Experimental verification of homogeneity in polymer gels

Abstract

The realization of an ideal polymer network that is free from heterogeneity is one of the ultimate goals in polymer science. Heterogeneity is known to be an inherent property of polymer networks. To realize an ideal polymer network, we need to develop methods to achieve a homogeneous network structure and to confirm the network homogeneity. This is a dilemma, as the former method needs to be verified by the latter method, while the latter method needs to be examined by the former method. To resolve this situation, a series of studies on polymer networks with well-defined properties is needed. We recently designed and fabricated novel Tetra-polyethyleneglycol (PEG) hydrogels. Characterization by small angle neutron scattering, infrared spectroscopy, nuclear magnetic resonance and tearing experiments indicates that Tetra-PEG gels have highly suppressed heterogeneity. In this review, we show a series of experimental results from Tetra-PEG gels and discuss the results in terms of network homogeneity. Finally, using Tetra-PEG gels as a model system, we examine models for predicting the elastic modulus of polymer gels and show that Tetra-PEG gels are useful as a model system for evaluating models that predict the physical properties of polymer networks.