Dynamic color in stimuli-responsive cholesteric liquid crystals

Abstract

is the acronym used around the English-speaking world to aid children in the memorization of the traditional colors of the rainbow (red, orange, yellow, green, blue, indigo, and violet). Color surrounds us and the ability to change color by external stimuli (heat, force, light exposure, magnetic or electric field) continues to be leveraged for many present day applications. This review focuses on the state of the art in the use of cholesteric liquid crystals (CLCs) as color changing optical materials. After a brief summary of thermal and electrically induced color changes, the bulk of the article describes recent efforts in photoresponsive CLCs, materials in which light is used to control the color output.

Photoresponsive Cholesteric Liquid Crystals

“…Through controlling the pitch in a certain range, the reflection wavelength can be adjusted into the visible region. The inherent reflectivity of CLCs and the capability for dynamic color change by external stimuli have led to extensive research of CLCs with an eye toward applications in color filters, reflectors, and reflective displays [89,90]. Due to the advantages of light over other stimuli, photoresponsive CLCs have been thought as smart materials in which light is being employed to control the light.…”

A temperature-mapping molecular sensor for polyurethane-based elastomers

“…1,2 In the case of common polymerbonded explosives, which typically contain explosive crystals embedded in a binder such as urethane-crosslinked polybutadiene, in-situ measurement of the temperature without disturbing the micro-and mesoscale mechanical properties is quite challenging. Thermochromic polymers which use microencapsulated leuco dyes or liquid crystals have been widely studied, [3][4][5][6] but cannot give spatial resolution throughout the polymer and can themselves introduce undesirable defects. A method that could analyze microscale temperature localization post-mortem after an impact or shock-loading event with submicron spatial resolution and no alteration of local mechanical properties is highly desirable.…”

Tuning of the Reflection Properties of Templated Cholesteric Liquid Crystals using Phase Transitions

“…As interesting as these materials are, there are a number of drawbacks for non-display applications being investigated. The first is that the switching behaviour is reversed for many applications where there is a desire for the color to be 'off' and then turned 'on' upon application of a stimulus [3]. Second, the single film reflection is usually limited to 50% due to the single handedness of the chiral mesoscale structure [4].…”

“…Second, the single film reflection is usually limited to 50% due to the single handedness of the chiral mesoscale structure [4]. Third, the ability to tune the color rather than switch it on and off would enable simplicity in the design of a number of display and nondisplay applications [3].…”