  The long-wave dynamics of liquid films on isothermal substrates show a
dynamic competition between various physical mechanisms. If the destabilizing
effect of thermocapillarity overcomes the stabilizing effect of surface tension
and gravity, the liquid film ruptures in finite time, through the formation of
primary and secondary thermocapillary finger structures.
  The long-wave evolution dynamics are compared for two different substrate
types: isothermal non-porous and isothermal porous for small Biot number in a
zero gravity environment. The multi-time-scale dynamics is revealed through
time scales obtained from a method of similarity solutions. It is observed that
with an isothermal porous substrate, in zero gravity, secondary thermocapillary
structures are damped through imbibition and that primary thermocapillary
structures persist for long times without rupture.
