Engineering Surface Micro-structure to Control Fouling and Hysteresis in Droplet Based Microfluidic Bioanalytical Systems

This paper presents the principle, fabricated structure, characterization and experimental results obtained for a new class of surfaces—“hydrophobic non-fouling surfaces”—for droplet-based microfluidics. Building on the theory of wetting of rough surfaces, we have developed novel surfaces which are chemically hydrophilic, i.e., the droplet is in contact with a non-fouling hydrophilic material but has high contact angle as a result of thermodynamically stabilized air traps beneath the droplet. This paper also presents the experimental characterization of rough superhydrophobic surfaces, dynamic measurements of sliding angles of water droplets, and a modeling approach to estimate bounds on contact angle hysteresis—a major dissipative mechanism in droplet based microfluidic systems. A comprehensive study of the dependence of hysteresis on texture parameters is presented to evaluate the current model, propose a modification, and show that the two models—original and modified—provide useful bounds on the hysteresis of the surface.