Ice Nucleation In 3D Network Structure Of Polyacrylamide Hydrogel

Recently,antifreezing hydrogelhasaroused many attentions in the research area of flexible and wearable devices due to its stable conductivity and mechanical properties at low temperatures.There have been quite a lot studies making significant progress in the applications of antifreezing hydrogel.Yet,the mechanism of ice nucleation in the hydrogelremainsunclear.Herein,we reporteda quantitative studyof the ice nucleation in polyacrylamide hydrogel based on a microdroplet suspension method,which was employed as a hydrogel model system.It follows that:(1)The nucleation barriers and effective nucleation temperature of polyacrylamide hydrogel were quantitatively obtainedthrough theln(τV)～1/T(△T)profileswithin the framework of nucleation theories.It was found that the polyacrylamide hydrogels could significantly increase the nucleation barrier of ice.Besides,the effective nucleation temperature of ice could be lowered to-50℃ by polyacrylamide hydrogel from-40℃ in ultrapure water system.(2)The details of nucleation processes arecaptured by high-speed cameras.It was found that asignificant difference of the ice nucleation arisebetween ultrapure water and water in polyacrylamide hydrogels.Under asufficiently high supercooling,numerous nuclei formed uniformly throughout thewater droplet within a short time(about100ms).While inpolyacrylamide hydrogel,the ice nucleation started in a very small local area at the very beginning of ice nucleation,and then spread to the whole droplet.The heterogeneous nucleation promoted by the tiny foreign particles in water is regarded as the mainly reason for the difference between the water and polyacrylamide hydrogel systems.The tiny foreign particles were served as gelation sites,which would be embedded during the gelation processes and could hardly promote the ice nucleation process.In summary,the details of ice nucleation process in polyacrylamide hydrogel have been revealed.And the antifreeze properties of polyacrylamide hydrogel have been quantitatively studied.It’s expected that these results could provide fundamental instructionsfor the study of antifreezing hydrogel.