The Influence of Counter‐Ion Concentration on the Aggregation Behaviour of Viscoelastic Detergents

Abstract

Abstract The influence of excess Sodiumsalicylate (NaSal) on the properties of viscoelastic detergent solutions of Cetylpyridiniumsalicylate (CPySal) has been studied by static and dynamic light scattering, electric birefringence and rheological measurements. It is observed that the rodlike micelles which are present in these solutions and which are responsible for the elastic behavior grow rapidly in length with the increase of the NaSal concentration until the NaSal reaches 5 · 10 −4 M. At this excess NaSal a 1 · 10 −3 M CPySal solution contains rods which are at least 2000 Å long. To higher concentrations of NaSal the lengh L and the molecular weight M w of the micelles is independent on the NaSal concentration. The elasticity and the electric birefringence disappear for NaSal concentration above 5 · 10 −3 M. The loss of these properties is believed to be due to the coiling of the long rods. In the viscoelastic region the viscosity of the solutions is shear rate dependent. It decreases with increasing shear rate.