Control of size and shape of micelles, of flow properties, and of pH-values in aqueous CTAB-solutions via photoreactions of solubilizates

Abstract

The influence of in situ photochemical transformations of aromatic solubilizates on the flow properties of aqueous micellar solutions of cetyltrimethylammonium bromide was investigated, using Ostwald-viscometers in cases of Newtonian flow and a rotating viscometer in cases of non Newtonian flow behaviour, i. e. rheopexy, thixotropy, and viscoelasticity. Newtonian flow was observed in systems containing trans and/or cis-stilbene derivatives or nonpolar 9-substituted anthracenes as solubilizates which are photochemically cis-trans isomerized or photodimerized, respectively, whereby the viscosity changed. Non Newtonian flow was observed in systems containing 9-anthracene carboxylic acid which could be photodimerized while a change of flow behaviour occurs simultaneously. In these systems pH changes were observed upon irradiation. Static light scattering experiments at low angles indicated that spherical micelles differing in radius exist in the systems exhibiting Newtonian flow, while in the non Newtonian systems rod-like aggregates differing in length are present.