Anisotropic fluid with phototunable dielectric permittivity

Abstract

Dielectric permittivity, a measure of polarisability, is a fundamental parameter that dominates various physical phenomena and properties of materials. However, it remains a challenge to control the dielectric permittivity of materials reversibly over a large range. Herein, we report an anisotropic fluid with photoresponsive dielectric permittivity (200 < ε < 18,000) consisting of a fluorinated liquid-crystalline molecule (96 wt%) and an azobenzene-tethered phototrigger (4 wt%). The reversible trans-cis isomerisation of the phototrigger under blue and green light irradiation causes a switch between two liquid-crystalline phases that exhibit different dielectric permittivities, with a rapid response time (<30 s) and excellent reversibility (~100 cycles). This anisotropic fluid can be used as a flexible photovariable capacitor that, for example, allows the reversible modulation of the sound frequency over a wide range (100 < f < 8500 Hz) in a remote manner using blue and green wavelengths.

Implementation of a cylindrical distribution function for the analysis of anisotropic molecular dynamics simulations.

“…27 Polar nematic order gives rise to extremely large ferroelectric polarisations, 25 which are of interest to both fundamental and applied science. [28][29][30][31] We simulated a polar nematic configuration of the NF material RM554 (Figure 3a) 32 by taking an isotropic configuration of 680 molecules with liquid-like density of 1.1 g cm 3 and applying a static electric field (0.1 V nm -1 ) along the y-axis; this gives a large polar order parameter (<P1>) of ~ 0.9 and an orientational order parameter (<P2>) of ~ 0.65. Following this, a production MD simulation (without biasing field) of 250 ns was performed from this polar configuration at a temperature of 375 K with anisotropic pressure coupling; note that, as with prior simulations, the polar order is essentially constant over the entire production run.…”

A new order of liquids: polar order in nematic liquid crystals

“…More recently, Nishikawa et al employed a photoisomerisable azobenzene additive (using DIO as a nematic host) to demonstrate a ferroelectric nematic material in which irradiation controls the dielectric permittivities (Fig. 6(d)), 41 demonstrating a photovariable capacitor which enables modulation of sound frequencies (in the range of 0.1-8.5 kHz).…”

A New Order of Liquids: Polar Order in Nematic Liquid Crystals

“…More recently, Nishikawa et al employed a photoisomerisable azobenzene additive (using DIO as a nematic host) to demonstrate a ferroelectric nematic material in which irradiation controls the dielectric permittivities (Figure 6d). 40 Nishikawa et al find a photoresponsive dielectric permittivity of 200 < ε < 18,000, and demonstrate a photovariable capacitor which enables modulation of sound frequencies (in the range of 0.1-8.5 kHz).…”