Water-mediated ordering of nanoparticles in electric field

TL;DR

This paper demonstrates through molecular simulations that water-mediated electric fields can induce strong orientational forces on nanoparticles, enabling electrically controlled nanoparticle ordering for potential applications in nanomechanical devices.

Contribution

It reveals a novel mechanism where water mediates electric field effects to align nanoparticles, expanding understanding of electro-nanomechanical control.

Findings

Electric fields comparable to DNA polyion fields can torque nanoparticles.

Water polarization depends on field direction and polarity.

Nanoparticles as small as 1 nm2 can be aligned by these forces.

Abstract

Interfacial polar molecules feature a strongly anisotropic response to applied electric field, favoring dipole orientations parallel to the interface. In water, in particular, this effect combines with generic orientational preferences induced by spatial asymmetry of water hydrogen bonding under confined geometry, which may give rise to a Janus interface. The two effects manifest themselves in considerable dependence of water polarization on both the field direction relative to the interface, and the polarity (sign) of the field. Using molecular simulations, we demonstrate strong field-induced orientational forces acting on apolar surfaces through water mediation. At a field strength comparable to electric fields around a DNA polyion, the torques we predict to act on an adjacent nanoparticle are sufficient to overcome thermal fluctuations. These torques can align a particle with surface as small as 1 nm2. The mechanism can support electrically controlled ordering of suspended nanoparticles as a means of tuning their properties, and can find application in electro-nanomechanical devices.