Thermal Marangoni-driven dynamics of spinning liquid films

Thinning dynamics in spin coating of viscous films is influenced by many physical processes. Temperature gradients are known to affect thin liquid films through their influence on the local fluid surface tension as Marangoni stresses. We show here experimentally and numerically that adding a static temperature gradient has a significant effect on the equilibrium film thickness and height profile reached in spin coating. Most notably, we find that the thickness of the resulting thin film in spin coating scales linearly with the strength of the thermal surface tension gradient. Once equilibrated, the thin film height profile is controlled by the temperature profile. For small but nonnegligible Marangoni number (Ma) the surface has a negative curvature at the center and reaching equilibrium takes progressively longer with smaller Ma. In this limit, the steady state reached is set by competition between Marangoni effects and the disjoining pressure.