Structure and morphology of polymer-stabilized cholesteric diffraction gratings

We report a study of polymer network morphology in planar diffraction grati ngs formed from polymer-stabilized cholesteric liquid crystals. Photopolyme rizing a mesogenic monomer yields a regular sawtooth morphology, composed o f polymer sheets running at an acute angle between thick, uniformly aligned bundles which reside on the opposing substrates. To explain this morpholog y and evidence of two grating vectors in the diffraction pattern, we propos e a model for the liquid-crystal director where out-of-phase twists at the surfaces gear into an interior twist, which has half the period of the surf ace twist, via splay distortions running between the substrates. The morpho logy also changes significantly when a nonmesogenic monomer is substituted or when selectively polarized states of UV radiation are used to cure the p olymer. (C) 2000 American Institute of Physics. [S0003-6951(00)03524-5].