THE PHYSICS OF ULTRATHIN SOLID-FLUID-SOLID FILMS: FROM SURFACE INSTABILITIES TO ISOLATED POCKETS OF FLUID

摘要

This chapter describes the physical processes that occur in free-standing ultrathin trilayer films consisting of a fluid layer sandwiched in between two solid layers,. We have recently referred to these films as "Dutcher films"; these are namedafter the group of John Dutcher, whose experiments motivated these computational studies [1-3], An interesting instability arises in these films if the total film thickness is thin enough that van der Waals forces acting across it are sufficiently strong to deform the solid layers. In other words, the van der Waals forces can favor the formation and growth of instabilities (resulting in the dewetting of fluid films on substrates or film breakup in free-standing fluid films). In contrast, the elasticity of the solid capping layers resist the bending deformations required for instability growth. However, for very thin films the van der Waals forces are sufficiently strong that the solid layer begins to deform. The surface instabilities grow with time because of the van der Waals forces, but are restricted by both the deformation energy of the solid layer and the transport kinetics of the fluid layer. In particular, small-wavelength deformations in the solid layer are more energetically unfavorable, while large-wavelength deformations would require the transport of fluid material over kinetically-prohibitive distances. Hence, the competition between energetics and kinetics selects a characteristic wavelength for undulation growth.