Effect of periodic grooving topography on dynamics of Insoluble surfactant-laden thin film flow

Abstract

Targeting the flowing of insoluble surfactant-laden film over topography substrate, the lubrication theory is adopted to derive the evolution equations of thin liquid film thickness and interfacial surfactant concentration. The flowing characteristics of the film on topography surfaces, and the influence of topography structure are examined based on the numerical simulation with PDECOL code. The results show that when the thin film of insoluble surfactant flows over periodic grooving topography, the depression appears at the negative step, while the ridge is shaped at the positive step, both of which increase gradually with time going by. Compared with the case of the flat base, the surfactant-laden film spreading speed is enhanced. Increasing the groove depth or reducing the groove steepness leads to the increase of the rupture possibility of the film. Improving the groove width promotes the film flowing. The decrease of the steepness can cause the film to form a ridge feature before entering into the first groove. Gravity has the opposite effects on the up-hilling and down-hilling processes of liquid film flow, which causes the flow stability to deteriorate. Conjoining pressure induced by intermolecular forces can accelerate the film, giving rise to a notable dewetting phenomenon, while disjoining pressure has an adverse effect.