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.
Highlights
Dielectric permittivity, a measure of polarisability, is a fundamental parameter that dominates various physical phenomena and properties of materials
The dielectric permittivity could be photocontrolled over a large range (200 < ε < 18,000) with a rapid response time (
It is noteworthy that such a large dielectric permittivity does not depend on the macroscopic orientation of the dioxane unit in the mesogenic core (DIO) molecules (Supplementary Fig. 7 and Supplementary Note 1); we used non-oriented DIO molecules in this study
Summary
Characterisation of the ferronematogenic molecule (DIO) and phototrigger molecules. The key material of the present work is the aforementioned DIO (Fig. 1a) that exhibits three mesophases during the cooling process [N (173.6–84.5 °C) → M (84.5–68.8 °C) → NF (68.8–34 °C)]29. The dielectric permittivity in the cis state (ε′ = ~200) was maintained for a long time (>10 h) at 50 °C owing to the long half-life of Azo-F (Supplementary Fig. 13) These results confirm that our LC blend exhibits large phototunability of dielectric permittivity (~200 < ε′ < ~18,000), rapid photoresponsivity (photoresponse time < 30 s), good fatigue resistance (~100 cycles), and high thermal stability in the cis state (>10 h), all of which are essential factors for their practical application. When the driving temperature was not in the appropriate range (for example, at 45 or 60 °C), the dielectric spectra in the trans and cis states were almost identical to each other, and large photoinduced changes in permittivity could not be observed (Supplementary Fig. 15). Because fluidic materials generally provide more flexibility, processability, and scalability than solid materials, our LC blend is expected to have various applications
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