Optical birefringence measurements on a rod-like liquid crystal (8OCB),
imbibed in silica channels (7 nm diameter), are presented and compared to the
thermotropic bulk behavior. The orientational and positional order of the
confined liquid evolves continuously at the paranematic-to-nematic and sizeably
broadened at the nematic-to-smectic order transition, resp., in contrast to the
discontinuous and well-defined second-order character of the bulk transitions.
A Landau-de-Gennes analysis reveals identical strengths of the nematic and
smectic ordering fields (imposed by the walls) and indicates that the smectic
order is more affected by quenched disorder (originating in channel tortuosity
and roughness) than the nematic transition.Comment: 3 pages, 4 figure
