Structural response of a highly viscous aluminoborosilicate melt to isotropic and anisotropic compressionsThe local state of cations inside the Å ngstrom-scale interlayer spaces is one of the controlling factors for designing sophisticated two-dimensional (2D) materials consisting of 2D nanosheets. In the present work, the molecular mechanism on how the interlayer cation states are induced by the local structures of the 2D nanosheets is highlighted. For this purpose, the local states of Na cations in inorganic 2D materials, in which the compositional fluctuations of a few percent are introduced in the tetrahedral and octahedral units of the 2D nanosheets, were systematically studied by means of 23 Na magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) and 23 Na multiple-quantum MAS (MQMAS) NMR spectroscopy. In contrast with an uniform distribution of Na cations expected so far, various well-defined cation states sensitive to the local structures of the 2D nanosheets were identified. The tunability of the interlayer cation states along with the local structure of the 2D nanosheets, as the smallest structural unit of the 2D material, is discussed. V C 2014 AIP Publishing LLC. [http://dx.

A wide variety of parameters as, e.g., temperature, humidity, particle size, and cation state are known to influence the agglomeration process of two-dimensional (2D) nanosheets, called self-assembly, in inorganic layered materials. The detailed studies on which parameters are decisive and how they influence the self-assembly, however, have not been performed yet. Here, the long-term self-assembly was studied for layered stevensite and hectorite, and compared with our previous data of saponite for elucidating an influence of local states of the interlayer cations. The results were analyzed with respect to a recently established rheological model, in which 2D nanosheets migrate parallel to the layer direction aided by water molecules as lubricants [K. Sato et al., J. Phys. Chem. C, 2012, 116, 22954]. With decreasing the strength of the local electric fields facing to the interlayer spaces, cation positions split into two or three, which makes the distribution of water molecules more uniformly. These water molecules enhance the rheological motion of the 2D nanosheets parallel to the layer direction, thus accelerating the self-assembly process.

To gain an insight into earthquake slip weakening due to thermal pressurization, microscopic molecular structures associated with water desorption are investigated for layered-hectorite nanoparticles by positronium (Ps) annihilation spectroscopy, thermogravimetry and di®erential thermal analysis (TGÀDTA) and time-resolved length-change measurement with high resolution dilatometry. The large macroscopic length change of $ 6% occurs simultaneously with the formation of open spaces with the size of $ 7 Å when water molecules are desorbed from the interlayer spaces.

Adsorption behavior of cesium (Cs) into angstrom-scale open spaces for the saponite clay mineral is investigated by making use of positronium (Ps) annihilation spectroscopy together with thermogravimetry and differential thermal analysis (TG–DTA). Ps annihilation spectroscopy reveals two kinds of open spaces with their sizes of ~ 3 Å and ~ 10 Å, respectively, after baking at 423 K for 8 h under the vacuum condition at ~ 10-5 Torr. The large open space is found to survive for the Cs -type saponite due to less hydration of the Cs cations even after the exposure to the air for 200 h. It is thus inferred that Cs is locally adsorbed in the angstrom-scale open spaces in the saponite clay minerals.

The rheological mechanism of long-term self-assembly triggered by H 2 O molecules was studied for unmilled and mechanochemically-milled saponite nanoparticles by means of thermogravimetry and differential thermal analysis (TG-DTA), dilatometry (DLT), and positronium (Ps) lifetime spectroscopy. For unmilled saponite, the adsorption of H 2 O molecules due to hydration caused volume expansion arising from an increase in the basal spacing as well as weight gain with a time scale of ∼10 h. Ps lifetime spectroscopy revealed two kinds of voids with sizes of ∼0.3 nm and ∼0.9 nm for unmilled saponite before hydration. The intensity of the larger void component in the annihilation spectra decreased from ∼9 % to ∼5 % with increasing time up to ∼100 h and correspondingly the intensity of the smaller void component increased from ∼5 % to ∼9 % due to long-term rheological self-assembly. Both the weight gain and volume expansion were largely suppressed for milled saponite, indicating that the adsorption of H 2 O molecules is reduced. Furthermore, the larger void disappeared and a single void component, corresponding to a void size slightly larger than the original smaller void, was formed for milled saponite. The intensity of this void, created as a result of destruction, decreased with increasing time up to ∼100 h.