Wetting of a plane with a narrow solvophobic stripe

ABSTRACT

We present a numerical study of a simple density functional theory model of fluid adsorption occurring on a planar wall decorated with a narrow deep stripe of a weaker adsorbing (relatively solvophobic) material, where wall-fluid and fluid-fluid intermolecular forces are considered to be dispersive. Both the stripe and outer substrate exhibit first-order wetting transitions with the wetting temperature of the stripe lying above that of the outer material. This geometry leads to a rich phase diagram due to the interplay between the pre-wetting transition of the outer substrate and an unbending transition corresponding to the local evaporation of liquid near the stripe. Depending on the width of the stripe, the line of unbending transitions merges with the pre-wetting line inducing a two-dimensional wetting transition occurring across the substrate. In turn, this leads to the continuous pre-drying of the thick pre-wetting film as the pre-wetting line is approached from above. Interestingly we find that the merging of the unbending and pre-wetting lines occurs even for the widest stripes considered. This contrasts markedly with the scenario where the outer material has the higher wetting temperature, for which the merging of the unbending and pre-wetting lines only occurs for very narrow stripes.

GRAPHICAL ABSTRACT

Keywords:

• Wetting
• classical density functional theory

Acknowledgments

PY is grateful to Dr Miguel Dúran-Olivencia from the Chemical Engineering Department of Imperial College for numerous stimulating discussions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

We acknowledge financial support from the Engineering and Physical Sciences Research Council (EPSRC) of the U.K. through Grants No. EP/L027186, EP/L020564 and EP/K503733 (EPSRC-Imperial College Pathways to Impact-Impact Acceleration Award), by the European Research Council (ERC) through Advanced Grant No. 247031 and FIS2015-66523-P (MINECO/FEDER, UE).