title: Density effects on collapse, compression, and adhesion of thermoresponsive polymer brushes.
abstract: 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. [Macromolecules 2005, 38, 174]. We further show that, in contrast to swelling, adhesion between two PNIPAM brushes appears to be rather insensitive to their molecular structure.
authors: Institut des Nanosciences de Paris, UMR 7588 CNRS-Université Paris 6, 140 rue de Lourmel, 75015 Paris, France.
authors: Ibrahim B
authors: IB
authors: Malham
authors: Lionel
authors: L
authors: Bureau