Destabilising effect of long-range forces in thin liquid films on <i>wettable</i> substrates

Abstract

Using optical microscopy, we followed the evolution of thin and initially smooth liquid polymer films on wettable solid substrates for different surrounding media. For thicknesses between 30 and 110 nm, we observed an instability of the film, eventually leading to the formation of nanodroplets on a remaining wetting layer. Exchanging the surrounding medium allowed to reverse the process and to re-establish a smooth film. Our results are in accordance with theoretical considerations and computer simulations. Weak but long-ranged dispersion forces may have drastic consequences concerning the morphology of thin liquid films even if short-range interactions force the film to stay on the substrate.