Liquid Piezoelectric Materials: Linear Electromechanical Effect in Fluid Ferroelectric Nematic Liquid Crystals

Abstract

The first demonstration of converse piezoelectricity in 3D fluids is presented by measuring a linear electromechanical effect in ferroelectric nematic liquid crystals. The observed piezoelectric coupling constant below 6 kHz electric field is larger than 1 nC/N, comparable to, or better than, values for the strongest solid piezoelectric materials. Symmetry considerations indicate that the alignment of the ferroelectric nematic liquid crystal in the experimental study is not optimized, so the observed signal is likely only a fraction of the theoretically achievable signal. Understanding the electromechanical response of ferroelectric nematics will enable mechanical energy harvesting and open up a new avenue for developing fluid actuators, micro positioners, and electrically tunable optical lenses.

Self-Consistent Explanation of the Untwist Alignment of Ferroelectric Nematic Liquid Crystals with Decreasing Cell Thickness and Deviation of the Surface Easy Axis Experimented upon Using the Brewster Angle Reflection Method

“…The FNLC substance used in this study was FNLC-919 (Merck, Rahway, NJ, USA) [9][10][11]17]. The original phase sequence is as follows [10]; Iso.…”

“…The emergence of FNLCs challenges this classical understanding, thereby eliciting profound interest in FNLCs from the viewpoints of both material physics and the development of novel applications [8,9]. Recently, the first demonstration of converse piezoelectricity using FNLC substances that exhibit significant ferroelectricity at room temperature was published [10,11], and these results pave the way to the realization of flexible actuators that cannot be realized with solid materials. Studies on the unique electrical attributes of FNLCs have demonstrated that they can be distinguished from ordinary LCs using methods such as temperaturedependent dielectric constant measurements [6,12] and the detection of second harmonic generation [7,13].…”

“…This phenomenon eliminates the intrinsic π-twist alignment associated with the polar molecular alignment structure, thus giving rise to a planar alignment state. Studies towards obtaining the ferroelectric nematic phase (N F ) have focused on two LC materials, DIO and RM734, though in recent years other FNLCs have been reported such as FNLC-919 [9][10][11]17], which exhibits significant ferroelectricity at room temperature. In this study, we used FNLC-919 as it is easy to handle in experiments without a thermostat.…”

Polarization Coupling between Ferroelectric Liquids and Ferroelectric Solids: Effects of the Fringing Field Profile

“…The discovery of the ferroelectric nematic phase [1][2][3][4][5] was a groundbreaking event, since the combination of fluidity in ferroelectric fluid and its polar coupling to electric fields allow the observation of a whole new world of phenomena, which are rapidly becoming the focus of an increasing number of scientists, as demonstrated by the large number of peer review articles already published on the subject [6][7][8][9][10][11][12][13][14][15][16].…”

Fluid jets and polar domains, on the relationship between electromechanical instability and topology in ferroelectric nematic liquid crystal droplets

“…The N F liquid crystalline materials represent the first fully liquid ferroelectric systems ever found and their peculiar combination of fluidity and polarity has opened the gate to a whole world of new phenomena, which are rapidly becoming the focus of the liquid crystals and soft material scientific communities. 5–13…”