Nanoscale Wetting Under Electric Field from Molecular Simulations - Multiscale Molecular Methods in Applied Chemistry - page 161

þ e 0 E 0
4

D < 2 g lv cos y 0 = P : (10)

g lv

The extended expression enables studies of phase instability in dispersions of
charged particles like ionic colloids. In the context of this review, it helps to explain
electrostriction or electrowetting in a confinement maintaining equilibrium with
a field-free aqueous bath. Brunet et al . discussed the use of electric field to tune
mixing/demixing equilibria in a multicomponent system [ 64 , 65 ].

3 Molecular Thermodynamics

3.1 Water in Hydrophobic Confinement and Applied Field

Stabilization of liquid phase under an applied field conforms to experimental
observations of electrostriction as the field attracts more water into the exposed
region. The behavior is captured in several simulation studies, both in the bulk
[ 66 , 67 ] and confined [ 7 , 53 , 61 , 66 , 68 ] regimes. On the other hand, some studies
reported field induced depletion or evaporation in bulk [ 69 ] and confined [ 57 ]
water; hence it is of interest to discuss the underlying differences between these
works.
Some of these differences can be attributed to different thermodynamic
conditions (Fig. 1 ). Studying confined water in a field-exposed confinement, open
to water flow from the external, field-free bath, is an entirely different situation
from the case of an isobaric system, closed to water exchange. In the former
scenario, water in confinement responds to applied field by increasing the density

Fig. 1 Imposed external conditions lead to different responses of confined water to electric field.
Left : field free water in a hydrophobic confinement. Right : field-exposed systems. Top : isobaric,
mass conserving system of variable lateral dimensions. Bottom : isochoric confinement subject to
applied field, and open to exchange of water with field-free aqueous bath