2020 Impact factor 1.890
Soft Matter and Biological Physics

Eur. Phys. J. E 6, 421-424 (2001)

Instabilities during the evaporation of a film: Non-glassy polymer + volatile solvent

P.G. de Gennes

Collège de France, 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France


(Received 18 October 2001)

We consider solutions where the surface tension of the solvent $\gamma _\mathrm{s}$ is smaller than the surface tension of the polymer $\gamma _\mathrm{p}$. In an evaporating film, a "plume" , of solvent-rich fluid, then induces a local depression in surface tension, and the surface forces tend to strengthen the plume. We give an estimate (at the level of scaling laws) for the minimum thickness $e^{\ast }$ required to obtain this instability. We predict that a) $e^{\ast }$ is a decreasing function of the solvent vapor pressure $
p_\mathrm{v}(e^{\ast }\sim p_\mathrm{v}^{-1/2})$; b) $e^{\ast }$ should be very small (< 1 micron) provided that the initial solution is rather dilute; c) the overall evaporation time for the film should be much longer than the growth time of the instability. The instability should lead to distortions of the free surface and may be optically observable. It should dominate over the classical Benard-Marangoni instability induced by cooling.

68.60.Bs - Mechanical and acoustical properties.
68.43.Mn - Adsorption/desorption kinetics.
68.03.Hj - Structure, measurements and simulations.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001