Modifying Surfaces with the Primary and Secondary Faces of Cyclodextrins To Achieve a Distinct Anti-icing Capability

Heterogenous ice nucleation (HIN) induced by organic materials is a long-lasting issue in wide-ranging fields from cryobiology to atmospheric physics, but efforts for controlling HIN are still restricted by incomplete understanding of its mechanism. In this work, distinct anti-icing capabilities were achieved by experimentally investigating the HIN behavior on the surfaces modified with the primary face (PF) and secondary face (SF) of cyclodextrins (CDs) (i.e., α-1,4-linked d-(+)-glucopyranose with two relatively flat and hydroxylated faces). To achieve this, CDs were first immobilized to the surfaces through selectively binding the PF and SF of CDs onto the solid surfaces; as such, either PF or SF is exposed to liquid water. Interestingly, HIN temperature and delay time assays indicate that HIN is depressed when the PF of CDs (which matches with the ice lattice) is exposed to liquid water whereas the HIN is facilitated when the SF of CDs (which mismatches with the ice lattice) is exposed to liquid water. This deviates from the common thought that surfaces with a template of ice lattice match facilitate the HIN. Instead, ¹H NMR studies show that the resonances of hydroxyl (OH) in the SF of CDs are most deshielded due to the formation of intramolecular hydrogen bonds, in comparison to that of OH in the PF of CDs, which weakens the interaction between the OH groups on the SF and water molecules. Thus, the distinct anti-icing capabilities of the PF and SF of CDs can be achieved and established by the distinct interactions between OH groups on the two faces and water, which is of great potential for practical applications. The molecular-level interactions between surfaces and water molecules may be a more appropriate criterion for forecasting materials' HIN ability.