Stereo-selective swelling of imprinted cholesteric networks.

Molecular chirality, and the chiral symmetry breaking of resulting macroscopic phases, can be topologically imprinted and manipulated by cross-linking and swelling of polymer networks. We present a new experimental approach to stereo-specific separation of chiral isomers by using a cholesteric elastomer in which a helical director distribution has been topologically imprinted by cross-linking. This makes the material unusual in that is has a strong phase chirality, but no molecular chirality at all; we study the nature and parameters controlling the twist-untwist transition. Adding a racemic mixture to the imprinted network results in selective swelling by only the component of "correct" handedness. We investigate the capacity of demixing in a racemic environment, which depends on network parameters and the underlying nematic order.