Liquid Nanodroplets Spreading on Chemically Patterned Surfaces

TL;DR

This study uses large-scale atomistic simulations to investigate how liquid nanodroplets spread on chemically patterned surfaces, revealing how pattern wavelength and surface interactions influence wetting behavior and spreading dynamics.

Contribution

It provides new insights into the wetting kinetics of nanodroplets on patterned surfaces, highlighting the transition from partial to selective spreading based on pattern wavelength.

Findings

Small wavelength patterns lead to partial spreading on both regions.

Large wavelength patterns cause droplets to spread only on wetting regions.

Precursor films spread rapidly on wetting areas depending on interaction strength.

Abstract

Controlling the spatial distribution of liquid droplets on surfaces via surface energy patterning can be used to control material delivery to specified regions via selective liquid/solid wetting. While studies of the equilibrium shape of liquid droplets on heterogenous substrates exist, much less is known about the corresponding wetting kinetics. We make significant progress towards elucidating details of this topic by studying, via large-scale atomistic simulations, liquid nanodroplets spreading on chemically patterned surfaces. A model is presented for lines of polymer liquid (droplets) on substrates consisting of alternating strips of wetting (equilibrium contact angle approximately 0 degrees) and non-wetting (equilibrium contact angle approximately 90 degrees) material. Droplet spreading is compared for different wavelength of the pattern and strength of surface interaction on the wetting strips. For small wavelength, droplets partially spread on both the wetting and non-wetting regions of the substrate to attain a finite contact angle less than 90 degrees. In this case, the extent of spreading depends on the interaction strength in the wetting regions. A transition is observed such that, for large wavelength, the droplet spreads only on the wetting region of the substrate by pulling material from non-wetting regions. In most cases, a precursor film spreads on the wetting portion of the substrate at a rate strongly dependent upon interaction strength.