Instability of nanometric fluid films on a thermally conductive substrate

TL;DR

This paper investigates the stability of nanometric fluid films on thermally conductive substrates under uniform heating, revealing complex instability mechanisms and oscillatory behaviors influenced by temperature dynamics.

Contribution

It introduces a comprehensive analysis of thermally induced instabilities in thin films considering both fluid/substrate interactions and Marangoni forces, highlighting the importance of self-consistent temperature calculations.

Findings

Complex interplay of instability mechanisms identified.

Oscillatory free surface dynamics observed with self-consistent temperature.

Oscillations absent when temperature is assumed to follow film thickness.

Abstract

We consider thin fluid films placed on thermally conductive substrates and exposed to time-dependent spatially uniform heat source. The evolution of the films is considered within the long-wave framework in the regime such that both fluid/substrate interaction, modeled via disjoining pressure, and Marangoni forces, are relevant. We analyze the problem by the means of linear stability analysis as well as by time-dependent nonlinear simulations. The main finding is that when self-consistent computation of the temperature field is performed, a complex interplay of different instability mechanisms results. This includes either monotonous or oscillatory dynamics of the free surface. In particular, we find that the oscillatory behavior is absent if the film temperature is assumed to be slaved to the current value of the film thickness. The results are discussed within the context of liquid metal films, but are of relevance to dynamics of any thin film involving variable temperature of the free surface, such that the temperature and the film interface itself evolve on comparable time scales.