Interplay of internal stresses, electric stresses and surface diffusion in polymer films

摘要

We investigate two destabilization mechanisms for elastic polymer films andput them into a general framework: first, instabilities due to in-plane stressand second due to an externally applied electric field normal to the film'sfree surface. As shown recently, polymer films are often stressed due toout-of-equilibrium fabrication processes as e.g. spin coating. Via anAsaro-Tiller-Grinfeld mechanism as known from solids, the system can decreaseits energy by undulating its surface by surface diffusion of polymers andthereby relaxing stresses. On the other hand, application of an electric fieldis widely used experimentally to structure thin films: when the electricMaxwell surface stress overcomes surface tension and elastic restoring forces,the system undulates with a wavelength determined by the film thickness. Wedevelop a theory taking into account both mechanisms simultaneously and discusstheir interplay and the effects of the boundary conditions both at thesubstrate and the free surface.