Murthy S S
School of Physical Sciences, Jawaharlal Nehru University, New Delhi, 110 067, India.
Cryobiology. 1998 Mar;36(2):84-96. doi: 10.1006/cryo.1997.2064.
In the determination of the solid-liquid phase equilibria in the aqueous mixtures of dimethyl sulfoxide (Me2SO) and ethylene glycol (EG) one often encounters the problem of equilibrium crystallization. In the present report the above aqueous solutions are equilibrated for crystallization in a dielectric cell during which the dielectric method is used for monitoring the extent of crystallization. The melting temperatures are then measured by using the dielectric technique in combination with the differential scanning calorimeter. The equilibrium phase diagram of Me2SO is found to be eutectic with two compounds formed of water and Me2SO in the ratio of 3:1 and 2:1. In the case of EG solutions it is eutectic with a 1:1 compound formation. It is suggested that the greater depression of the freezing point of water due to the complex formation and hence the attendant increase in the viscosity near the freezing point is the reason for the sluggish crystallization in these solutions. The variation of the glass transition temperature with composition is also examined in the above solutions along with the aqueous solutions of a number of other cryoprotectants. The glass-forming tendency of these solutions is discussed in terms of complex formation. An attempt is made to distinguish between good and bad glass-forming additives in terms of complex formation and ice clathrate formation.
在测定二甲基亚砜（Me2SO）与乙二醇（EG）的含水混合物中的固 - 液相平衡时，常常会遇到平衡结晶的问题。在本报告中，上述水溶液在介电池中进行结晶平衡，在此过程中使用介电方法监测结晶程度。然后结合差示扫描量热仪，利用介电技术测量熔点温度。发现Me2SO的平衡相图为共晶，有两种由水和Me2SO按3:1和2:1比例形成的化合物。对于EG溶液，其为共晶且形成1:1的化合物。有人认为，由于形成络合物导致水的冰点降低幅度更大，进而在冰点附近伴随粘度增加，这是这些溶液中结晶缓慢的原因。还研究了上述溶液以及许多其他冷冻保护剂的水溶液中玻璃化转变温度随组成的变化。根据络合物形成情况讨论了这些溶液的玻璃形成倾向。尝试根据络合物形成和冰笼形物形成来区分良好和不良的玻璃形成添加剂。
