Droplet deformation and alignment for high-efficiency polarization-dependent holographic polymer-dispersed liquid-crystal reflection gratings.

Droplet deformation and alignment are achieved in holographic polymer-dispersed liquid-crystal reflection gratings by applying an in situ shear during recording. High diffraction efficiency (99%) is obtained for light polarized parallel to the shear, with nearly zero efficiency for perpendicular polarization, and no increase of incoherent scattering. Permanent polarization dependence is related to stress-induced morphology changes of liquid-crystal droplets that are frozen by polymerization. The system is studied by electron microscopy and modeled by anisotropic coupled-wave and scattering theory. The morphology is consistent with the theory of small deformations of liquid droplets in fluid flow. Diffraction efficiency measurements are in agreement with theory incorporating this morphology as well as concomitant orientation and alignment of liquid-crystal molecules.

Synthesis of L-fucose 2-, 3-, and 4-sulphates.

Treatment of L-fucose with an excess pf pyridine-sulphur trioxide gave an equilibrium mixture of mono-, di-, and tri-sulphates. L-Fucose was sulphated under optimal conditions for monosulphate formation, and the monoester fraction was isolated by chromatography on DEAE-cellulose. The isomeric L-fucose 2-, 3-, and 4-sulphates (1-3) were separated on a DEAE-cellulose column by elution with borate buffer. The structures of 1-3 were established by electrophoresis, colour tests, periodate oxidation, and, for the 2-isomer, by comparison with a specimen of 1 that had been definitively synthesised via methyl 3,4-O-isopropylidene-alpha-L-fucopyranoside (6) and methyl alpha-L-fucopyranoside 2-(barium sulphate) (5). The latter was rapidly hydrolysed in hot, dilute acetic acid to 1 and methyl alpha-L-fucopyranoside (4).