Adhesion of latex films. Part IV. Dominating interfacial effect of the surfactant

Our aim was to study the effect of various surfactants on the adhesion prop erties of latex films. For this purpose, a model monodisperse, surfactant-f ree, core-shell latex was synthesized, The core was a random copolymer of s tyrene and butyl acrylate. The shell consisted of a styrene/butyl acrylate/ methacrylic acid terpolymer with 10 wt% of methacrylic acid. Sodium dodecyl sulfate (SDS) and various ethoxylated nonionic surfactants were post-added to the latex Lit increasing concentrations. The adhesion of the correspond ing films was measured by peeling at 180 degrees. The shapes of the curves relating the peel energy to the surfactant concentration were similar, irre spective of the nature of the surfactant. namely a decrease to a constant p lateau level. This means that in these systems, the: influence of a weak bo undary layer at the interface dominates all other possible effects of the s urfactant. This was confirmed by surface analysis and peel experiments with surfactant-free films contacted with spin-coated SD layers of increasing t hickness. The reasons why the deleterious interfacial effect of the surfact ant overwhelms all others are discussed.