SELF-ASSEMBLY AND DESORPTION BEHAVIOR OF POLY(ETHYLENE GLYCOL) MONOLAYERS ON SILICA

Monolayers of poly(ethylene glycol) 1500 were grown by dispersing and drying a dilute solution of the polymer on a silica substrate. Atomic force imaging of these thin films reveals self-assembly of vertically oriented polymer chains that eventually leads to dendritic structures on a mesoscopic length scale. Thermal annealing and desorption of such structures were investigated under ultrahigh vacuum using X-ray photo electron spectroscopy and temperature-programmed desorption. The carbo n Is signal of the polymer starts to decrease before the onset of deso rption. This observation can be rationalized by structural reordering of the polymer chains on the surface. Atomic force microscopy images p rove that the decrease of the characteristic X-ray photoelectron spect roscopy signal at low temperatures is correlated with the transition o f the two-dimensional dendritic structures to three-dimensional microd roplets of the polymer on the surface. As the temperature increases, t his surface dewetting process is followed by dissociative desorption o f the polymer, shrinking of the microdroplets, and finally complete de pletion of the surface.