Cholesteric elastomers: Deformable photonic solids - art. no. 041803

A mechanical strain applied to a monodomain cholesteric elastomer modulates and eventually unwinds the helical director distribution. There are simila rities with the classical problem of an electric field applied to a cholest eric liquid crystal, but also differences. Frank elasticity is of minor imp ortance unless the gel is very weak. The interplay is rather between the di rector being helically anchored to the rubber elastic matrix and the extern al mechanical field. Stretching perpendicular to the helix axis induces the uniform unwound state via the elimination of sharp, pinned twist walls abo ve a critical strain. Below the critical strain the coarsening of the direc tor distribution is not accompanied by an increase but rather by an affine decrease in the pitch, Unwinding through conical director states occurs whe n the elastomer is stretched along the helical axis, Finally we consider ch olesteric elastomers in a classical device geometry with an electric field applied along the pitch axis and hence transverse to the director orientati on.