Inhibition effect of sugar-based amphiphiles on eutectic formation in the freezing–thawing process of aqueous NaCl solution

DSC and simultaneous XRD–DSC measurements were carried out to clarify the interaction among the ingredients in a ternary aqueous solution composed of NaCl, a sugar-based amphiphile or free sugar, and water. Two aspects of the inhibition of eutectic formation were suggested through the addition of the sugar amphiphile. One was the retention of the glass state of the eutectic phase, and the other was the trapping of NaCl hydrate into the sugar moiety of the amphiphilic aggregate. The difference between the free sugar and the amphiphilic one in terms of the trapping of NaCl hydrate was attributable to their dissimilarity in the dissolution state. The results indicated that the free sugars in water could interact with NaCl hydrate on the basis of their various hydroxyl groups. On the other hand, the sugar-based amphiphiles generated a self-assembly aggregate in the system, and interacted with NaCl hydrate by a salting-in effect with their sugar moiety in the freezing–thawing process. It was confirmed that the number of sugar units played an important role in trapping NaCl hydrate in the system. The effects of the structural isomerism in the sugars were slight with regard to the inhibition of eutectic formation.