Nonionic surfactant and temperature effects on the viscosity of hydrophobically modified hydroxyethyl cellulose solutions

Abstract

Nonionic surfactant and temperature effects on the viscosity of hydrophobically modified hydroxyethyl cellulose (HMHEC) solutions are investigated experimentally. Weak shear thickening at intermediate shear rates takes place for HMHEC at moderate concentrations, and becomes more significant at lower temperatures. While this amphiphilic polymer in surfactant free solution does not turn turbid by heating up to 95oC, its mixture with nonionic surfactant shows a lower cloud point (CP) temperature than does a pure surfactant solution. For some mixture cases, phase separation takes place at temperatures as low as 2oC. The drop of cloud point temperature is attributed to an additional attractive interaction between mixed micelles via chain bridging. With increasing temperature, the viscosity of a HMHEC-surfactant mixture in aqueous solution first decreases, but then rises considerably until around the cloud point (Fig. 1). The observed viscosity increase can be explained by the inter-chain association due to micellar aggregation.