Constant-volume heat capacity at glass transition

We analyze the jump of heat capacity at glass transition, and calculate the constant-volume heat capacity change ΔCv at glass transition in the common glass formers. The experimental heat capacity jump ΔCp includes both dynamic and dilation's contributions. The ΔCv removes the dilation's contribution, and only refers to the dynamic contribution. We find that the ratio ΔCv/ΔCp does not change with the liquid fragility, and almost keeps a constant: 0.85. The results might have implications for a fundamental understanding to the nature of glass transition.