Destabilization and dry-spot nucleation in thin liquid films on partially wetting substrates using a low-pressure air-jet

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute. The rupture of a thin liquid film on a partially wetting substrate can be initiated by external forces. In this manuscript we present experiments and numerical simulations of the effects of a laminar axisymmetric air-jet impinging on triethylene glycol films. We numerically calculate stagnation pressures and shear stress distributions that are used in a model for the thin liquid film dynamics. Experimentally, we distinguish three regimes: 1) the depressions made by low pressure air-jets level out, 2) for intermediate pressures a single dry-spot is nucleated that grows with a constant dewetting speed, whereas 3) for higher pressure air-jets the film is thinned and a large number of dry-spots nucleate, grow and leave a droplet pattern behind. In the third regime the dewetting speed was not independent of local film thickness. Numerical simulations show a qualitative agreement with the experimental observations. This work is part of the research programme ‘Contact Line Control during Wetting and Dewetting’ (CLC) of the ‘Stichting voor Fundamenteel Onderzoek der Materie (FOM)’, which is financially supported by the ‘Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)’. The CLC programme is co-financed by ASML and Océ.