Curtain coating in microfluidics and the phenomenon of nonlocality in dynamic wetting

Curtain coating on a length scale typical of microfluidics is investigated theoretically in the framework of an earlier developed theory where dynamic wetting is treated as essentially a process of formation of a new liquid-solid interface. The results demonstrate that the actual dynamic contact angle between the free surface and the solid boundary depends not only on the wetting speed and material constants of the contacting media, as in the so-called 'slip models', but also on the flow field/geometry in the vicinity of the moving contact line. In other words, for the same wetting speed the dynamic contact angle can be varied by manipulating the flow conditions. This outcome is consistent with the conclusions drawn earlier from macroscopic experiments.