Density effects on collapse, compression, and adhesion of thermoresponsive polymer brushes.

We probe, using the surface forces apparatus, the thermal response of poly(N-isopropylacrylamide) (PNIPAM) brushes of various grafting densities, grown from plasma-activated mica by means of surface-initiated polymerization. We thus show that dense thermoresponsive brushes collapse gradually as temperature is increased and that grafting density greatly affects their ability to swell: the swelling ratio of the brushes, which characterizes the thickness variation between the swollen and the collapsed state, is found to decrease from approximately 7 to approximately 3 as the number of grafted chains per unit area increases. Such a result, obtained with an unprecedented resolution in grafting density, provides qualitative support to calculations by Mendez et al.

Growth and stability of a self-assembled monolayer on plasma-treated mica.

Increasing the range of surfaces that can be studied using the surface forces apparatus, e.g., for friction measurements, requires chemical modification of the surface of mica, which may be achieved by grafting self-assembled monolayers (SAMs) onto plasma-modified mica.