Effect of Organized Assemblies, Part VII: Adsorption Behavior of Polyoxyethylated Nonyl Phenol at Silica−Cyclohexane Interface and Its Efficiency in Stabilizing the Silica−Cyclohexane Dispersion

Abstract

The adsorption behavior of a series of nonionic polyoxyethylated nonyl phenol surfactants having same hydrocarbon chain length but varying oxyethylene chain has been studied spectrophotometrically at the silica−cyclohexane interface. The adsorption density is found to be independent of the number of oxyethylene units throughout the adsorption isotherms, except at higher surface coverage, where the adsorption density decreases with the increase in the number of oxyethylene units. The settling rate of the silica particles in cyclohexane decreases with the increase in adsorption density as well as oxyethylene chain length. On the other hand, the sediment volume decreases with the increase in the adsorption density, with a minimum for the surfactant having the least number of oxyethylene units. Surfactants with a longer oxyethylene chain partitions preferentially to the bulk solvent at higher concentrations, as a result of the change in the polarity of the medium. On the basis of adsorption density, settling ...