The nature of friction of polymers in high elastic and glasslike states

Abstract

AbstractThe temperature dependence of the friction of polymers against hard surface is characterized by two maxima: main and low temperatures. The main maximum observed in the glass transition range, contrary to the widespread opinion, is not associated with the maximum of the mechanical losses observed in polymers. The temperature dependence of the friction force consists of three ranges. In the high elasticity range, with decreasing temperature, the friction force is observed to increase according to the molecular kinetic theory of the friction of rubberlike polymers. The nature of the friction for all polymers in this range is associated with the mechanical losses in the surface monomolecular layer of the polymer. The bulk‐mechanical losses in the polymer are not essential. The deviation from the theoretical dependence and the decrease of the friction force below a certain temperature in the transition range are associated mainly with the decrease in the actual contact area of suriaces of the friction pair at the glass transition of the polymer. In the glasslike state, for polymers the friction is essentially dependent on the bulk‐mechanical losses in the polymer at elastic and forced elasticity strain of the roughnesses in the polymer layer being in contact with a solid. Therefore, the low temperature maximum is associated with the maximum of the mechanical losses observed in the same range of temperature at dynamic tests. For polymers with no maximum of the mechanical losses at low temperatures, the maximum of the friction can be attributed to the increase in the adhesion forces and the drop in the actual contact area at temperatures at which the forced elasticity mechanism of compression of the polymer roughnesses is not realized.