(281b) Fundamental Study of Adsorption Behavior of Ethoxylated Nonionic Surfactants from Organic Solvents on Various Surfaces

Ethoxylated nonionic surfactants represent an important class of nonionic surfactants with applications in detergency, cosmetics and pharmacy. Most of these applications involve adsorption of the surfactants from their solutions onto various polymeric interfaces. Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) allows to carry out fundamental studies of adsorption of these surfactants onto various surfaces. Gold surface was used as a model surface and adsorption behavior of these surfactants was established from their solutions in aqueous and hydrophobic solvent. Effect of the number of ethylene oxide groups per surfactant molecule and the concentration of the surfactant solutions was quantified. QCM-D also provides information about kinetics of adsorption process. It was observed that for the concentrations above the critical micelle concentration (CMC), the surfactants first adsorb as whole micelles and these micelles break to form a uniform layer of surfactant on the gold surface. The dissipation data obtained was used to calculate thickness and viscosity of the adsorbed layer. It was observed that the adsorption of the surfactants is completely reversible in the case of gold surface. Ethoxylated nonionic surfactants interact with Poly-acrylic acid to form a complex. Membrane immobilized poly-acrylic acid is shown to be useful for separation of ethoxylated nonionic surfactants from hydrophobic solvent. Amount of the surfactant adsorbed per mole of carboxyl group of PAA was reported in the earlier study. However, due to the nonuniform pore size and interconnectivity of the pores it was not possible to estimate available surface area and accessible carboxyl groups in the cross-linked PAA network. To overcome this difficulty, in the present study, a thin layer of PAA was coated on the gold surface by spin coating and the surface was used to study the adsorption behavior of the surfactants using QCM-D. The adsorption isotherm of these surfactants from their solutions (pure component and mixtures) onto various fabric samples was also developed. The concentration of the solution was determined using Gas Chromatography ? Flame Ionization Detector (GC-FID) before and after the adsorption and the adsorbed amount was calculated from the concentration difference.