Showing papers in "Clay science in 2018"

Laser beam induced orientation control of a nanosheet liquid crystal by employing an objective lens with a low numerical aperture

Abstract: Optical manipulation of nanosheet liquid crystals prepared by exfoliation of inorganic layered crystals realizes local and on-demand orientation control of nanosheets. Although a tightly focused laser beam by using an objective lens with a high numerical aperture (NA) is typically employed for the optical manipulation to enhance the gradient force of an irradiated laser beam, the dominant driving force of the optical orientational manipulation of nanosheets has recently been attributed to the scattering force, suggesting that an objective lens with a high NA is not indispensible for the nanosheet manipulation. In this study, we carried out optical orientational manipulation of nanosheets using an objective lens with low NA, 0.4, and compared the results with those obtained by a lens with high NA, 1.2. Orientational manipulation was realized with both of the lenses, and the size of the manipulated domain using a lens with NA=0.4 was smaller than that obtained by using a lens with NA=1.2. The domain size increased with the irradiated laser power, reflecting the dominant contribution of scattering force to the optical manipulation of nanosheet liquid crystals.

INFLUENCE OF GLUCURONIC ACID AND GALACTURONIC ACID ON THE PRECIPITATION RATE AND POLYMORPHISM OF CALCIUM CARBONATE MINERALS IN SOLUTIONS WITH Mg2+ IONS

Abstract: Uronic acids are common organic molecules that are released from microbes and plants in the earth’s surface environments. To evaluate the effect of uronic acids on the precipitation rate and polymorphism of calcium carbonate (CaCO3) minerals, precipitation experiments of CaCO3 minerals were performed in systems containing glucuronic acid and galacturonic acid using the batch method with a 100 mL solution at 25°C. Each solution contained 5.0 mM Ca2+ and Mg2+, and 20.0 mM HCO3 ions with 0.00, 0.01, 0.05, 0.1, 0.5, and 1.0 mM of glucuronic acid or galacturonic acid. Additionally, the adsorption experiments with these uronic acids were performed on the surface of calcite and aragonite to confirm their adsorption affinity for the surfaces of CaCO3 minerals. The results showed that both uronic acids inhibited the precipitation of CaCO3 minerals with increasing the concentrations. The inhibition effect of galacturonic acid was much greater than that of glucuronic acid. In addition, only aragonite was formed as a stable polymorph in solutions containing no uronic acid due to the effect of Mg2+ ions. However, galacturonic acid inhibited the formation of aragonite and enhanced the formation of calcite as a stable polymorph of CaCO3 minerals, whereas glucuronic acid showed no significant effect on the polymorphism at concentrations below 1.0 mM. These adsorption experiments revealed that galacturonic acid exhibited much greater adsorption on both surfaces of aragonite and calcite compared to glucuronic acid. Consequently, the extent of the effect on the precipitation rate and polymorphism is consistent with the adsorption affinity of uronic acids for the surfaces of CaCO3 minerals.

Effect of intercalated amide molecules on interlayer condensation of layered silicate rub-15

Abstract: Topotactic conversion of layered silicates into zeolites through interlayer condensation is advantageous for the synthesis of zeolites with unusual compositions, structures, and/or morphologies that have not been obtained using conventional hydrothermal methods. Recently, layered silicate RUB-15 was successfully converted to sodalite with relatively few defects through interlayer condensation by refluxing in N-methylformamide (NMF). However, the effect of NMF, an amide molecule, on the interlayer condensation of RUB-15 is not yet fully understood. In this study, RUB-15 was refluxed or heated in one of four amides: NMF, formamide (FA), N,Ndimethylformamide (DMF), and N-ethylformamide (NEF) to understand the effect of amide molecules on the interlayer condensation in terms of both the size of the amide molecules and their interactions with the layered silicate. On the basis of the powder X-ray diffraction patterns and solid-state 29Si MAS NMR spectra of refluxed or heat-treated products, both NMF and DMF are well suited for interlayer condensation of RUB-15, and the most optimal amide is NMF because it produces the fewest defects. FA (smaller than NMF) and NEF (larger than DMF) are less suitable as interlayer organic species for sodalite formation. It was also found that interlayer condensation of layered octosilicate proceeded in the presence of NMF by refluxing, whereas the condensation did not proceed in DMF by refluxing. These results strongly suggest that the matching in size of the amide molecules with respect to the surface structures of the layered silicates and their interactions play major roles in the interlayer condensation.