Destabilising effect of long-range forces in thin liquid films on wettable substrates

¹ Institut de Chimie des Surfaces et Interfaces, CNRS 15, rue Jean Starcky, B.P. 2488, 68057 Mulhouse Cedex, France
² Department of Chemical Engineering, Indian Institute of Technology Kanpur, U.P. 208016, India
³ Institut Curie, Université Pierre et Marie Curie 11, rue Pierre et Marie Curie, 75231 Paris Cedex 05, France

Received: 20 July 1998
Accepted: 27 February 1999

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.