Directional wetting on chemically patterned substrates

Abstract

The directional wetting behavior of chemically defined stripe-patterned anisotropic surfaces is presented. The equilibrium shapes of asymmetric droplets, arising from patterns of alternating hydrophilic and hydrophobic stripes with dimensions in the low-micrometer range, are investigated in relation to the stripe widths. Owing to the well-defined small droplet volume, the equilibrium shape as well as the observed contact angles exhibit unique scaling behavior. Additionally, we investigate the motion of liquid from surface areas with low macroscopic wettability toward areas with a higher wettability. The density of self-assembled fluoroalkylsilane monolayers in terms of the number and width of the stripes, as defined by the chemical patterning, proves to be of paramount importance. Linear and radial patterns are presented, which induce liquid movement along the chemically defined stripes giving rise to a macroscopic gradient in surface energy.