Coarsening dynamics of dewetting nanodroplets on chemically patterned substrates

Dewetting of evaporating thin films over nanometer-scale topographies

A lubrication model is used to study dewetting of an evaporating thin film layer over a solid substrate with a nanometer-scale topography. The effects of the geometry of the topography, the contact angle, the film thickness, and the slippage on the dewetting have been studied. Our results reveal that the evaporation enhances the dewetting process and reduces the depinning time over the topography. Also it is shown that the depinning time is inversely proportional to the slippage and increasing the contact angle may considerably reduce the depinning time, while the film thickness increases the depinning time.

Interaction of 3D dewetting nanodroplets on homogeneous and chemically heterogeneous substrates

Long-time interaction of dewetting nanodroplets is investigated using a long-wave approximation method. Although three-dimensional (3D) droplets evolution dynamics exhibits qualitative behavior analogous to two-dimensional (2D) dynamics, there is an extensive quantitative difference between them. 3D dynamics is substantially faster than 2D dynamics. This can be related to the larger curvature and, as a consequence, the larger Laplace pressure difference between the droplets in 3D systems. The influence of various chemical heterogeneities on the behavior of droplets has also been studied. In the case of gradient surfaces, it is shown how the gradient direction could change the dynamics. For a chemical step located between the droplets, the dynamics is enhanced or weakened depending on the initial configuration of the system.

Coarsening dynamics of nanodroplets on topographically structured substrates

Employing a biharmonic boundary integral method with linear elements, coarsening dynamics of nanodroplets on topographical step heterogeneity is investigated. It is shown that the step height and droplet configuration have an influential effect on the dynamics. Increasing the step height slows down the process while locating the droplets close to the step boosts the coarsening rate. Considering a slip boundary condition enhances the dynamics and reveals a transition in the droplet migration direction. Our results reveal that increasing the surface wettability weakens the dynamics. Various types of the disjoining pressure over the step are also considered and their effects on the coarsening are investigated.