Sulfoxide Surfactants

Abstract

A novel group of nonionic surfactants, which we term ester sulfoxides, derived from 2-hydroxy-4-(methylthio) butyric acid are characterized in this thesis. The physico-chemical properties, equilibrium and dynamic properties, and microemulsion behavior of these surfactants are investigated. Based on the physico-chemical properties, the sulfoxide nonionic surfactant molecules presented good surface activity, good foaming, wetting ability and laundry detergency performance. Equilibrium surface tensions were determined for a number of molecules. The Langmuir adsorption isotherm is satisfactory for describing the adsorption behavior of the sulfoxide surfactant at the air/water interface. Adsorption kinetics onto the air/water interface was studied for an ester sulfoxide molecule with 8 carbon atoms in the tail of the surfactant. Comparing the experimental dynamic surface tension profiles of the surfactant solutions with the diffusion-controlled kinetic model indicate that the adsorption of this surfactant molecule onto the air/water interface is diffusion-controlled for dilute solutions at 25°C. HLD parameters of longer-chain surfactants were obtained and compared to that of alcohol ethoxylates. Ester sulfoxides are much less temperature sensitive than alcohol ethoxylates, and have a temperature coefficient similar to that of ionic surfactants. The ester sulfoxide moiety was determined to be as hydrophilic as ~5 ethylene oxide units according to the Cc value of the HLD parameters.