We investigate a lyotropic mixture presenting in the calamitic nematic phase (NC) and its corresponding calamitic cholesteric phase (ChC), where a small amount of the chiral agent (brucine sulfate) was added. Different experimental techniques (polarized optical microscopy and laser conoscopy) were used to characterize the phases. The main technique employed in the analysis of the structure and local ordering at nanoscale is the Small-Angle X-ray Scattering, where advanced modeling analysis were applied. The lyotropic nematic mixtures was composed of potassium laurate/potassium sulfate/dodecanol/water and the cholesteric phases were obtained from these mixtures, by adding the chiral molecule, brucine sulfate. From an advanced modeling analysis, we show that the micellar overall shape is not modified by the doping with brucine. However, the presence of the brucine between micelles in the ChC phase imposes a higher correlation between micelles along the direction of the pseudo-lamellar ordering. Finally, the order parameter 〈P_2 〉 was calculated and these values for the phases NC and ChC are 0.8133(6) and 0.747(2), respectively, indicating a slightly higher orientational ordering in the NC phase.
Magnetic fluids or ferrofuids (FF) are colloidal suspension of magnetic nanoparticles in a liquid carrier. When a material is illuminated with a high-intensity light, typically nanosecond, picosecond and femtosecond pulsed laser beam, its refractive index n2 and absorption coefficient β depend on the light intensity I. The Z-Scan (ZS) nonlinear optical and the Small-Angle X-Ray Scattering (SAXS) techniques are used to investigate the structure and nonlinear optical properties of magnetite nanoparticles dispersed in a colloid and trapped in thin films. n2 and β were measured as a function of the intensity of an external applied magnetic field H. Different relative orientations of the field with respect to the light-polarization direction were investigated. When the external magnetic field is applied to the colloidal sample (H parallel to the light-polarization direction), β increases with the field, ranging from 1.5 cm/GW (without field) to 2.4 cm/GW (2700 Oe). For the field direction perpendicular to the light polarization direction, β decreases to 1.0 cm/GW (2700 Oe) and after remains stable. These values allowed us to evaluate some elements of the third-order nonlinear optical susceptibility tensor χ^((3)). The SAXS experiments revealed that when the eld is applied, small linear aggregates are formed in the direction of H. Considering that the nanoparticles rotate to align their magnetic moment parallel to the applied field direction, and the particle's magnetic moment is aligned along the ⟨111⟩ lattice direction of the nanoparticle’s crystalline structure, our results indicate an optical anisotropy in magnetite. The calculated third-order nonlinear optical susceptibility, along the ⟨111⟩ direction, is Imχ_xxxx^((3))=2.0(3)×〖10〗^(-20) m^2/V^2, while its average along the other two orthogonal directions is 1/2 (Imχ_yyyy^((3))+Imχ_zzzz^((3)) )=0.9(3)×〖10〗^(-20) m^2/V^2. For the thin-film sample, however, the n2 and β values do not change when the field of 1600 Oe is applied. Within the experimental error, n_2 does not seem to change with field for the colloidal samples. CNPq, FAPESP, CAPES, INCT-FCx and NAP-FCx.
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