DSC Study on Cooperative Relaxation in 1,2-propanediol

Cooling rate dependence of the cooperative relaxation in 1,2-propanediol was investigated in terms of the nonlinear Adam-Gibbs (AG) enthalpy relaxation theory using differential scanning calorimetry. The AG parameters were obtained using a curve-fitting method. The results indicated that the model parameters show strong dependence on the cooling rates. Those obtained at higher cooling rates are in good agreement with the published data. The fitting results were used to estimate the microscopic parameters of the cooperative rearranging region (CRR), in particular the size of the CRR (z*) and the configurational state available to it (W*). It was found that the W* recommended for polymers led to physically meaningless z* for 1,2-propanediol. Johari's method, which was based on the AG theory, yielded around 3 molecules in the CRR, but the W* was anomalistically higher than those of polymers. It is di±cult to reconcile the Adam-Gibbs' z* with the results obtained using Donth's formula. An argument is presented that a new physical meaning should be given to conventional Adam-Gibbs' z* for molecular H-bond liquids.