293 research outputs found
Re-entrant ferroelectricity in liquid crystals
The ferroelectric (Sm C) -- antiferroelectric (Sm C) -- reentrant
ferroelectric (re Sm C) phase temperature sequence was observed for system
with competing synclinic - anticlinic interactions. The basic properties of
this system are as follows (1) the Sm C phase is metastable in temperature
range of the Sm C stability (2) the double inversions of the helix
handedness at Sm C -- Sm C and Sm C% -- re-Sm C phase
transitions were found (3) the threshold electric field that is necessary to
induce synclinic ordering in the Sm C phase decreases near both Sm
C -- Sm C and Sm C -- re-Sm C phase boundaries, and it has
maximum in the middle of the Sm C stability region. All these properties
are properly described by simple Landau model that accounts for nearest
neighboring layer steric interactions and quadrupolar ordering only.Comment: 10 pages, 5 figures, submitted to PR
Controlling spontaneous chirality in achiral materials : liquid crystal oligomers and the heliconical twist-bend nematic phase
Peer reviewedPublisher PD
Dielectric response of a ferroelectric nematic liquid crystalline phase in thin cells
We studied dielectric properties of a polar nematic phase (NF) sandwiched
between two gold or ITO electrodes, serving as a cell surfaces. In bulk, NF is
expected to exhibit a Goldstone mode (phason), because polarization can
uniformly rotate with no energy cost. However, because the coupling between the
direction of nematic director and polarization is finite, and the confinement,
even in the absence of the aligning surface layer, induces some energy cost for
a reorientation of polarization, the phason dielectric relaxation frequency is
measured in a kHz regime. The phason mode is easily quenched by a bias electric
field, which enables fluctuations in the magnitude of polarization to be
followed in both, the ferronematic and nematic phases. This amplitude (soft)
mode is also influenced by boundary conditions. A theory describing the phase
and amplitude fluctuations in the NF phase shows that the free energy of the
system and, consequently, the dielectric response are dominated by
polarization-related terms with the flexoelectricity being relevant only at a
very weak surface anchoring. Contributions due to the nematic elastic terms are
always negligible. The model relates the observed low frequency mode to the
director fluctuations weakly coupled to polarization fluctuations
Helical phases assembled from achiral molecules : Twist-bend nematic and helical filamentary B4 phases formed by mesogenic dimers
Funding Information: National Science Centre (Poland) under the grant no. 2016/22/A/ST5/00319. Special acknowledgement and thanks to professor Dong Ki Yoon's group for providing the AAO membranes.Peer reviewedPublisher PD
Molecular curvature, specific intermolecular interactions and the twist-bend nematic phase : the synthesis and characterisation of the 1-(4-cyanobiphenyl-4-yl)-6-(4-alkylanilinebenzylidene-4-oxy)hexanes (CB6O.m)
EG and DP acknowledge the support of the National Science Centre (Poland): (Grant Number 2016/22/A/ST5/00319). RW gratefully acknowledges The Carnegie Trust for the Universities of Scotland for funding the award of a PhD scholarship.Peer reviewedPostprin
Multiple Etiologies to Myocardial Injury in COVID-19
In patients with acute myocardial injury secondary to coronavirus disease-2019 (COVID-19), cardiovascular magnetic resonance imaging can identify the underlying pathology. We highlight a case of acute myocardial injury secondary to COVID-19, which demonstrated both epicardial vessel thrombosis and the recently described phenomenon of microvascular thrombosis. (Level of Difficulty: Advanced.
Critical behavior of the optical birefringence at the nematic to twist bend nematic phase transition
This research was supported by the National Science Centre (Poland) under the grant no. 2016/22/A/ST5/00319. NV acknowledges the support of the Slovenian Research Agency (ARRS), through the research programme P1-0055.Peer reviewedPublisher PD
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