Thermophysical Properties Study Of Polyhydroxy Antifreeze At Low Temperature

The polyhydroxy antifreeze (polyalcohol, sugar) are widely used in manyfields at present time. But there are no consistent evaluation criteria andmicro-mechanism explanation for the anti-freezing properties till now. In this study,differential scanning calorimetry (DSC) is employed to investigate thethermophysical properties of the polyhydroxy antifreeze at low temperature, withthe aim to explore the underlying relationship between the molecular structures andthe anti-freezing properties. The main results are list below:1. For the same molality of the polyalcohol aqueous solutions, more hydroxylsin molecule lead to higher water anti-freezing activity (aw) and molar anti-freezingactivity (AFmole) of antifreeze. While the high hydroxyl concentration in thesolutions gives more opportunity for the formation of (-OH)-(-OH) hydrogen bondsbetween the solute molecules and lead to relative poor bond ability with the water.2. Isomeric polyalcohols have different anti-freezing abilities. It is found thathydroxyls linked to the internal carbon bond more water molecules than those endgroups.3. For the pentoses, higher molality of their aqueous solutions results in morehydrogen bonds between solutes and water molecules. But the ability of bondingwith water decreased from the point of view of the single pentose molecule.4. The sugar alcohols have relative higher awand AFmolethan those of theirsugar counterparts, which indicates that the hydroxyl has stronger hydrogenbonding ability than that of the carbonyl.5. The molecular dynamics simulation is employed to predict the freezingproperties of two isomeric polyalcohol aqueous solutions at low temperature. Thesimulation results are validated by DSC. The self-diffusion coefficient inpolyalcohol aqueous solution has been given using the trajectory analysis. It showsthat the self-diffusion coefficient decrease linearly with reduction of the systemtemperature. The apparent activation energy of different polyhydroxy antifreezecan be compared through the Arrhenius relationship between the self-diffusioncoefficient and temperature.