The Enthalpy Relaxation Behaviors Of Linear Polyalcohols

As a kind of commonly cryoprotectants, linear polyalcohols are widely used in freeze-drying and cryopreservation, and they are often used as model systems in the study of the non-equilibrium characteristic of the freeze-drying product. The reasons are that its molecular structure is simple, glass forming ability is strong and thermal events in the cooling and heating are typical, such as glass transition and enthalpy relaxation behaviors. In this paper glassy sorbitol undergo two kinds of thermal history:one is cooling-heating experiment in different cooling rates, the other is annealing in different annealing temperature, with the aim to explore the predictive power of the two different phenomeno logical models. The main results are list below:1. Two kinds of thermal history can be fitted very well by TNM, the fit quality depends heavily on the values of the averaged square deviation (?), the smaller the ?, the better the quality of fitting. It is found that the fitted curves agree very well with respective experimental data employed in a single curve fitting. However, the parameters calculated under one thermal history often fail to capture the experimental peaks produced under other thermal history. Moreover, the multi-curve fittings eliminate the parameter incompatibility produced in single-curve fitting, and the parameters calculated under 12-curves can capture the all experimental peaks. Therefore, the multi-curve fitting method determining the TNM parameters are more reliable.2. Whether AGV is suitable for multi-curve fitting is studied. It is found that with the different of the input parameters, the averaged square deviation (?) is fluctuated. Comparing the method of four parameters fitted at the same time with the method of T2 fixed and other parameters searched at the same time, it proved the validity of the four parameters fitted at the same time. It is believed that the parameters calculated under 12-curves AGV model can capture all experimental specific heat capacity.3. AGV parameters and Donth method are applied to calculate the CRR parameters, the two calculation results can not consistent. It is suggested that this may be a common character of small molecule hydrogen bond of the liquid. Here, z* can be seen as the number of hydrogen bonding associated cluster in CRR, which each group contains a certain number of molecules. The value of W* obtained by AGV model seems to be anomalistically higher than those of polymer, the reason may be that W* represent chain segment in polymer, but it appears hydrogen bond disconnected and reassembled in small molecular hydrogen bond liquid in the process of cooperatively rearrangement, so it has more W*.4. The vitrification phenomenon of EG/G mixtures with different concentration were investigated. The glass transition and TNM parameters were obtained by extrapolation method, all TNM parameters showed good linearity. Obtained kinetics fragility of EG using the same extrapolation method, proved the strong liquid behavior of EG is good than glyceroL Besides, the CRR parameters of EG were extrapolated.