In order to examine the validity of entropically based nonlinear Adam-Gibbs equation (AGV) on the describing of cooperative relaxation of H-bond molecular liquid, differential scanning calorimetry (DSC) was employed to obtain the specific heat capacities (C_p) of 1,2-propanediol (PD) and its aqueous solutions in the range of 115～230 K. Curve fitting technology was used to obtain the AGV model parameters. The results indicated that AGV formula can be used to reproduce the experimental normalized C_p curves of present systems. Different relaxation behaviors were found between PD and its aqueous solutions, but the water content shows neglectable effect on the relaxation behaviors in aqueous solutions. The activation energies (Δμ') and the sizes of cooperatively rearranging region (z*) were analyzed using AGV model and Johari’s thermodynamic method. Physically reasonable z* can only be obtained when larger values of configuration numbers (W*) were chosen. For pure compound, Johari’s method yielded 3 PD molecules in the coopera-tively rearranging region (CRR), but the values of W* seems to be anomalistically higher than those of polymers. The length scales of CRR (ξ_CRR) were also estimated from the tem-perature fluctuation theory proposed by Donth. With the variation of the composition, ξ_CRR obtained using Donth’s method was consistent with the Δμ' and non-exponential parameter analysis. But the number of molecules included in the CRR was 350 for PD, which seemed to be no possibility to reconcile it with the z* in AG sense.

Key words: cooperative relaxation, 1,2-propanediol, aqueous solution, differential scanning calorimetry