CONTINUUM MODEL OF HETEROGENEOUS GELS - FORMATION AND ELASTIC PROPERTIES

A kinetic model of heterogeneous gel formation and a method to calcula te gel stiffness are proposed, with application to the elastic propert ies of polyacrylamide gels. The model is based on assumptions about nu cleation and growth of dense regions, governed by the concentration of monomer units (p(o)) crosslink agent (c(o)) and rate constants for ch ain propagation and curing. It is shown that at low c(o) the polymer a nd crosslink densities inside and outside an inclusion are almost the same and that the gel may be regarded as homogeneous. But the differen ce between densities increases sharply with c(o), giving growth of het erogeneities. Calculation of the elastic modulus was performed using a self-consistent method. Stiffness grows with p(o) at fixed c(o), but goes through a maximum as a function of c(o) at fixed p(o). The theore tical analysis is in qualitative agreement with the experimental data.