Wettability of MXene films

Abstract

Hypothesis: One of the highlighted properties of Ti₃C₂T_x MXene compared to other 2D nanomaterials is its hydrophilicity. However, the broad range of static contact angles of Ti₃C₂T_x reported in the literature is misleading. To elucidate the experimental values of the static contact angles and get reproducible contact angle data, it is wiser to perform the advancing and receding contact angle measurements on smooth and compact Ti₃C₂T_x layers and focus on deep understanding of the physical basis behind the wettability, which is provided by contact angle hysteresis.

Experiments: Measurements of the advancing and receding contact angle on mono-, bi, and trilayer Ti₃C₂T_x on two different substrates were performed. As substrates, UV-ozone treated silicon wafer and silicon wafer functionalized by (3-aminopropyl)triethoxysilane, were used.

Findings: The values of the advancing contact angle on Ti₃C₂T_x on both substrates were proved to be independent of the number of Ti₃C₂T_x layers, demonstrating a negligible effect of the background substrate wettability. In addition, a giant contact angle hysteresis (44-52 °) was observed on very smooth surface, most likely as a result of chemical heterogeneity arising from the diversity of surface terminal groups (F, O, and OH). The findings reported in this study provide a comprehensive understanding of the wettability of MXene.

Keywords: Contact angle; MXene; Surface energy; Surface modification; Wettability.