No abstract

Commercially available woven fabrics (e.g., nylon-or PET-based fabrics) possess inherently re-entrant textures in the form of cylindrical yarns and fibers. We analyze the liquid repellency of woven and nano-textured oleophobic fabrics using a nested model with n levels of hierarchy that is constructed from modular units of cylindrical and spherical building blocks. At each level of hierarchy, the density of the topographical features is captured using a dimensionless textural parameter D * n . For a plain-woven mesh comprised of chemically treated fiber bundles (n = 2), the tight packing of individual fibers in each bundle (D onto the fibers of a commercial woven nylon fabric.

A durable, conformal coating was developed based on the use of very low surface tension fluorodecyl polyhedral oligomeric silsesquioxane (Fluoro-POSS) cage-like molecule and a fluorinated elastomer. When this coating is applied, the resulting oleophobic fabrics resist surface wetting by a wide range of liquids having high to very low surface tension values, while remaining durable after repeated washing and abrasion testing. Collected data indicated minimal interference to air flow and moisture vapor through the conformally coated textiles. While textiles having said repellent treatment have been prepared previously by dip and spray coating in non-continuous laboratory applications, in 2012 the US Army Natick Research Development and Engineering Center successfully demonstrated a continuous, scalable application of Fluoro-POSS-treated textiles by way of a 24-inch-wide pad/dry/cure treatment. Material syntheses will be reported, and coating solution preparation and pilot-scale coating parameters will be discussed. Comparative data on surface, chemical and physical properties of lab-scale against pilot-scale coated repellent treated fabrics will be presented. These will include measurement of oleophobic coated fabrics’ contact angle using various liquids such as water and hazardous chemicals, as well as evaluation of chemical permeation test results and physical properties. Future work will examine the effects of different concentrations of low surface tension fluoropolymers and elastomers, hierarchical re-entrant nanostructures, and optimal processing and curing conditions.

A computational clothing design tool is used to examine the effects of different clothing design features upon performance. Computational predictions of total heat and mass transfer coefficients of the clothing design tool showed good agreement with experimental measurements obtained using a sweating thermal manikin for four different clothing systems, as well as for the unclothed bare manikin. The specific clothing design features examined in this work are the size and placement of air-permeable fabric vents in a protective suit composed primarily of a fabric-laminated polymer film layer. The air-permeable vents were shown to provide additional ventilation and to significantly decrease both the total thermal insulation and the water vapor resistance of the protective suit.

Nylon 6 electrospun nanofibers were deposited on plasma-pretreated woven fabric substrates with the objective of improving adhesion between them. The prepared samples were evaluated for adhesion strength and durability of nanofiber mats by carrying out peel strength, flex resistance, and abrasion resistance tests. The test results showed significant improvement in the adhesion of nanofiber mats on woven fabric substrates due to atmospheric plasma pretreatment. The samples also exhibited good flex and abrasion resistance characteristics. X-ray photoelectron spectroscopy and water contact angle analyses indicate that plasma pretreatment introduces radicals, increases the oxygen content on the substrate surface, and leads to formation of active chemical sites that may be responsible for enhanced cross-linking between the substrate fabric and the electrospun nanofibers, which in turn increases the adhesion properties. The work demonstrates that the plasma treatment of the substrate fabric prior to deposition of electrospun nanofiber mats is a promising method to prepare durable functional materials.