Disorder effects in low concentration dispersions of small quartz spheres in cyanobiphenyl liquid crystals

A photopyroelectric study of the specific heat and the thermal conductivity of small quartz sphere (aerosil) dispersions in heptylcyanobiphenyl (7CB) and octylcyanobiphenyl (8CB) liquid crystals with a concentration rho(s) = 0.005 g cm(-3) is reported. The thermal conductivity data show that, even a t this low concentration, the elastic strain introduced in the liquid cryst al by the aerosil particle is not completely annealed at the nematic-isotro pic (NI) phase transition. In 8CB, annealing has been found at the smectic- nematic phase transition, while in the case of 7CB it occurs in the nematic phase also. Moreover, the depression of the NI transition temperature has been found to be much smaller than the one predicted by a random field mode l in which quenched disorder simply affects the average order of the sample and no effects of the elastic strain are considered. [S1063-651X(99)50911- 2].