Impacts of External Electric Fields on Structures and Alignments of Ring Molecules

Ring molecules, which lack free ends, exhibit unique
chemical and
physical properties, making them promising candidates for nanodevice
applications. Unlike their linear counterparts with two free ends,
the behavior of ring molecules in water under external electric fields
(EF) is not well understood. In this research, we employ molecular
dynamics (MD) simulations to explore the structural and alignment
behavior of two ring molecules of different sizesC30H60 and C60H120in water,
under 300 K, 1 bar and various EF conditions, including direct current
EF (DC EF), alternating current EF (AC EF), and circular polarized
EF (CP EF) at different frequencies. Our findings reveal the following:
(1) both large and small rings exhibit two free energy minima. For
C60H120, these correspond to collapsed and stretched
configurations, while for C30H60, they represent
open and closed configurations. (2) The applied EF can regulate the
depth of these free energy minima. For C60H120, no EF, AC EF, and high-frequency CP EF favor the collapsed state,
while DC EF and low-frequency CP EF promote the stretched configuration.
In the case of C30H60, no EF and high-frequency
CP EF favor the open-ring state, whereas all other EF conditions tend
to close the ring. (3) Both ring molecules align with the directional
EF to minimize disruption of the hydrogen-bond network, with C60H120 showing a stronger alignment effect than
C30H60 due to its longer structure. (4) Under
CP EF, ring molecules exhibit rotation driven by the rotating EF,
but there is a lag in the angle between the EF vector and the molecule’s
elongation. Higher frequency CP EF shows less ability to capture and
align the molecule. This research enhances our understanding of how
ring molecules behave in water under external EF and provides a theoretical
foundation for future engineering applications involving controlled
manipulation of these molecules.