  Switchable and adaptive substrates emerged as valuable tools for the control
of wetting and actuation of droplet motion. Here we report a computational
study of the dynamics of an unstable thin liquid film deposited on a switchable
substrate, modelled with a space and time varying contact angle. With a static
pattern, all the fluid is drained into droplets located around contact angle
minima, whereas for a sufficiently large rate of wettability variation a state
consisting of metastable rivulets is observed. A criterion discriminating
whether rivulets can be observed or not is identified in terms of a single
dimensionless parameter. Finally, we show and explain theoretically how the
film rupture times, droplet shape and rivulet life time depend on the pattern
wavelength and speed.
