Adhesion Energy Hysteresis and Friction between Ultrathin Polyglutamate Films Measured with the Surface Forces Apparatus

Abstract

Adhesion and friction forces between deposited monolayers of poly({gamma}-methyl L-glutamate){sub x} co-({gamma}-n-octadecyl L-glutamate){sub y}--a hairy rod polymer having a rigid main chain rod and alkyl side chains containing either 1 or 18 C atoms--were measured using the surface forces apparatus technique. By performing dynamic (time-dependent) adhesion energy and friction experiments as a function of temperature T, the authors obtained the energy loss spectra for these quasi two-dimensional films. The measured adhesion energy losses or hysteresis as a function of temperature are shown to be related to the interdigitation of the octadecyl side chains, caused by different molecular motions that have been previously shown to be active at different temperatures. Friction experiments probed the energy dissipation processes arising from lateral motion. Assuming that the molecular dissipation processes are the same in both types of measurements (adhesion and friction), they used a previously derived simple formula to relate quantitatively the adhesion energy hysteresis and friction forces.