Layer Charge Density Research Articles

Crystal chemistry characteristics and dispersion performance of Ca-montmorillonite with different layer charge density

The correlation between crystal chemistry characteristics and dispersion performance of Ca-montmorillonite with different layer charge density was studied. The four kinds of purified montmorillonite were characterized by XRD, XRF, FTIR, SEM, TEM, BET, TG-DTG, Zeta potential, and Molecular dynamics simulation (MD). The XRD analysis results show that the d(001) value of the four kinds of Ca-montmorillonite are 1.51 nm, 1.51 nm, 1.53 nm, and 1.50 nm, respectively, and the calculation results of layer charge density show that the semi-unit cell charge density are 0.38, 0.53, 0.61, and 0.69, respectively. The charge density is positively correlated with the mass content of MgO. The FTIR analysis results show that with the increase of layer charge density, the couple vibration wave number of Si–O–Mg and Mg–O move towards the high frequency region, from 464.70 cm−1 to 466.36 cm−1 and from 517.12 cm−1 to 520.41 cm−1. The SEM analysis results show that the higher layer charge density of montmorillonite, the worse exfoliation between layers and the thicker layer thickness, The images of TEM show that montmorillonites are mainly composed of a clearly layered structure. The results of BET show that with the increase of charge density, the BET surface area, micropore area and total pore volume gradually increase from 32.69 m2 g−1 to 64.50 m2 g−1, from 4.87 m2 g−1 to 18.24 m2 g−1, and from 0.06 cm3 g−1 to 0.12 cm3 g−1 , respectively, while PSDs and pore diameter decrease from 7.88 nm to 1.74 nm, and from 7.65 nm to 5.47 nm. The results of TG and DTG show that with the increase of charge density, the removal temperature of free water and inter-layer water increase from 80 °C to 100 °C and 139 °C to 155 °C, respectively. The simulation results of MD show that with the increase of layer charge density, the number of hydrogen bonds increase from 186 to 271 and the adsorption energy increases from −1467.11 to −1874.32 kcal mol−1. The particle size increases from 701 nm(Mt1) to 1576 nm(Mt4) with the layer charge density, and the absolute value of Zeta potential, colloidal value and expansion capacity of montmorillonites suspension decrease with the increase of the layer charge density, which further indicates that the dispersion of montmorillonites decrease with the increase of layer charge density.

Development of Nanosized Mica Particles from Natural Mica by Sonication/Organic Intercalation Method for Pearlescent Pigment

In this study, the possibility of reducing natural mica particles to nanosizes without damaging its surface properties and smooth flake shape for pearlescent pigment application was investigated by using the sonication delamination method. For this purpose, the layer charge density of the natural mica mineral was reduced using surfactant intercalation followed by maximum exfoliation of mica interlayers with the help of sonication. Therefore, the delamination was achieved in a simple and more energy-efficient way by the sonication process and, in turn, the dimensions of mica were reduced to nanoscale with smooth surface features. With this new delamination process, the lowest particle thickness values were obtained as 0.061 microns after only 1 h sonication period. The results were found to be much significant when compared to the literature. Furthermore, the unique pearlescent pigment properties of mica particles were attributed to the characteristic shape and nanosized mica, which are coated with TiO2.

In Situ 3D-to-2D Transformation of Manganese-Based Layered Silicates for Tumor-Specific T1-Weighted Magnetic Resonance Imaging with High Signal-to-Noise and Excretability.

Recently, Mn(II)-based T1-weighted magnetic resonance imaging (MRI) contrast agents (CAs) have been explored widely for cancer diagnosis. However, the "always-on" properties and poor excretability of the conventional Mn(II)-based CAs leads to high background signals and unsatisfactory clearance from the body. Here, we report an "in situ three-dimensional to two-dimensional (3D-to-2D) transformation" method to prepare novel excretable 2D manganese-based layered silicates (Mn-LSNs) with extremely high signal-to-noise for tumor-specific MR imaging for the first time. Our observations combined with density functional theory (DFT) calculations reveal that 3D metal (Mn, Fe, Co) oxide nanoparticles are initially formed from the molecular precursor solution and then in situ transform into 2D metal (Mn, Fe, Co)-based layered silicates triggered by the addition of tetraethyl orthosilicate, which provides a time-saving and versatile way to prepare novel 2D silicate nanomaterials. The unique ion-exchangeable capacity and high host layer charge density endow Mn-LSNs with an "ON/OFF" pH/GSH stimuli-activatable T1 relaxivity with superb high signal-to-noise (640-, 1200-fold for slightly acidic and reductive changes, respectively). Further in vivo MR imaging reveals that Mn-LSNs exhibit a continuously rapid T1-MRI signal enhancement in tumor tissue and no visible signal enhancement in normal tissue, indicating an excellent tumor-specific imaging. In addition, Mn-LSNs exhibit a rapid excretion from the mouse body in 24 h and invisible organ toxicity, which could help to solve the critical intractable degradation issue of conventional inorganic CAs. Moreover, the tumor microenvironment (pH/GSH/H2O2) specific degradability of Mn-LSNs could help to improve the penetration depth of particles into the tumor parenchyma. Developing this novel Mn-LSNs contrast agent, together with the already demonstrated capacity of layered silicates for drug and gene delivery, provides opportunities for future cancer theranostics.

Comprehensive Characterization of the Structure and Gel Property of Organo-Montmorillonite: Effect of Layer Charge Density of Montmorillonite and Carbon Chain Length of Alkyl Ammonium

In this work, the effect of layer charge density of Na-montmorillonite (Na-MT) and carbon chain length of alkyl ammonium on the structure and gel property of organo-montmorillonite (organo-MT) was studied by using X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetric (TG) analysis, contact angle test, molecular dynamics (MD) simulation, and gel apparent viscosity determination experiment. The results of XRD show that Na-MT with lower layer charge density is easier to swell after intercalation of alkyl ammonium, and the basal spacing of organo-MT increases with the increase of carbon chain length. The results of FTIR show that the absorption bands at 2924 cm−1 and 2853 cm−1 shift towards low frequency region with the increase of carbon chain length, and the absorption bands at 515 cm−1 and 463 cm−1 move towards high frequency region when the layer charge density increases. The mass loss of organo-MT evidently increases with the increase of layer charge density of Na-MT or carbon chain length of alkyl ammonium. The contact angle test results are well in line with the TG data and reveal that alkyl ammonium with longer carbon chain can significantly improve the hydrophobicity of organo-MT. MD simulation indicates that, when the layer charge density is low, the distribution of alkyl ammonium gradually changes from parallel double layers to partially inclined distribution with the increase of carbon chain length, but when the layer charge density is high, the distribution of alkyl ammonium gradually changes from three layers into four layers. The test results of the apparent viscosity of the gel formed by organo-MT in xylene show that the apparent viscosity of organo-MT gel is negatively correlated with the layer charge density of Na-MT and positively correlated with the carbon chain length of alkyl ammonium.

Structural Characterization of Octahedral Sheet in Dioctahedral Smectites by Thermal Analysis

The structures of octahedral sheets of dioctahedral phyllosilicates show cis-vacant (cv) and trans-vacant (tv) configurations due to the different distributions of the octahedral cations over cis- and trans-sites. On the basis of the different dehydroxylation temperatures, a thermal analysis is an effective method used to identify the cv and tv configurations of an octahedral sheet in dioctahedral smectites. The proportions of cv and tv configurations were determined by fitting the derivative thermogravimetry (DTG) curves. A wide range of cv and tv proportions were detected in the samples. The dehydroxylation temperatures of samples consisting of cv configuration are about 150 to 200 °C higher than those consisting of tv configurations. The samples were classified as tv varieties when octahedral Fe3+ > 0.46 mol/FU, and the pure tv dioctahedral smectites were found when Fe3+ > 1.8 mol/FU. A clear linear relationship was found between the content of octahedral Fe3+ and Al3+ and the proportion of cv and tv configurations. The substitution of Al3+ by Fe3+ in the octahedral sheets is the main factor for the formation of tv varieties. There was no relationship detected between the layer charge density, octahedral Mg2+ content, and the proportion of tv and cv. The present results indicate that the iron content has a significant effect on the structure of the octahedral sheet.

Modeling of Quantum Dot Channel (QDC) Si FETs at Sub-Kelvin for Multi-State Logic

Multi-state room temperature operation of SiOx-cladded Si quantum dots (QD) and GeOx-cladded Ge quantum dot channel (QDC) field-effect transistors (FETs) and spatial wavefunction switched (SWS)-FETs have been experimentally demonstrated. This paper presents simulation of cladded Si and Ge quantum dot channel (QDC) field-effect transistors at 4.2°K and milli-Kelvin temperatures. An array of thin oxide barrier/cladding (∼1nm) on quantum dots forms a quantum dot superlattice (QDSL). A gradual channel approximation model using potential and inversion layer charge density nQM, obtained by the self-consistent solution of the Schrodinger and Poisson’s equations, is shown to predict I-V characteristics up to milli-Kelvin temperatures. Physics-based equivalent circuit models do not work below 53°K. However, they may be improved by adapting parameters derived from quantum simulations. Low-temperature operation improves noise margins in QDC- and SWS-FET based multi-bit logic, which dissipates lower power and comprise of fewer device count. In addition, the role of self-assembled cladded QDs with transfer gate provides a novel pathway to implement qubit processing.

Ion Exchange of Layered Alkali Titanates (Na2Ti3O7, K2Ti4O9, and Cs2Ti5O11) with Alkali Halides by the Solid-State Reactions at Room Temperature.

Ion exchange of layered alkali titanates (Na2Ti3O7, K2Ti4O9, and Cs2Ti5O11) with several alkali metal halides surprisingly proceeded in the solid-state at room temperature. The reaction was governed by thermodynamic parameters and was completed within a shorter time when the titanates with a smaller particle size were employed. On the other hand, the required time for the ion exchange was shorter in the cases of Cs2Ti5O11 than those of K2Ti4O9 irrespective of the particle size of the titanates, suggesting faster diffusion of the interlayer cation in the titanate with lower layer charge density.

Effect of Crystal Chemistry Properties on the Distribution Characteristics of H2O and Na+ in Na-Montmorillonite Interlayer Space: Molecular Dynamics Simulation Study

At monolayer hydration state, the spatial distribution of H2O and Na+ in the interlayer of Na-montmorillonite (Na-MT) with different crystal chemistry properties was investigated by the molecular dynamics simulation method. The simulation results show that when layer charge density increases, H2O will move and form hydrogen bonds with O in tetrahedral surfaces (Ot) at a distance of 1.676 ± 0.043 Å. The impact of isomorphic substitution on the relative concentration of H2O depends largely on the layer charge density of Na-MT, when layer charge density is high, H2O move obviously to both sides of Na-MT sheets with the increase of octahedral substitution ratio. Nevertheless, Na+ coordinate with Ot at a distance of 2.38 Å, and the effect of isomorphic substitution ratio on the diffusion of Na+ is opposite to that of H2O. The mobility of both H2O and Na+ decreases with the increase of layer charge density or tetrahedral substitution ratio. The radial distribution function of Na-Ow (O in H2O) shows that the coordination strength between Na+ and Ow decreases with the increase of layer charge density or tetrahedral substitution ratio, and Na+ are hydrated by four H2O at a Van der Waals radius of 2.386 ± 0.004 Å. The research results can provide a theoretical basis for the efficient application of Na-MT at the molecular and atomic levels.

Effect of Layer Charge Density on Hydration Properties of Montmorillonite: Molecular Dynamics Simulation and Experimental Study.

Four kinds of Ca-montmorillonite with different layer charge density were used to study the effect of charge density on their hydration properties by molecular dynamics simulation and experiments. The research results of Z-density distribution of water molecules, Hw (hydrogen in water molecules), and Ca in the interlayer of montmorillonite show that the hydration properties of montmorillonite are closely related to its layer charge density. If the charge density is low, the water molecules in the interlayers are mainly concentrated on the sides of the central axis about –1.3 Å and 1.5 Å. As the charge density increases from 0.38semi-cell to 0.69semi-cell, the water molecules are distributed −2.5 Å and 2.4 Å away from the siloxane surface (Si-O), the concentration of water molecules near the central axis decreases, and at the same time, Ca2+ appears to gradually shift from the vicinity of the central axis to the Si-O surface on both sides in the montmorillonite layer. The simulation results of the radial distribution function (RDF) of the Ca-Hw, Ca-Ow (oxygen in water molecules), and Ca-Ot (the oxygen in the tetrahedron) show that the Ca2+ and Ow are more tightly packed together than that of Hw; with the increase of the charge density, due to the fact that the negative charge sites on the Si-O surface increase, under the action of electrostatic attraction, some of the Ca2+ are pulled towards the Si-O surface, which is more obvious when the layer charge density of the montmorillonite is higher. The results of the RDF of the Ot-Hw show that with the increase of charge density, the number of hydrogen bonds formed by Ot and Hw in the interlayers increase, and under the action of hydrogen bonding force, the water molecules near the central axis are pulled towards the two sides of Si-O surface. As a result, the arrangement of water molecules is more compact, and the structure is obvious. Correspondingly, the self-diffusion coefficient shows that the higher the layer charge density, the lower the self-diffusion coefficient of water molecules in interlayers is and the worse the hydration performance of montmorillonite. The experimental results of the experiments fit well with the above simulation results.

Effect of Layer Charge Characteristics on the Distribution Characteristics of H2O and Ca2+ in Ca-Montmorillonites Interlayer Space: Molecular Dynamics Simulation.

The charge characteristics of montmorillonite have significant effects on its hydration and application performances. In this study, a molecular dynamics simulation method was used to study the influence of the charge position and charge density of montmorillonite on the distribution of H2O and Ca2+ in layers. The results showed that when the layer charge is mainly derived from the substitution among ions in the tetrahedron, a large number of Hw and Ot are combined into a hydrogen bond in the interlayer, thus the water molecules are more compactly arranged and the diffusion of water molecules among the layers is reduced. In addition, the Ca2+ are diffused to the sides by a concentrated distribution in the central axis of the layer. As the charge density of the montmorillonite increases, the polarity of the Si–O surface increases, which lesds to the deterioration of the diffusibility of the water molecules and the structure of the water molecules in the interlayers is more stable. The increase in the layer charge density lesds to the expansion of the isomorphic substitution range of the crystal structure, which results in a more dispersed distribution of Ca2+ among the layers under the action of electrostatic attraction between the substituted negative sites and the Ca2+.

Transformation of boehmite into 2:1 type layered aluminosilicates with different layer charges under hydrothermal conditions

In this study, beidellite, paragonite and other 2:1 type layered aluminosilicates with high layer charges (2:1 type LA-HLC) were synthesized under hydrothermal conditions by using boehmite as a precursor. The concentrations of dissolved Al from boehmite precursor had important effects on the mineral components of the hydrothermal products and the layer charge density of the resultant minerals. A combination of 2:1 type LA-HLC, paragonite, and minor beidellite formed at a relatively high concentration of dissolved Al, while beidellite with a small amount of 2:1 type LA-HLC was produced at a low concentration of dissolved Al. The resultant 2:1 type LA-HLC exhibited poor swelling ability when treated with ethylene glycol. A solid-state transformation mechanism was proposed for the transformation based on the HRTEM images and EDS analyses, which showed that lattice fringes representing (001) faces of 2:1 type layered aluminosilicates (2:1 type LA) were parallel to the (020) direction of boehmite. The successful transformation of boehmite into 2:1 type LA provides insights to well understand the formation of 2:1 type LA in geological processes and offer a facile preparation approach for the synthesis of 2:1 type LA with different layer charges.

Geochemical and mineralogical characterization of smectites from the Ventzia basin, western Macedonia, Greece

AbstractThree samples of bulk smectite clay from the Pilori and Velanida bentonite deposits of the Ventzia basin, western Macedonia, Greece, were characterized in detail. Chemical analyses and X-ray diffraction (XRD; Rietveld method) showed that the samples are rich in Fe and Mg (8–13 mass% and 6–10 mass% as oxides, respectively) and contain ~60–65 mass% smectite. The high Fe and Mg content as well as the high Cr (0.3–0.5 mass%) and Ni content (0.1–0.3 mass%) are consistent with the formation of these clays from ultramafic precursor sediments of the Vourinos ophiolite complex. Both XRD and infrared spectroscopy indicate the presence of other clay minerals besides smectite, such as minor amounts of kaolinite, trioctahedral-rich palygorskite, serpentine and talc (depending on the sample). The position of the d060 reflection (1.51–1.52 Å) is compatible with either high Fe content or partial trioctahedral character, or probably both. The predominance of ferruginous smectite or nontronite was confirmed by infrared spectroscopy, but the minor presence of a trioctahedral magnesian smectite in some of the samples cannot be excluded. Layer charge densities, determined by the νO-D (oxygen-deuterium IR-stretching) method calibrated against the structural formula method, are in the 0.48–0.52 eq/FU range. Various methods point to the existence of a significant amount of tetrahedral charge, which is typical of ferruginous smectites. The major exchangeable cation is Mg2+ (73–90%), which represents a special property of these materials compared with other bentonites.

Rietveld Structure Refinement of Cu-Trien Exchanged Nontronites.

The Rietveld analysis of X-ray powder diffraction patterns is used widely for obtaining the structural information of clay minerals. However, the complex hydration behavior and the variability of interlayer contents are often considered difficult to be described correctly by a simple structure model. In the present work, the use of Cu-triethylenetetramine (Cu-trien)-exchanged nontronites has been proposed to simplify the interlayer structure. This method provides a potential to obtain the structural information of nontronites, for example, the layer charge density, occupancies of cis-octahedral sites, and the iron content by the Rietveld analysis from the X-ray powder diffraction patterns. The approach was demonstrated on three Cu-trien-exchanged nontronite samples. The Rietveld refinements were carried out first on the purified samples and the results showed a good peak fitting between measured and calculated patterns. The refined iron content and the occupancies of cis-octahedral sites are in general agreement with the reference data, which have been obtained from chemical and thermal analyses. The refinement of layer charge density showed lower values compared with the reference. It may be due to the assumption of temperature factor of Cu-trien in the interlayer. A raw sample with natural impurities was chosen to test the applicability of this method. The refinement pattern of the raw sample led to good agreement with the observed data. The results of the iron content and the occupancies of cis-octahedral sites showed the same tendency as purified samples. This study showed that this approach allows for obtaining some structural details of nontronites directly from X-ray powder diffraction patterns of Cu-trien-exchanged samples.

Formation of Arrested States in Natural Di- and Trioctahedral Smectite Dispersions Compared to Those in Synthetic Hectorite — A Macro- and Microrheological Study

AbstractThe effect of natural clay-mineral properties on the rheological behavior of dispersion is very important in new geotechnical and industrial applications. The colloidal behavior of natural clay minerals with various octahedral structures was investigated using macro- and microrheological measurements and compared with the behavior of synthetic hectorite. In the present study montmorillonite (dioctahedral smectite of Volclay), natural hectorite (trioctahedral smectite of SHCa-1 Source Clay), and the synthetic trioctahedral smectite Laponite®, with lateral layer dimensions of 277, 100, and 30 nm, respectively, were used. The structure formation, kinetics of aging, and broad bandwidth viscoelastic response (10-2 — 106 rad/s) of their dispersions were obtained using mechanical shear and squeeze flow rheometry combined with diffusing wave spectroscopy (DWS) and multiple particle tracking (MPT) microrheology. State diagrams were determined at inherent pH considering the clay-mineral and NaCl concentrations as well as the kinetics of structure formation and sample aging. Due to the larger mean layer diameter and greater layer-charge density of natural clay-minerals, their sol—gel transitions occurred at higher solid and NaCl concentrations than those of Laponite®. Structure formation was faster at pH < pHPZC,edge than at pH > pHPZC,edge (point of zero charge at the edge). The long-term aging of natural clay-mineral samples was less pronounced in the glass state than in the gel state, in contrast to the findings for Laponite®. The storage modulus, G’, of clay-mineral dispersions in arrested states remained essentially constant in a wide frequency range (up to 100 rad/s), as expected. The corresponding plateau value of G’ depends on the number of particle contacts per volume and, hence, increased with decreasing particle size at a given concentration. The dissipation mechanisms determining the high-frequency loss modulus, G", however, are independent of particle size and, accordingly, the high-frequency crossover of G’ and G" shifted to higher values when the particle size decreased. The MPT data revealed structural refinement on the submicrometer length scale during the aging of weak hectorite gels, which was similar to the results for Laponite®. No refinement, however, occurred for montmorillonite in the glass or strong gel state.

Routine investigation of structural parameters of dioctahedral smectites by the Rietveld method

Abstract X-ray powder diffraction (XRD) in combination with the Rietveld method is a common technique for crystal structure analysis. However, almost all minerals of the smectite group show turbostratic disorder preventing the direct application of Rietveld refinement. Ufer et al. (2004) proposed to overcome this limitation by using a single layer model with the BGMN program. This model is now routinely used for quantitative phase analysis of smectite-containing samples. However, the refinement of some important structural features, such as the layer charge density (LCD) and the octahedral iron content has not been achieved successfully yet. Typically, these structural features can be obtained only by analytical methods which require purified smectite samples. The project was firstly aimed to prove the validity of the refinement of selected structural parameters by using a set of purified and well-characterized samples and then applied this method to raw bentonites with natural impurities. The Rietveld refinements were carried out on the X-ray powder diffraction patterns of the Cu-triethylenetetramine (Cutrien) exchanged dioctahedral smectites to avoid the problems of unknown cation species and complex hydration behavior in the interlayer. The refinements of the occupancy of octahedral iron and the LCD led to reasonable results for iron-poor purified samples. The application of the structure model to Cutrien -exchanged smectite-rich samples with natural impurities, e.g. bentonites without previous purification, showed that some important structural details of turbostratically disordered dioctahedral smectites can be determined by the Rietveld method from XRD patterns of the Cutrien -exchanged samples. The technique may be applied in routine structural characterization of raw smectites in bulk rock samples without a prior chemical analysis of purified smectite fractions.

Measurements of vertical electric field in a thunderstorm in a Chinese inland plateau

Abstract. A balloon-borne instrument was designed to measure the electric field in thunderstorms. One case of thunderstorm was observed in the Pingliang region (35.57∘ N, 106.59∘ E; and 1620 m above sea level, a.s.l.) of a Chinese inland plateau, through penetration by the balloon-borne sounding in the early period of the mature stage. Results showed that the sounding passed through seven predominant charge regions. A negative charge region with a depth of 800 m located near the surface, and a positive charge region appeared in the warm cloud region; their mean charge densities were −0.44 ± 0.136 and 0.43 ± 0.103 nC m−3, respectively. Five charge regions existed in the region colder than 0 ∘C, and charge polarity alternated in a vertical direction with a positive charge at the lowest region. The mean charge densities for these five regions were 0.40±0.037 nC m−3 (−9.5 to −4 ∘C), -0.63±0.0107 nC m−3 (−18 to −14 ∘C), 0.35±0.063 nC m−3 (−27 to −18 ∘C), -0.36±0.057 nC m−3 (−34 to −27 ∘C), and 0.24±0.06 nC m−3 (−38 to −34 ∘C). We speculated that the two independent positive charge regions in the lower portion are the same charge region with a weak charge density layer in the middle. The analysis showed that the real charge structure of the thunderstorm is more complex than the tripole model, and the lower dipole is the most intensive charge region in the thunderstorm. Keywords. Meteorology and atmospheric dynamics (atmospheric electricity)

Onset of Osmotic Swelling in Highly Charged Clay Minerals.

Delamination by osmotic swelling of layered materials is generally thought to become increasingly difficult, if not impossible, with increasing layer charge density because of strong Coulomb interactions. Nevertheless, for the class of 2:1 layered silicates, very few examples of delaminating organo-vermiculites were reported in literature. We propose a mechanism for this repulsive osmotic swelling of highly charged vermiculites based on repulsive counterion translational entropy that dominates the interaction of adjacent layers above a certain threshold separation. Based on this mechanistic insight, we were able to identify several organic interlayer cations appropriate to delaminate highly charged, vermiculite-type clay minerals. These findings suggest that the osmotic swelling of highly charged organoclays is a generally applicable phenomenon rather than the odd exemption.

Layer charge robust delamination of organo-clays.

To date delamination of organo-clays is restricted to highly charged, vermiculite-type layered silicates (e.g. n-butylammonium vermiculites) while – counterintuitively – low charged, smectite-type layered silicates do not delaminate although their Coulomb interactions are much weaker. Guided by previous findings, we now identified organo-cations that allowed for extending the delamination of organo clays to charge densities in the regime of low charged smectites as well. Upon intercalation of protonated amino-sugars like N-methyl-d-glucamine (meglumine) robust delamination of 2 : 1 layered silicates via repulsive osmotic swelling in water is achieved. This process is stable over a wide range of charge densities spanning from smectites (layer charge x ∼ 0.3 charges per formula unit Si4O10F2, p.f.u.) to vermiculites (x ∼ 0.7 p.f.u.). It is evidenced that a combination of first, a sufficiently large charge equivalent area (bulkiness) of meglumine with second, a significant hydrophilicity of meglumine leads to swelling above a threshold d-spacing of ≳17.5 Å in moist air (98% r.h.). Hereby, electrostatic attraction is critically weakened, causing the onset of repulsive osmotic swelling which leads to utter delamination. Moreover, meglumine renders delamination tolerant to charge heterogeneities typically found in natural and synthetic clays.

Low-frequency electrical conductivity of aqueous kaolinite suspensions: surface conductance, electrokinetic potentials and counterion mobility

AbstractThe low-frequency conductivity of aqueous kaolinite suspensions has been measured as a function of volume fraction and concentration of KCl, K2SO4and BaCl2, respectively. These measurements were interpreted with a theoretical model accounting for surface conductivity and particle shape. For the first time, an internally consistent data set was established by measuring all parameters necessary to solve the relevant equations. The simultaneous availability of surface conductivity, surface charge density and diffuse layer charge density permitted the estimation of counterion mobilities in the stagnant layer and a consistency check for the evaluation procedure of the conductivity experiments. In agreement with current literature results, monovalent counterions were found to have a Stern layer mobility similar to their bulk mobility, whereas the mobility of divalent counterions in this layer is reduced by a factor of ∼2.

Tunable High-Pressure Field Operating on a Cationic Biphenyl Derivative Intercalated in Clay Minerals

We propose a methodology for applying a pseudo uniaxial pressure to an organic molecule under ordinary temperature and pressure, namely by intercalation into smectites. The pseudo pressure on a biphenyl derivative (BP) was estimated from the averaged dihedral angle around the central bond of BP. In a high hydrostatic pressure field, biphenyl takes a planar conformation. In the interlayer space of synthetic saponite (SSA), the averaged dihedral angle of BP at a loading level of 27% versus the cation exchange capacity was ~26.3°, which indicates that the pseudo pressure applied to BP in the SSA interlayer space corresponds to 0.99 GPa. The high pseudo-pressure field in the interlayer space of SSA was also confirmed by absorption measurements. The dihedral angle around the central bond of the biphenyl moiety decreased to enhance the planarity of the molecule, mainly in response to the electrostatic force that operates between the negatively charged SSA layer and the interlayer cation. The pseudo pressure operating on BP in the smectite interlayer space could be controlled by varying the smectite layer charge density and/or the BP loading level. By using this methodology, controllable pseudo high-pressure properties of organic molecules can be obtained at ordinary temperatures and pressures.