Wideband reflection wavelength tuning by bending of cholesteric liquid crystal elastomer films

Abstract

Cholesteric liquid crystal elastomers (CLCEs), which exhibit selective reflection derived from a helical molecular structure, are receiving a great deal of attention because they deform largely due to the cross-linked polymer chains. Reflection wavelength of a CLCE film can be tuned by mechanical stretching that induces a change in the helical pitch. However, stretch-induced reflection wavelength tuning has some issues such as a large load required and a limited tuning range. In this paper, reflection wavelength of a CLCE film is tuned facilely and widely by bending. Outward and inward bendings cause blue and red shifts, respectively. Bending-buckling load required for the reflection tuning is much lower than stretching one, which is proved experimentally and theoretically. By considering the bending behavior of materials, we can impose large strain on a CLCE film and tune reflection wavelength over 300 nm, which is almost the whole region of visible light. This wideband reflection wavelength tuning by low-load bending leads to expanding applications of CLCEs.