Residual stresses in thin polymer films cause rupture and dominate early stages of dewetting

Abstract

In attempting to reduce the size of functional devices, the thickness of polymer films has reached values even smaller than the diameter of the unperturbed molecule. However, despite enormous efforts for more than a decade, our understanding of the origin of some puzzling properties of such thin films is still not satisfactory and several peculiar observations remain mysterious. For example, under certain conditions, such films show negative expansion coefficients or show undesirable rupture although energetically they are expected to be stable. Here, we demonstrate that many of these extraordinary effects can be related to residual stresses within the film, resulting from the preparation of these films from solution by fast evaporation of the solvent. Consequently, depending on thermal history and ageing time, such films show significant changes even in the glassy state, which we quantify by dewetting experiments and corresponding theoretical studies. Identifying the relevance of frozen-in polymer conformations gives us a handle for manipulating and controlling properties of nanometric thin polymer films.

Solvent retention in thin polymer films studied by gas chromatography

“…The final thinning of the film is then due solely to solvent evaporation [2]. Most of the solvent evaporates during the last step of the spin-coating, but it is known that some solvent is still present in the films at the end of the spin-coating [1,3,4] and that the polymer chains are quenched in a nonequilibrated state [5][6][7][8]. Spin-coated films are therefore generally annealed above the glass transition temperature of the polymer to dry the films and let the polymer relax to equilibrium.…”

Mechanism of spontaneous hole formation in thin polymeric films

“…8,9 Inspired by the experimental investigations in Ref. 5, we will here theoretically explain why and show how holes can spontaneously develop in thin films of a viscoelastic polymer melt. As recognized in Ref.…”

“…Spontaneous rupture and dewetting of thin polymer films (>20 nm) above the glass transition temperature [4][5][6] have been discussed in an immense amount of scientific papers but still remains unresolved. This is a surprising phenomenon since intermolecular forces were considered to stabilize a film.…”

“…As recognized in Ref. 5, it is a consequence of what they referred to as residual stresses in the polymer, originating from fast evaporation of the solvent during the preparation of these films from a polymeric solution. In this paper, our concern is about the film deformation in the initial stages of the hole generation (see Fig.…”

Dry-spot nucleation in thin liquid films on chemically patterned surfaces

“…Buguin et al (1999) and Noblin et al (2006) studied inertial effects. Reiter (1992;Reiter 1993;Reiter et al 2005) and Xie et al (1998) investigated the dewetting of ultrathin films of polymer melts on Si wafers. The effect of slip at the solidliquid interface on the formation and growth of dry patches was studied by Seemann et al (2001), , Kargupta et al (2004), andFetzer et al (2005).…”