Substrate-Enhanced Mechanochromic Sensitivity in Stimuli Response Textiles

Abstract

Textiles that show dynamic color with strain may be of interest for information encryption, anticounterfeiting, and camouflage applications. In this work, extrusion of polymer-dispersed liquid crystals on fabrics was performed to achieve structurally colored, visibly responsive coatings. The mechanochromic response was examined using visible reflectance spectroscopy or a smart phone camera. Upon strain of the free-standing liquid crystal-polymer films, a blue shift in the peak reflectance was observed with a mechanochromic sensitivity of 0.3 nm/% strain. Application of the coating on a black fabric substrate increased the mechanochromic sensitivity 3- to 40-fold. The enhanced mechanochromic sensitivity was attributed to the color contrast of the liquid crystal color with the substrate, as well as decreased liquid crystal opacity upon stretching. Visible changes in color upon strain were observed with a smart phone camera and quantified with ΔE. Minimal visible color change was observed when stretching the coated fabric to 10%; noticeable color change was observed when the coated fabric was strained to 15%. Thus, the opacity of the liquid crystal and the color contrast between the liquid crystal and the substrate can be important factors to facilitating the use of coatings that are initially blue and undergo a blue shift upon stretching.