Instabilities induced by solvent evaporation in plane layers
Context Coatings are often obtained by drying a suspension or a dilute solution.
The relationship between the drying kinetics and the coating quality is a complex problem involving
coupled heat and mass transfers in a medium whose properties strongly evolve during the drying.
During the drying, the solvent evaporation
induces a decreasing of the temperature and of the solvent concentration at the surface. Buoyancy or
surface tension driven instabilities may then temporary appear, induced by gravity and/or surface tension. For polymer solutions, a stong increase of the solution viscosity results from increased polymer concentration.
Results An experimental set-up has been previously developed in the laboratory (cf. Toussaint et al., IJHMT 2008). The apparition and wavelength of
the thermal convective patterns have been characterized for a large range of
Pr, Ra and Ma numbers.
Theoretical and numerical studies have been developped to
analyze the respective contributions of the different mechanisms on the destabilisation of the flow (thermal versus solutal, Rayleigh-Bénard versus Bénard-Marangoni), as a function of the two control parameters, initial thickness and initial viscosity. The transient behavior is taken into account explicitly (non-normal approach, numerical simulation).
The figure below is an illustration of solutal Marangoni convection occuring for a thin film configuration. Comparison of simulations with constant and varying viscosity shows that the effect of viscosity is
significant in promoting the non-uniformity of solute concentration. Results are in agreement with the mechanism suggested in the litterature (Bassou et Rharbi, Langmuir, 25, 2009) to explain wrinkles observed
on dry films. They can be viewed as the signature of Bénard-Marangoni convection occuring at the beginning of drying and resulting in concentration fluctuations that are frozen at the latter stages.
- Experimental characterization of buoyancy and surface tension
driven convection during the drying of a polymer solution
G.Toussaint, H.Bodiguel, F.Doumenc, B.Guerrier, C.Allain IJHMT 51, (2008).
- Simulation of
transient Rayleigh-Bénard-Marangoni convection induced by
O.Touazi, E.Chenier, F.Doumenc, B.Guerrier
IJHMT 53, 4 (2010).
- Rayleigh-Bénard-Marangoni Convection due to Evaporation : a Linear
Non-normal Stability Analysis
F. Doumenc, T. Boeck, B. Guerrier, M. Rossi
JFM 648, (2010).
- Numerical study of convection induced by evaporation in cylindrical
B.Trouette, E.Chenier, C.Delcarte, B.Guerrier
EPJ-ST "Interfacial Fluid Dynamics and Processes" 192 (2011).
- Transient Rayleigh-Bénard-Marangoni solutal convection
B.Trouette, E.Chenier, F.Doumenc, C.Delcarte, B.Guerrier
Phys. Fluids 24 (2012).
- Free convection in drying binary mixtures: solutal versus thermal instabilities
F.Doumenc, E.Chénier, B.Trouette, T.Boeck, C.Delcarte, B.Guerrier, M.Rossi
IJHMT 63 (2013).
- Surface deformation and film corrugation during drying of polymer solutions induced by Marangoni phenomena
Yiantsios, S.K. Serpetsi, F.Doumenc, B.Guerrier
IJHMT 89 (2015).