Thermosolutal Marangoni instability in a viscoelastic liquid film: effect of heating from the free surface

• Published in: Journal of fluid mechanics Vol. 909
• Main Authors: Sarma, Rajkumar, Mondal, Pranab Kumar
• Format: Journal Article
• Language: English
• Published: Cambridge, UK Cambridge University Press 25.02.2021
• Subjects: Aquatic reptiles; Binary mixtures; Boundary conditions; Elasticity; Fluids; Formability; Free surfaces; Gravity; Gravity effects; Heat conductivity; Instability; Investigations; JFM Papers; Parameter identification; Phase diagrams; Polymer films; Polymers; Solutes; Solvents; Stability; Stability analysis; Stratification; Substrates; Surface stability; Temperature gradients; Viscoelastic liquids; Viscoelasticity; Marangoni convection; viscoelasticity; thin films
• ISSN: 0022-1120; 1469-7645
• DOI: 10.1017/jfm.2020.880

We investigate the Marangoni instability in a thin polymeric liquid film heated from the free surface. The polymeric solutions are usually a binary mixture of a Newtonian solvent with a polymeric solute, and exhibit viscoelastic behaviour. In the presence of a temperature gradient, stratification of these solutes can take place via the Soret effect, giving rise to the solutocapillary effect at the free surface. Considering this cross-diffusive effect and incorporating the effects of gravity, here we analyse the stability characteristics of this polymeric film when bounded between its deformable free surface and a poorly conductive rigid substrate. Linear stability analysis around the quiescent base state reveals that, under the combined influences of thermosolutocapillarity and the elasticity of the liquid, apart from the monotonic disturbances, two different oscillatory instabilities can emerge in this system. The characteristics of each instability mode are discussed, and a complete stability picture is perceived in terms of the phase diagrams, identifying the model parameter regimes for which a particular instability mode becomes dominant.