A series of progress in the study of ion controlled recrystallization of ice crystals by Institute of chemistry, Chinese Academy of Sciences

Icing is a common phase transition process in nature The ice crystal near the ground can provide necessary reaction interface and carrier for many chemical reactions, and then deeply affect the change of surface environment and geological structure Icing is also an important scientific problem in the fields of life, atmosphere, ocean, environment, aerospace and so on, which has been attached great importance by scientists for a long time With the support of NSFC, the Ministry of science and technology and the Chinese Academy of Sciences, the researchers of the Key Laboratory of the Green Printing Institute of the Institute of chemistry have carried out in-depth and systematic research on ice nucleation, ice growth and recrystallization inhibition in recent years They found the ionic effect of heterogeneous ice nucleation (SCI Adv., 2016, 2, e1600345); revealed the Janus mechanism of antifreeze protein regulating ice nucleation (proc Natl Acad SCI U.S.A., 2016, 113, 14739-14744.); found that graphene oxide can control ice crystal growth and recrystallization, and applied graphene oxide to cryopreservation for the first time (angel Chem Int ed.),  2017, 56, 997 –1001 ）。 Ice recrystallization is a kind of Oswald ripening phenomenon (in the process of ice crystal evolution, because the surface energy of large ice crystal is smaller than that of small ice crystal, leading to the large ice crystal becoming larger and the small ice crystal becoming smaller or even disappearing) This phenomenon widely exists in nature Ice recrystallization plays an important role in many aspects, such as food storage, survival of organisms in extremely cold areas, cryopreservation of cells and organs, glacier movement, ocean current changes and ozone content in the atmosphere Therefore, it is very important to study the mechanism of ice recrystallization and realize the regulation of ice recrystallization process Recently, they worked with Professor Zeng Xiaocheng of the University of Nebraska Lincoln to study the effect of ions on ice recrystallization They found that the type of ions in the aqueous solution has a great influence on the size of the recrystallized ice domain: when there are fluorine ions in the aqueous solution, the size of the recrystallized ice domain is small; when there are iodine ions in the aqueous solution, the size of the recrystallized ice domain is large; by using different ions, the size of the ice domain can be continuously adjustable in the range of 20 μ m to 280 μ m (Figure 1) Figure 1 The influence of ion type on the domain size of ice crystal after recrystallization Further molecular dynamics simulation shows that the distribution coefficients of different ions in ice crystal and water are different: fluorine ions tend to stay in water, while iodine ions can be wrapped in ice crystal (Figure 2) In the process of recrystallization, there will be a large number of fluorine ions in the ice water interface, which will inhibit the growth of ice crystal; on the contrary, because the ice crystal contains iodine ions, it is easier to grow As a result, the domain sizes of ice crystals are different after recrystallization in different ionic aqueous solutions In this way, the experimental method of recrystallization combined with theoretical simulation reveals the distribution coefficient of ions in ice water and the molecular mechanism leading to different recrystallization results Fig 2 molecular dynamics simulation reveals that the distribution coefficients of different ions in ice water are quite different Because the domain size of ice crystal is adjustable in a large range, and ice recrystallization is a process of dynamic stability, ice recrystallization provides a new method for controlled preparation of two-dimensional and three-dimensional porous materials by ice template method Fig 3 shows the assembly of polymer, quantum dot and polymer colloid particles into 2D and 3D materials with adjustable pore size using recrystallized ice crystal as template The work was published in nature communication (NAT Commun., 2017, 8, 15154.) Fig 3 preparation of 2D and 3D porous materials with different components by ice template method