Early time instability in nanofilms exposed to a large transverse thermal gradient: Improved image and thermal analysis

Liquid nanofilms exposed to a large transverse thermal gradient undergo an instability featuring an array of nanopillars whose typical pitch is tens of microns. In earlier works, a comparison of this pitch with the fastest growing wavelength predicted by three different models based on linear instability showed closest agreement with a long wavelength thermocapillary mechanism in which gravity plays no role. Here, we present improved feature extraction techniques, which allow identification of the fastest growing wavelength at much earlier times than previously reported, and more realistic simulations for assessing thermal gradients, which better approximate the actual experimental system. While these improvements lead to better agreement with the thermocapillary mechanism, there persists a quantitative discrepancy with theory which we attribute to a number of experimental challenges.