Quasi-Ordered Structure in Highly Cross-Linked Poly(acrylamide) Gels

Abstract

By means of small-angle light scattering and turbidity measurements, we have studied the growth of highly cross-linked poly(acrylamide) gels, and show that they are endowed with a quasi-ordered structure. A peak at finite angle in the scattering profiles is observed, revealing the presence of a characteristic length scale in the range of a few micrometers. This length is larger for higher cross-linker content. The role of aggregation of the bis(acrylamide) cross-linker in determining the final structure of the gel is investigated by studying the polymerization of a pure bis(acrylamide) solution. The time evolution of the turbidity of the gels and the scattering profiles of the bis(acrylamide) solution suggest that cross-linker aggregation leads to two-phase separation. However, this process is arrested at a microscopic scale by the onset of gelation. The resulting structure is characterized by larger pores than in gels at standard cross-linker concentration, as can be seen from electrophoretic migration o...