title: Microwetting of pH-Sensitive Surface and Anisotropic MoS2Surfaces Revealed by Femtoliter Sessile Droplets.
abstract: Understanding the microwettability of anisotropic molybdenum disulfide crystal is critically important in separation and processing of this material in liquid. In this work, static microwetting properties of MoS2face (MF) and MoS2edge (ME) surfaces in water are revealed by the morphology of femtoliter interfacial droplets. The oil droplets with different size distribution were produced from heterogeneous nucleation and growth of nanodroplets during the solvent exchange under controlled flow and solution conditions, and were polymerized for droplet morphology characterization to reveal the relative wettability of the droplets on surfaces. We first demonstrate that the shape of the nanodroplets is responsive to the surface charges on a model pH sensitive substrate of gold coated with a self-assembled monolayer of two types of thiol. The experimental results on MoS2substrates indicate that (1) oil contact angle of the droplets on ME surface is much larger than that on MF surface at pH 3.0, suggesting that the ME surface is more hydrophilic than MF; (2) the droplets are pinned by the layered nanostructure on MoS2edge. The fundamental understanding of microwettability elucidated in this study may allow for an improved control of the interaction between anisotropic MoS2surfaces and the surrounding liquid environment, which is critically important for many industrial applications such as flotation and catalysis systems.
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta , Edmonton, Alberta T6G 1H9, Canada.
authors.forename: Zhenzhen
authors.initials: Z
authors.lastname: Lu
authors.affiliation: Soft Matter & Interfaces Group, School of Engineering, RMIT University , Melbourne, Victoria 3001, Australia.
authors.forename: Ziyang
authors.initials: Z
authors.lastname: Lu
authors.affiliation: Soft Matter & Interfaces Group, School of Engineering, RMIT University , Melbourne, Victoria 3001, Australia.
authors.forename: Shuhua
authors.initials: S
authors.lastname: Peng
authors.affiliation: Soft Matter & Interfaces Group, School of Engineering, RMIT University , Melbourne, Victoria 3001, Australia.
authors.forename: Xuehua
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta , Edmonton, Alberta T6G 1H9, Canada.
authors.forename: Qingxia
authors.initials: Q
authors.lastname: Liu