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Influence of Solution Composition on the Formation of Surface Nanodroplets by Solvent Exchange
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posted on 2016-01-27, 00:00 authored by Ziyang Lu, Shuhua Peng, Xuehua ZhangSolvent exchange is a simple process
of forming surface nanodroplets
on an immersed substrate. In this process, the droplets nucleate and
grow in response to transient oversaturation when a good solvent of
the droplet liquid is displaced by a poor solvent. Here we will show
how the final droplet size is influenced by solution composition in
the solvent exchange. To do this, we produced water droplets on a
hydrophilic substrate and cyclohexane droplets on a hydrophobic substrate
by using a tertiary system of cyclohexane, ethanol, and water. The
composition of the good solvent was varied systematically in the one-phase
region on the phase diagram. We found that the key feature closely
related to the droplet size is the area (A) in the
phase diagram defined by the phase boundary and the concentration
ratio between the good solvent and the droplet liquid. This area reflects
the excessive amount of droplet liquid in the tertiary mixture, which
can be complicated by bulk droplet formation during solvent exchange.
We will also show that the droplet volume per unit surface area also
increases with A. The findings from this work will
provide guideline for the selection of solution conditions to achieve
a desirable droplet size and number density on the surface.