Unexpected Hydrophobicity on Self-Assembled Monolayers Terminated with Two Hydrophilic Hydroxyl Groups (2102.03095v1)

Abstract: Current major approaches to access surface hydrophobicity include directly introducing hydrophobic nonpolar groups/molecules into surface or elaborately fabricating surface roughness. Here, for the first time, molecular dynamics simulations show an unexpected hydrophobicity with a contact angle of $82^o$ on a flexible self-assembled monolayer terminated only with two hydrophilic OH groups ($(OH)_2!-!SAM$). This hydrophobicity is attributed to the formation of a hexagonal-ice-like H-bonding structure in the OH matrix of $(OH)_2!-!SAM$, which sharply reduces the hydrogen bonds between surface and water molecules above. The unique simple interface presented here offers a significant molecular-level platform for examining the bio-interfacial interactions ranging from biomolecules binding to cell adhesion.