Critical cooling rates to avoid ice crystallization in aqueous cryoprotectant solutions containing polymers

Abstract

The critical cooling rates for the avoidance of ice formation and hence the promotion of the vitreous state have been determined for butane-2,3-diol and a number of other cryoprotectants in the presence of poly(ethyleneglycol) and polyvinylpyrrolidone. The dependence of the critical cooling rates on the molecular weight of poly(ethyleneglycol) has been investigated. The technique employed was the application of isothermal emulsion differential scanning calorimetry to construct time–temperature–transformation curves from which continuous-cooling–transformation curves were calculated. The results indicate that the addition of polymers markedly reduces the cooling rates required to avoid ice crystallization and that poly(ethyleneglycol) is more efficient than polyvinylpyrrolidone in this respect. Of the poly(ethyleneglycol)s studied, it is shown that that with a molecular weight of 400 reduces the critical cooling rate to a greater degree than those of higher molecular weights.