arXiv subjects

Ewa Górecka

Publications and source records attributed to Ewa Górecka.

6 recordsLinked to original sources

arXiv2026

Competing ferroelectric and smectic order: modulated structures through molecular design

We demonstrate that the balance between polar and positional order can be systematically tuned through molecular engineering, providing direct control over the emergence of polar and modulated liquid-crystalline phases, allowing for versatile strategy for the design of functional ferroelectric soft materials. We show that polar orthogonal smectic phases (SmAF and SmAAF), promoted by the self-segregation of aromatic cores and sufficiently long terminal chains, are readily destabilized by strong longitudinal dipolar interactions that energetically penalize parallel alignment of molecular dipoles within a smectic layer. In contrast, the tilted ferroelectric SmCF phase is remarkably robust across the entire homologous series, indicating that molecular tilt efficiently relieves dipolar frustration within the smectic layers. We further demonstrate that the interplay between microsegregation and electrostatic interactions stabilizes the new modulated SmCM phase, characterized by incommensurate electron-density waves, particularly for compounds with short terminal chains. For longer homologs controlling the spatial distribution of fluorinated molecular fragments and terminal-chain length enabled the targeted formation of broken-layer-type modulated polar phases (2D or 3D).

cond-mat.soft↗

arXiv2025

Helix alignment, chevrons, and edge dislocations in twist-bend ferroelectric nematics

We explore surface alignment and edge dislocations in the recently discovered twist-bend ferroelectric nematic, NTBF, in which the vector of spontaneous polarization follows an oblique helicoidal trajectory around a polar twist-bend axis. In a planar cell, the polar axis aligns at some angle to the rubbing direction to mitigate surface electric charge. We demonstrate that the pseudolayers in planar cells form chevron defects, a hallmark defect of one-dimensionally positionally ordered phases, such as smectic A and smectic C. The polar character of the twist-bend axis prevents the cores of NTBF edge dislocations from splitting into semi-integer disclinations, in stark contrast to dislocations in paraelectric and ferroelectric chiral nematics. The tilt of pseudolayers around the defect core allows us to estimate the elastic penetration length as being close to the pitch of NTBF. Compression/dilation stresses around the core modify the heliconical tilt angle of molecules as evidenced by a substantial variation in local birefringence. The climb of dislocations exhibits high mobility, allowing the system to equilibrate the temperature-dependent pitch. The uncovered properties facilitate the development of NTBF materials for electro-optical applications, such as electrically controlled diffraction lattices and structural colors.

cond-mat.soft↗

arXiv2025

Competition between mirror symmetry breaking and translation symmetry breaking in ferroelectric liquid crystals with increasing lateral substitution

The recently discovered heliconical ferroelectric nematic (NTBF) phase is a unique example of spontaneous chiral symmetry breaking in a proper ferroelectric fluid. In this study, we investigate four homologous series of mesogenic compounds, differing in the degree of fluorination of the mesogenic core and bearing lateral alkoxy substituents of varying lengths, to understand how molecular architecture influences the formation and stability of the NTBF phase. Increasing the length of the lateral chain lowers the phase transition temperatures and suppresses smectic layer formation, enabling the emergence of the NTBF phase which replaces the orthogonal ferroelectric smectic A (SmAF) phase. This indicates a competition between lamellar and heliconical polar ordering, driven by the interplay of strong molecular dipoles and the self-segregation of chemically incompatible molecular segments that typically favor layered structures. Notably, the NTBF phase in these compounds exhibits exceptionally short helical pitch lengths, on the order of a few hundred nanometers, as revealed by selective light reflection and atomic force microscopy (AFM). Furthermore, for one of the studied compounds AFM imaging of one compound revealed a regular array of screw dislocations within the NTBF phase, suggesting a possible link to more complex modulated or twist-grain-boundary-like structures.

cond-mat.soft↗

arXiv2025

Spontaneous polar and chiral symmetry breaking in ordered fluids -- heliconical ferroelectric nematic phases

It is known that the chiral interaction described by Dzyaloshinskii-Moriya (DMI) term lead to the plethora of topological structures of magnetic spins, such as helical or skyrmion phases. Here we present the that analogues electrical DMI can lead to similar structural complexity of electric dipoles in soft matter. We report on a new polar liquid phase in which achiral molecules spontaneously form a heliconical structure. The helical pitch is comparable to the wavelength of visible light and unwinds critically at the transition to a uniformly polar, ferroelectric nematic phase. Although this new liquid crystalline phase resembles the twist-bend nematic phase, the mechanism of its formation is different and is attributed to electrical interactions that cause non-collinear arrangement of electric dipoles, similarly as observed for spins in magnetic systems.

cond-mat.soft↗

arXiv2024

Nematic and smectic phases with proper ferroelectric order

A material showing a sequence of three ferroelectric liquid crystalline phases below the paraelectric nematic phase has been synthesized and studied. The polar order of molecules appearing due to the dipole-dipole interactions in the NF phase is preserved also in the smectic phases: orthogonal SmAF and tilted SmCF. The ferroelectric ground state of both smectic phases is confirmed by their second harmonic generation activity and polarization switching. In the SmCF phase the polarization becomes oriented to the electric field by decreasing the tilt angle to zero. Although both smectic phases are ferroelectric in nature, their dielectric response is found to be very different.

cond-mat.soft↗

arXiv2024

Polar order in a fluid like ferroelectric with a tilted lamellar structure -- observation of a polar smectic C (SmC${_\textrm{P}}$) phase

The discovery of fluid states of matter with spontaneous bulk polar order is appreciated as a major discovery in the fields of soft matter and liquid crystals. Typically, this manifests as polar order superimposed atop conventional phase structures and is thus far limited to orthogonal phase types. Here we report a family of materials which exhibit a previously unseen state of matter which we conclude is a polar smectic C phase, and so we term it SmC${_\textrm{P}}$. The spontaneous polarisation of the SmC${_\textrm{P}}$ phase is over two orders of magnitude larger than that found in conventional ferroelectric SmC phase of chiral materials used in some LCD devices. Fully atomistic molecular dynamics simulations faithfully and spontaneously reproduce the proposed structure and associated bulk properties; comparison of experimental and simulated X-ray scattering patterns shows excellent agreement. The materials disclosed here have significantly smaller dipole moments than typical polar liquid crystals such as RM734 which suggests the role of molecular electrical polarity in generating polar order is perhaps overstated, a view supported by consideration of other molecular systems.

cond-mat.soft↗