ADHESION ENERGY HYSTERESIS AND FRICTION BETWEEN ULTRATHIN POLYGLUTAMATE FILMS MEASURED WITH THE SURFACE FORCES APPARATUS

Adhesion and friction forces between deposited monolayers of poly(gamm a-methyl L-glutamate)(x)-co-(gamma-n-octadecyl L-glutamate)(y)-a ''hai ry rod'' polymer having a rigid main chain rod and alkyl side chains c ontaining either 1 or 18 C atoms-were measured using the surface force s apparatus technique. By performing dynamic (time-dependent) adhesion energy and friction experiments as a function of temperature T, we ob tained the energy loss spectra for these quasi two-dimensional films. The measured adhesion energy losses or hysteresis as a function of tem perature are shown to be related to the interdigitation of the octadec yl side chains, caused by different molecular motions that have been p reviously shown to be active at different temperatures. Friction exper iments probed the energy dissipation processes arising from lateral mo tion. Assuming that the molecular dissipation processes are the same i n both types of measurements (adhesion and friction), we used a previo usly derived simple formulate relate quantitatively the adhesion energ y hysteresis and friction forces.