Rheological properties of model alkali-soluble associative (HASE) polymer in ionic and non-ionic surfactant solutions

The rheological properties of 0.5 wt.% aqueous solution of hydrophobically alkali-soluble emulsions (HASE) at around pH 9 in the presence of cationic, anionic and non-ionic surfactants were examined. The results revealed that the presence of surfactant below a critical concentration c* (around cmc of surfactant) strengthened the associating network through the formation of mixed polymer hydrophobic group/surfactant aggregates. The increased strength was due to an increase in the number of mechanically active, inter-molecular hydrophobic junctions and lifetime of the average junctions. Above c*, the results showed that the presence of cationic or anionic surfactant disrupted and weakened the associating network caused by a decrease in number of these junctions and strength of the overall network structure. At the same time, free cations of surfactant molecules screened the carboxyl-anion charges on the polymer backbone, which decreased the electrostatic repulsion between polymer chains. In the presence of non-ionic surfactant, the results showed a further reinforcement of associating network attributed to the formation of bilayers, which were stabilized as large vesicles. (C) 1999 Elsevier Science B.V. All rights reserved.