arXiv subjects

Marcell Tibor Máthé

Publications and source records attributed to Marcell Tibor Máthé.

5 recordsLinked to original sources

arXiv2026

Shear-mode Direct Piezoelectric Response of Ferroelectric Nematic Liquid Crystals

Piezoelectricity (linear coupling between mechanical deformation and electric signal) was originally observed only in solid crystals. Recently, it was discovered that liquid ferroelectric nematic liquid crystals are also piezoelectric. However, so far only their converse piezoelectric signals (applied voltage-induced mechanical deformation) were measured quantitatively. In this work, we have carried out periodic shear-induced electric current and oscillatory rheology measurements on the two archetypic ferroelectric nematic compounds, RM734 and DIO. From temperature, frequency and strain dependent results of the first and second harmonic current signals together with the results from oscillatory rheometry, we were able to quantitatively determine the shear-mode direct piezoelectric coupling constants. These values are similar for both materials and are compared to results of previous converse piezoelectric measurements. We propose a physical mechanism in which the flow alignment of ferroelectric polarization leads to the direct piezoelectric response.

cond-mat.soft↗

arXiv2025

Giant Electro-Viscous Effects in Polar Fluids with Paraelectric-Modulated Antiferroelectric-Ferroelectric Phase Sequence

The recently discovered ferroelectric nematic liquid-crystal material DIO exhibits an antiferroelectric (AF) phase, characterized by a sinusoidally modulated structure between the paraelectric (P) and ferroelectric (F) nematic phases. Although these sinusoidal modulated structures associated with the P-AF-F phase sequence is commonly observed in solid ferroelectrics, their presence in soft matter systems is scarce. This study is aimed at examining the macroscopic properties of DIO, identifying unique rheological properties, such as switching between shear thinning and shear thickening behaviors at certain shear rate in the ferroelectric nematic phase. Additionally, a significant electroviscous effect is observed, with the viscosity increasing by 70 times under an ultra-low electric field of 0.15 V um-1 at the AF-F transition.

cond-mat.soft↗

arXiv2023

Fluid ferroelectric filaments

Freestanding slender fluid filaments of room temperature ferroelectric nematic liquid crystals are described. They are stabilized either by internal electric fields of bound charges formed due to polarization splay, or by external voltage applied between suspending wires. The phenomenon is similar to those observed in dielectric fluids, such as deionized water, except that in ferroelectric nematic materials the voltages required are 3 orders of magnitudes smaller and the aspect ratio is much higher. The observed ferroelectric fluid threads are not only unique and novel, but also offer measurements of basic physical quantities, such as the ferroelectric polarization and viscosity. Ferroelectric nematic fluid threads may have practical applications in nano-fluidic micron-size logic devices, switches, and relays.

cond-mat.soft↗

arXiv2023

Electric field-induced interfacial instability in a ferroelectric nematic liquid crystal

Studies of sessile droplets and fluid bridges of a ferroelectric nematic liquid crystal in externally applied electric fields are presented. It is found that above a threshold, the interface of the fluid with air undergoes a fingering instability or ramification, resembling to Rayleigh-type instability observed in charged droplets in electric fields or circular drop-type instabilities observed in ferromagnetic liquids in magnetic field. The frequency dependence of the threshold voltage was determined in various geometries. The nematic director and ferroelectric polarization direction was found to point along the tip of the fingers that appear to repel each other, indicating that the ferroelectric polarization is essentially parallel to the director. The results are interpreted in connection to the Rayleigh and circular drop-type instabilities.

cond-mat.soft↗

arXiv2022

Ferroelectric nematic liquid crystal thermo-motor

A thermal gradient-induced circular motion of particles placed on ferroelectric nematic liquid crystal sessile drops is demonstrated and explained. Unlike hurricanes and tornadoes that are the prime examples for thermal motors and where turbulent flows are apparent, here the texture without tracer particles appears completely steady indicating laminar flow. We provide a simple model showing that the tangential arrangement of the ferroelectric polarization combined with the vertical thermal gradient and the pyroelectricity of the fluid drives the rotation of the tracer particles that become electrically charged in the fluid. These observations provide a fascinating example of the unique nature of fluid ferroelectric liquid crystals.

cond-mat.soft↗