,2' - 5', 2" : 5" 2"-tetrathiophene) dicarboxamide (DNC(18)DOc4T), were designed and synthesized. Whereas DNC(18)3T and DNC(5)DOc3T did not form gels with organic solvents, DNC(n)DOc3T(n =8, 16, 18) and DNCgDOc4T were found to form gels with certain organic solvents. These are the first examples of low molecular-weight organic gels containing an oligothiophone moiety. It is of interest to note that while DNC(8)DOc3T forms opaque gels with alcohols, such as ethanol and isopropanol, DNC(16)DOc3T, DNC(18)DOc3T and DNC(18)DOc4T formed transparent gels with hydrocarbon solvents such as heptane, octane undecane and others. It is shown that the intermolecular hydrogen bonding and intermolecular interaction between the long alkyl chain in the N-alkylcarboxamide group as well as the incorporation of an alkyl group at the P-position of the thiophene ring play an important role for the formation of gels. The xerogel showed three-dimensional networks of fibrous bundle structure. DNC(18)DOc3T/benzonitrile gel and DNC(18)DOc4T/benzonitrile gel were found to function as a new type of electrochromic materials, exhibiting a reversible color changes on electrochemical oxidation and reduction.
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Record 38 of 70
Author(s): Zeng, F; Sun, ZW; Wu, SZ; Liu, XX; Wang, ZY; Tong, Z
Title: Preparation of highly charged, monodisperse nanospheres
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS, 203 (4): 673-677 MAR 15 2002
Abstract: A two stage shot growth emulsifier-free polymerization was applied to prepare styrene(St)/sodium styrenesulfonate (NaSS) latices. The latex particles prepared in the pure water medium were monodisperse and highly charged spheres, but their particle diameters were all higher than 120 nm. By using the two-stage shot growth copolymerization at 70 degreesC in the mixed reaction medium of water and acetone, we successfully prepared monodisperse, highly charged nanospheres with the smallest particle diameter of 89 nm. As the acetone content in the mixed reaction medium was increased to an acetone/H2O ratio of around 0.125, the particle diameter decreased to minimum, and then the particle diameters increased with increasing acetone content in the mixed reaction medium. The conversion-time curves for the first stage emulsifier-free copolymerization of St/NaSS in the mixed reaction medium with varied acetone contents show that the polymerization rate first increased with increasing acetone content, and then decreased. The enhanced rate of polymerization in the lower acetone content results from the increase in the number of primary particle in the reaction medium. As the acetone content was further increased, the solubility of St in the reaction medium further increased, making the copolymerization somewhat like the dispersion polymerization and thus causing increased particle size.
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Record 39 of 70
Author(s): Liu, P; Liang, D; Tong, Z; Liu, XX
Title: Synthesis and luminescence properties of novel europium and terbium complexes with triblock copolymer ligand
Source: MACROMOLECULES, 35 (5): 1487-1488 FEB 26 2002
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Record 40 of 70
Author(s): Wu, SZ; Zeng, F; Li, FX; Tong, Z
Title: Phase stability of the photoconductive polysiloxane-based photorefractive composites
Source: POLYMER-PLASTICS TECHNOLOGY AND ENGINEERING, 40 (5): 627-634 2001
Abstract: This article discusses the phase stability of the photoconductive poly siloxane-based photorefractive composites as studied by the light-scattering method. The photorefractive properties of the composites were studied by the two-beam coupling technique. The effects of the electric field on the photorefractive property of the composites were investigated as well. The phase stability was found to be dependent on the chromophore concentration and storage temperature. The two-beam coupling gain coefficient of the composites increased with increasing electric field and chromophore content.
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Record 41 of 70
Author(s): Liu, P; Tong, Z
Title: A novel greenish blue-emitting amorphous molecular material: 2,5-bis{4-[2-naphthyl(phenyl)amino]phenyl}thiophene
Source: CHINESE JOURNAL OF CHEMISTRY, 19 (10): 979-982 OCT 2001
Abstract: A novel greenish blue-emitting amorphous molecular material, 2,5-bis {4-[2-naphthyl(phenyl) amino] phenyl}thiophene (BN-pA-1T), was designed and synthesized. Its molecular properties, glass-forming property, and application to an organic EL device were investigated.
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Record 42 of 70
Author(s): Wang, CY; Sun, QL; Tong, Z; Liu, XX; Zeng, F; Gao, F
Title: Binding of ionic derivative of pyrene to strong polyelectrolyte
Source: CHEMICAL JOURNAL OF CHINESE UNIVERSITIES-CHINESE, 22 (7): 1265-1267 JUL 2001
Abstract: Binding of pyrene probe cation of 1-pyrenemethylamine hydrochloride (PyMeAH(+)) to sulfonate polyelectrolyte PAMPS in aqueous solution was investigated by the relative fluorescent intensity I-E/I-M of the excimer to monomer. The saturation amount of repeat unit AMPS for the polyelectrolyte bound to one PyMeAH(+) ion was about 2.5 estimated from the maximum on the curve of I-E/I-M vs. the probe concentrations. The increase of the ionic strength of the solution by adding salt or excess alkali ions of 10(-4) mol/L greatly reduced the I-E/I-M value. This fact suggested that the probe cation PyMeAH+ form a loose ion pair with the sulfonate anion on the polyelectrolyte.
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Record 43 of 70
Author(s): Wang, C; Sun, Q; Tong, Z; Liu, X; Zeng, F; Wu, S
Title: Interaction of cetyltrimethylammonium bromide and poly(2-(acrylamido)-2-methyl-propanesulfonic acid) in aqueous solutions determined by excimer fluorescence
Source: COLLOID AND POLYMER SCIENCE, 279 (7): 664-670 JUL 2001
Abstract: The binding interaction of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and anionic poly(2-(acrylamido)-2-methylpropanesulfonic acid) (PAMPS) in dilute aqueous solutions was studied using the excimer fluorescent emission of the cationic probe 1-pyrenemethylamine hydrochloride (PyMeA . HCl). In the absence of CTAB, the saturation binding of PyMeAH(+) on PAMPS is about 2.4 AMPS repeat units for one probe cation as determined by the relative emission intensity, I-E/I-M, of the excimer to monomer. With increasing CTAB concentration, I-E/ I-M firstly increases, reaches a maximum, then decreases to zero. The I-E/I-M maximum indicates a critical aggregation concentration (cac) of 10(-5) mol/l for CTAB in PAMPS solutions. The CTAB concentration at which I-E/I-M is zero is exactly equal to the PAMPS concentration, indicating that the probe cation is thoroughly excluded from the binding site of PAMPS by the CTAB cation and the equivalent stoichiometric aggregation is formed between CTAB and PAMPS. The blueshift of the excimer emission and the excitation spectra shows that the decrease of I-E/I-M with increasing CTAB concentration above the cac is caused mainly by the decrease of the static excimer.
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Record 44 of 70
Author(s): Yang, YY; Zeng, F; Xie, XL; Tong, Z; Liu, XX
Title: Phase separation and network formation in poly(vinyl methyl ether)/water solutions
Source: POLYMER JOURNAL, 33 (5): 399-403 2001
Abstract: Cloud point temperature T-clo and dynamic moduli were measured on aqueous solutions of two poly(vinyl methyl ether) (PVME) samples with molecular weight of 1.16 X 10(4) and 2.57 X 10(4), respectively and M-w/M-n = 1.84 for both samples. The T,I, at which the solution becomes turbid is at around 32.5 degreesC without obvious molecular weight dependence due to their broad molecular weight distribution. The frequency omega dependence of the storage modulus G' and loss modulus G" observed within linear viscoelasticity region indicates that the PVME/water solution exhibits homogeneous fluid behavior at 25 degreesC below T-clo, while shows a plateau zone for G' at 34 degreesC above T-clo, suggesting the appearance of network structure at this temperature. A sharp increase in G' and G" was observed at about 32.5 degreesC with increasing temperature of a PVME/water solution, indicating that at this temperature the network begin to form. These results imply that the network structure is formed accompanying the phase separation in PVME/water solutions due to the hydrophobic bonding between polymer chains.
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Record 45 of 70
Author(s): Ren, BY; Tong, Z; Gao, F; Liu, XX; Zeng, F
Title: Fluorescence and X-ray diffraction studies on binding and complexes of surfactants and dansylated polyelectrolytes with sulfonate groups
Source: POLYMER, 42 (17): 7291-7298 AUG 2001
Abstract: Binding of cationic surfactant cetyltrimethylammonium bromide (CTAB) on polyelectrolytes ADDan containing different amounts of sulfonate groups was studied by fluorescence spectrum of dansyl labels in aqueous solution. With increasing concentration of CTAB, there was an abrupt drop in the emission maximum wavelength lambda (em) and a sharp increase in the relative intensity RF defined as the ratio of emission in the presence of CTAB to that without CTAB. The critical aggregation concentration (cac) determined from the former was about 3 x 10(-5) mol/l without obvious dependence on polymer charge density. Solid complex films of polyelectrolyte-surfactant of CTAB or dodecyltrimethylammonium chloride (DTAC) were obtained by precipitation and their fluorescence anisotropy r indicated a high mobility of the dansyl chromophore. The r-value for ADDan-CTAB complexes obviously decreased as the charge density of the polyelectrolyte increased while the r for ADDan-DTAC complexes was slight decline, suggesting the contribution of alkyl tails of the surfactant to local mobility. It was the first time to find that the higher the charge density of the polyelectrolyte, the less polar the micellar aggregation of polyelectrolyte-surfactant complex becomes in dilute aqueous solution, which remains in the solid complex. SAXS of the solid complexes illustrated a long-range ordered lamella structure with the long period d of 3.87 and 3.04 nm for CTAB and DTAC complexes, respectively. (C) 2001 Published by Elsevier Science Ltd.
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Record 46 of 70
Author(s): Yang, YY; Zeng, F; Tong, Z; Liu, XX; Wu, SZ
Title: Phase separation in poly(N-isopropyl acrylamide)/water solutions. II. Salt effects on cloud-point curves and gelation
Source: JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 39 (9): 901-907 MAY 1 2001
Abstract: The cloud-point temperatures (T-clo's) of poly(N-isopropyl acrylamide) (PNI-PAM)/water solutions with NaCl, NaBr, or NaI were measured. All these salts reduced the T-clo's of PNIPAM/water solutions to different extents, in the following order: NaCl > NaBr > NaI. The higher the concentration of the added salt was, the more greatly T-clo dropped. A dynamic viscoelasticity investigation of the PNIPAM/water solutions with the salts indicated that during phase separation, the system changed from a homogeneous fluid into a physically crosslinked network, and the addition of salts also reduced the temperature at which this change began. The gelation temperature (T-gel,) and the scaling exponent of the PNIPAM/water solutions with NaBr were obtained with dynamic scaling theory, and T-gel was found to be close to T-clo. That the addition of salts to the solution decreased T-clo and T-gel to the same extent further proved that the network structure was formed with the phase separation in the PNIPAM/water solutions. (C) 2001 John Wiley & Sons, Inc.
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Record 47 of 70
Author(s): Zeng, F; Wu, SZ; Li, FX; Tong, Z
Title: Temperature dependence of the photorefractive property of PMMA-based composite
Source: EUROPEAN POLYMER JOURNAL, 37 (3): 459-462 MAR 2001
Abstract: Temperature dependence of the photorefractive (PR) property of poly(methyl methacrylate) (PMMA)-based polymer composite is presented. The electrooptic and PR properties of PMMA-based polymer composite have been studied in the temperature range of 22-60 degreesC. The effects of electric field on the PR property of the material have been investigated as well. The experimental results show that the electrooptic coefficient first increases slightly with the enhancing temperature and eventually saturates. This behavior is attributed to the temperature activated orientational mobility of the second-order nonlinear chromophores. Diffraction efficiency first increases with the increasing temperature, and then decreases as the temperature is further enhanced; while the diffraction efficiency increases with the increasing field strength. (C) 2001 Elsevier Science Ltd. All rights reserved.
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Record 48 of 70
Author(s): Ren, BY; Tong, Z; Gao, F; Liu, XX; Zeng, F
Title: Charge density effects on the fluorescence behavior of dansyl labels to strong polyelectrolytes
Source: POLYMER, 42 (5): 2001-2006 MAR 2001
Abstract: Fluorescent spectra of dansyl-labeled copolymers containing 2-acrylamido-2-methylpropanesulphonic acid (AMPS) and N,N-dimethyl-acrylamide (DMAA) with 0.2 mol% chromophore were observed in aqueous solution. Two emission bands appeared at 336 and 533 nm for protonated and unprotonated species of the label, respectively. These wavelengths were independent of the mole fraction F-AMPS of AMPS ranging from 0.186 to 0.738 but the relative intensity I-336/I-533 increased proportionally to F-AMPS. The locally excited emission (LE), b* band of the dansyl label was found at. 405 nm when the chromophore concentration was decreased below 1.45 x 10(-5) mol/l. With increasing charge density in the solid copolymer the b* band was strengthened and the a* band for the twisted intramolecular charge-transfer state was weakened and even disappeared owing to the existence of ion-pair attractions. It was found that for the copolymer in dimethyl sulfoxide (DMSO)/tetrahydrofuran (THF) mixtures the change in charge density did not alter the emission wavelength lambda (em) of the a* band. The charge density dependence fur the threshold of DMSO/THF composition, at which the relative emission intensity RF abruptly decreased, was similar to that inducing the volume phase transition in the corresponding polyelectrolyte gels. (C) 2000 Elsevier Science Ltd. All rights reserved.
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Record 49 of 70
Author(s): Tong, Z; Ren, BY; Gao, F
Title: Dual behavior of polyelectrolyte and ionomer for an ionizable polymer containing sulfonate groups in DMSO/THF mixtures
Source: POLYMER, 42 (1): 143-149 JAN 2001
Abstract: A dansyl labeled polyelectrolyte (ADDan60) was prepared by copolymerization of ionizable monomer 2-(acrylamido)-2-methylpropanesulphonic acid (AMPS) with N,N-dimethylacrylamide (DMAA) and N-[2-[[[5-(N,N-dimethylamino)-1-naphthalenyl]-sulfonyl]amino]ethyl]-2-propenamide (DANSAEP, 0.2 mol%). Reduced viscosity eta(sp)/c, electrolytic conductivity kappa, and fluorescent spectrum of ADDan60 in DMSO/THF mixtures were measured as functions of the volume fraction V-THF Of THF. In the region of V-THF < 0.7, the emission maximum lambda(em), relative intensity R-F of ADDan60 in DMSO/THF to that in DMSO, and anisotropy ratio r indicated that the polymer maintained its solvation layer not to change so much as the bulk solvent and exhibited a polyelectrolyte behavior, as observed from eta(sp)/c and kappa. Once V-THF was beyond 0.70, the solvation layer was changed leading to the ion pair formation in an avalanche manner, which induced chain aggregation and phase transition due to the dipole attraction. The results suggest a behavior transition in ionizable polymers from polyelectrolyte into ionomer induced by medium polarity. (C) 2000 Elsevier Science Ltd. All rights reserved.
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Record 50 of 70
Author(s): Zeng, F; Liu, XX; Tong, Z; Yang, YY; Wu, SZ
Title: Thermal reversible gelation during phase separation of poly(N-isopropyl acrylamide)/water solution
Source: SCIENCE IN CHINA SERIES B-CHEMISTRY, 43 (4): 428-434 AUG 2000
Abstract: By dynamic viscoelastic measurement for PNIPAM/water solution it has been found that below the phase separation temperature (about 32 degrees C), the system is homogeneous fluid; while upon being heated to about 32 degrees C, the solution undergoes phase separation and the storage modulus G' increases sharply and exceeds the loss modulus G", indicating the physical network formation during the phase separation. Based on the percolation model, the gel points T-gel were obtained by applying the dynamic seating theory (DST) and Winter's criterion. The critical exponent n was also obtained to be 0.79 through DST, which is different from 0.67, the critical point of chemically crosslinked network predicted through DST. The obtained n value reflects the special property of physical network being different from chemical network.
Record 51 of 70
Author(s): Gao, F; Yan, Y; Ren, BY; Tong, Z
Title: Fluorescence spectra of pyrene labeled polyelectrolytes with sulfonate groups in water and DMSO
Source: CHEMICAL JOURNAL OF CHINESE UNIVERSITIES-CHINESE, 21 (6): 976-979 JUN 2000
Abstract: 1-Pyrenylmethyl-methacrylamide (PyMA) was synthesized, and applied to copolymerizing with AMPS and DMAA to get a series of pyrene labeled polymers with sulfonate groups. The molar fraction of sulfonate monomer AMPS in these samples varies from 0. 032 6 to 0. 896. In DMSO and water, the profile of fluorescence spectrum of pyrene labeled polyelectrolytes is analogous to that of PyMA when F-AMPS < 0. 449, while the [0,1] emission peak abruptly increased as F-AMPS greater than or equal to 0. 449, The so-called polarity scale of pyrene, I-1/I-3 Of pyrene labeled polyelectrolytes in DMSO and in water decreases gradually with increasing FAMPS representing the charge density of the samples. I-1/I-3 also decreases gradually with the increase in polymer concentration in water. The results imply that there exists the hydrophobic aggregation through locally electrostatic attraction even in polyelectrolyte/polar solvent system, in contrast to the traditional polyelectrolyte theory. However, I-1/I-3 Of these polyelectrolytes remains almost a constant with increasing NaCl concentration of aqueous solution up to 0. 75 mol/L, indicating the electrostatic attraction cannot be simply screened.
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Record 52 of 70
Author(s): Gao, F; Ren, BY; Yan, Y; Tong, Z
Title: Changes in solvation state of strong polyelectrolytes in DMSO/THF mixtures
Source: ACTA PHYSICO-CHIMICA SINICA, 16 (5): 450-453 MAY 2000
Abstract: The fluorescent spectra of two series of sulfonated polyelectrolytes respectively labeled with dansyl and pyrenyl groups were determined as a function of volume fraction phi(THF) of THF in DMSO/THF mixed solvents. When phi(THF) less than or equal to 0.65, the maximum wavelength lambda(em) and the intensity RF relative to that in DMSO for a* band of dansylated samples, as well as I-1/I-3 for pyrene labeled samples varied slightly with increasing (phi(THF), indicating the capability of polyelectrolyte to maintain its chain solvation stable. As long as phi(THF) beyond 0.70, there was an abrupt drop in R-F and lambda(em) showing the sudden change in the chain solvation layer. I-1/I-3 decreased with an increase in the charge density of polyelectrolyte samples, suggesting the existence of aggregated structure even in pure DMSO.
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Record 53 of 70
Author(s): Tong, Z; Zeng, F; Zheng, X; Sato, T
Title: Inverse molecular weight dependence of cloud points for aqueous poly(N-isopropylacrylamide) solutions
Source: MACROMOLECULES, 32 (13): 4488-4490 JUN 29 1999
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Record 54 of 70
Author(s): Ren, BY; Gao, F; Tong, Z; Yan, Y
Title: Solvent polarity scale on the fluorescence spectra of a dansyl monomer copolymerizable in aqueous media
Source: CHEMICAL PHYSICS LETTERS, 307 (1-2): 55-61 JUN 25 1999
Abstract: A copolymerizable fluorescent monomer N-[2-[[[5 -(N,N-dimethylamino)-1-naphthalenyl] sulfonyl]-amino]ethyl]-2-propenamide (DANSAEP) was synthesized, which exhibits dual fluorescence due to the twisted intramolecular charge transfer in the excited state. The emission maximum lambda(em) shifts from 463.3 nm in n-hexane to 530.0 nm in water, showing solvent polarity dependence. The relations between lambda(em) and the conventional solvent polarity parameters E-T(30) or Z are linear, dividing solvents into protic and aprotic groups. Kamlet's linear solvation energy relationship gives a good description for lambda(em) as a solvent polarity scale. The increment of dipole moment Delta mu at the excited state was estimated as 5.09 D with the solvatochromic analysis. (C) 1999 Elsevier Science B.V. All rights reserved.
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Record 55 of 70
Author(s): Zeng, F; Tong, Z; Sato, T
Title: Molecular chain properties of poly( N-isopropyl acrylamide)
Source: SCIENCE IN CHINA SERIES B-CHEMISTRY, 42 (3): 290-297 JUN 1999
Abstract: A series of poly( N-isopropyl acrylamide) (PNIPAM) samples with molecular weight ranging from 2.23 x 10(4) to 130 x 10(4) and molecular weight distribution M-w/M-n less than or equal to 1.28 were obtained by free radical polymerization and repeat precipitation fractionation. The molecular weight M-w, second virial coefficient A(2) as well as the mean-square-root radius of gyration [S-2] for PNIPAM samples in tetrahydrofuran (THF) were determined by light scattering, and the relations were estimated at A(2) proportional to M-w(-0.25) and [S-2](1/2) = 1.56 x 10(-9) M-w(0.56). The intrinsic viscosity for THF: solution and methanol solution of PNIPAM samples was measured and the Mark-Houwink equations were obtained as [ eta] = 6.90 x 10(-5) M-0.73 (THF solution) and [eta] = 1.07 x 10(-4) M-0.71 (methanol solution). The above results indicate that both THF and methanol are good solvents for PNIPAM. The limit characteristic ratio C-infinity for PNIPAM in the two solutions was determined to be 10.6 by using Kurata-Stockmayer equation, indicating that the flexibility of PNIPAM chain is close to that of polystyrene. The intrinsic viscosity for the aqueous solution of PNIPAM was measured at 25-30.5 degrees C. The result demonstrates that PNIPAM chain begins to shrink at 25 degrees C, and from about 30 degrees C onward the molecular chain shrinks much more sharply till the solution becomes macroscopically unstable at 32 degrees C.
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Record 56 of 70
Author(s): Liu, XX; Tong, Z; Gao, F
Title: Novel shrinking-swelling hysteresis in DMSO/THF mixtures of copolymer gels containing sulphonate groups
Source: POLYMER INTERNATIONAL, 47 (2): 215-220 OCT 1998
Abstract: The swelling volume of copolymer gels made from 2-(acrylamido)-2-methylpropanesulphonic acid (AMPS; electrolyte monomer), N,N-dimethylacrylamide (DMAA; comonomer) and N,N'-methylenebis(acrylamide) (BIS; crosslinker) was measured in mixtures of two organic solvents, dimethyl sulphoxide (DMSO) and tetrahydrofuran (THF) at 25 degrees C. A volume phase transition was observed in the gels having 43.18 mol% AMPS with different counterions K+, Na+ and H+, when the THF concentration in the mixture increased beyond a certain value. We observed a swelling-hysteresis between the shrinking and swelling curves, i.e. more DMSO was required to make a shrunk gel start to swell again than to cause the volume shrinking. This hysteresis stems from the formation of ion pairs and/or multiplets in the ionizable gels when the medium polarity is decreased. An excess of DMSO is required to reduce the ionization energy for making the shrunk gel swell again in the DMSO/THF mixture. These aggregates and multiplets do not seem to be entirely removed by the swelling process and act as additional physical crosslinks, so that the DMSO concentration required to induce the shrunk gel to swell becomes higher in the next swelling process, showing another hysteresis. The release of bound water from the solvating layer after shrinkage may be another possible reason for this hysteresis. (C) 1998 Society of Chemical Industry.
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Record 57 of 70
Author(s): Zheng, X; Tong, Z; Xie, XL; Zeng, F
Title: Phase separation in poly(N-isopropyl acrylamide) water solutions I. Cloud point curves and microgelation
Source: POLYMER JOURNAL, 30 (4): 284-288 1998
Abstract: Cloud point curve was determined on binary and ternary aqueous solutions of several fractionated poly(N-isopropyl acrylamide) (PNIPA) samples with the molecular weight M-eta = 11.3 x 10(4)-210 x 10(4) and the molecular weight distribution M-w/M-n = 1.21-1.62. In both the binary and ternary solutions, the cloud point temperature T-clo slightly increases viith the increase in molecular weight of PNIPA. The concentration dependence for the binary solution is weak while it becomes obvious for the ternary solution containing two different PNIPA samples in water; i.e., the molecular weight distribution alters the shape of the cloud point currie. The storage and loss moduli G' and G " for the PNIPA sample of M-eta = 210 x 10(4) in water at concentrations 2.2-8.5 wt% were measured at several temperatures encompassing the T-clo. The results indicate that the solution changes from a homogeneous fluid into viscoelastic microgels suspended in a liquid phase during the phase separation. This physical network is considered to be jointed via the intermolecular hydrophobic bonding between the N-isopropyl groups, which may provide a model system for the structure change or proteins induced in the denaturation.
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Record 58 of 70
Author(s): Liu, XX; Hu, O; Tong, Z; Gu, J
Title: Volume phase transition of copolymerized sulfonic acid gels in mixed organic solvents
Source: CHEMICAL JOURNAL OF CHINESE UNIVERSITIES-CHINESE, 19 (3): 460-463 MAR 1998
Abstract: Radical copolymerization of 2-acrylamido-2-methylpropane sulfonic acid(AMPS) with 2-hydropropyl methacrylate (HPM) was conducted in ethylene glycol/water (1:1 in weight) at 70 degrees C. The azeotropic composition was found at the monomer molar ratio of AMPS/HPM as 8/2, Three sulfonic gels were prepared at this composition with the crosslinker N,N'-methylene-bis(acrylamide) of 2%, 3% and 5% (molar percentage), and referred to as G02, G03 and G05, respectively, As expected from their polyelectrolyte nature, these gels swell in dimethyl sulfoxide(DMSO) but shrink in tetrahydrofuran(THF) at 25 degrees C, The volume phase transition takes place in the G02 and G03 swollen in DMSO/THF mixtures when THF content is increased beyond 55%similar to 60% (volume ratio), In ethanol/THF mixture, however, no volume phase transition was found though the gel still shrunk with increasing THF. The dipole-dipole interaction model in less-polar medium was adopted to interpret these results with the concept of preferential solvation.
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Record 59 of 70
Author(s): Zeng, F; Zheng, X; Tong, Z
Title: Network formation in poly(N-isopropyl acrylamide) water solutions during phase separation
Source: POLYMER, 39 (5): 1249-1251 MAR 1998
Abstract: Evidence from dynamic viscoelasticity measurements has been found for reversible network formation via the physical association of hydrophobic side-groups during phase separation at around 33 degrees C in a 1.22 wt.% aqueous solution of poly(hi-isopropyl acrylamide) (PNIPA) having a molecular weight of 2.1 x 10(6). The frequency omega dependence of the dynamic storage and loss moduli G' and G " showed homogeneous fluid behaviour at 25 degrees C, while at 35 degrees C, a plateau zone was found in the G' versus omega curve and G' was larger than G ", indicating the formation of a network. The increase in G' was instantaneous at the phase separation temperature and was not a progressive process. (C) 1997 Elsevier Science Ltd. All rights reserved.
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Record 60 of 70
Author(s): Zeng, F; Tong, Z; Yang, XZ
Title: Differences in vibrational spectra of poly(N-isopropyl acrylamide) from water solution before and after phase separation
Source: EUROPEAN POLYMER JOURNAL, 33 (9): 1553-1556 SEP 1997
Abstract: Two poly(N-isopropyl acrylamide) (PNIPA) samples were prepared by drying the 5 wt% water solution of PNIPA either at 25 degrees C without phase separation (referred to as I-B) or at 38 degrees C after phase separation (I-C). PNIPA sample I-A was directly cast from its acetone solution. The IR absorbance of CH3 asymmetric stretch related to the CH2 symmetric stretch is higher for the samples I-C and I-A when compared with the same absorbance ratio for the sample I-B. At the same time, the vibration frequencies of amide I and II for I-C are similar to those for I-A, but obviously different from those for I-B. Raman scattering intensities corresponding to the CH3 and CH2 vibrations also depend on the sample preparation methods. A simple model simulation suggests that the above observations would be attributed to the configuration change in the side chain of the amide group. The trans isomer is dominant in sample I-B and cis isomer dominant in samples I-A and I-C. (C) 1997 Elsevier Science Ltd.
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Record 61 of 70
Author(s): Zeng, F; Tong, Z; Feng, HQ
Title: Nmr investigation of phase separation in poly(N-isopropyl acrylamide)/water solutions
Source: POLYMER, 38 (22): 5539-5544 OCT 1997
Abstract: H-1 and C-13 n.m.r. spectra of poly(N-isopropyl acrylamide) (PNIPA) in D2O and CDCl3 were measured at several temperatures encompassing the lower critical solution temperature (LCST) about 32 degrees C of the PNIPA/water solution, using a high resolution n.m.r. spectrometer (500 MHz for proton). The PNIPA/CDCl3 is homogeneous in the temperature ranging from 16 to 36 degrees C and the hydrogen bonds of the amide groups are weakened by the solvation of CDCl3 and broken by heating. In the PNIPA/D2O solution, the proton and C-13 spectra are well resolved below the LCST. Whereas at temperatures above the LCST, all the resonance peaks except that for water proton became broad and the spectra lost their fine structure. The integral intensity of the water proton relative to that of the lone proton in the isopropyl group increases with increasing temperature, suggesting that some water molecules appear to be released out of the hydrated shells around the polymer chains. When the solution was heated from 22 to 35 degrees C, the spin-lattice relaxation time T-1 for the proton of the methyl group in the isopropyl residue increased, while that for the protons of the methylene and methyne groups of the backbone chain decreased. This indicates that during heating the relaxation of the isopropyl side chain slows down and that of the main chain speeds up. The phase separation was qualitatively interpreted with the Nemethy-Scheraga model for the hydrophobic bonding. (C) 1997 Elsevier Science Ltd.
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Record 62 of 70
Author(s): Liu, XX; Hu, O; Tong, Z
Title: Viscosity behavior of polyelectrolyte copolymers containing sulfonate groups in mixed organic solvents
Source: JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 35 (9): 1433-1438 JUL 15 1997
Abstract: Copolymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS, monomer I)with 2-hydropropyl methacrylate (HPM, monomer 2) was conducted in ethylene glycol/water (1 : 1 in weight) at 70 degrees C. The reactivity ratios estimated from the copolymer composition at low conversion are r(1) = 2.31 +/- 0.25 and r(2) = 11.70 +/- 1.05. The azeotropic composition was found at the monomer mole ratio AMPS/HPM equal to 8/2. Viscosity of these copolymers was measured in dimethyl sulfoxide (DMSO) and DMSO/tetrahydrofuran (THF) mixed solvent at 25 +/- 0.05 degrees C. Polyeletrolyte behavior was observed for all the copolymers, even in the mixed solvent containing 65 wt % of THF. The reduced viscosity at constant polymer concentration decreased with increasing THF content in the mixed solvent. The copolymers having AMPS repeat units more than 42 mol % precipitated in the mixed solvent when the THF was beyond 68 wt %. The viscosity reduction and precipitation in the copolymer solutions with increasing THF can be attributed to the dipole-dipole attraction between ion-pairs formed in less-polar medium. This is helpful in understanding the volume phase transition in highly charged hydrogels caused by mixing solvents. (C) 1997 John Wiley & Sons, Inc.
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Record 63 of 70
Author(s): Liu, XX; Tong, Z; Cao, XW; Hu, O
Title: Volume phase transition of polyelectrolyte gels in dimethyl sulfoxide/tetrahydrofuran mixtures
Source: POLYMER, 37 (26): 5947-5949 DEC 1996
Abstract: Copolymer gels were prepared from 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS), N,N-dimethylacrylamide (DMAA, comonomer) and N,N'-methylenebis(acrylamide) (BIS). The mole fraction of AMPS were 0.2674 and 0.4318, respectively, with the same BIS mole fraction of 0.013. These gels with counterions H+, Na+, and K+ were swollen at 25 degrees C in mixtures of dimethyl sulfoxide (DMSO) and tetrahydrofuran (THF). A volume phase transition was observed at the THF volume fraction of about 0.58, indicating that the volume phase transition in a polyelectrolyte gel occurs when the medium polarity decreases sufficiently for ion-pair formation. On changing the counterion, the fraction of DMSO in the solvent mixture which is required to initiate swelling decreases in the order Na+, H+, and K+, the same as for counterion condensation in identical gels. Copyright (C) 1996 Elsevier Science Ltd.
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Record 64 of 70
Author(s): TONG, Z; YI, YH; LIU, XX
Title: COPOLYMERIZATION OF 2-ACRYLAMIDO-2-METHYLPROPANE SULFONIC-ACID WITH 2-HYDROPROPYL METHACRYLATE
Source: POLYMER BULLETIN, 35 (5): 591-597 NOV 1995
Abstract: Copolymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS, monomer 1) with 2-hydropropyl methacrylate (monomer 2) was conducted in pure water at 80 degrees C. The reactivity ratios estimated from the compositional data of the copolymers at low conversion are r(1)=0.04+/-0.04 and r(2)=6.30+/-0.48, and values of Q(1) and e(1) are 0.16 and 1.37, respectively. Copolymer microstructure predicted by statistical calculation shows mean sequence length of M(1) shorter than 2. These results can be attributed to the strong repulsion between the ionized chain radical and charged monomer of AMPS.
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Record 65 of 70
Author(s): LIU, XX; TONG, Z; HU, O
Title: SWELLING EQUILIBRIA OF HYDROGELS WITH SULFONATE GROUPS IN WATER AND IN AQUEOUS SALT-SOLUTIONS
Source: MACROMOLECULES, 28 (11): 3813-3817 MAY 22 1995
Abstract: Swelling equilibria for five sulfonate gels were carried out in water and in aqueous solutions of NaCl, KCl, CaCl2, Na2SO4, K2SO4, and CaSO4 with concentrations ranging from 10(-6) to 1 M;at 25 degrees C. These samples were the same DS series of gels used in our previous paper, which were copolymerized using the ionizable monomer 2-(acrylamido)-2-methylpropanesulfonic acid (AMPS), the comonomer N,N-dimethylacrylamide (DMMA), and the cross-linker N,N'-methylenebis(acrylamide) (BIS). The mole fraction f of AMPS in the gel network ranged from 0.0899 to 0.6076. Before swelling the proton in the gel was exchanged by neutralization to the same cation as that in the salt solution to be equilibrated. The swelling capacity increases with increased charge density in the gels and with decreasing salt concentration. NaCl or KCl solutions more concentrated than 1 M were needed to screen the charge interaction in the DS50 (f = 0.4318) and DS70 (f = 0.6076) samples. The swelling ratios of DS50 and DS70 gels swollen in pure water acid in the salt solutions were found to depend on the counterion species in the increasing sequence as Ca2+, Na+, and K+, which cannot be interpreted with the concept of ionic strength. These phenomena seem to be the results of counterion condensation.
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Record 66 of 70
Author(s): TONG, Z; MEISSNER, K; WOLF, BA
Title: PHASE-EQUILIBRIA AND INTERFACIAL-TENSION BETWEEN COEXISTING PHASES FOR THE SYSTEM WATER 2-PROPANOL POLY(ACRYLIC ACID)
Source: MACROMOLECULAR CHEMISTRY AND PHYSICS, 196 (2): 521-527 FEB 1995
Abstract: The cloud point curve, tie-lines and interfacial tensions were measured for solutions of 50 mol-% neutralized (counter-ion Na-circle plus) poly(arylic acid) (mass-average molar mass (M) over bar(w) = 9 700 g/mol; polydispersity index (M) over bar(w)/(M) over bar(w) = 2,0) in the mixed solvent water/2-propanol at 30 degrees C. Due to the non-uniformity of the polymer, the end-points of the tie-lines are not situated on the cloud-point curve. The interfacial tension sigma - determined by means of the spinning drop method - increases in sigmoidal manner with R(t1), the length of the tie-line, expressed in terms of weight fractions. An evaluation of these data in a double-logarithmic plot of sigma.M(-0,5) versus R(t1) yields a critical exponent of 4,23 as compared with 3,85 in the case of binary systems. The dependence of a on w(w), the over-all weight fraction of water in the mixture, can also be expressed as a power-law choosing (w(cw)-w(w))/w(cw) as the concentration variable (w(cw): critical weight fraction of water); for the present system the exponent of the resulting equation amounts to 2,33 as compared with 2,0 for toluene/polyisobutylene/poly(dimethylsiloxane).
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Record 67 of 70
Author(s): TONG, Z; LIU, XX
Title: SWELLING EQUILIBRIA AND VOLUME PHASE-TRANSITION IN HYDROGELS WITH STRONGLY DISSOCIATING ELECTROLYTES
Source: MACROMOLECULES, 27 (3): 844-848 JAN 31 1994
Abstract: Several sulfonic acid copolymer gels were prepared by radical copolymerization of N,N-dimethylacrylamide (DMAA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) using N,N'-methylenebisacrylamide (BIS) as the cross-linker. The concentration of pregel solutions and BIS content in dried gels were held constant at 0.75 mol/L and 1.3 mol %, respectively, while the mole fraction f of AMPS in dried gels determined by elemental analysis varied from 0 to 0.608. Swelling ratios for our sample of f = 0.468 were compared with those for an acrylic acid copolymer gel of f = 0.494 and 25 degrees C in aqueous buffers from pH = 2 to pH = 10 at 0.01 M ionic strength, and the results indicated that even in the gel state the sulfonic acid group could dissociate completely in the whole pH range. Therefore, f in this work can be designated to represent the charge density in the swollen gels. The swelling capacity observed in pure water at 25 degrees C increases monotonically with increasing f, showing a higher increasing rate when f > 0.3 without any sign of counterion condensation. The experimental swelling curve was interpreted with the Flory-Huggins theory and with the Hasa-Ilavsky-Dusek (HID) theory, but both theories failed to provide a reasonable approach to the swelling equilibria in our gels with a large amount of strongly dissociating electrolytes. The reciprocal of polymer volume fraction in a swollen gel, 1/phi, predicted with the Flory-Huggins theory was much higher than that observed when f > 0.2, while the calculated results given by the HID theory using the experimental nominal value of chain density were considerably lower than measured data in the entire f range. A volume phase transition occurred in these gels when f > 0 when the acetone volume fraction V-a in the acetone/water mixture was beyond a certain value, and this transition could be attributed to the weakening of electrostatic repulsion during increasing V-a in the mixture.
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Record 68 of 70
Author(s): TONG, Z; LIU, XX
Title: DYNAMIC-MECHANICAL BEHAVIOR OF POLYELECTROLYTE GELS WITH SULFONIC-ACID GROUPS
Source: MACROMOLECULES, 26 (18): 4964-4966 AUG 30 1993
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Record 69 of 70
Author(s): TONG, Z; LIU, XX
Title: SWELLING EQUILIBRIA AND VOLUME PHASE-TRANSITION OF PARTIALLY NEUTRALIZED POLY(ACRYLIC ACID) GELS
Source: EUROPEAN POLYMER JOURNAL, 29 (5): 705-709 MAY 1993
Abstract: Seven ionized gel samples of poly(acrylic acid) made by radical polymerization and having stoichiometric neutralization degree (f) ranging from 0 to 1, were examined. The ionization degree (alpha) is about a half the value of f for each sample. The data of swelling equilibrium in water as a function of alpha were interpreted with the Konak-Bansil equation; fair agreement was obtained if the effect of counterion condensation was considered. Volume phase transition in water/acetone was considered. Volume phase transition in water/acetone mixtures was found for five samples with high alpha values; the acetone concentration needed to induce the transition became lower for samples with higher alpha.
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Record 70 of 70
Author(s): TONG, Z
Title: APPARENT 2ND VIRIAL COEFFICIENT-GAMMA FOR TERNARY SOLUTIONS OF 2 POLYMERS IN A SOLVENT
Source: MACROMOLECULES, 24 (20): 5734-5735 SEP 30 1991
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