Polymerisation of twist-bend nematic textures for electro-optical applications.

Polymer-stabilised liquid crystals (PSLCs) have recently been used to maintain the focal conic domains (FCDs) typical of the smectic A phase in the nematic phase for smart window applications. The newly discovered twist-bend nematic phase of bent-shaped dimers also exhibits FCDs due to its pseudo-layered structure. The variety of topological defects in the N phase is arguably even greater than in the smectic A phase, but the N phase is often metastable and usually crystallises at room temperature, which hinders its use in electro-optical applications.

Do Aqueous Suspensions of Smectite Clays Form a Smectic Liquid-Crystalline Phase?

Bottom-up strategies for the production of well-defined nanostructures often rely on the self-assembly of anisotropic colloidal particles (nanowires and nanosheets). These building blocks can be obtained by delamination in a solvent of low-dimensionality crystallites. To optimize particle availability, determination of the delamination mechanism and the different organization stages of anisotropic particles in dispersion is essential.

Biaxiality-driven twist-bend to splay-bend nematic phase transition induced by an electric field.

Although the existence of the twist-bend (N) and splay-bend (N) nematic phases was predicted long ago, only the former has as yet been observed experimentally, whereas the latter remains elusive. This is especially disappointing because the N nematic is promising for applications in electro-optic devices. By applying an electric field to a planar cell filled with the compound CB7CB, we have found an N-N phase transition using birefringence measurements.

Probing permanent dipoles in CdSe nanoplatelets with transient electric birefringence.

Zinc-blende CdSe semiconducting nanoplatelets (NPL) show outstanding quantum confinement properties thanks to their small, atomically-controlled, thickness. For example, they display extremely sharp absorption peaks and ultra-fast recombination rates that make them very interesting objects for optoelectronic applications. However, the presence of a ground-state electric dipole for these nanoparticles has not yet been investigated.

Liquid-Crystalline Suspensions of Photosensitive Paramagnetic CeF Nanodiscs.

The design of high-performance energy-converting materials is an essential step for the development of sensors, but the production of the bulk materials currently used remains costly and difficult. Therefore, a different approach based on the self-assembly of nanoparticles has been explored. We report on the preparation by solvothermal synthesis of highly crystalline CeF nanodiscs.

Dispersions of Goethite Nanorods in Aprotic Polar Solvents.

Colloidal suspensions of anisotropic nanoparticles can spontaneously self-organize in liquid-crystalline phases beyond some concentration threshold. These phases often respond to electric and magnetic fields. At lower concentrations, usual isotropic liquids are observed but they can display very strong Kerr and Cotton-Mouton effects (i.

Electric-field-induced shape transition of nematic tactoids.

The occurrence of new textures of liquid crystals is an important factor in tuning their optical and photonics properties. Here, we show, both experimentally and by numerical computation, that under an electric field chitin tactoids (i.e.

A liquid-crystalline hexagonal columnar phase in highly-dilute suspensions of imogolite nanotubes.

Liquid crystals have found wide applications in many fields ranging from detergents to information displays and they are also increasingly being used in the 'bottom-up' self-assembly approach of material nano-structuration. Moreover, liquid-crystalline organizations are frequently observed by biologists. Here we show that one of the four major lyotropic liquid-crystal phases, the columnar one, is much more stable on dilution than reported so far in literature.

Hybrid nanocomposites with tunable alignment of the magnetic nanorod filler.

For many important applications, the performance of polymer-anisotropic particle nanocomposite materials strongly depends on the orientation of the nanoparticles. Using the very peculiar magnetic properties of goethite (α-FeOOH) nanorods, we produced goethite-poly(hydroxyethyl methacrylate) nanocomposites in which the alignment direction and the level of orientation of the nanorods could easily be tuned by simply adjusting the intensity of a magnetic field applied during polymerization. Because the particle volume fraction was kept low (1-5.

Electric-field alignment of chitin nanorod-siloxane oligomer reactive suspensions.

Uniaxially anisotropic chitin-silica nanocomposite solids have been obtained thanks to the electric field-induced macroscopic alignment of liquid-crystalline reactive cosuspensions. We demonstrate how chitin nanorods (260 nm long, 23 nm thick) can be aligned upon the application of an alternating current (ac) electric field, and within water-ethanol suspensions containing reactive siloxane oligomers (D(h) ∼ 3 nm). The alignment at the millimeter length scale is monitored by in situ small-angle X-ray scattering (SAXS) and polarized light optical microscopy.

In-situ SAXS study of aqueous clay suspensions submitted to alternating current electric fields.

Aqueous colloidal suspensions of clay platelets display a sol/gel transition that is not yet understood. Depending on the nature of the clay, liquid-crystalline behavior may also be observed. For example, the suspensions of beidellite display a nematic phase whereas those of montmorillonite do not.

Tailoring highly oriented and micropatterned clay/polymer nanocomposites by applying an a.c. electric field.

Clay/polymer nanocomposites have recently raised much interest because of their widespread industrial applications. Nevertheless, controlling both clay platelet exfoliation and orientation during polymerization still remains challenging. Herein, we report the elaboration of clay/polymer nanocomposite hydrogels from aqueous suspensions of natural swelling clays submitted to high-frequency a.

The complex phase behaviour of suspensions of goethite (alpha-FeOOH) nanorods in a magnetic field.

In 1902, Majorana reported the magneto-optical properties of aqueous colloidal suspensions of mixed iron oxides. Oddly enough, the magnetic-field induced birefringence displayed a non-monotonic dependence upon field intensity. This behaviour was later interpreted as due to the existence in these sols of at least two different chemical species.

Zenithal gliding of the easy axis of a nematic liquid crystal.

We present experimental evidence of zenithal gliding of the nematic easy axis on a polyimide surface. The reorientation dynamics of the easy axis under external torque, and its relaxation, are extremely slow processes which cannot be described by a single exponential time. They show similarities with aging phenomena previously encountered in glassy systems.