The science of the total environment

Chirality and liquid crystals are both widely expressed in nature and biology Helical assembly of mesophasic molecules and colloids may produce intriguing chiral liquid crystals To date, chiral liquid crystals of 2D colloids have not been explored As a typical 2D colloid, graphene is now receiving unprecedented attention However, making macroscopic graphene fibres is hindered by the poor dispersibility of graphene and by the lack of an assembly method Here we report that soluble, chemically oxidized graphene or graphene oxide sheets can form chiral liquid crystals in a twist-grain-boundary phase-like model with simultaneous lamellar ordering and long-range helical frustrations Aqueous graphene oxide liquid crystals were continuously spun into metres of macroscopic graphene oxide fibres; subsequent chemical reduction gave the first macroscopic neat graphene fibres with high conductivity and good mechanical performance The flexible, strong graphene fibres were knitted into designed patterns and into directionally conductive textiles

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Graphene chiral liquid crystals and macroscopic assembled fibres

A wide variety of cation-exchangeable layered transition metal oxides and their relatively rare counterparts, anion-exchangeable layered hydroxides, have been exfoliated into individual host layers, i.e., nanosheets. Exfoliation is generally achieved via a high degree of swelling, typically driven either by intercalation of bulky organic ions (quaternary ammonium cations, propylammonium cations, etc.) for the layered oxides or by solvation with organic solvents (formamide, butanol, etc.) for the hydroxides. Ultimate two-dimensional (2D) anisotropy for the nanosheets, with thickness of around one nanometer versus lateral size ranging from submicrometer to several tens of micrometers, allows them to serve either as an ideal quantum system for fundamental study or as a basic building block for functional assembly. The charge-bearing inorganic macromolecule-like nanosheets can be assembled or organized through various solution-based processing techniques (e.g., flocculation, electrostatic sequential deposition, or the Langmuir-Blodgett method) to produce a range of nanocomposites, multilayer nanofilms, and core-shell nanoarchitectures, which have great potential for electronic, magnetic, optical, photochemical, and catalytic applications.

Nanosheets of oxides and hydroxides: Ultimate 2D charge-bearing functional crystallites.

Cellulose nanocrystals (CNCs), produced by the acid hydrolysis of wood, cotton or other cellulose-rich sources, constitute a renewable nanosized raw material with a broad range of envisaged uses: f ...

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Cellulose nanocrystal-based materials: from liquid crystal self-assembly and glass formation to multifunctional thin films

We report on the controlled synthesis of single-crystal platelets of alpha- and beta-Co(OH)2 via homogeneous precipitation using hexamethylenetetramine as a hydrolysis agent. The alpha- and beta-Co(OH)2 hexagonal platelets of several micrometers in width and about 15 nm in thickness were reproducibly yielded in rather dilute CoCl2 solutions in the presence and absence of NaCl at 90 degrees C, respectively. The phase and size control of the products were achieved by varying both CoCl2 and NaCl concentrations. Polarized optical microscope observations revealed clear liquid crystallinity of colloidal suspensions of these high aspect-ratio platelets. The as-prepared alpha-Co(OH)2 containing interlayer chloride ions was intercalated with various inorganic or organic anions, keeping its high crystallinity and hexagonal platelike morphology.

Selective and Controlled Synthesis of α- and β-Cobalt Hydroxides in Highly Developed Hexagonal Platelets

Ordering particles at the nanometre length scale is a challenging and active research area in materials science. Several approaches have so far been developed, ranging from the manipulation of individual particles to the exploitation of self-assembly in colloids. Nanometre-scale ordering is well known to appear spontaneously when anisotropic organic moieties form liquid-crystalline phases; this behaviour is also observed for anisotropic mineral nanoparticles resulting in the formation of nematic, smectic and hexagonal mesophases. Here we describe a lyotropic liquid-crystalline lamellar phase comprising an aqueous dispersion of planar solid-like sheets in which all the atoms involved in a layer are covalently bonded. The spacing of these phosphatoantimonate single layers can be increased 100-fold, resulting in one-dimensional structures whose periodicity can be tuned from 1.5 to 225 nanometres. These highly organized materials can be mechanically or magnetically aligned over large pH and temperature ranges, and this property can be used to measure residual dipolar couplings for the structure determination of biomolecules by liquid-state NMR. We also expect that our approach will result in the discovery of other classes of mineral lyotropic lamellar phases.

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Swollen liquid-crystalline lamellar phase based on extended solid-like sheets

Aqueous suspensions of goethite (alpha-FeOOH) nanorods form a mineral lyotropic nematic phase that aligns in a very low magnetic field (20 mT for samples 20 microm thick). The particles orient along the field direction at intensities smaller than 350 mT, but they reorient perpendicular to the field beyond 350 mT. This outstanding behavior is also observed in the isotropic phase which has a very strong magnetic-field induced birefringence that could be interesting for applications. We interpret these magnetic effects as resulting from a competition between a nanorod remanent magnetic moment and a negative anisotropy of its magnetic susceptibility.

Outstanding magnetic properties of nematic suspensions of goethite (α-FeOOH) nanorods

Colloidal dispersions are natural candidates to produce materials structured at the nanometer scale because of their propensity to self-organize into colloidal (liquid) crystals. Not only do they fall in the right size range (up to the wavelength of light necessary for photonic applications) but anisometric colloids also exhibit different length scales in different directions. Moreover, so called mineral liquid crystals [1] are also particularly susceptible to external fields. An inherent disadvantage of colloids is their polydispersity, which is, for example, supposed to suppress the formation of smectic liquid crystals, while mineral particles also suffer from sedimentation due to a large density difference with the solvent. Their phase behavior is further complicated by size fractionation and kinetic effects. In this Communication we present a very (over 50%) polydisperse system of Goethite (a-FeOOH) nanorods where these apparent disadvantages meet to produce a wealth of concurrent phases ranging from the isotropic, nematic and columnar to—surprisingly—even a smectic phase. Our findings suggest that employing such polydisperse mineral nanorods gives access to diverse nanostructured materials, as an alternative to the route that has recently successfully employed mineralized virus suspensions. [2]

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Smectic Liquid-Crystalline Order in Suspensions of Highly Polydisperse Goethite Nanorods

https://hal-enpc.archives-ouvertes.fr/hal-00722662/document

Relationship between turbidity and total suspended solids concentration within a combined sewer system.

We performed small-angle X-ray scattering (SAXS) experiments on oriented samples of laponite clay gels obtained by slow evaporation. The SAXS patterns are clearly anisotropic, which demonstrates the existence of nematic-like orientational correlations of the laponite disc-like particles. The iso-intensity lines of the SAXS patterns are elliptical and roughly homothetic over the whole scattering vector range examined in this experiment. The value of the nematic order parameter, , derived from the SAXS patterns is comparable to that of usual liquid crystals. This large value proves the importance of orientational correlations in these gels at concentrations higher than 0.02 g·cm−3, even in the absence of shear.

https://iopscience.iop.org/article/10.1209/epl/i2002-00159-8/pdf

Bruno J. Lemaire

Papers

Swollen liquid-crystalline lamellar phase based on extended solid-like sheets

Outstanding magnetic properties of nematic suspensions of goethite (α-FeOOH) nanorods

Smectic Liquid-Crystalline Order in Suspensions of Highly Polydisperse Goethite Nanorods

Relationship between turbidity and total suspended solids concentration within a combined sewer system.

The measurement by SAXS of the nematic order parameter of laponite gels