Dependence of linear viscoelastic critical strain and stress values on extent of gelation for a thermally activated gelling system

A large body of literature is focused on the accurate determination of a gel point for systems undergoing a sol-gel phase transition. Investigation into the limiting strain and stress for linear viscoelastic behaviour at various stages of a phase transition such as gelation is a subject that is rarely commented on. The small amplitude oscillatory rheological behaviour of a biopolymer cross-linker system through a thermally activated sol-gel transition is presented. Mechanical spectra were interpreted through application of the gelation criteria of Chambon and Winter (Winter and Chambon 1986; Chambon and Winter 1987), where the (so-called gel strength) parameter S, and relaxation exponent, n are obtained. A detailed study of the limit of linear viscoelasticity yields important trends in critical stress (σ°_c) and critical strain (γ°_c) limits highlighting the possible experimental difficulties associated with mechanical measurements obtained in close proximity to the gel point. Received: 17 March 2000 Accepted: 2 October 2000