Network swelling competing with translational entropy in autophobic polymer dewetting

¹  Département de Physique, Faculté des Sciences, Université Libre de Bruxelles - Bd du Triomphe, CP 223, Belgium, EU
²  Physikalisches Institut, Universität Freiburg - Freiburg, Germany, EU
³  Université Claude Bernard Lyon 1, Ingénierie des Matriaux Polymères (IMP, UMR CNRS 5223) 69622 Villeurbanne Cedex, France, EU
⁴  Laboratoire Léon Brillouin, CEA Saclay - Gif-sur-Yvette Cedex, France, EU

Corresponding author: msferraz@ulb.ac.be

Received: 15 October 2009
Accepted: 14 April 2010

Abstract

Autophobic dewetting of a thin polystyrene (PS) layer on a cross-linked PS film has been studied with optical microscopy and neutron reflection. For two different cross-linking densities, the increase in contact angle and the fast decrease of both dewetting velocity and slippage length as a function of dewetting time indicate that the dewetting dynamics is controlled by the penetration of free linear polymer chains into the cross-linked film and the concomitant stretching of the network mesh: the loss of entropy of the network favors dewetting, while partial chain interdiffusion between the layers increases friction and eventually stabilizes the top film. In a second series of experiment, we modified the entropy of the network by swelling it with linear chains from a reservoir of identical polymers prior to depositing the top PS film. Once equilibrated, a stable interface without considerable interdiffusion between network and top film was achieved. Without such interdiffusion, a constant contact angle and a constant slippage length were observed.