Thin liquid films from polyoxyethylene-polyoxypropylene-block copolymer on the surface of fused quartz

Abstract

The thickness of thin liquid films, formed from solutions of a polyoxyethylene-polyoxypropylene-block copolymer (Lutrol F127 or poloxamer 407) on a substrate of fused quartz was measured using the microinterferometric method. The polymer adsorption at the air/liquid interface was studied by surface tension measurements in the absence and presence of 0.15 M NaCl. CMC and the thickness of the adsorption layers were determined from the surface tension data. The polymer adsorption at the SiO 2/aqueous solution interface was studied using a spectrophotometric method, based on the colored polymer–iodine complex. The conformation of the adsorbed molecules at both interfaces was determined as being a ‘brush’. The influence of the electrolyte concentration on the thickness of the thin liquid films was investigated. It was found that, for NaCl concentration higher than 10 −2 M, the film thickness remained constant. A conclusion was made that 10 −2 M NaCl was the electrolyte concentration, above which the electrostatic disjoining pressure was fully suppressed and film stability might be explained by the influence of the steric component of the disjoining pressure.