Effect of t-octylphenoxylpolyethoxyethanol (TX-100) on the dilute aqueous solution phase diagrams, surface activity and micellization behavior of non-ionic silicone surfactants (SS) in aqueous media

Abstract

Dilute aqueous solution phase diagrams, surface tension, dynamic light scattering (DLS) and dilute solution viscosity measurements have been made in aqueous solutions of nonionic silicone surfactants (SS) in presence of t-octylphenoxylpolyethoxyethanol (TX-100). Critical micelle concentration, thermodynamic parameters of association, interfacial characteristics such as pC20, surface excess, Γmax , area per adsorbed molecule, a1s along with the size and shape and intrinsic viscosities of the associates have been determined and discussed to ascertain the effect of TX-100 as an additive in SS aqueous solutions. The importance of hydrophobic/hydrophilic (hp/hl) ratio of the SS rather than their molecular architecture and molar mass on their overall interaction with TX-100 micelles has been reflected in the above parameters for the mixture solutions. It was observed that the mixed species in SS aqueous solutions in TX-100 are more hydrophilic in nature and the overall association process in the mixture solutions is entropy driven. TX-100 addition to SS micellar solutions induces the dissociation of SS micelles. As compared to the room temperature, the mixed micelles at elevated temperatures were large in size suggesting that the ellipsoidal micelles in mixed state grow along their major axis that is typically characteristic of the micelles of the individual nonionic SS or TX-100 surfactants at temperatures close to the turbid point.