Inhomogeneity in gelation and nonuniversality of sol-to-gel transitions studied by a computer simulation model

Effects of the quality of a solvent on the sol-to-gel transition are studied by a computer simulation model. A nearest neighbor interaction of strength $J$ between the polymeric units is introduced to control the quality of the solvent. The Metropolis algorithm is used to move the monomers and microgels that react with their neighboring units with a rate of reaction. The critical exponents for the sol-to-gel transition are found to depend on the nature of solvent, i.e., the exponent $\beta$ for the gel fraction and the exponent $\gamma$ for the weight average degree polymerization vary with the values of $J$. The dynamic evolution of the structure of gel networks is analyzed by collective structure factors. Due to the competition between the effect of dilution and the coagulation of clusters, a phase-separated gel network seems to emerge, leading to inhomogeneities. We also find that the interplay between the rate of the reaction and the energy parameters that represent the quality of solvents determines the final morphology of gel networks.