Robustness of Hydrophobic and Oleophobic Fabrics

A hydrophobic and oleophobic surface can be defined as a surface with an apparent contact angle higher than 90° both for water and oil. Robustness is used to describe the property of a hydrophobic and oleophobic rough surface to resist the penetration by a liquid under a pressure. The robust pressure of a rough surface is the most common expression of robustness. The robust pressure depends on the surface tension and Laplace pressure of the liquid, and the surface energy and the structure of the rough surface.;Robustness can be measured and modeled by pushing a droplet into a hydrophobic and oleophobic surface with another surface. Since a capillary bridge forms between the two surfaces, capillary forces, capillary profiles and wetting behavior of liquid bridges between two surfaces are reviewed. In the initial phase of this research, a robustometer was constructed and its characteristics were determined using flat smooth substrates. Then, the capillary profiles of liquid bridges were modeled for symmetric/asymmetric and bi-concave/bi-convex shapes, where gravity was negligible. Good agreement was found between theoretical and experimental profiles of the liquid bridges. When an external force was applied to a droplet, both the Laplace pressure and profile of the liquid would change, which was manifest in the spread and penetration of the drop on the rough surface. The capillary forces for liquid bridges between smooth film substrates were also modeled, and excellent agreement was found between the experimental results and theoretical analysis. With the effective action area known, robust pressure was expressed as robust force per unit area. In addition, for a liquid under an applied force, the Laplace pressure can also be obtained.;In order to study the robustness of parallel monofilaments and fabrics against liquids under pressures, they were tested with the robustometer by compressing a drop on their surface with a polytetrafluoroethylene film. The robust pressures were obtained from the robust forces and action areas, which were compared among different fabrics and liquids. From the capillary force analysis, the Laplace pressure was calculated for each pair of substrates with a liquid. In addition, guidance will be provided to avoid or reduce chemical warfare agent (CWA) hazards adhered to the hydrophobic and oleophobic fabrics, during the interaction between the wipe and liquids.