Understanding the Influence of Polymer Mechanical Properties on Mechanochromic Behavior of Cholesteric Liquid Crystals

Mechanically responsive materials show promise in many areas including smart textiles and flexible displays. In certain applications like sensing, it is desirable for materials to respond to an external or environmental stimulus with a macroscopic color change. Military applications can take place in extreme temperature environments where power sources are limited, so having a material that responds to mechanical stimulus is desirable. One interesting class of mechanically responsive materials are mechanochromic cholesteric liquid crystals (CLC). These molecules form helical structures that reflect a wavelength of light proportional to their helical pitch.<br/>While interesting, the utility of these molecules is limited, requiring them to be blended into polymers for many applications. Previous studies have shown this approach still allows for the inherent mechanochromic behavior. What remains is the question of how the polymer matrix viscoelastic properties affect the selective reflection band (SRB) of the blended CLC molecules. In the present study, we first conducted design-of-experiments and machine learning to predict the macroscopic color of a three-component CLC mixture. Rheological experiments were then conducted to understand the effect of strain rate and oscillation on color change. Finally, visible reflection spectroscopy on CLC-polymer blends suggest differences in SRB depending on the mechanical properties of the polymer matrix.