Water breakthrough pressure of cotton fabrics treated with fluorinated silsesquioxane/fluoroelastomer coatings

Breakthrough pressure is an important parameter associated with the performance of water-resistant fabrics. Hydrostatic testing has been utilized to experimentally determine the breakthrough pressure of commercial cotton fabrics treated with various combinations of octakis(1H,1H,2H,2H-perfluorodecyl) polyhedral oligomeric silsesquioxane (F-POSS), a compound with the lowest reported solid surface energy, and the commercial fluoroelastomer, Tecnoflon®. The breakthrough pressure values (amounting to a few inches of water) were found to be similar to predicted values based on the geometry of the samples and the surface energy of the components. The theoretical predictions, however, do not explain all differences observed among samples, such as the fact that a single dip coating with both F-POSS and Tecnoflon® produced a higher breakthrough pressure than a single dip coating in either F-POSS or Tecnoflon®, or sequential dip coating (in either order) of the two components. SEM analysis of the coated fabrics indicated that coatings were conformal at the microscale, but did result in sub-micron scale roughness. Although this roughness may help to increase the contact angles with water, the breakthrough pressure appeared to be primarily determined by the geometry of the individual filaments.