Stabilising effect of topography on thin film flows for coating applications

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Thin liquid films flowing over an inclined solid substrate have the propensity to form large-amplitude free-surface waves propagating with a coherent shape and characteristic speed - a commonly observed and well-known instability. Not surprisingly, the appearance of such wave patterns, on the surface of a fluid layer, is an unwanted feature in many technological applications involving coating operations connected to print manufacturing processes; for example the manufacture of solar cells or paper production.Existing experimental data shows that the interaction of the film flow with substrate that contains repeating topographic features is able to delay the on-set of instability resulting in a higher topography-dependent critical condition for the onset of instability. However, while there are theoretical models for flow over periodic topography available in the literature, until now no evidence has appeared showing that any of them are able to predict and capture the experimentally observed stabilisation effects. The purpose of the project is therefore to develop theoretical models capable of predicting the conditions leading to the onset of free-surface instability for as wide a range as possible of the governing parameters of interest. By developing such models, to understand the interaction of the parameters involved and to identify safe operating windows for defect free coating, there is the potential to either eliminate completely or to minimise their detrimental effects in an industrial context, by enabling manufactures to predict and utilise operating windows and conditions that guarantee the production of a metered steady film. To this end, the project will involve collaboration with representatives from both academia and industry.