Effects of temperature on the flow dynamics of a model HASE associative polymer in nonionic surfactant solutions

The interaction between a model hydrophobically modified, alkali-soluble emulsion (HASE) polymer and a nonionic surfactant, C12EO4, was investigated in this work. The addition of the nonionic surfactant increases the viscosity and moduli of the polymer up to the maximum concentration of 0.1 M. The low-shear viscosity, plateau modulus, and hence the effective junction density increase linearly with surfactant concentration up to 0.01 M. However, above 0.01 M, the plateau modulus tapers off while the rise in viscosity becomes steeper. From the Arrhenius plots of both the low-shear viscosity and longest relaxation time, the activation energy of dissociation of the hydrophobes from the aggregated junction for the pure HASE polymer was found to be of the order of 50 kJ mol(-1). In the presence of 0.00025-M surfactant, an increase in the activation energy of approximately 10% was observed, and results from the enhancement of the hydrophobic junctions by the surfactant molecules. At higher surfactant concentrations between 0.001 and 0.01 M, the Arrhenius plots show two distinct regions, yielding activation energies of 30 kJ mol(-1) at temperature T < 25 degrees C and 75 kJ mol(-1) at T > 25 degrees C. This corresponds to the transition, at approximately 25 degrees C, from large, mixed, spherical micellar aggregates to a large bilayered structure formed by the polymer-surfactant aggregrates. The size of these bilayers increases dramatically with temperature, as is confirmed by the decrease in the number of effective network junctions at T > 25 degrees C. At T < 25 degrees C, the effective junction density remains almost constant with temperature, and the reduction in the activation energy is probably due to a decrease in the functionality of polymer hydrophobes. Above 0.01M, the surfactant molecules form larger bilayers or vesicles with the associated polymer hydrophobes, resulting in a solid, gellike structure. The gel system exhibits increasing viscosity profiles with increase in temperature, and the transition temperature was shifted from 25 to 8 degrees C.