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.