Thermorheological properties of a Carbopol gel under shear

摘要

An experimental investigation of the thermo-rheological properties of aqueous solutions of a commercial polyacrylic acid(Carbopol?)at various concentrations is presented. The rheological parameters of the solutions are assessed by performing increasing/decreasing controlled stress stepped ramps and interpreting the results within the framework of a recent model which can correctly describe the irreversibility of deformation states in a range of low deformation rates, Putz and Burghelea[39]. For each polymer concentration a temperature invariance of the elastic moduli, consistency and the power law index is found. Below a critical temperature T _c, the measured yield stress can be described by an Arrhenius type dependence. Above T _c an anomalous temperature dependence is observed which manifests itself through an increase of the yield stress with the temperature. A qualitative but yet incomplete understanding of this anomalous behavior can be obtained within the framework of the Eyring theory of flow as an activated process. A phenomenological interpretation for the emergence of the critical temperature T _c is given. The concentration dependence of elastic moduli, consistency and the Arrhenius pre-factors consistently indicate the existence of an overlap concentration c ~({black star})which we interpret as an onset of jamming of swollen polyacrylic acid molecules. A detailed comparison of the experimental findings with results from the literature is presented and several open questions are stated.