FORCES BETWEEN SOLID SURFACES ACROSS POLYMER MELTS AS REVEALED BY ATOMIC FORCE MICROSCOPY

摘要

Forces between solid surfaces across polymer melts are poorly understood despite their fundamental importance and their relevance for making composite materials. Such force measurements reveal information on the structure of polymers at surfaces and of confined polymers. Experiments with the atomic force microscope and polyisoprene (PI) confirmed theoretical predictions that no long-range force should be present in thermodynamic equilibrium. In poly(dimethyl siloxane) (PDMS) repulsive forces are observed at high molar mass. We attribute this to the formation of an immobilized layer caused by a slow release of adsorbed segments enhanced by entanglement. In low molar mass PDMS attractive forces were observed which we can not yet explain. Attaching a hydroxyl end group to PI or PDMS chains lead to repulsive forces caused by the formation of a brush-like structure.