Complex formation between anionic polyelectrolytes and cationic/nonionic mixed micelles

Abstract

Turbidimetry has been used to study the formation of complexes between anionic polyelectrolytes, i.e., poly(sodium styrenesulfonate) and poly(sodium acrylate); and cationic micelles, i.e., dimethyldodecylamine oxide, and mixed micelles of Triton X-100 and dodecyltrimethylammonium bromide. At fixed ionic strength, complex formation and concomitant phase separation occur abruptly upon increase in micelle surface charge density σ. σ is controlled by pH titration, in the case of the amine oxide surfactant, or by adjustment of surfactant composition, in the mixed micelle system. The micelle surface charge density required for phase separation increases with ionic strength. The corresponding phase boundary is a smooth line for the mixed micelle system but displays a discontinuity for the amine oxide system at conditions of pH and ionic strength where this micelle appears to undergo a sphere-rod transition. At fixed ionic strength, the mole fraction of ionic head groups in the micelle at incipient phase separation is much smaller for the amine oxide micelle than for the mixed cationic/nonionic micelle. This effect is attributed to the bulky nonionic surfactant head groups in the latter which increase the distance of closest approach between polyion segments and the ionic surfactant head groups.