Modeling of Self-cleaning Superoleophobic Aerosol Barrier

Aerosol droplets are defined as colloid liquid particles dispersed in air with less than 1 mum diameter. Aerosols may contain hazardous liquids such as toxic or radioactive chemicals and can be harmful, thus efficient filtration is essential to maintain clean air. The accumulation of aerosol droplets on an aerosol barrier brings down the filtration efficiency by filling the voids and changing the structure of the aerosol barrier. A superoleophobic aerosol barrier can slow the effect of accumulated liquid and increase the durability of the barrier. In addition, an appropriately designed structure is essential to make the accumulated liquid condense and roll off the aerosol barrier, increasing its lifetime.;This study begins with introduction of definitions such as Young's contact angle, surface tension, the Wenzel model and Cassie-Baxter model, which are used to predict apparent contact angle of droplets on rough surfaces. The Wenzel model is used to describe the complete wetting condition, while the Cassie-Baxter model is used to describe composite wetting conditions. Based on the metastable Cassie-Baxter model developed by Marmur, the equilibrium contact angle of droplets on a rough surface can be predicted. This model is used in the research presented below for a rough surface with a multi-scale rough structure.;In addition to predicting the apparent contact angle, the profile of droplets on surfaces including flat surface, fibers, yarns and fabrics are simulated. For liquid drops captured by a cylindrical fiber, two types of droplet shape can be formed depending on the ratio between droplet volume and fiber radius. A clamshell droplet is formed when a small droplet is captured by a fiber with relatively large fiber diameter. As the droplet grows, it tends to spread along the axial and circumferential directions of the fiber. A clamshell transitions to a barrel droplet when it grows large enough for the two circumferential edges from opposite sides meet. Surface Evolver (SE) simulation is used to predict the relation between transition volume as a function of fiber radius and equilibrium contact angle.;The cylindrical fiber calculations were extended to include conical fibers to study the motion and equilibrium position of droplets captured by a conical fiber and the transition condition of a droplet on a conical fiber as a function of deposition position and equilibrium contact angle. In order to have a comprehensive understanding of the motion of clamshell and barrel droplets, Gibbs free energy (GFE) of the system was calculated. GFE gradient as a function of deposition position was discovered, which indicates that droplets can be directionally driven by the curvature of the surface.