Eur. Phys. J. E (2017) 40: 26
https://doi.org/10.1140/epje/i2017-11514-8

Tips and Tricks

Formation of surface nanodroplets of viscous liquids by solvent exchange

¹ Soft Matter & Interfaces Group, School of Engineering, RMIT University, VIC 3001, Melbourne, Australia
² Physics of Fluids group, Department of Science and Engineering, Mesa+ Institute, and J. M. Burgers Centre for Fluid Dynamics, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands

^* e-mail: xuehua.zhang@rmit.edu.au

Received: 30 November 2016
Accepted: 16 February 2017
Published online: 10 March 2017

Abstract

Surface nanodroplets are essential units for many compartmentalised processes from catalysis, liquid-liquid reactions, crystallization, wetting and more. Current techniques for producing submicron droplets are mainly based on top-down approaches, which are increasingly limited as scale reduces. Herein, solvent exchange is demonstrated as a simple solution-based approach for the formation of surface nanodroplets with intermediate and extremely high viscosity (1 000 000 cSt). By solvent exchange, the viscous droplet liquid dissolves in a good solvent that is then displaced by a poor solvent to yield surface droplets for the oversaturaion pulse at the mixing front. Within controlled flow conditions, the geometry of droplets of low and intermediate viscosity liquids can be tailored on the nano and microscale by controlling the flow rate. Meanwhile for extremely viscous liquids, the droplet size is shown to be dependent on the liquid temperature. This work demonstrates that solvent exchange offers a versatile tool for the formation of droplets with a wide range of viscosity.