Tunable Wettability of Polymer Films by Partial Engulfment of Nanoparticles

TL;DR

This study demonstrates that nanomeniscus formation between nanoparticles and surfaces significantly influences wettability, enabling tunable surface properties through controlled nanostructuring, which contradicts traditional models like Wenzel or Cassie-Baxter.

Contribution

It introduces the role of nanomeniscus in wettability control, providing a new perspective beyond classical models and demonstrating how nanoparticle morphology affects surface wettability.

Findings

Wettability decreases linearly with nanoparticle height.

Nanomeniscus causes negative capillary pressure, increasing contact angle.

Surface coverage by nanoparticles also affects wettability.

Abstract

A series of poly(methyl methacrylate) (PMMA) surfaces decorated by Cu nanoparticles (NP) with gradually varied morphology were prepared by high-pressure CO2 treatment at various time spans. Combining the characterizations of transmission electron microscopy (TEM) and atomic force microscopy (AFM), an accurate 3-dimensional view of the morphology of the surfaces was presented. Subsequently, the wettability of the surfaces decreases near-linearly with the increase of the apparent height of the decorating NPs in both static (static contact angle) and dynamic (contact angle hysteresis) aspects. The observed tendency contradicts to the Wenzel or Cassie-Baxter model and is explained by the contribution of nanomeniscus formed between the decorating NP and the flat substrate. The capillary pressure from this meniscus is negative and results in the increase of the contact angle with the apparent height (H_N) of the Cu NPs decorating the PMMA surface. In addition, the effect of the coverage (C_N) by NPs on the wettability can be explained on the same basis. Our experiment demonstrates the important influence of the nanomeniscus on the wettability, which is usually not taken into account. The results in this work provide a comprehensive understanding of how nanostructure affects the wettability of the decorated surfaces and shed light on how to obtain certain wettability through nanostructuring of the surface morphology.