Effect of Hydration States on the Anti-Icing/Frosting Performance of Zwitterionic Hydrogel-Coated Surfaces

Zwitterionic polymers have gained considerable research attention because of their unique properties and have been widely used in many biomedical and electrochemical applications. Recently, zwitterionic polymers have been investigated for use as anti-icing/frosting surfaces; however, key factors influencing their anti-icing/frosting performance and effectiveness under real operational conditions remain underexplored. Therefore, in this study, we quantitatively analyze the hydration states of zwitterionic hydrogels synthesized from polymerizable zwitterions, such as carboxybetaine methacrylate (CBMA), 2-methacryloyloxyethyl phosphorylcholine (MPC), and sulfobetaine methacrylate (SBMA). We focused on the effect of these hydration states on anti-icing/frosting performance in practical environments through a thermodynamic approach. The fractions of freezable water were 14% in pCBMA, 16% in pMPC, and 34% in pSBMA. The activation energy for ice formation within the hydrogel was observed as pCBMA (101.71 kJ mol^-1) > pMPC (74.32 kJ mol^-1) > pSBMA (59.82 kJ mol^-1), suggesting that the zwitterionic hydrogel-coated surface makes ice formation more challenging compared to the uncoated bare substrate (45.79 kJ mol^-1). We confirm that a reduction in the freezable water fraction within the hydration state can enhance the anti-icing/frosting performance. Our results demonstrate that zwitterionic hydrogels with strong interaction energies offer significant potential as anti-icing/frosting coatings. This work also reveals the in-depth mechanism of ice propagation and frost growth on hydrogel coatings and proposes insights that can be used to efficiently design future anti-icing/frosting coatings.