Thermoreversible gelation strongly coupled to coil-to-helix transition of polymers

This paper theoretically studies thermoreversible gelation driven by aggregation of helices formed on the polymer chains. Two fundamentally different cases of (i) multiple association of single helices and (ii) association by multiple helices with multiplicity k (such as double helices (k=2), triple helices (k=3), etc.) are treated on the basis of different equations. The helix length distribution on a polymer chain (or assemble of chains for multiple helices) is derived as a function of polymer concentration and temperature. Theoretical calculation of the total helix content in the solution is compared with experimental data of optical rotation in iota-carrageenan solutions at different polymer concentrations. It is shown that at low temperature there is a sharp transition from network to bundle state (pair, triplet, etc.). To confirm such a network/pairing transition, we carried out Monte Carlo simulation of polymer solution in which hydrogen-bonded zipper-like cross-links are formed.     

Three-Dimensional Nanoparticle Arrays Templated by Self-Assembled Block-Copolymer Gels

Water-soluble triblock copolymers (PEO-PPO-PEO) are utilized to provide thermoreversible micellar templates for three-dimensional nanoparticle arrays. The triblock forms a cubic micellar structure with typical dimensions of tens of nanometers. The temperature-dependent amphiphilic nature of the block copolymers provides increased structure control and allows the use of pre-made silica and gold nanoparticles as well as globular proteins. Using rheology and small-angle neutron scattering (SANS), we characterize the influence of the nanoparticles on the local particle structure and on the macroscopic mechanical properties. We are able to incorporate significant quantities of nanoparticles into the block copolymer gel without destroying the ordered structure. Contrast matching SANS demonstrates that some level of the template structure is transferred to the nanoparticles. This study demonstrates the feasibility and potential of using this simple approach to generate novel nanoparticles-polymer composites.     

Comparative Study on the Collapse Transition of Poly(N-isopropylacrylamide) Gels and Magnetic Nanoparticles Loaded Poly(N-isopropylacrylamide) Gels

A novel polymer gel exhibiting simultaneous temperature and magnetic field sensitivity has been prepared and studied. Poly(N-isopropylacrylamide) (PNIPA) and magnetic nanoparticles (magnetite, Fe₃O₄) loaded PNIPA gel beads with mm size and monolith gels with cm size were prepared. The dependence of swelling degree on the temperature has been studied. The effects of cross-linking density and the presence of magnetic nanoparticles on the equilibrium swelling degree as well as on the collapse transition have been investigated. Swelling kinetic measurements were also made. By comparing the equilibrium swelling properties of PNIPA and magnetite loaded PNIPA gels it was found that the built in magnetic nanoparticles do not modify the temperature sensitivity of these gels. Within the experimental accuracy the temperature of the collapse transition was not sensitive to the presence of magnetic particles. We have compared the swelling behaviour of mm size gel beads to the cm size monolith gels in order to study the influence of surface skin layer on the swelling equilibrium. It was established that the extent of surface skin formation was decreased by the presence of magnetic particles.     

聚丙烯酰胺/酚醛树脂的胶凝反应动力学探讨

两性聚丙烯酰胺;水溶性酚醛树脂;聚合物水凝胶;聚丙烯酰胺/酚醛树脂的胶凝反应动力学探讨     

The effect of topological constraints on polymer network pressure

Recent data on comparative osmotic deswelling of poly(acrylic acid) gels and solutions shows that the difference between osmotic pressure of the gel and of the solution, P_gel (c, f) − P_solution (c, f), taken at equal polymer concentration (c) and fraction of the ionized acrylic acid monomers (f), changes its sign from negative to positive as the concentration c increases; this effect is enhanced with increasing f whereby it is shifted toward lower concentrations. In order to explain this effect, a model is suggested for the elastic pressure of the gel network which takes into account the effect of topological constraints combined with the effect of network ionization. According to the model, the sign-change of P_gel − P_solution originates from the topological constraints on conformations of the network; the ionization of the network chains enhances this effect and shifts it to the concentration range of the experiment. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1833–1841, 1997     

Effect of quinone derivatives and sulfhydryl compounds on swelling of poly(4-vinylpyridine) gels in organic solvents

Interactions of sulfhydryl compounds and quinone derivatives with poly(4-vinylpyridine) gels have been studied. Adsorption of long-chain sulfhydryl compounds onto gels causes the gel to swell, whereas oxidation of the adsorbed sulfhydryl compound to disulfide by a quinone derivative results in the gel shrinking. The higher the donating ability of the sulfhydryl compound, the stronger its interaction with a quinone derivative and thus the faster the removal from the gels, as revealed by HPLC. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 795–798, 1997     

Liquid Crystalline Polymer Gels: Preparation and Swelling Behavior of Cellulose-based Networks

Cellulose organo gels with liquid crystalline (LC) order have been prepared by crosslinking cellulose chains with a difunctional unit, adipoylchloride, or a monofunctional molecule containing a reactive double bond, 4-pentenoil chloride. Both gels display a reversible change from LC order to isotropic phase by changing the amount of solvent. The relation between the critical concentration at which the LC phase is stable, and the degree of crosslinking depends on the crosslinking agent. Both gels swell in dimethylacetamide and acetone: however the degree of swelling decreases with the degree of crosslinking in dimethylacetamide, while an increase is observed in acetone. This particular behavior can be explained by taking into account the different composition of the networks. © 1997 John Wiley & Sons, Ltd.     

New Supramolecular Drug Carriers: The Study of Organogel Conjugated Gold Nanoparticles

An aqueous solution of sodium citrate stabilized gold nanoparticles (AuNP) in the presence of N-lauroyl-L-alanine (C₁₂ALA) forms a stable gel. The structure of the gel and the distribution profile of AuNP in it were analyzed. Will nanoparticles separated from each other with sodium citrate behave in the same way in solution and trapped in the gel matrix? Will the spatial limitation of solvent molecules aggregate nanoparticles and destroy their homogeneity? These questions are very important from the point of view of the use of gold nanoparticles, trapped in the gel structure as carriers of drugs in the slow-release process. The lack of homogeneity of this distribution will have a major impact on the rate of release of the appropriate amount of therapeutic drug from the matrix. In this work, we attempt to answer these questions. The performed biological assays revealed that both C₁₂ALA and C₁₂ALA-AuNP show an excellent level of biological neutrality. They might be used as a transporting medium for a drug delivery without affecting the drug’s activity.     

Opal Gels Templated Synthesis of Structured Titania Materials

Summary: Core/shell opal gels of sulfonated polystyrene were used as templates to synthesize structured crystalline titania materials. Under acidic conditions, opal materials with hollow spheres of controllable shell thickness and cavity size were prepared. Under neutral conditions, inverse opal inorganic materials with a tunable pore size were prepared. It is crucial that proton ions induce a preferential sol/gel process, forming titania in the gel.

Scanning electron micrograph of the interior region of a structured titania material derived from the G1 template used here. The inset shows broken spheres in which the internal cavity can be observed.     

Transesterification of poly(N,N-diethylacrylamide-co-glycol methacrylate) with diethyldithiophosphate: Facts and implications

Ester exchange reaction of poly(N,N-diethylacrylamide-co-glycol methacrylate) with O,O-diethyldithiophosphate is shown to result in attachment of functional dithio phosphate group onto gels. The presence of N,N-diethylacrylamide moieties in the gels causes the gels to collapse when heated above the lower critical solution temperature, whereas ionization of the dithio groups at pH > 1.6 leads to drastic swelling. Selectivity of diethyldithio group toward metal ions enables gels to preferentially bind copper over zinc or calcium. © 1996 John Wiley & Sons, Inc.