Role Of Flexoelectricity Research Articles

Intertwined Flexoelectricity and Stacking Ferroelectricity in Marginally Twisted hBN Moiré Superlattice.

Moiré superlattices in twisted van der Waals homo/heterostructures present a fascinating interplay between electronic and atomic structures, with potential applications in electronic and optoelectronic devices. Flexoelectricity, an electromechanical coupling between electric polarization and strain gradient, is intrinsic to these superlattices because of the lattice misfit strain at the atomic scale. However, due to its weak magnitude, the effect of flexoelectricity on moiré ferroelectricity has remained underexplored. Here, the role of flexoelectricity in shaping and modulating the moiré ferroelectric patterns in twisted hBN homojunction is unveiled. Enhanced flexoelectric effects induce unique stacking ferroelectric domains with hollow triangular structures. Interlayer bubbles influence domain shape and periodicity through local electric field modulation, and tip-stress enables the reversible manipulation of domain area and polarization direction. These findings highlight the impact of flexoelectric effects on moiré ferroelectricity, offering a new tuning knob for its manipulation.

On the measurement of the bend elastic constant in nematic liquid crystals close to the nematic-to-SmA and the nematic-to-NTB phase transitions

ABSTRACT We propose to measure the ratio of the bend elastic constant over the splay elastic constant of a nematic phase by using an optical method based on the measurement of the birefringence of homeotropic/planar hybrid samples. This method is compared to the classical measurements using the Freedericksz transition under AC electric field and its advantages and disadvantages are discussed. Both methods are applied to the measurement of and close to the nematic-to-SmA phase transition of the liquid crystal 8CB and the nematic-to-NTB phase transition of the mixture 8CB + 50 wt% CB7CB. The role of flexoelectricity in these measurements is analysed, as well as the role of the pretilt angle and the anchoring energy of the molecules on the plates limiting the samples.

The collusion of flexoelectricity and Hopf bifurcation in the hearing mechanism

How do the weak sound waves get amplified in a cochlea? This deceptively simple question has attracted a fair amount of attention and several creative mechanisms have been proposed that purport to understand how the inner ear’s hair cells actively collude to achieve the requisite sensitivity, frequency selectivity, range and nonlinear amplification. Some of the proposed mechanisms target the nature of the mechanoelectric transduction mechanism while others adopt a more dynamical systems approach and focus on the fact that stereocilia of the hair cells operate on the verge of an instability phenomenon—the so-called Hopf bifurcation. In this work, we propose a physics-based model to understand how flexoelectricity, a universal electromechanical coupling that exists in all dielectric substances, facilitates the mechanics of the active motion of hair bundles. A key feature of our model is that we eschew a “black-box” approach, and all parameters are well-defined physical quantities such as membrane bending modulus, geometrical characteristics and others. Furthermore, the model is derived from the well-accepted principles of mechanics and soft matter physics. While the role of flexoelectricity in the hearing mechanism has been noted before, we show for the first time that flexoelectricity is an essential ingredient in inducing the Hopf bifurcation state considered responsible for several highly nonlinear and peculiar features of the hearing mechanism. We find that the biomembranes’ bending modulus and the intracellular charge concentration (which for instance could represent K+ or Ca2+) are the two key control parameters that significantly impact the stability of the system and hence the hearing mechanism. Our work highlights the importance of flexoelectricity, confirms earlier assertions that the cochlea amplifies the acoustic stimuli through its exceptional electromechanical energy conversion property, and provides insights into how physical properties such as biomembranes’ bending modulus impact the performance of the hearing system.

Role of flexoelectricity in electro-optical properties of hybrid aligned nematic layers

The electro-optical effects occurring under the action of AC and DC electric field in hybrid aligned nematic layers placed between crossed polarizers were simulated numerically. Switching between dark and bright states of such systems was analyzed. The role of flexoelectricity in the behavior of the layers was studied, thanks to the fact that the flexoelectric contribution to switching was present in the DC case and cancelled in the AC case. It was found that fast switching was favored by negative flexoelectric parameters or by large difference between voltages at which the both states existed.

Mechanosensitivity of cell membranes. Ion channels, lipid matrix and cytoskeleton.

Physical and biophysical mechanisms of mechano-sensitivity of cell membranes are reviewed. The possible roles of the lipid matrix and of the cytoskeleton in membrane mechanoreception are discussed. Techniques for generation of static strains and dynamic curvatures of membrane patches are considered. A unified model for stress-activated and stress-inactivated ion channels under static strains is described. A review of work on stress-sensitive pores in lipid-peptide model membranes is presented. The possible role of flexoelectricity in mechano-electric transduction, e.g. in auditory receptors is discussed. Studies of flexoelectricity in model lipid membranes, lipid-peptide membranes and natural membranes containing ion channels are reviewed. Finally, possible applications in molecular electronics of mechanosensors employing some of the recognized principles of mechano-electric transduction in natural membranes are discussed.