Delamination and Renovation of a Molecular Surfactant-Polymer Boundary Lubricant Film

We have studied the behavior tinder compression and shear of two molecularly smooth mica surfaces immersed in aqueous solutions of a dimeric cationic surfactant and air oppositely charged polyelectrolyte-neutral diblock copolymer by using a surface force apparatus-nanotribometer, SFA-N. The surfactant and copolymer coadsorb as a mix molecular boundary lubricant Film on the negatively charged mica Surfaces leading to low friction in a sliding mechanical contact. However, under fritting conditions, shearing can induce different dynamic transitions of the confined films. Transitions front the initial low friction steady state to new steady states of low or high friction can be induced when the sliding velocity is increased above certain values. These dynamical transitions occur together with thickness reduction of the confined film. A reverse transition to the low friction steady state accompanied by the renovation of the Film can be triggered by reintroducing some matter in the contact, via increasing the amplitude of the fritting cycles.