arXiv subjects

Michał Czerwiński

Publications and source records attributed to Michał Czerwiński.

5 recordsLinked to original sources

arXiv2026

Ternary liquid crystalline mixture showing broad antiferroelectric smectic C$_A$* and glassy hexatic smectic X$_A$* phases

A ternary liquid crystalline mixture was designed to obtain a tilted hexatic smectic phase in the glassy state. Structural, electro-optic, and dielectric properties of the mixture are investigated, and selected measurements are also performed for its pure components. In particular, the electron density profile perpendicular to smectic layers is determined from the X-ray diffraction data and compared to the results of density functional theory calculations both for the mixture and pure components. Comparison of the experimental smectic layer spacing and tilt angle in the mixture allows us to assess whether molecular dimerization is likely to occur. On the mesoscopic scale, the helical pitch is determined in the SmC$_A$* phase of the mixture, and selective reflection of light is observed under a polarizing microscope in the SmC*, SmC$_A$*, and SmX$_A$* phases. The glass transition in the smectic X$_A$* phase is observed in calorimetric results. At the same time, the dielectric spectra do not directly reveal the primary $α$-process, although the secondary $β$- and $γ$-processes are detected. Overall, the results show that the ternary mixture stabilizes a broad SmC$_A$* phase and enables vitrification of the hexatic SmX$_A$* phase, while the structural data suggest a change in the molecular organization between the SmC* and SmC$_A$* phases.

cond-mat.soft↗

arXiv2025

The role of terminal groups in non-chiral rod-like compounds on the formation of polar fluids

The emergence of ferroelectric mesophases in non-chiral liquid crystal (LCs) has sparked fundamental interest in the molecular mechanisms governing polarity. In this study, we investigate how terminal molecular groups influence the formation and stability of polar phases by analyzing six compounds from three homologous series. Specifically, we compare newly synthesized homologs with a nitro group, which predominantly exhibit polar mesophases, to previously reported structurally related analogs containing either a cyano group or a fluorine atom as terminal fragment. Density Functional Theory (DFT) calculations provide insights into electronic surface potential (ESP) distributions, revealing alternating regions of positive and negative charge density along the molecular axis, consistent with Madhusudana model of polar phase stabilization. We propose the ESP-derived parameter quantifying terminal electrostatic charge, revealing a direct correlation between the negative to positive charge ratio at the molecular termini and the formation of ferroelectric or antiferroelectric mesophases. To validate this hypothesis, we analyze the molecular structure-mesomorphic behavior relationship of other known non-chiral compounds that exhibit polar phases, demonstrating the critical role of terminal groups in determining mesophase polarity. Our findings enhance the understanding of the molecular origins of ferroelectricity in non-chiral LCs, paving the way for the rational design of next-generation functional polar soft materials.

cond-mat.mtrl-sci↗

arXiv2025

Polar Nematic Phases with Enantiotropic Ferro- and Antiferroelectric Behavior

The recent discovery of a new ferroelectric nematic (NF) liquid crystalline phase became of utmost interest for the liquid crystal (LC) and the whole soft and condensed matter fields. Contrary to the previously known ferroelectric LC materials, whose ferroelectric characteristics were much weaker, new polar nematics exhibit properties comparable to solid ferroelectrics. This discovery brought about tremendous efforts to further explore compounds showing these phases, and fascinating physical properties have been reported. Herein, we present the first synthesized compounds with the enantiotropic ferro- (NF) and antiferroelectric (NX) nematic phases. The enantiotropic nature and an unprecedentedly broad temperature range of NF and NX phases are confirmed by various experimental techniques: polarized-light optical microscopy (POM) observations, different scanning calorimetry (DSC), dielectric spectroscopy, second harmonic generation (SHG), and molecular modeling. The presented achievements in designing achiral compounds that exhibit enantiotropic polar nematic phases with ferro- and antiferroelectric properties significantly contribute to the development of multicomponent mixtures with a broad temperature range of NF and NX phases down to room temperature. Furthermore, this accomplishment considerably enhances the general understanding of the structural correlations that promote polar nematic liquid crystal phases with high thermodynamic stability. Finally, this work may benefit various applications in photonic devices.

cond-mat.soft↗

arXiv2025

Glassforming liquid crystalline equimolar mixtures of MHPOBC and fluorinated compounds -- structural, optical, and dielectric properties

Three liquid crystalline equimolar mixtures are formulated, each containing the MHPOBC compound and the homolog from the 3FmHPhF6 series with m = 4, 5, and 6. The properties of the mixtures are investigated by differential scanning calorimetry, polarizing optical microscopy, X-ray diffraction, electro-optic measurements, and UV-Vis-NIR and dielectric spectroscopies. In all mixtures, the smectic A*, smectic C*, and smectic C$_A$* phases are observed. Each mixture can be supercooled and forms the glass of smectic C$_A$* at 225-238 K. The glass transition temperature decreases with the increasing C$_m$H$_{2m}$ chain length in the 3FmHPhF6 molecule. The tilt angle in the smectic C$_A$* phase reaches 36.5-37.5°. The selective reflection of light in the visible and near-infrared spectral ranges is observed, with a strong dependence of the reflected light's wavenumber on temperature.

cond-mat.soft↗

arXiv2025

The balance between paraelectricity and ferroelectricity in non-chiral smectic homologs

Non-chiral liquid crystals (LCs) exhibiting ferroelectricity, distinguished by their dynamic responsiveness to external stimuli and high spontaneous polarization, provide renewed impetus for research into this area of soft matter and open novel application possibilities. Consequently, identifying structural elements within LC compounds that promote ferroelectricity in non-chiral systems is of critical importance. In this work, two homologs of rod-like compounds, with phenyl and ester groups in the rigid core substituted by fluorine atoms, differing by a single methylene unit, were synthesized and comprehensively analyzed using complementary experimental techniques and quantum-mechanical modeling. This systematic study presents the first documented instance in which such a minimal structural modification markedly influences the polarity of smectic phases in two homologs, without substantially altering phase transition temperatures, particularly the sequence and temperature ranges of smectic and nematic phases. Additionally, findings reveal that the longer homolog, which exhibits paraelectric phases, demonstrates a pronounced capacity to maintain ferroelectric phases in mixtures. These results provide new insights into the critical structure-property relationships between molecular architecture and ferroelectric characteristics in LCs, facilitating the targeted design of non-chiral compounds with polar phases. Moreover, the properties of the studied mixtures underscore the potential to develop multicomponent LC mixtures with stable ferroelectric properties in a broad temperature range, a feature of considerable significance for practical applications.

cond-mat.mtrl-sci↗