Textured polymer surfaces formed by self-assembly: Preparation and tribological characterization

Self-assembled block copolymer and random copolymer films were prepared as model systems of textured/structured cosmetic coatings for friction studies related to the tactile touch of skin. Characterization by AFM showed that different micrometer and nanometer size surface structures were obtained by controlling the polymer concentration and annealing conditions. Friction forces were measured with the Surface Forces Apparatus (SFA) at a low sliding speed of 3 µm/s in a standard setup and at a more realistic speed of 10 cm/s with a special attachment for high speed rotational sliding. Glassy polymer surfaces commonly showed static friction at low speed, whereas only kinetic friction was found for polymers above their T_g. A random roughness pattern with a sawtooth-like cross section, made from a polymer above its T_g, gave high friction at low speed, but its friction coefficient was reduced at high speed due to less time for local entanglement and relaxations. Its friction response was also more strongly affected by humidity than that of glassy polymer films. This work provides structure-property characteristics of bio-inspired self-assembled textures for future development of thin coatings on skin using eco-sustainable polymers.