A Fluid Liquid-Crystal Material with Highly Polar Order

5 years ago

A Fluid Liquid-Crystal Material with Highly Polar Order

Koki Sago, Hiroki Higuchi, Shin-ichi Yamamoto, Yasuhiro Haseba, Hirotsugu Kikuchi, Yasushi Okumura, Hiroya Nishikawa, Kazuya Shiroshita

An anomalously large dielectric permittivity of ≈104 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−2, 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. An anomalously large dielectric permittivity of ≈104 is found for a liquid-crystal compound having a 1,3-dioxane unit (DIO) in the high-fluid mesophase temperature range. In addition, DIO shows ferroelectric-like polarization of 4.4 µC cm−2, which is several hundred times larger than those of conventional ferroelectric chiral smectic C materials, and second-harmonic-generation activity.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adma.201702354