Finite Volume Effects in Water Nanodroplets: A Molecular Level Investigation

TL;DR

This paper explores how finite volume effects influence the structure and behavior of water nanodroplets at molecular and macroscopic levels.

Contribution

The study reveals distinct orientational ordering and coupling behaviors of water at different aqueous interfaces due to finite volume effects.

Findings

Water nanodroplets in oil and oil nanodroplets in water show different orientational ordering.

Finite volume effects cause significant intramolecular coupling outside droplets and intermolecular coupling inside.

Finite volume effects lead to structural heterogeneity and electrostatic differences in water droplets.

Abstract

Aqueous interfaces are responsible for a plethora of
processes.
At the nanoscale, interfaces are overwhelmingly influenced by finite
volume effects that are thought to impact both molecular level and
macroscopic properties. Here, finite volume effects are investigated
using electrophoretic mobility and vibrational sum frequency scattering
of water nanodroplets in oil and oil nanodroplets in water, made from
the same chemicals. Notably, there is a substantial difference in
the orientational ordering of water between the two aqueous interfaces.
Isotope dilution studies reveal that water outside the oil droplets
participates significantly in intramolecular coupling, while water
inside the droplets predominantly exhibits intermolecular coupling.
These spectral variations underlie different water structures, pointing
to a larger heterogeneity inside water droplets, which are explained
by finite volume effects that include a pronounced difference in electrostatics.

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