Liquid-crystal lens-cells shaped like a plano-convex Fresnel lens with homogeneous alignment are prepared. Their focal length can be varied from the value f e for an extraordinary ray to nearly f o for an ordinary ray by applying an electric field across the cell. The response and recovery times within several seconds are attained in the liquid-crystal lenses. More transparent (\gtrsim80%) variable-focus liquid-crystal lenses are achieved in the double-layered structure of two identical liquid-crystal Fresnel lenses with a mutually orthogonal optic axis.

The synthesis of three liquid crystals with the general formula N, N'-bis( p a l koxyp henylbenz ylidene )-a,a'-bi-p-toluidine where the alkoxy group is represented by methoxy (BABT; nematic range of 253-370 " C ) , n-butoxy (BBPT; nematic range of 232-331 O C ) , and benzyloxy (BBzPT; nematic range 270-346 " C ) is reported. The liquid crystals were synthesized by the condensation of the appropriate 4'-alkoxybiphenyl-4-carboxaldehyde with a,a'-bi-p-toluidine. The aldehydes were prepared by a five-step procedure starting with Mydroxybiphenyl. BABT was chromatographically evaluated. BABT operating in the supercooled nematic region at 230 O C provided better separations of methyibenzanthracene Isomers than conventional SE-30, Dexsii 300, and Silicon Gum MS2211 columns.The development of high-temperature liquid crystals for use as stationary phases in gas-liquid chromatography (GLC)is rapidly gaining appreciation. The topic was recently reviewed by Kelker ( I ) and Janini ( 2 ) . Several recent applications of liquid crystal phases have been reported (3-11). Our