Modification Of The Near-Infrared Signature Of Textile Fabrics Via Colloidal Self-Assembly

Abstract

This thesis presents a novel method to modify the near-infrared (NIR) reflectance of textile fabrics using colloidal self-assembly of polystyrene (PS) particles via electrostatic and convective forces. This work studies the effect of particle coating on a textile fabric where the size of the particle is of same order of magnitude as the incident wavelength of light, which has not been studied for textiles. Sulfate functionalized PS particles were deposited on cationic cotton, poly(allylamine hydrochloride) (PAH) coated nylon-cotton, and cationic cellophane film. The nylon-cotton fabric was obtained from the Army Camouflage Uniform (ACU) and contained three colors. Spherical particles of 0.2, 0.5, and 1.0 ?m in diameter and a non-spherical, mushroom cap shaped particle, 1.2 ?m in diameter, were used. The PS particles were deposited onto the substrates using aqueous suspensions. Scanning electron microscopy (SEM) was used to assess particle deposition on fibers. SEM revealed that the particles were able to conformally coat both nylon and cotton fibers despite their small radius of curvature. Micrographs showed two smaller particles had longer range, single layer coverage of particles on the fibers, while the larger particles were prone to agglomerate. The NIR reflectance of the PS particle coatings textiles materials was assessed using the testing method specified in the US Army standard MILDTL-44436A. NIR reflectance data was collected with a spectrophotometer equipped with an integrating sphere to collect diffuse light scatter. The effect of the particle coating on the NIR reflectance was assessed using average reflectance spectra and principal component analysis (PCA). The spectra analysis showed that the change in reflectance on fabric substrates ranged from 0 to 6 units. The PCA effects test was used to confirm that the particle coatings significantly changed the reflectance of the substrates. The analysis also revealed that the particle size influenced the reflectance of the fabrics and that the mushroom cap particle behaved more similarly to the smaller spherical particle than the 1.0 ?m particle. The PCA results also confirmed the dyes on the nylon-cotton substrate significantly altered the reflectance behavior. Potential improvements to the deposition procedure and particle selection for altering the reflectance of fabrics are also proposed.