An anomalously large dielectric permittivity of ≈10 is found in the mesophase temperature range (MP phase) wherein high fluidity is observed for a liquid-crystal compound having a 1,3-dioxane unit in the mesogenic core (DIO). In this temperature range, no sharp X-ray diffraction peak is observed at both small and wide Bragg angles, similar to that for a nematic phase; however, an inhomogeneous sandy texture or broken Schlieren one is observed via polarizing optical microscopy, unlike that for a conventional nematic phase. DIO exhibits polarization switching with a large polarization value, i.e., P = 4.4 µC cm , and a parallelogram-shaped polarization-electric field hysteresis loop in the MP phase. The inhomogeneously aligned DIO in the absence of an electric field adopts a uniform orientation along an applied electric field when field-induced polarization switching occurs. Furthermore, sufficiently larger second-harmonic generation is observed for DIO in the MP phase. Second-harmonic-generation interferometry clearly shows that the sense of polarization is inverted when the +/- sign of the applied electric field in MP is reversed. These results suggest that a unidirectional, ferroelectric-like parallel polar arrangement of the molecules is generated along the director in the MP phase.
Superhigh-ε materials that exhibit exceptionally high dielectric permittivity are recognized as potential candidates for a wide range of next-generation photonic and electronic devices. In general, achieving a high-ε state requires low material symmetry, as most known high-ε materials are symmetry-broken crystals. There are few reports on fluidic high-ε dielectrics. Here, we demonstrate how small molecules with high polarity, enabled by rational molecular design and machine learning analyses, enable the development of superhigh-ε fluid materials (dielectric permittivity, ε > 104) with strong second harmonic generation and macroscopic spontaneous polar ordering. The polar structures are confirmed to be identical for all the synthesized materials. Furthermore, adapting this strategy to high–molecular weight systems allows us to generalize this approach to polar polymeric materials, creating polar soft matters with spontaneous symmetry breaking.
A novel chiral nematic phase with a polar helical order is realized via the introduction of helical twisting power into a polar nematogen. The properties of the induced polar nematic (polar cholesteric: Np*) phase differ from those of the conventional cholesteric (N*) phases existing thus far. Np*, which is a new class of N* structures, is characterized not only by its helically twisted nematic director, but also by a continuously twisted polarization. Transmission spectroscopy and helical pitch measurements in a wedge cell revealed that the half‐helical pitch in the Np* phase vanished because of the polar response in the Np* helix. The inner polar director in the Np* phase is confirmed in dielectric and second‐harmonic‐generation studies. Furthermore, this unique Np*LC, which corresponds to a half‐/full‐pitch helix, enables ultrafast electro‐optic switching (τ < 20 µs), and proposes new potential applications for electrically interchangeable photonic bandgaps.
In recent years, ferroelectric nematic liquid crystals have attracted considerable attention owing to their unique properties such as a colossal polarization, high electro-optic activity, and high fluidity. However, despite large efforts in designing and developing new ferrofluid molecules based on molecular parameters, the control and stabilization of ferroelectric nematic phase transitions remain challenging. Here, we discuss the impact of mixing 1,3-dioxane-tethered fluorinated (DIO) diastereomer molecules, namely transDIO and cisDIO, in controlling the ferroelectric nematic phase transition, using X-ray diffraction to investigate the effect of smectic cybotactic cluster formation. Our results show that the ferroelectric nematic phase transition can be tuned by a smooth exchange of the ferroelectric nematic transDIO and non-liquid crystal cisDIO components, where the similar dipole and molecular backbone of the two components ensures a consistent macroscopic polarization of the diastereomeric-controlled ferroelectric nematic phase.
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