Biaxial Stretching of Nearly Critical Gels with Extremely Sparse Network Structures

Nearly critical gels, which are obtained slightly beyond the gel point, have very low modulus due to their extremely sparse network structures. The nonlinear elasticity of such sparse polymer networks is intriguing, but their very low modulus has prevented the characterization of the large deformation behavior. The present study investigates the biaxial stress-strain behavior of nearly critical gels by means of a custom-built tensile tester optimized for soft gels. The biaxial data show that the cross-effect of strains becomes smaller as the gels approach the gelation point, and that the effect vanishes in the nearly critical gels.