Lyotropic bicontinuous cubic phase single crystals investigated using high-resolved X-ray scattering

Single crystals of an $Ia\bar{3}d$ bicontinuous direct cubic phase formed by a non-ionic surfactant in water are investigated using high-resolved X-ray diffraction. The shape of the Bragg peaks confirms the existence of a 3D long-range order inside the cubic phase. A weak diffuse scattered intensity signal is measured very near the Bragg peaks. We attribute this signal to thermal diffuse scattering (TDS) and we give an estimation of the contribution of elastic waves to this TDS

An X-ray scattering study of flow-aligned samples of a lyotropic liquid-crystalline hexagonal phase

Large flow-aligned samples of the hexagonal mesophase of the (sodium dodecylsulfate, pentanol, water) ternary system were produced by merely sucking the material into flat glass capillaries. These samples were examined by polarized light microscopy and X-ray scattering. In the plane of the hexagonal lattice, the "ϕ-mosaic" is only $\cong 0.1^\circ$ because the dense (10) hexagonal planes lie parallel to the flat glass plates of the capillaries. In contrast, the "χ-mosaic" of the C6 axis reaches 5-10° because the samples undergo a thermomechanical instability of the columns already investigated by Oswald et al. in detail on the (C12EO6, H2O) system. Anisotropic thermal diffuse scattering is observed around the Bragg peaks and its description in the frame of an elastic continuum model provides estimates of the elastic constants. On heating the samples, we observed a clear splitting of four of the (10) hexagonal lattice reflections. This splitting is the defining signature of the thermomechanical instability by which the columns form zig-zags. The fact that two of the (10) reflections are not affected by the instability demonstrates that it is confined to the plane of the capillary. The influence of temperature on the thermomechanical instability was also studied in detail

Exploring the facets of “soft crystals” using an Atomic Force Microscope

We obtained monocrystalline droplets in a thermotropic cubic phase, of approximate size 100μm, deposited on a flat surface. The facets of these soft crystals are explored using both an optical microscope and an AFM. The height of individual steps on the principal facets and the lateral distance between steps in vicinal facets are measured using AFM in imaging (tapping) mode. Moreover, the elastic modulus is measured locally, using the AFM tip (in contact mode) as a local rheological probe

New investigation on the tetragonal liquid-crystalline phase or SmQ

Chiral liquid crystals, for which twist and smectic order strongly compete, can exhibit complex architectures. This is the case of the SmQ phase which shows a high degree of 3D order (tetragonal or hexagonal) as well as a liquid signature. We have combined X-ray scattering and optical observations on a new compound exhibiting a SmQ phase to discriminate between the two models proposed by A.M. Levelut et al. (J. Phys. II 7, 981 (1997)) at the molecular level for the phase with the I4122 space group

Freezing-induced self-assembly of amphiphilic molecules

International audienceThe self-assembly of amphiphilic molecules usually takes place in a liquid phase, near room temperature. Here, using small angle X-ray scattering (SAXS) experiments performed in real time, we show that freezing of aqueous solutions of copolymer am-phiphilic molecules can induce self-assembly below 0°C