Unexpected hydrophobicity on self-assembled monolayers terminated with two hydrophilic hydroxyl groups

Current major approaches to access surface hydrophobicity include directly introducing hydrophobic nonpolar groups/molecules onto the surface or elaborately fabricating surface roughness. Here, for the first time, molecular dynamics simulations show an unexpected hydrophobicity with a contact angle of 82 degrees on a flexible self-assembled monolayer terminated only with two hydrophilic OH groups ((OH)(2)-SAM). This hydrophobicity, verified by a water slip phenomenon characterizing the friction on the (OH)(2)-SAM surface, 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 the surface and the water molecules above. The unique simple interface presented here offers a significant molecular-level platform for examining the bio-interfacial interactions ranging from biomolecule binding to cell adhesion.

Automated summary

This study demonstrates unexpected hydrophobicity on a self-assembled monolayer terminated with only two hydrophilic hydroxyl groups, attributing it to the formation of a hydrogen-bonding structure that reduces the hydrogen bonds between the surface and water molecules. This unique interface offers a significant platform for investigating bio-interfacial interactions.