Micellar growth in presence of alcohols and amines: A viscometric study

Viscosity measurements have been made to study the effect of alcohols (C-3-C8OH) and amines (C4C8NH2) on the micellar growth of 0.2 M cetylpyridinium chloride in the presence and absence of 0.1 M potassium chloride (KCl). The studies have been performed in aqueous solutions between 25 and 40 degrees C at intervals of 5 deg. The presence of 0.1 M KCl or organic additive of lower chain length (C3OH, C4OH, or C4NH2) singly or jointly has little effect on the viscosity of micellar solutions. As the chain length of the additive increases, the viscosity increases with the increase of additive concentration, the magnitude being substantial in presence of 0.1 M KCl. However, for equal chain lengths, the effect was greater for n-alcohols. In few cases, viscosity shows a peaked behavior when the concentration of the additive was increased beyond the maximum viscosity value. Increased effectiveness of additives in the presence of added salt was discussed in light of electrostatic and hydrophobic forces operating in the solution which are always responsible for growth processes. Changes of the effective Mitchell-Ninham parameter of the surfactant in the presence of various additives were related to viscosity behavior of the solution. Temperature dependence of the viscosity was used to compute the free energy of activation, Delta G*, for the viscous flow.