Department of Chemical and Biomolecular Engineering, University of Melbourne , Parkville, VIC 3010, Australia.
Soft Matter & Interfaces Group, School of Engineering, RMIT University , Melbourne, VIC 3001, Australia.
Langmuir. 2016 Nov 1;32(43):11197-11202. doi: 10.1021/acs.langmuir.6b02204. Epub 2016 Sep 28.
The formation and morphology of microscopic droplets on a chemically modified surface are important for many droplet-related applications. In this study, we examined the formation and morphological characteristics of nanodroplets produced in the same process of solvent exchange on a gold surface coated with a methyl-terminated alkanethiol monolayer. From atomic force microscopy images, we obtained the contact angles of polymerized nanodroplets in 12 combinations of the length of a straight alkyl chain and the type of droplet liquid. Our results show a significant decrease in the number density of the droplets as the number of methyl groups extends from 8 to 12 or 14. The contact angle of the droplets on octanethiol is significantly larger than that on dodecanethiol or tetradecanethiol, possibly because of the screening effect from the monolayer. Our results demonstrate that under the same solution conditions the morphology of surface nanodroplets is sensitive to the detailed molecular structures of the monolayer on the substrate. This finding has important implications for understanding static wetting on the microscopic scale and the origin of three-phase contact line pinning.
在化学改性表面上，微观液滴的形成和形态对于许多与液滴相关的应用非常重要。在这项研究中，我们研究了在金表面上涂有甲基封端的烷硫醇单层的溶剂交换过程中产生的纳米液滴的形成和形态特征。从原子力显微镜图像中，我们获得了在直链烷基链的长度和液滴液体的类型的 12 种组合中聚合纳米液滴的接触角。结果表明，随着甲基数量从 8 增加到 12 或 14，液滴的数密度显著降低。在辛硫醇上的液滴接触角明显大于在十二硫醇或十四硫醇上的液滴接触角，这可能是由于单层的屏蔽效应。我们的结果表明，在相同的溶液条件下，表面纳米液滴的形态对基底上单分子层的详细分子结构敏感。这一发现对于理解微观尺度上的静态润湿和三相接触线钉扎的起源具有重要意义。
