Strain-Dependent Wetting of Graphene

TL;DR

This study uses atomistic simulations to reveal that graphene's wetting properties are highly sensitive to mechanical strain, affecting its contact angle and anisotropic wetting behavior, which has implications for nanotechnology applications.

Contribution

The paper introduces a first-principles machine learning approach to predict water contact angles on graphene and uncovers the strain-dependent wetting behavior of free-standing graphene.

Findings

Graphene's contact angle is approximately 72 degrees, indicating weak hydrophilicity.

Tensile strain reduces graphene's hydrophilicity, increasing the contact angle.

Compressive strain induces ripples and anisotropic wetting, causing contact angle hysteresis.

Abstract

Understanding how water wets graphene is critical for predicting and controlling its behaviour in nanofluidic, sensing, and energy applications. A key measure of wetting is the contact angle made by a liquid droplet against the surface, yet experimental measurements for graphene span a wide range, with no consensus for free-standing graphene. Here, we use a machine learning potential with ab initio accuracy to provide an atomistic first-principles prediction for this unsolved problem, finding a weakly hydrophilic contact angle of $72.1 \pm 1.5 \deg$. More importantly, we unveil that graphene's wetting properties are highly sensitive to mechanical strain: tensile strain makes graphene significantly less hydrophilic, while compressive strain induces coherent ripples around the droplet, resulting in pronounced anisotropic wetting and contact angle hysteresis. We show that there is a strong coupling between the three-phase contact line and the intrinsic thermal ripples of free-standing graphene, which contributes to this strain sensitivity. Our results demonstrate that the wettability of 2D membranes are governed not only by their chemistry but also by their dynamic morphology, introducing a new class of wetting behaviour unique to atomically thin materials that offers an additional explanation for variability in experimental measurements. These findings reveal that mechanical strain may be a practical route to controlling wetting in 2D nanomaterials-based technologies, with promising consequences for nanofluidic and nano-filtration applications.