An Experimental study on solidification of a binary Mixture inside a Cryovial

Abstract

Cryopreservation is the technology of preserving biological cells at very low temperature which is very important for medical science. The survival of cell in cryopreservation technique depends on various parameters like- cryoprotectant (CPA) type, CPA concentration, cooling rate. Cells are suspended in a binary solution inside a cryovial which is submerged into liquid nitrogen. The binary solution solidifies due to extreme low temperature and its solidification behavior decides the survival of biological cell. The objective is to determine the effect of concentration on solidification of binary mixture. Glycerol is widely used cryoprotective agent therefore aqueous solution of glycerol is taken as binary solution. Present work focuses on design of experimental setup and analyzing the results of experiment. Effect of glycerol concentration on solidification of aqueous glycerol solution has been studied experimentally. The experiment was performed for aqueous glycerol with different molar concentraion of glycerol i. e. 0.3 M, 0.6 M, 0.9 M and 1.2 M. Variation of temperature with time during solidification of each solution was presented. The experiment was also performed for pure water and results were compared with aqueous glycerol (binary solution) results. For each experiment, solution was filled in a cryovial (used in cryopreservation) and thermocouples were placed along the axis of cryovial at different heights. After comparing the results of pure water with aqueous glycerol, it was concluded that unlike pure water, solidification of glycerol takes place gradually. Formation of “mushy zone” was observed during solidification of aqueous glycerol. Addition of glycerol decreases the freezing point of solution and with increase in concentration, solidification temperature further decreases. Results of experiment also revealed that addition of glycerol into water prevents the crystallization of ice and make it amorphous. The effect of concentration on coefficient of expansion of solution after solidification was also recorded.