Formulation of Liquid Crystal Coatings for Color Changing Fabrics

Liquid crystals (LCs) are a unique class of responsive soft material. Cholesteryl ester based LCs are capable of self-assembling into helical structures. The pitch length of the of the helix dictates the reflected color. Depending on the composition, the length of the pitch can be affected by temperature (temperature sensitive formulations) or mechanical strain (shear sensitive formulations. There is a growing interest in utilizing thermochromic and mechanochromic LC to produce responsive, color changing fabrics.

In this work, our goal is to achieve responsive color changing fabrics. Our approach is to formulate LC containing coatings to apply to cotton textiles. To achieve thermochromic fabrics, we formulated temperature sensitive liquid crystals from 60 wt% cholesteryl oleyl carbonate, 30wt% cholesteryl pelargonate, and 10wt% cholesteryl benzoate. When applied to cotton, thermochromic properties were achieved. A color change from colorless to green/yellow was observed when heated. However, the samples had an oily texture and the thermochromic properties lasted 3 days. To improve the properties of the resulting fabric, the LC was incorporated into a commercially available textile paint (Speedball Transparent Screen Printing Base). Various ratios of LC to paint base (from 1:0.5 to 1:3) were examined. The type of fabric (knit vs. woven (twill)) were also explored. The thermochromic properties after heat setting were investigated. The color change upon heating was captured with a smart phone and further quantified in CIE LAB color space using ∆E. We determined that thermochromic properties were most visible (confirmed by greatest ∆E calculated) on black cotton twill using a 1:0.5 ratio of LC to base. The thermochromic behavior was observed for at least 10 days. The same approach was used a shear sensitive liquid crystal formulation (52 wt.% cholesteryl oleyl carbonate, 24 wt.% cholesteryl pelargonate, and 24 wt.% cholesteryl chloride). The LC was combined in a 1:3 ratio of LC to paint base and applied to a knit cotton textile. The mechanochromic properties of the fabrics (i.e. color change with stretch) are currently being investigated. Overall, we have formulated liquid crystals with commercial textile paint to encapsulate the LC. This approach minimizes oily when applied to textiles and appears to improve the stability of the LC while maintaining the responsive properties of the LC.