(452g) A Thermodynamic Model for the Wetting Characteristics of Hierarchical Physically-Patterned Surfaces

Recent advances in nanotechnology have allowed for the creation of biologically-inspired superhydrophobic surfaces, which have a variety of applications including self-cleaning glass, low-drag surfaces and microfluidics. These surfaces are often made by incorporating roughness on micro and nano length scales, though a solid understanding of the role of hierarchical roughness in causing superhydrophobicity remains elusive. We present a two-dimensional thermodynamic model of the wetting of a hierarchically-grooved surface for droplets with negligible Bond number. By investigating wetting phase diagrams over the microscale parameter space, we find that surfaces with single-scale roughness are superhydrophobic only in small regions of the phase space—most notably in regions where the surface features are much smaller than the size of the droplet—while the addition of nanoscale roughness greatly extends the region of phase space in which the surface is superhydrophobic, so that even droplets with sizes on the order of those of the microscale features display high contact angles.