arXiv subjects

Alexey Eremin

Publications and source records attributed to Alexey Eremin.

15 recordsLinked to original sources

arXiv2026

Tunable parametric vibrations in fluid ferroelectric fibres

Freely suspended ferroelectric-nematic fibres combine 1D fluidity with macroscopic spontaneous polarisation. Under alternating electric fields, we observe a sequence of dynamical states, from subthreshold pulsations to polarity-dependent axial flow, and sustained transverse oscillations. We show that the oscillatory state arises from a parametric instability of a liquid string whose effective tension is dominated by the electrical polarisation-field coupling contribution. A Floquet model incorporating finite-time polarisation switching captures the observed resonance tongues, modal selection, and square-wave response. These results establish ferroelectric-nematic fibres as electrically programmable fluid resonators coupling polar order and interfacial flow with nonlinear vibration.

cond-mat.soft↗

arXiv2025

Magnetomechanical Coupling in Ferronematic Phases: Influence of Spindle-Shaped Nanodopants on Liquid Crystalline Order

Ferronematic phases, composed of liquid crystals doped with magnetic nanoparticles, exhibit unique magnetomechanical coupling effects that are of interest for responsive materials. In this study, we investigate the influence of spindle-shaped α-Fe_2O_3 nanoparticles functionalized with a mesogen-decorated polymer brush on the phase behavior and field-induced transitions of a nematic host (5CB). Differential scanning calorimetry (DSC), refractometry, and dielectric spectroscopy reveal a non-monotonic dependence of the nematic-isotropic transition temperature on particle concentration, indicating a competition between stabilizing and destabilizing effects. The order parameter increases with increasing nanoparticle content, in contrast to non-magnetic reference systems, suggesting an alignment effect induced by the magnetic rather than the geometric anisotropy axis of the dopants. Capacitance measurements of the Freedericksz transition show a pronounced shift in threshold fields, with a critical concentration marking a transition to enhanced magnetic responsiveness. Additional information on nanospindle diffusion correlated to the direction-dependent flow of the nematic host was inferred from comparison of Moessbauer spectroscopy and rheology data. Our findings provide insights into the interplay of magnetic and geometric anisotropy in ferronematic systems and highlight their potential for applications in tunable soft matter devices.

cond-mat.soft↗

arXiv2025

Splay Stiffening and Twist Softening in a Ferroelectric Nematic Liquid Crystal

The recent discovery of ferroelectric nematics-genuine 3D ferroelectric fluids-has underscored the importance of electrostatic interactions in shaping the physical behaviour of soft matter systems. In this paper, we investigate the mechanical properties of ferroelectric nematics by directly comparing the splay and twist elastic constants in a liquid crystal system that exhibits both nonpolar and ferroelectric nematic phases. Our results reveal that polar ordering results in increased splay rigidity and a concomitant reduction in twist elasticity.

cond-mat.soft↗

arXiv2025

Nanostructured multiferroic liquids: on the way to fluid ferroelectric magnets

Responsiveness to multiple stimuli and adaptivity are paramount for designing smart multifunctional materials. In soft, partially ordered systems, these features can often be achieved via self-assembly, allowing for the combination of diverse components in a complex nanostructured material. Here, we demonstrate an example of a liquid that simultaneously displays both ferroelectric and ferromagnetic types of order. This material is a nanostructured liquid crystalline hybrid comprising ferrimagnetic barium hexaferrite nanoplatelets suspended in a ferroelectric nematic host. Director-mediated interactions drive the self-assembly of nanoplatelets in an intricate network. Due to the couplings between the polar electric and magnetic types of order, this material demonstrates magnetically driven electric and nonlinear optical responses, as well as electrically driven magnetic response. Such multiferroic liquids are highly promising for applications in energy harvesting, nonlinear optics, and sensors.

cond-mat.soft↗

arXiv2023

Fluid fibres in true 3D ferroelectric liquids

We demonstrate an exceptional ability of a high-polarisation 3D ferroelectric liquid to form freely-suspended fluid fibres at room temperature. Unlike fluid threads in modulated smectics and columnar phases, where translational order is a prerequisite for forming liquid fibres, recently discovered ferroelectric nematic forms fibres with solely orientational molecular order. Additional stabilisation mechanisms based on the polar nature of the mesophase are required for this. We propose a model for such a mechanism and show that these fibres demonstrate an exceptional non-linear optical response and exhibit electric field-driven instabilities.

cond-mat.soft↗

arXiv2023

Permeation dynamics of active swimmers through anisotropic porous walls

Natural habitats of most living microorganisms are distinguished by a complex structure often formed by a porous medium such as soil. The dynamics and transport properties of motile microorganisms are strongly affected by crowded and locally anisotropic environments. Using \chlamy as a model system, we explore the permeation of active colloids through a structured wall of obstacles by tracking microswimmers' trajectories and analysing their statistical properties. Employing micro-labyrinths formed by cylindrical or elongated pillars, we demonstrate that the anisotropy of the pillar's form and orientation strongly affects the microswimmers' dynamics on different time scales. Furthermore, we discuss the kinetics of the microswimmer exchange between two compartments separated by an array of pillars.

cond-mat.soft↗

arXiv2023

Role of ionic surfactant in magnetic dynamics of self-assembled dispersions of nanoplatelets

In complex colloidal systems, interparticle interactions strongly affect the dynamics of the constituting particles. A study of the dynamical response also provides invaluable information on the character of those interactions. Here we demonstrate how tuning the electrostatic interactions by an ionic surfactant in dispersions of magnetic nanoplatelets leads to developing new dynamic modes in magnetic response spectra. The collective modes can be induced or suppressed by either varying the concentration ratio of the magnetic nanoplatelets (MP) to the surfactant or increasing the MP concentration reflecting the nanoscale characteristics of this fluid magnet.

cond-mat.soft↗

arXiv2022

Polarisation-driven magneto-optical and nonlinear-optical behaviour of a room-temperature ferroelectric nematic phase

Nematics with a broken polar symmetry is one of the fascinating recent discoveries in the field of soft matter. High spontaneous polarisation and the fluidity of the ferroelectric nematic $N_{\mathrm{F}}$ phase make such materials attractive for future applications and interesting for fundamental research. Here we explore the polar and mechanical properties of a room-temperature ferroelectric nematic and its behaviour in a magnetic field. We show that $N_{\mathrm{F}}$ is much less susceptible to the splay deformation than to the twist. The strong splay rigidity can be attributed to the electrostatic self-interaction of the polarisation avoiding the polarisation splay.

cond-mat.soft↗

arXiv2021

Delay-induced blow-up in a planar oscillation model

In this paper we study a system of delay differential equations from the viewpoint of a finite time blow-up of the solution. We prove that the system admits a blow-up solution, no matter how small the length of the delay is. In the non-delay system every solution approaches to a stable unit circle in the plane, thus time delay induces blow-up of solutions, which we call "delay-induced blow-up" phenomenon. Furthermore, it is shown that the system has a family of infinitely many periodic solutions, while the non-delay system has only one stable limit cycle. The system studied in this paper is an example that arbitrary small delay can be responsible for a drastic change of the dynamics. We show numerical examples to illustrate our theoretical results.

math.DS↗

arXiv2021

Magnetic Tilting in Nematic Liquid Crystals driven by Self-Assembly

Self-assembly is one of the crucial mechanisms allowing to design multifunctional materials. Soft hybrid materials contain components of different nature and exhibit competitive interactions which drive self-organisation into structures of a particular function. Here we demonstrate a novel type of a magnetic hybrid material where the molecular tilt can be manipulated through a delicate balance between the topologically-assisted colloidal self-assembly of \rev{magnetic nanoparticles} and the anisotropic molecular interactions in a liquid crystal matrix.

cond-mat.soft↗

arXiv2021

Electrooptics of mm-scale polar domains in the ferroelectric splay nematic phase

The recent discovery of the ferroelectric splay nematic phase has opened the door to experimental investigation of one of the most searched liquid crystal phases in decades, with high expectations for future applications. However, at this moment, there are more questions than answers. In this work, we examine the formation and structure of large polar nematic domains of the ferroelectric splay nematic material RM734 in planar liquid crystals cells with different aligning agents and specifications. We observe that confining surfaces have a strong influence over the formation of different types of domains, resulting in various twisted structures of the nematic director. For those cells predominantly showing mm-scale domains, we investigate the optical and second harmonic generation switching behaviour under applications of electric fields with a special focus on in-plane fields perpendicular to the confinement media rubbing direction. In order to characterize the underlying structure, the polar optical switching behaviour is reproduced using a simplified model together with Berreman calculations.

cond-mat.soft↗

arXiv2020

Diffusive dynamics of elongated particles in active colloidal suspensions of motile algae

Swimming microorganisms can influence the diffusion of passive particles. The effect of this swimmer-particle interaction depends on different properties, such as the hydrodynamic field of the swimmer and the relative sizes of microorganisms and particles. We investigated an enhancement of the diffusion of silica doublets in a suspension of microalgae Chlamydomonas reinhardtii in a flat capillary. Depending on the concentration of microswimmers, the translational and rotational diffusion constants increase by several orders of magnitude in the presence of the swimming algae. For low concentrations of algae, the doublets exhibit Brownian motion in a fluctuating flow field generated by multiple swimmers. One can observe strong, diffusive transport caused by occasional large displacements. At high swimmer concentration, the algae form dense clusters, where the rotational motion of the doublets shows a subdiffusive behaviour while the translational motion remains diffusive.

cond-mat.soft↗

arXiv2020

On droplets coalescence in a quasi-2D fluid

The coalescence of droplets plays a crucial role in nature and modern technology. Various experimental and theoretical studies explored droplet dynamics in 3D and on 2D solid or liquid substrates. In this paper, we demonstrate the coalescence of isotropic droplets confined in thin quasi-2D liquids -- overheated smectic films. We observe the merging of micrometer-sized flat droplets using high-speed-imaging and analyse the shape transformations of the droplets on the timescale of milliseconds. Our studies reveal the scaling laws of the coalescence time, which exhibits a different dependence on the droplet geometry than in case of droplets on a solid substrate. A theoretical model is proposed to explain the difference in behaviour.

cond-mat.soft↗

arXiv2017

Brownian dynamics of elongated particles in a quasi-2D isotropic liquid

We demonstrate experimentally that the long-range hydrodynamic interactions in an incompressible quasi 2D isotropic fluid result in an anisotropic viscous drag acting on elongated particles. The anisotropy of the drag is increasing with increasing ratio of the particle length to the hydrodynamic scale given by the Saffman-Delbrück length. The micro-rheology data for translational and rotational drags collected over three orders of magnitude of the effective particle length demonstrate the validity of the current theoretical approaches to the hydrodynamics in restricted geometry. The results also demonstrate crossovers between the hydrodynamical regimes determined by the characteristic length scales.

physics.flu-dyn↗

arXiv2017

Realization of hydrodynamic experiments on quasi-2D liquid crystal films in microgravity

Freely suspended films of smectic liquid crystals are unique examples of quasi two-dimensional fluids. Mechanically stable and with quantized thickness of the order of only a few molecular layers, smectic films are ideal systems for studying fundamental fluid physics, such as collective molecular ordering, defect and fluctuation phenomena, hydrodynamics, and nonequilibrium behavior in two dimensions (2D), including serving as models of complex biological membranes. Smectic films can be drawn across openings in planar supports resulting in thin, meniscus-bounded membranes, and can also be prepared as bubbles, either supported on an inflation tube or floating freely. The quantized layering renders smectic films uniquely useful in 2D fluid physics. The OASIS team has pursued a variety of ground-based and microgravity applications of thin liquid crystal films to fluid structure and hydrodynamic problems in 2D and quasi-2D systems. Parabolic flights and sounding rocket experiments were carried out in order to explore the shape evolution of free floating smectic bubbles, and to probe Marangoni effects in flat films. The dynamics of emulsions of smectic islands (thicker regions on thin background films) and of microdroplet inclusions in spherical films, as well as thermocapillary effects, were studied over extended periods within the OASIS (Observation and Analysis of Smectic Islands in Space) project on the International Space Station. We summarize the technical details of the OASIS hardware and give preliminary examples of key observations.

cond-mat.soft↗