Thermodynamic approach to the dewetting instability in ultrathin films

TL;DR

This paper develops an analytical thermodynamic model for thermocapillary dewetting in ultrathin films, aligning with linear theory and experiments, and reveals that dewetting follows the path of minimum energy loss.

Contribution

It introduces a thermodynamic approach to describe thermocapillary dewetting, providing analytical insights and identifying boundary conditions for minimum viscous dissipation.

Findings

Thermodynamic approach agrees with linear theory and experiments.

Dewetting follows the path of minimum energy loss.

Zero tangential stress at the film-substrate boundary minimizes viscous dissipation.

Abstract

The fluid dynamics of the classical dewetting instability in ultrathin films is a non-linear process. However, the physical manifestation of the instability in terms of characteristic length and time scales can be described by a linearized form of the initial conditions of the films's dynamics. Alternately, the thermodynamic approach based on equating the rate of free energy decrease to the viscous dissipation [de Gennes, C. R. Acad. Paris.v298, 1984] can give similar information. Here we have evaluated dewetting in the presence of thermocapillary forces arising from a film-thickness (h) dependent temperature. Such a situation can be found during pulsed laser melting of ultrathin metal films where nanoscale effects lead to a local h-dependent temperature. The thermodynamic approach provides an analytical description of this thermocapillary dewetting. The results of this approach agree with those from linear theory and experimental observations provided the minimum value of viscous dissipation is equated to the rate of free energy decrease. The flow boundary condition that produces this minimum viscous dissipation is when the film-substrate tangential stress is zero. The physical implication of this finding is that the spontaneous dewetting instability follows the path of minimum rate of energy loss.