Biaxial ferromagnetic liquid crystal colloids

The design and practical realization of composite materials that combine fluidity and different forms of ordering at the mesoscopic scale are among the grand fundamental science challenges. These composites also hold a great potential for technological applications, ranging from information displays to metamaterials. Here we introduce a fluid with coexisting polar and biaxial ordering of organic molecular and magnetic colloidal building blocks exhibiting the lowest symmetry orientational order. Guided by interactions at different length scales, rod-like organic molecules of this fluid spontaneously orient along a direction dubbed “director,” whereas magnetic colloidal nanoplates order with their dipole moments parallel to each other but pointing at an angle to the director, yielding macroscopic magnetization at no external fields. Facile magnetic switching of such fluids is consistent with predictions of a model based on competing actions of elastic and magnetic torques, enabling previously inaccessible control of light.

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Liquid-crystal-based topological photonics

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2020525118 ◽

2021 ◽

Vol 118 (4) ◽

pp. e2020525118

Author(s):

Hamed Abbaszadeh ◽

Michel Fruchart ◽

Wim van Saarloos ◽

Vincenzo Vitelli

Keyword(s):

Liquid Crystal ◽

Geometric Phase ◽

Soft Matter ◽

Light Propagation ◽

Orientational Order ◽

Building Blocks ◽

Photonic Materials ◽

Nematic Director ◽

Optical Axes ◽

Topological States

Liquid crystals are complex fluids that allow exquisite control of light propagation thanks to their orientational order and optical anisotropy. Inspired by recent advances in liquid-crystal photo-patterning technology, we propose a soft-matter platform for assembling topological photonic materials that holds promise for protected unidirectional waveguides, sensors, and lasers. Crucial to our approach is to use spatial variations in the orientation of the nematic liquid-crystal molecules to emulate the time modulations needed in a so-called Floquet topological insulator. The varying orientation of the nematic director introduces a geometric phase that rotates the local optical axes. In conjunction with suitably designed structural properties, this geometric phase leads to the creation of topologically protected states of light. We propose and analyze in detail soft photonic realizations of two iconic topological systems: a Su–Schrieffer–Heeger chain and a Chern insulator. The use of soft building blocks potentially allows for reconfigurable systems that exploit the interplay between topological states of light and the underlying responsive medium.

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Reversible microscale assembly of nanoparticles driven by the phase transition of a thermotropic liquid crystal

10.26434/chemrxiv.5691169 ◽

2017 ◽

Author(s):

Niamh Mac Fhionnlaoich ◽

Stephen Schrettl ◽

Nicholas B. Tito ◽

Ye Yang ◽

Malavika Nair ◽

...

Keyword(s):

Phase Transition ◽

Liquid Crystal ◽

Self Assembly ◽

Nematic Phase ◽

Hierarchical Control ◽

Building Blocks ◽

Model System ◽

Microscopic Level ◽

Reversible Process ◽

Thermotropic Liquid Crystal

The arrangement of nanoscale building blocks into patterns with microscale periodicity is challenging to achieve via self-assembly processes. Here, we report on the phase transition-driven collective assembly of gold nanoparticles in a thermotropic liquid crystal. A temperature-induced transition from the isotropic to the nematic phase leads to the assembly of individual nanometre-sized particles into arrays of micrometre-sized aggregates, whose size and characteristic spacing can be tuned by varying the cooling rate. This fully reversible process offers hierarchical control over structural order on the molecular, nanoscopic, and microscopic level and is an interesting model system for the programmable patterning of nanocomposites with access to micrometre-sized periodicities.

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A Sustainable Improvement of ω-Bromoalkylphosphonates Synthesis to Access Novel KuQuinones

Organics ◽

10.3390/org2020010 ◽

2021 ◽

Vol 2 (2) ◽

pp. 107-117

Author(s):

Mattia Forchetta ◽

Valeria Conte ◽

Giulia Fiorani ◽

Pierluca Galloni ◽

Federica Sabuzi

Keyword(s):

Metal Oxides ◽

Phosphonic Acid ◽

Organic Molecules ◽

Building Blocks ◽

Reaction Conditions ◽

Phosphonic Acids ◽

Sustainable Improvement ◽

Phosphonate Esters ◽

First Time ◽

Complex Organic

Owing to the attractiveness of organic phosphonic acids and esters in the pharmacological field and in the functionalization of conductive metal-oxides, the research of effective synthetic protocols is pivotal. Among the others, ω-bromoalkylphosphonates are gaining particular attention because they are useful building blocks for the tailored functionalization of complex organic molecules. Hence, in this work, the optimization of Michaelis–Arbuzov reaction conditions for ω-bromoalkylphosphonates has been performed, to improve process sustainability while maintaining good yields. Synthesized ω-bromoalkylphosphonates have been successfully adopted for the synthesis of new KuQuinone phosphonate esters and, by hydrolysis, phosphonic acid KuQuinone derivatives have been obtained for the first time. Considering the high affinity with metal-oxides, KuQuinones bearing phosphonic acid terminal groups are promising candidates for biomedical and photo(electro)chemical applications.

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Chiroptical activity of hydroxycarboxylic acids with implications for the origin of biological homochirality

Communications Chemistry ◽

10.1038/s42004-021-00524-z ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Jana Bocková ◽

Nykola C. Jones ◽

Uwe J. Meierhenrich ◽

Søren V. Hoffmann ◽

Cornelia Meinert

Keyword(s):

Amino Acids ◽

Lactic Acid ◽

Organic Molecules ◽

Building Blocks ◽

Aliphatic Chain ◽

Monocarboxylic Acids ◽

Hydroxycarboxylic Acids ◽

Polarised Light ◽

Suitable Target ◽

Anisotropy Spectra

AbstractCircularly polarised light (CPL) interacting with interstellar organic molecules might have imparted chiral bias and hence preluded prebiotic evolution of biomolecular homochirality. The l-enrichment of extra-terrestrial amino acids in meteorites, as opposed to no detectable excess in monocarboxylic acids and amines, has previously been attributed to their intrinsic interaction with stellar CPL revealed by substantial differences in their chiroptical signals. Recent analyses of meteoritic hydroxycarboxylic acids (HCAs) – potential co-building blocks of ancestral proto-peptides – indicated a chiral bias toward the l-enantiomer of lactic acid. Here we report on novel anisotropy spectra of several HCAs using a synchrotron radiation electronic circular dichroism spectrophotometer to support the re-evaluation of chiral biomarkers of extra-terrestrial origin in the context of absolute photochirogenesis. We found that irradiation by CPL which would yield l-excess in amino acids would also yield l-excess in aliphatic chain HCAs, including lactic acid and mandelic acid, in the examined conditions. Only tartaric acid would show “unnatural” d-enrichment, which makes it a suitable target compound for further assessing the relevance of the CPL scenario.

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A chiral–racemic lyotropic chromonic liquid crystal system

Soft Matter ◽

10.1039/d0sm02013c ◽

2021 ◽

Author(s):

Jordan K. Ando ◽

Peter J. Collings

Keyword(s):

Liquid Crystal ◽

Optical Microscopy ◽

Orientational Order ◽

Molecular Assemblies ◽

Polarized Optical Microscopy ◽

Crystal System ◽

System P ◽

Liquid Crystal System

A lyotropic chromonic liquid crystal consists of oriented molecular assemblies in solution. If the molecules are chiral, the helical pattern of orientational order is revealed by the stripes seen with polarized optical microscopy.

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The interplay between spatial and heliconical orientational order in twist-bend nematic materials

Physical Chemistry Chemical Physics ◽

10.1039/d0cp06633h ◽

2021 ◽

Vol 23 (7) ◽

pp. 4055-4063

Author(s):

R. Saha ◽

C. Feng ◽

C. Welch ◽

G. H. Mehl ◽

J. Feng ◽

...

Keyword(s):

Liquid Crystal ◽

Correlation Length ◽

Orientational Order ◽

Smectic Phase ◽

Sulfur Containing

In sulfur containing liquid crystal dimers we find that at the transition to the NTB phase the positional correlation length drops. The nanoscale periodicity was also observed in the upper range of a smectic phase that forms below the NTB state.

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Liquid Crystal Ordering in the Hexagonal Phase of Rod-Coil Diblock Copolymers

Polymers ◽

10.3390/polym12061262 ◽

2020 ◽

Vol 12 (6) ◽

pp. 1262

Author(s):

Mikhail A. Osipov ◽

Maxim V. Gorkunov ◽

Alexander A. Antonov

Keyword(s):

Liquid Crystal ◽

Order Parameter ◽

Density Functional ◽

Diblock Copolymers ◽

Microphase Separation ◽

Hexagonal Phase ◽

Orientational Order ◽

Order Parameters ◽

Copolymer Composition ◽

Rigid Rod

Density functional theory of rod-coil diblock copolymers, developed recently by the authors, has been generalised and used to study the liquid crystal ordering and microphase separation effects in the hexagonal, lamellar and nematic phases. The translational order parameters of rod and coil monomers and the orientational order parameters of rod-like fragments of the copolymer chains have been determined numerically by direct minimization of the free energy. The phase diagram has been derived containing the isotropic, the lamellar and the hexagonal phases which is consistent with typical experimental data. The order parameter profiles as functions of temperature and the copolymer composition have also been determined in different anisotropic phases. Finally, the spatial distributions of the density of rigid rod fragments and of the corresponding orientational order parameter in the hexagonal phase have been calculated.

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Line broadening in the electron resonance spectra of spin probes dissolved in anisotropic media: the effect of nuclear spin quantization

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1977.0023 ◽

1977 ◽

Vol 353 (1672) ◽

pp. 87-102 ◽

Cited By ~ 13

Keyword(s):

Liquid Crystal ◽

Liquid Crystals ◽

Nuclear Spin ◽

Dynamic Properties ◽

Orientational Order ◽

Anisotropic Media ◽

Approximate Theory ◽

Spin Probes ◽

Line Broadening ◽

Electron Resonance

The line broadening in the electron resonance spectra of monoradicals dissolved in anisotropic media, such as liquid crystals, provides a valuable probe of both the orientational order and the molecular dynamics. However, the fast-motion relaxation theory employed to extract this information from the linewidths assumes that the nuclear spin is quantized along the direction of the magnetic field. This approximation is only correct when the symmetry axis of a uniaxial liquid crystal is either parallel or perpendicular to the field. We have therefore removed this assumption and have developed a general theory of line broadening valid for all orientations of the liquid crystal. The theory is then used to evaluate the angular dependence of the linewidths and this is compared with the dependence predicted by the approximate theory, for two classes of nitroxide spin probes. These comparisons reveal that for steroidal spin probes the error, introduced by assuming the nuclear spin to be quantized along the field, is confined to the dynamic properties derived from the linewidths. In contrast, significant errors appear in both the dynamic and static properties obtained from an analysis of the linewidth variations for fatty acid spin probes based on the approximate theory. It would seem that the exact theory must be employed to obtain precise information from linewidth investigations of liquid crystals, except when the orientational order is extremely small.

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