X-ray scattering study of smectic ordering in a silica aerogel

We have studied, via x-ray scattering, the nematic to smectic-A (NA) translational ordering of the liquid-crystal--forming compound octylcyanobiphenyl (8CB) incorporated into the pores of a silica aerogel. We find that the aerogel dramatically alters 8CB phase behavior, eliminating the NA transition found at T=TNA=33.7 ^∘{}C in bulk samples and replacing it by a short range smectic ordering having a correlation length which at TNA is {ξ}{~}40 {}, much smaller than the aerogel pore and nematic domain size ξₚ{~}200 {}. As T is lowered this smectic disorder is eliminated from the pores, {ξ} increasing continuously over a 20 ^∘{}C range to saturate at ξₚ for TTNA-20 ^∘{}C.