In the present work, a detailed analysis of the glassy behavior and the relaxation dynamics of the liquid crystal dimer α-(4-cyanobiphenyl-4'-yloxy)-ω-(1-pyrenimine-benzylidene-4'-oxy) heptane (CBO7O.Py) throughout both nematic and smectic-A mesophases by means of broadband dielectric spectroscopy has been performed. CBO7O.Py shows three different dielectric relaxation modes and two glass transition (T_{g}) temperatures: The higher T_{g} is due to the freezing of the molecular motions responsible for the relaxation mode with the lowest frequency (μ_{1L}); the lower T_{g} is due to the motions responsible for the two relaxation modes with highest frequencies (μ_{1H} and μ_{2}), which converge just at their corresponding T_{g}. It is shown how the three modes follow a critical-like description via the dynamic scaling model. The two modes with lowest frequencies (μ_{1L} and μ_{1H}) are cooperative in the whole range of the mesophases, whereas the highest frequency mode (μ_{2}) is cooperative just below some crossover temperature. In terms of fragility, at the glass transition, the ensemble (μ_{1H}+μ_{2}) presents a value of the steepness index and μ_{1L} a different one, meaning that fragility is a property intrinsic to the molecular motion itself. Finally, the steepness index seems to have a universal behavior with temperature for the dielectric relaxation modes of liquid crystal dimers, being almost constant at high temperatures and increasing drastically when cooling the compound down to the glass transition from a temperature about 3/4T_{NI}.
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http://dx.doi.org/10.1103/PhysRevE.97.012704 | DOI Listing |
Sci Rep
January 2025
School of Earth and Environmental Sciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, UK.
Dienia is a small, pantropical genus of epidendroid Malaxideae orchids. The floral lip is upwardly directed and does not serve as a landing platform for pollinators. This role has been assumed by sepals and/or gynostemium or whole inflorescence.
View Article and Find Full Text PDFInorg Chem
January 2025
Department of Chemistry, Western Michigan University, Kalamazoo, Michigan 49008, United States.
The supramolecular binding exclusively by H-bonds of SeO, MoO and WO ions to form nanojars of the formula [EO⊂{-Cu(μ-OH)(μ-pz)}] (; E = Se, Mo, W; = 28-34; pz = pyrazolate) was studied in solution by electrospray ionization mass spectrometry, variable temperature, paramagnetic H NMR and UV-vis spectroscopy, and in the solid state by single-crystal X-ray crystallography. These large anions allow for the observation of a record nanojar size, (E = Mo, W). Six crystal structures are described of nanojars of varying sizes with either SeO, MoO or WO entrapped ions, including the first example of a cocrystal of two different nanojars in crystallographically unique positions, and .
View Article and Find Full Text PDFPhys Rev Lett
December 2024
Department of Physics, The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
The morphology and kinetics of the crystal growth front have been poorly explored at the particle level. Here, we experimentally observe the crystal growth front in liquid with single-particle kinetics using colloid systems and reveal a surface layer of polymorphic crystal near the solid-solid transition when the two crystals form a low-energy coherent interface. The thickness of the surface crystal can exceed 50 particles and grows logarithmically with the temperature as approaching the solid-solid transition which follows premelting theory.
View Article and Find Full Text PDFNanoscale
January 2025
Department of Materials Science, Institute of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan.
Pyrrole in a cholesteric liquid crystal was discharged using a Tesla coil to generate pyrrole radicals, affording linear-shaped nano-ordered pyrrole oligomers. Subsequently, the electrochemical polymerisation of a pre-oriented pyrrole oligomer having good affinity for liquid crystals was performed to achieve polypyrrole-imprinted asymmetry from the cholesteric liquid crystal structure. The resultant polymers were analysed using polarising optical microscopy observations, scanning electron microscopy, electrochemistry, optical spectroscopy, and electron spin resonance.
View Article and Find Full Text PDFJ Mater Chem B
January 2025
Smart Photonic Materials, Faculty of Engineering and Natural Sciences, Tampere University, Tampere, P.O. Box 541, FI-33101, Finland.
As biomimicry advances, liquid crystal elastomers (LCEs) are gaining attention for their (multi-)stimuli-responsiveness and reversible shape morphing. Introduction of dynamic bonds into the LCEs provides versatile means towards programmable shape morphing and adaptation to environmental cues, and new designs for dynamic LCEs are actively sought for. Here, we present a supramolecular LCE that integrates shape memory programming, humidity sensitivity, and photochemical actuation.
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