NANOTRIBOLOGY ON A POLYMER NETWORK FILM

Scanning force microscopy (SFM) of topography, frictional force, and s tiffness on thin gelatin films reveals an entire spectrum of tribologi cal behavior. Images display two distinct phases of gelatin whose char acteristics relate to the degree of crystallinity. Dissimilar regimes of velocity- and load-dependent friction and wear on each phase indica te glassy, rubbery, or melt behavior. Of fundamental importance is the finding that energy transferred to the film in the vicinity of the sl iding SFM microasperity modifies film response. Moderate frictional he ating melts the highly crystalline phase, but reversibly induces rubbe ry behavior on the partially amorphous phase. More extreme frictional heating melts the latter and allows the liberated molecules to reassoc iate irreversibly into the highly crystalline phase. This relatively s low process (minutes) is imaged in real time on the submicron scale. R elaxation from rubbery to glassy behavior upon termination of perturba tive scanning is extremely slow (hours) and also is characterized in f rictional images. However, in this case the imaging process itself has tens the relaxation, apparently by providing energy to activate some r elaxational processes. (C) 1996 American Vacuum Society.