Short chains at solid surfaces: wetting transition from a density functional approach

TL;DR

This study uses a microscopic density functional theory to explore how short chain molecules adsorb on solid surfaces and how their wetting transition temperatures vary with chain length and interaction strength.

Contribution

It provides new insights into the dependence of wetting and surface critical temperatures on chain length using a density functional approach.

Findings

Wetting temperature decreases with chain length, reaching a plateau for longer chains.

Surface critical temperature increases with chain length, then levels off.

End segments preferentially adsorb in the first layer, middle segments in the second.

Abstract

A microscopic density functional theory is used to investigate the adsorption of short chains on attractive solid surfaces. We analyze the structure of the adsorbed fluid and investigate how the wetting transition changes with the change of the chain length and with relative strength of the fluid-solid interaction. End segments adsorb preferentially in the first adsorbed layer whereas the concentration of the middle segments is enhanced in the second layer. We observe that the wetting temperature rescaled by the bulk critical temperature decreases with an increase of the chain length. For longer chains this temperature reaches a plateau. For the surface critical temperature an inverse effect is observed, i.e. the surface critical temperature increases with the chain length and then attains a plateau. These findings may serve as a quick estimate of the wetting and surface critical temperatures for fluids of longer chain lengths.