Studies On Characterization Of Polymer Gels And Their Intelligent Behavior

With the fast development of life science, it is increasingly necessary to reveal the diversity of organisms and their conformational complexity. Most organism tissues exist in the nature in the form of soft matter. As far as now, polymer hydrogels are known as the systems that have unique properties mostly resembling the organisms in conformation. Especially, polymer hydrogels can gently respond to the environmental changes, and have more bionic and soft-matter characteristics than other polymer systems. However, it is much more complicated and difficult to characterize the network structure and physical properties of polymer hydrogels, particularly nature polymer hydrogels, than those of common polymer materials. Moreover, there is a lack of simple and reliable methods to characterize the diffusion behavior in hydrogels. Therefore, the aim of this thesis is to study the gelation process of chemical gels using the refractive index method and of physical gels of cellulose with various advanced techniques, and to explore a novel and simple method based on refractive index measurements for the study of molecular transport behavior and its application in the diffusion of various small or macromolecules in hydrogels. The current research belongs to intersectional field of subjects from polymer, biology and physics.The creative achievements of this thesis are as follows. (1) For the first time, the refractive index method was successfully used to monitor the free-radical crosslinking polymerization of iV,iV-dimethylacrylamide to reveal the mechanism of the gelation process. (2) A novel device based on the measurements of the refractive index was established for the first time to monitor the diffusion process in polymer hydrogels. (3) The established refractive index method was successfully employed to investigate the diffusion behavior of small or macromolecules (such as sucrose, DNA, ect. ) in hydrogels (such as agarose). (4) The thermally induced physical gelation process of cellulose in a NaOH/thiourea aqueous solution was revealed for the first time with the aid of various tools and the mechanism was elucidated.The main research contents and conclusions are divided into the following parts. In situ refractive index technique was used to study the gelation process in the free-radical cross-linking copolymerization (RCC) of N,N-dimethylacrylamide with N,N'-methylenebisacrylamide as the cross-linker. The change of refractive index was measured and used to monitor the gelation process. The influence of different polymerization conditions on the gelation process, such as monomer, cross-linker and initiator concentrations was investigated and discussed in detail. It is observed that the concentration of monomer, crosslinker and initiator has significant effect on the refractiveindex change. The increase of their concentration all contributed to the reaction rate after the gel point. Employing the steady-state kinetic model into the reaction system containing 1.0mol/l DMAAm, 0.003mol/l MBAAm, 0.003mol/l KGA, we obtained the relation curve between [M] and gelation time. Moreover, ln[M] varies linearly with gelation time at the early stage of the gelation reaction process. Therefore, the composite rate constant of the gelation reaction Kr was calculated to be 2.1 X 10-4s-1.An in-situ refractive index method was established to study the molecular diffusion process in hydrogels based on a self-made refractive index device. The sample solution diffused into the hydrogel contained in a triangular cell from the bottom to the up of the cell. Diffusion was monitored by recording the refraction of a laser beam when passing through the cell. The distribution of refractive index changes was obtained from the deviated distance of the linear beam and converted to the distribution of concentration. The diffusion process of sucrose in poly(acrylic acid) (PAAc) hydrogels was used to test this novel method. By employing Fick's second law, the diffusion behavior was investigated, and by fitting the theoretical curves to the experim...