Molecular dynamics study of surface-tethered S(CH2CH2O)6CH3: Helix formation and thermal disorder

We present the results of a molecular dynamics study of a set of surface-tethered S(CH2CH2O)6CH3 chains. In this study, we analyze helix formation, in addition to thermal disorder, and find that spontaneous helix formation and details of helix morphology depend on charge partitioning ascribed to oxygen and the methylene groups. The effects of varying surface coverage as well as chain–surface interaction strength indicate that a set of approximately 72 helical structures oriented predominantly normal to the surface are formed at near full coverage. This occurs even though thermal disorder clearly precludes a description based on the concept of a perfect crystalline monolayer. Thermal fluctuations in chain morphology in the vicinity of the terminal methyl groups lead to the exposure of oxygen to the external environment. We also find that the persistence of compact helix-containing domains at partial surface coverage results in the formation of well-defined cavities or void regions that expose the bare surface, even in the presence of strong chain–surface attractive interactions.

Graphical abstractMolecular dynamics simulations of short ethylene oxide chains tethered to surfaces reveal helical order and small cavities depending on the local surface density.Figure optionsDownload full-size imageDownload as PowerPoint slide