Molecular Insights into the Hydration of Zwitterionic Polymers

Preventing ice formation and accumulation on solid surfaces has always been a great challenge to address for various applications. By applying anti-icing coating on surfaces, we can efficiently reduce ice formation and adhesion. Recently, the new development of zwitterionic polymer coatings attracted a lot of attention due to their excellent anti-icing performance. Herein, we used Density Functional theory (DFT) to present a comprehensive understanding of the hydration behavior of two representative zwitterionic polymers, i.e., poly-sulfobetaine (polySB) and poly-phosphorylcholine (polyMPC), to unveil the molecular mechanism of their excellent anti-icing performance by providing a clear physical and chemical understanding of water-polymer interaction. The bonding analysis by crystal orbital Hamilton populations (COHP) showed strong interaction and covalent-nature bonds between the hydrogen atoms in water molecules and polymers' oxygen atoms. Electron density of states (DOS) and Bader charge analysis both further demonstrated the chemical nature of the water-polymer bonds. Interestingly, our modeling results also revealed that the addition of more water molecules will decrease the stability of the bond between adsorbed water molecules to the polymer. ? Such induced bond instability, along with the polymer's hydrophilic character, suggests that continuous association and dissociation of bonded water molecules serve as the key mechanism of inhibition of water clustering.