Interaction forces between pegylated star-shaped polymers at mica surfaces

Abstract

We present a study focused on characterizing the interaction forces between mica surfaces across solutions containing star-shaped polymers with cationic ends. Using the Surface Forces Apparatus, we show that the interaction forces in pure water between surfaces covered with the polymer can be adequately described by the dendronized brush model. In that framework, our experimental data suggest that the number of branches adsorbed at the surface decreases as the concentration of polymer in the adsorbing solution increases. The onset of interaction was also shown to increase with the concentration of polymer in solution up to distances much larger that the contour length of the polymer suggesting that the nanostructure of the polymer film is significantly different from a monolayer. High compression of the polymer film adsorbed at low polymer concentration revealed the appearance of a highly structured hydration layer underneath the polymer layer. The results support that charged polymer chains do not necessarily come into close contact with the surface even if strong electrostatic interaction is present. Altogether, our results provide a comprehensive understanding of the interfacial behavior of star-shaped polymers and revealed the unexpected role of hydration water in the control of the polymer conformation.