Effect of adsorbate orientation on intermicellar interaction

Abstract

The cloud point of Triton X-100 is measured in the presence of the adsorbates sodium salicylate (NaS), sodium meta-hydroxybenzoate (MHB), sodium para-chlorobenzoate (PCB), and aspirin. The adsorption of these molecules on the micelle is confirmed by FT NMR. The cloud point increases to different extents for the same concentration of NaS, MHB, and PCB and this is attributed to the different orientation of the molecule on the micelle. This indicates that the adsorbate orientation on the micellar surface is also one of the factors affecting the intermicellar interaction. The cloud point decreases with an increase in the concentration of aspirin and this is explained by the decrease in the hydration and the steric forces. The cloud point of the Triton X-100 and salicylic acid system is measured as a function of pH for two different concentrations of the acid. The results indicate that the cloud point depends on the number of salicylic acid molecules adsorbed per micelle and on the pK value of the acid.