INFLUENCE OF A NONIONIC SURFACTANT ON THE RHEOLOGY OF A HYDROPHOBICALLY ASSOCIATING WATER-SOLUBLE POLYMER

The rheological behavior of a 1% w/w commercial hydrophobically modifi ed (hydroxypropyl)guar (HMHPG) in water solution is examined in the pr esence of a low molecular weight nonionic surfactant. The linear and n onlinear response to steady and oscillatory shear flow, at different s urfactant concentrations around the cmc, is mainly compared with the r esponse of a 1% w/w aqueous solution of HMHPG alone, following a rheol ogical approach previously used by the authors. Below the cmc of the f ree surfactant in water, the rheological results show a reinforcement of the reversible associating network mainly due to an increase of the number of intermolecular hydrophobic associations, with hardly no mod ification of the average ''strength'' of the hydrophobic junctions. Ab ove the cmc, the rheological data show that there is a progressive wea kening leading to the disruption of the intermolecular hydrophobic jun ction network. Those results are interpreted in terms of interactions of surfactant molecules with the regions of intermolecular hydrophobic association. (C) 1996 Society of Rheology.