Mechanically Induced Helicity in Chiral Stimuli-Responsive Gels

Abstract

Mechanical and optical responses of chiral stimuli-responsive gels to macroscopic deformation are theoretically studied. We propose a simple elasticity model for the network of helical polymer chains by combining a statistical theory of a single polymer chain bearing induced helices recently presented by us [Macromolecules 2005, 38, 561] with the classical affine network theory. We find that the stress−strain relation of the network in a solution of chiral molecules has characteristic profiles different from sigmoidal ones observed in the conventional rubberlike materials. We also find that, as the network is uniaxially elongated or compressed, the chirality order parameter, which is proportional to the intensity of circular dichroism of the network, is enhanced in the intermediate region of elongation under certain conditions. Finally, we discuss the possibility of optical resolution of almost racemic mixtures of chiral molecules by using such networks.