Liquid nanodroplets spreading on chemically patterned surfaces

Controlling the spatial distribution of liquid droplets on surfaces via surface energy patterning can be used to deliver material to specified regions via selective liquid/solid wetting. Although studies of the equilibrium shape of liquid droplets on heterogeneous substrates exist, much less is known about the corresponding wetting kinetics. Here we present large-scale atomistic simulations of liquid nanodroplets spreading oil chemically patterned surfaces. Results are presented for lines of polymer liquid (droplets) on substrates consisting of alternating strips of wetting (equilibrium contact angle theta(0) = 0 degrees) and nonwetting (theta(0) similar or equal to 90 degrees) material. Droplet spreading is compared for different wavelength of the pattern and strength of surface interaction oil the wetting strips. For small A, droplets partially spread on both the wetting and nonwetting regions of the substrate to attain a finite contact angle less than 90 degrees. In this case, the extent of spreading depends oil the interaction strength in the wetting regions. A transition is observed such that, for large the droplet spreads only on the wetting region of the substrate by pulling material front nonwetting regions. In most cases, a precursor film spreads oil the wetting portion of the substrate at a rate strongly dependent on the width of the wetting region.