Negatively charged groups are immobilized on the neutral inorganic surfaces of kaolinite by a reaction between interlayer hydroxyls of kaolinite and 1,3-dimethylimidazolium dimethylphosphate (DMI+DMP−), an ionic liquid. This interlayer grafting gives the product possessing covalently-bonded DMP− moieties with DMI+. The successful grafting is confined by a lack of differences in the 1.26-nm diffraction line due to expansion of the kaolinite interlayers between the reaction products before and after washing with an excess amount of methanol at 60°C for 2 days, and by the presence of upfield signal at −10.0 ppm in the solid-state 31P nuclear magnetic resonance signal with magic angle spinning (31P MAS NMR) spectrum compared to the 31P liquid NMR signal of DMI−DMP+ in CDCl3 at 0.57 ppm. When the product obtained by the interlayer grafting is treated with 1 mol/L hydrochloric acid, the Fourier-transform infrared spectrum and thermogravimetric curve of the acid-treated product reveal complete removal of DMI+. Additionally, the XRD pattern of the product displays a decrease in the basal spacing from 1.26 to 1.03 nm accompanied by the 31P MAS NMR signal at −8.0 ppm which are present upfield from the 31P NMR signal at 0 ppm of phosphoric acid. Acid treatment using hydrochloric acid thus removed DMI+ from the interlayer space, but the DMP− moieties were converted into dihydrogen phosphate moieties that remained grafted to the interlayer surfaces of kaolinite. These results demonstrate the formation of a proton-exchangeable and asymmetrical layered inorganic solid.
A kaolinite-dimethylaminopyridine (DMAP) intercalation compound (Kaol-DMAP) was prepared for the first time by intercalation reaction of DMAP using an intermediate of methoxyl-modified kaolinite. The obtained intercalation compound displayed a 0.70-nm galley height based on its X-ray diffraction pattern and a band at 3637 cm−1 in the Fourier-transform infrared spectrum demonstrating the presence of hydrogen-bonded hydroxyls. Additionally, solid-state 13C nuclear magnetic resonance with cross polarization and magic angle spinning techniques revealed that the methyl groups in DMAP were present in a single environment. A comparison of these results with those for kaolinite intercalation compounds with pyridine and its derivatives reported previously demonstrates that the orientation of intercalated DMAP was mostly perpendicular to the kaolinite layers.
Among colloidal systems of inorganic nanosheets prepared by exfoliation of inorganic layered crystals, binary colloids of two different nanosheet species are important for their multicomponent and multiphase coexistence, which is applicable to new materials. Nevertheless, electric response of binary nanosheet colloids has scarcely been paid attention although that of single-component nanosheet colloids has recently been investigated. We report herein the electric alignment of aqueous binary nanosheet colloids of niobate K4Nb6O17 and synthetic fluorohectorite, both of which have large lateral sizes of a few micrometers. In the binary colloids, the niobate nanosheets respond to an applied AC electric voltage to be aligned in parallel to the electric field. Although the clay nanosheets also respond to an AC electric field in their single-component colloids, their alignment is basically suppressed in the binary colloids. However, combined optical microscope observations of bright-field, polarized, and fluorescence detections indicate that large clay platelets are partly involved in the aligning motion of the niobate nanosheets. As a result, some of the clay platelets are aligned in parallel to the electric field. Colloidal liquid crystallinity of the niobate nanosheets contribute to the alignment of the clay particles by incorporating the latter particles to the liquid crystalline domains of the former ones.
In 2008, the authors created a system to quantify plasticity from image analysis of impressions of clay dough samples prepared under predetermined conditions, deformed using a drop weight device similar to the Pfefferkorn method, in order to improve the functionality of a computer programmed tool to support the design of ceramic bodies. This system was intended to evaluate the plasticity of clay dough for potter’s wheel molding, however it was also used to evaluate ceramic dough for casting and extrusion molding. Although good results were obtained for the clay dough for potter’s wheel molding made mainly of feldspar, silica stone, pottery stone, and clay, the plasticity index became negative in the evaluation of porous clay dough, causing a problem that deviated from the evaluation of the clay craftsman. The purpose of this study is to solve this problem. In order to compare the evaluation of the clay craftsman with the evaluation of the computer program, clay dough samples containing gairome clay, kaolin with two levels of particle size, bentonite, polyvinyl alcohol and diatomaceous earth were prepared. Each sample was further processed into samples with four levels of moisture content and deformed using a drop weight device. The deformed samples were subjected to image processing and binarized to calculate the deformation rate. The binarized image was processed into a line image by analyzing the binary vector. Vector analysis of contour shapes such as cracks was performed from the line image, and from the pass rate, the moisture content region where good plasticity can be obtained was estimated. In the calculation of plasticity index, the change of setting of plasticity potential plane and the application of curved surface were considered. Through these considerations, the problem of negative plasticity index was solved, and it was possible to roughly agree with the evaluation of the clay craftsman.