Effect of quenched disorder on the RI-RV, RII-RI, and liquid-RII rotator phase transitions in alkanes.

The ability of disorder to reduce the coupling between the distortion and tilt angle order parameters was tested over the R(I)-R(V) phase transition by measuring the specific heat in alkanes with different R(I) phase temperature range mixed with various concentrations of silica nanoparticles. It was found that the disorder significantly affects the character of the R(I)-R(V) transition, driving it toward a second-order character. The features about the R(II)-R(I) transition were progressively attenuated for increasing disorder in both alkanes, becoming very faint for the largest particle concentration, but the first-order character was maintained. Over the liquid-R(II) transition, the single peak observed in both the specific heat and the latent heat in the pure materials splits into two features, at different temperatures, as over the isotropic-nematic transition in liquid crystals.