Micro-friction of diazoresin/polyacrylic acid self-assembly films in water with atomic force microscopy

Ultrathin films composed of diazoresin (DR) and polyacrylic acid (PAA) were fabricated. The surface morphology of the films in water was measured using an atomic force microscopy (AFM). The self-assembly technique makes the surface rather flat and uniform. The friction force and its dependence on the velocity differ from the surface charge of the thin films. The friction force of repulsive DR/PAA film increases linearly with velocity and has lower values than that of attractive DR film over the full range of velocity. As the velocity increases, the attractive friction of DR film first decreases to a minimum at a velocity of 2 line/s and then increases all the way. When the surface is repulsive to the friction substrate, the friction of thin films that is determined by hydrated lubrication of polymer chains that is ultralubricated; when it is adhesive to the friction substrate, the friction is mainly contributed from the elastic deformation of adsorbed polymer chains in the low velocity region and from viscous sliding in the presence of hydrated-layer lubrication of the polymer chains in the higher velocity region.