EXPONENTIAL-GROWTH OF FINGERING INSTABILITIES OF SPREADING FILMS UNDER HORIZONTAL THERMAL-GRADIENTS

A thin liquid ribbon deposited on a wettable surface and subjected to a horizontal thermal gradient develops periodic fingers towards the cold region. We present an observation of the exponential growth regime, expected at early times, but not accessible in other driven fingering patterns induced by gravitational flows, spinning drops, or vertical thermal gradients. We have monitored the wavelength-lambda and the raising time-tau of the unstable mode of undulation of the contact line; we find that lambda-tau-2 is independent of the ribbon thickness, in agreement with a linear stability analysis.