Fluctuation-driven instability of nanoscale liquid films on chemically heterogeneous substrates

The instability and dewetting of bounded liquid films at the nanoscale are shown to strongly depend on thermal fluctuations. In this work, this fluctuation-driven instability of films on a chemically heterogeneous substrate is investigated both by a stochastic lubrication equation (SLE), which models thermal fluctuations with white noise, and by molecular dynamics (MD). Linear instability analysis for the SLE, considering slip and intermolecular forces of the heterogeneous substrates, is employed to derive a spectrum of the thermal capillary waves and their corresponding interface roughness, which are then quantitatively confirmed by numerical solutions for the SLE and MD. The fluctuation-driven instability is found to be enhanced by the slip and intermolecular forces, with the latter becoming dominant toward the final rupture. Moreover, the results suggest that a heterogeneous substrate can be approximated as a homogeneous one with effective (averaged) slip lengths and Hamaker constants for the intermolecular forces. The gradients of the slip and intermolecular forces due to the heterogeneities are shown not to affect the instability significantly.

Automated summary

The instability and dewetting of bounded liquid films at the nanoscale are found to be strongly influenced by thermal fluctuations. This study investigates the fluctuation-driven instability on a chemically heterogeneous substrate using a stochastic lubrication equation and molecular dynamics. The results show that slip and intermolecular forces enhance the fluctuation-driven instability, with the latter becoming dominant towards the final rupture. Additionally, the study suggests that a heterogeneous substrate can be approximated as a homogeneous one using effective slip lengths and Hamaker constants for the intermolecular forces, while the gradients of slip and intermolecular forces due to heterogeneity have little effect on the instability.