Spin coating of thin liquid films on an axisymmetrically heated disk

Abstract

Spin coating of nonvolatile thin liquid films on an axisymmetrically heated disk is studied numerically under lubrication and zero Biot number assumptions. Important effects such as viscosity, centrifugal force, external air shearing, surface tension, disjoining pressure, thermocapillarity (temperature dependent surface tension), and thermoviscosity (temperature dependent viscosity) are included in the simulation. Both thermocapillarity and thermoviscosity effects are shown to be able to significantly enhance the film depletion rate when the disk center is at a higher temperature than the disk outer edge. The enhancing effect of thermoviscosity on the film depletion is not sensitive to the film thickness change and is larger than that of the external air shearing even at a moderate radial temperature difference applied to the disk. The thermocapillarity effect on the film depletion is negligible at the earlier stage of spin coating when the film thickness is relatively large, but its significance increases and eventually becomes dominant when the film thickness is further reduced. When the applied disk temperature profile has a steep change, a double shock structure for the liquid film is generated. Measurement of the anchored shock profile may provide an alternative mechanism to determine the viscosity change with temperature of wall bounded thin liquid films.