Photochromic Liquid Hydrogels as Hosts for Holographic Materials

Abstract

AbstractThe goal of this project is to develop, fabricate, and test advanced optical materials for potential applications to real-time holography based on liquid crystalline polymer hydrogels. In this project, we are investigating the feasibility of increasing holographic capacity and lifetime by coupling a photochromic spyropyran dye to in a liquid crystalline polymer in which cholesteric order has been ‘captured.’ ‘Capture’ is being approached using a unique in-plane poling process with the helical polypeptide poly(α-benzyl-L-glutamate), PBLG, a biopolymer which is capable of maintaining cholesteric order in a liquid crystalline state. Subsequent in situ crosslinking of this aligned biopolymer is projected to offer increased birefringence of the host in the writing of a hologram. Given that a key issue is the magnitude of the real component of the refractive index, increasing the bireflingence may be a useful approach. In writing the hologram, the liquid crystals (LC's) go from isotropic to an ordered dispersion, a property which can be captured via crosslinking to improve holographic lifetime. In the following, the characterization of an aligned host LC system based on the biopolymer poly(α-benzyl-L-glutamate), PBLG, is presented. Inplane alignment is shown to depend on a number of variables, most notably the choice of solvent, polymer molecular weight, and field strength. The results show that optimal alignment of the PBLG LC is achieved with a 2.5% (w/w) concentration of a 118kD biopolymer in methylene chloride in an applied field of 10 kV/cm. Subsequent work will exploit this system as a host for a spiropyran dye for improved holographics.