Surfactant and Protein Interactions on Wettability Gradient Surfaces

Abstract

Surfaces with a gradient in wettability were made by diffusion of dichlorodimethylsilane along silicon dioxide surfaces. Interaction of surfactants and fibrinogen was then studied at the solid/liquid interface with the use of ellipsometry. Adsorption properties of surfactants like cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and pentaethyleneglycol mono n-dodecyl ether (C 12E 5) were investigated at different pH. All of the surfactants adsorbed at the hydrophobic (SiCH 3) part of the gradient and the adsorption was found to be essentially independent of pH in solution. At the hydrophilic (SiOH) part, on the other hand, adsorption was strongly influenced by pH, in a way that partly can be explained by electrostatic attraction or repulsion between the surfactants and the surface. In addition, there were also effects within the gradient region that provide new information about the role of the chemical groups on the solid surface and their interactions with surfactants. All surfactant adsorption was reversible upon rinsing with distilled water. A variety of detergents were used to desorb fibrinogen adsorbed to the gradient surfaces. All the surfactants were effective in desorbing proteins from the far hydrophobic part of the gradient, probably through competition with the protein on the surface. There were also transient effects of desorption in the gradient region as well as desorption effects at the hydrophilic part of the gradient that can mainly be explained in terms of interactions between the surfactants and the proteins.