Interlamellar Space Research Articles

Size‐Controlled Synthesis of Fe3O4 Magnetic Nanoparticles in the Layers of Montmorillonite

Iron oxide nanoparticles (Fe3O4‐NPs) were synthesized using chemical coprecipitation method. Fe3O4‐NPs are located in interlamellar space and external surfaces of montmorillonite (MMT) as a solid supported at room temperature. The size of magnetite nanoparticles could be controlled by varying the amount of NaOH as reducing agent in the medium. The interlamellar space changed from 1.24 nm to 2.85 nm and average diameter of Fe3O4 nanoparticles was from 12.88 nm to 8.24 nm. The synthesized nanoparticles were characterized using some instruments such as transmission electron microscopy, powder X‐ray diffraction, energy dispersive X‐ray spectroscopy, field emission scanning electron microscopy, vibrating sample magnetometer, and Fourier transform infrared spectroscopy.

Facile assembly for fast construction of intercalation hybrids of layered double hydroxides with anionic metalloporphyrin.

Anionic manganese tetrasulfonatophenyl porphyrin (MnTSPP) has been intercalated into the interlamellar space of Mg-Al and Ni-Al layered double hydroxides (LDHs) through the exfoliation/restacking approach by using exfoliated LDH nanosheets and guest molecules as building blocks. The obtained hybrids were characterized by a variety of analytical techniques such as CHN analysis, XRD, FTIR, SEM, HRTEM, UV-vis spectroscopy and thermal analysis. Interlayer spacings determined from XRD patterns reveal a perpendicular orientation of the MnTSPP anions between the hyroxylated layers of both LDHs. The results of zeta potential measurements give information about the surface charge change of LDH nanoparticles associated with the spontaneous coassembly process. The catalytic performance of the heterogeneous catalysts MnTSPP/Mg-Al LDH2.0 and MnTSPP/Ni-Al LDH1.0 for the epoxidation of cyclohexene was investigated using molecular oxygen as an oxidant and isobutylaldehyde as a co-reductant. The intercalated hybrids appear to be promising catalysts owing to their good catalytic activity and selectivity.

Elaboration of Amorphous-Clay Hybrid: (Al<sub>2</sub>Si<sub>2</sub>O<sub>7</sub>·1/2Li<sub>2</sub>O) Designed as a Single Ion Conducting Solid Electrolyte for Li-Ion Batteries

Keying of lithium chloride alkali halide salt into the interlamellar space of nacrite clay mineral leads to a stable hybrid material that after calcination under inert atmosphere at 723 - 873 K induces an amorphous metahybrid. The electrochemical impedance spectroscopy (EIS) was performed to investigate the electric/dielectric properties of the hybrid with various parameters: frequency and temperature. Equivalent circuit was proposed to fit the EIS data. The experiment results show that the ionic conduction mechanism is related to the motion of Li+ cations which are thermally activated, named the hopping model. Furthermore, the resulting metahybrid obtained from dehydroxylation of the formal hybrid shows a superionic behavior with high ionic conductivity up to 10﹣2 S·m﹣1, good electrochemical stability and can be used as a solid electrolyte material for Li-ion batteries.

Multiscale Water Dynamics within Dense Clay Sediments Probed by 2H Multiquantum NMR Relaxometry and Two-Time Stimulated Echo NMR Spectroscopy

2H NMR spectroscopy, relaxometry, and two-time correlation measurements are used to investigate the structural and dynamical properties of water molecules confined within the multiscale porous network of dense clay sediment. The residual quadrupolar splitting detected by 2H NMR spectroscopy is the fingerprint of the specific orientation of the water molecules pertaining to the first hydration shell of clay lamellae. Multiquantum 2H NMR relaxation measurements are used to quantify the distribution of the clay platelet orientations within the dense sediment. The average residence time of the water molecules confined within the clay interlamellar space is determined by exploiting 2H multiquantum NMR relaxation measurements under spin-locking conditions. Finally, long-time scale diffusion of the water molecules within the multiscale porous network of the clay sediment is quantified by measuring the attenuation of the 2H NMR two-time stimulated echo.

Bryophilous ascomycetes everywhere: Distribution maps of selected species on liverworts, mosses and Polytrichaceae*

Döbbeler, P. & Hertel, H. 2013. Bryophilous ascomycetes everywhere: Distribution maps of selected species on liverworts, mosses and Polytrichaceae. — Herzogia 26: 361–404.The biogeographical distributions of 21 selected species of ascomata-forming fungi that grow obligately on bryophyte gametophytes have been compiled and are presented as 27 dot maps. The maps are based on more than 1370 records, combing all hitherto published records (more than 970) with nearly 400 additional ones, cited here for the first time. Examples are given for European, holarctic, neotropical, tropical Afro-American, pantropical, Australasian, australsubantarctic, bipolar, nearly cosmopolitan, and endemic distribution patterns. Ten maps are devoted to nine fungal species found on foliose hepatics (Bryocentria brongniartii, Calonectria frullaniae, Dactylospora heimerlii, Epibryon deceptor, E. filiforme, E. pedinophylli, Octosporella jungermanniarum, Stenocybe nitida, Ticonectria perianthii), two maps refer to a species found on pleurocarpous mosses (Acrospermum adeanum), and 15 maps show the distributions of eleven taxa found on Polytrichaceae (Bryochiton perpusillus, Biyonectria phyllogena, Bryorella cryptocarpa, Dawsophila callichroma, D. polycarpa, Epibryon elegantissimum, E. pogonati-urnigeri, Hymenoscyphus erythropus, Lizonia sexangularis, Potridiscus polymoiphus, Potriphila navicularis). Host species are represented by liverworts (18 species), Polytrichaceae (29 species), and a few pleurocarpous mosses. Several new fungus-host relationships are revealed. Particular emphasis is placed on the multitude of systematically and biologically diverse groups to which these parasites belong. Sixteen genera from seven classes of Ascomycota are represented. Biological diversity is reflected in the varying degrees of host specificity, biotrophic or necrotrophic parasitism, and the colonization of distinct microniches (e.g. perianths of epiphyllous liverworts, interlamellar leaf spaces or male antheridial cups in Polytrichaceae). Some parasites are so common that screening potential host collections is a rewarding method of discovery. Other taxa are so rare that their observation was accidental and fortuitous, even in well-studied host groups. Bryochiton perpusillus and Epibryon pogonati-urnigeri, both occurring on a variety of Polytrichaceae, are the most well-documented species, with 234 and 236 records respectively. As it is typical of most obligate parasites such as the lichenicolous fungi, bryophilous ascomycetes tend to occur within the wider distribution ranges of their hosts. There are only a few examples of species whose distributions seem to be restricted to only a part of the area occupied by their hosts. Calonectria frullaniae, Potridiscus polymorphus, and Ticonectria perianthii are three such exceptions. The maps verify the hitherto largely ignored fact that many ascomycetes are widespread, and are regularly associated with bryophytes.

Pedoweathering and mineralogical change in cryosols an ultra-continental climate (Central Yakutia, Russia)

This study investigates the clay mineralogy of permafrost-affected soils derived from predominantly calcareous loess-like material under the cold ultra-continental climatic conditions of Central Yakutia. These soils are named “Palevye (Pale)” following the Russian Classification, or Cryosols (WRB, 2006). Based on the data obtained, the loess-like substrate of Central Yakutia is enriched by chlorite in comparison with that of the loess-like parent material of European Russia. The clay mineralogy of the fine size fractions (< 1µm) of all soil profiles is dominated by a smectitic mineral (most likely random mixed-layer illite-smectite and probably chlorite-smectite where smectite is ≥ 50 %), with subordinate chlorite and illite as well as the products of their transformation with smectite (vermiculite) layers < 50 % in the upper horizons, and finally traces of kaolinite. Pedogenesis has brought about change in the more acidic upper horizons, including a marked reduction in the expandability of the smectitic phase, possibly accounted for by the introduction of non-exchangeable hydroxy-Al into the interlamellar space and / or partial dissolving of smectitic phase, together with a relative reduction in the contents of both illite and chlorite. Illite has been at least partially transformed to a mixed-layer illite-vermiculite (smectite), whereas chlorite has either been completely decomposed or has transformed to a mixed-layer expandable component. In one profile, the smectitic mineral appears to be absent from the upper horizon, suggesting that it may have been completely decomposed. An alternative explanation is that it has been eluted or translocated down the profile to accumulate in a Bt horizon. The distribution of clay minerals relates to the change of pH values in the profiles (acidic in the upper part, neutral - slightly alkaline in the middle, and alkaline in the basal horizons) possibly determined by seasonal migration of dissolved carbonates.

Cold acclimation of NaCl secretion in a eurythermic teleost: Mitochondrial function and gill remodeling

Active chloride secretion, measured as short-circuit current (Isc) in ionocytes of opercular epithelia (OE) in the eurythermic, euryoxic, and euryhaline killifish or mummichog (Fundulus heteroclitus) was studied in cold (5°C) and warm (20°C) acclimated fish to determine if homeoviscous adaptation aided chloride secretion in the cold. Isolated opercular epithelia were cooled from 30°C to 0.2°C for warm and cold acclimated fish; from 30 to 8°C, Isc decreased with Q10=1.68 for warm and Q10=1.56 for cold acclimated tissues. By Arrhenius plots, there is a critical temperature, 8°C, below which aerobic Isc decreased sharply (Q10=6.90 for warm and 4.23 for cold acclimated tissues), suggesting a shift in mitochondrial efficiency of oxidative phosphorylation. In anaerobic conditions (0.5mM NaCN; N2 saturation), chloride transport continued at a lower rate, and Isc decrease with cooling below 8°C was less pronounced (Q10=2.95 for warm and 3.08 for cold), suggesting a shift in transporter function in plasma membrane. Under anaerobic conditions, NaCl secretion at 20°C was reversibly inhibited by hypotonic shock, indicating normal regulation of transport. Chloride secretion in warm-acclimated fish was supported mostly (75% at 20°C) by aerobic metabolism, whereas that for cold-acclimated fish was lower (55% at 20°C), suggesting a greater reliance on anaerobic metabolism in the cold. Once acclimated to cold, ionocytes may be temporarily incapable of increasing their aerobic ATP supply, even when warmed to 30°C. In cold acclimated fish there was increased polyunsaturated fatty acid composition of gill epithelium (consistent with homeoviscous adaptation) and gill remodeling, wherein epithelial cells filled the interlamellar space (interlamellar cell mass, ILCM) by as much as 70%, thus increasing diffusion distance against passive ion gain. Most ionocytes in these thickened epithelial masses became taller, still connecting basal lamina with the environment, consistent with the continuing transport rates at low temperatures. Whereas the low aerobic scope of cold-acclimated fish and thickened gill epithelium is appropriate to winter inactivity, metabolic depression and anaerobiosis, the large aerobic scope of warm-acclimated fish favors active foraging at high temperatures.

An unusual μ-1,2,3-squarato-bridged two dimensional coordination polymer: Crystal structure, thermal, photoluminescence and magnetic studies

A new 2D coordination polymer, {[NiII(squarate)(2,2′-bipy)(H2O)]·H2O}n, [squarate=3,4-dihydroxycyclobut-3-ene-1,2-dionate, 2,2′-bipy=2,2′-bipyridine], has been synthesized by using multi-oxygen donor squaric acid ligand and characterized by single crystal X-ray crystallographic and various spectroscopic studies. The structural analysis has revealed that the complex crystallizes in orthorhombic Pbca space group and it has 3D supramolecular structure. Within the complex, the squarato-dianion exhibits unusual μ-1,2,3 bridging mode with Ni(II) ions and 2D coordination sheets are formed through bridging the metal ions by squarato-anions. The 2D coordination sheets are packed along crystallographic b-axis and the 2,2′-bipyridyl (blocking ligand) moieties are hanging in the interlamellar spaces between the 2D coordination sheets. These 2D coordination sheets are further bridged by supramolecular π⋯π interactions using 2,2′-bipyridyl ligands leading to the formation of 3D supramolecular framework which acts as a metal–organic supramolecular host (MOSH). During formation of 3D supramolecular structure, 1D supramolecular channels are formed along the crystallographic c-axis. The guest water molecules get stability within such supramolecular channels through hydrogen bonding interactions with free oxygen atoms of bridging squarate ions. The thermal study indicates that the complex decomposes in three steps. The variable temperature magnetic measurements suggest that the complex is antiferromagnetic in nature. The complex exhibits solid-state photoluminescence spectra at room temperature due to π–π∗/n–π∗ transition of the squarate and 2,2′-bipyridine ligands. The present study points to the squarato-bridged metal complexes as unique model system to carry out the study on different bridging modes exhibited by the ligand.

High catalytic activity at low temperature in oxidative dehydrogenation of propane with Cr–Al pillared clay

A montmorillonite was pillared separately with chromium and aluminum polyoxocations (Cr–C and Al–C respectively) and also with an equimolar mixture of both polioxocations (Al–Cr–C). The resulting solids were characterized by scanning electron microscopy, energy dispersive spectrometry, thermal analysis, Fourier transform infrared spectroscopy, X-ray diffraction and nitrogen adsorption at −196°C. The inclusion of polycations in the interlamellar space led to modifications in the properties of the clay. An eleven fold increase in specific surface area with respect to the calcined starting clay was found for the Al–C, whereas a twofold increase was observed for the Cr–C; the value for the Al–Cr–C was only slightly higher than that for the latter. Diffractograms of the Cr–C showed the occurrence of a Cr2O3 phase. Catalytic activity in oxidative dehydrogenation of propane was assayed in the temperature range from 350°C to 450°C using Ar/C3H8/O2 (80/10/10) as reactant gas mixture. Propylene selectivity was found to be temperature-dependent, showing a maximum in the studied temperature range for the catalyst containing only aluminum, whereas remaining practically constant for the Cr-containing catalysts. Highly promising propylene yields at low temperature were obtained with the catalyst containing Al and Cr (Al–Cr–C): 9.3% at 350°C and 10.3% at 450°C.

Crystallization and microstructure of poly(butylene oxalate)

Crystal structure and morphology development of poly(butylene oxalate) (PBOX) during isothermal crystallization were studied with X-ray diffraction, time-resolved simultaneous small-angle X-ray scattering, differential scanning calorimetry, and optical microscopy. Results indicate that the decrease in the long period at low crystallization temperature indicated the occurrence of secondary crystallization in the interlamellar space. Meanwhile, the lamellar thickness slightly increased with crystallization temperatures due to the formation of thicker crystalline layers at high temperatures. The crystal growth rate of PBOX was analyzed by optical microscopy. Using values of the equilibrium melting temperature of 117.4 °C and the fold surface free energy of 32.37 erg/cm2 obtained by the Gibbs–Thomson theory, the nucleation parameter, Kg, of 97264 K2 and the lateral surface free energy of 17.68 erg/cm2 were determined from the Lauritzen and Hoffman equation. These values are comparable to various semicrystalline polymers previous reported and are not available up to now for PBOX in the literature.

XRD profile modeling approach tools to investigate the effect of charge location on hydration behavior in the case of metal exchanged smectite

This work aims to investigate the hydration behavior and structural properties of two dioctahedral smectites with contrasting location charge (beidellite SbId-1 and montmorillonite SWy-2) according to the nature of the bivalent compensator heavy metal cations (i.e. Hg (II), Ni (II), Ba (II) and Mg (II)). This study is achieved using XRD profile modeling approach based on the simulation of the 00lreflection which allowed us to determine structural characteristics along the c* axis related to the nature, abundance, size, position and organization of exchangeable cation and water molecule in the interlamellar space along the c* axis. The obtained results show that a heterogeneous hydration behavior is systematically observed in all studied samples and the structural models, used to fit samples with tetrahedral charge, are more heterogeneous than smectite with an octahedral sheets substitution. In the case of exchanged beidellite specimen, the proposed models are described by a mixed layer structure with variable abundance containing respectively, dehydrated (0W), mono-hydrated (1W) and bihydrated (2W) layers. Whereas, in the case of the montmorillonite, the absence of 0W hydration state is noted.

Use of a Silicone Gel Sheet Vaginal Mold in McIndoe Vaginoplasty

Use of a Silicone Gel Sheet Vaginal Mold in McIndoe Vaginoplasty

Optical parameters of the tunable Bragg reflectors in squid

Cephalopods (e.g. octopus, squid and cuttlefish) dynamically tune the colour and brightness of their skin for camouflage and communication using specialized skin cells called iridocytes. We use high-resolution microspectrophotometry to investigate individual tunable Bragg structures (consisting of alternating reflectin protein-containing, high-refractive index lamellae and low-refractive index inter-lamellar spaces) in live and chemically fixed iridocytes of the California market squid, Doryteuthis opalescens. This subcellular, single-stack microspectrophotometry allows for spectral normalization, permitting use of a transfer-matrix model of Bragg reflectance to calculate all the parameters of the Bragg stack-the refractive indices, dimensions and numbers of the lamellae and inter-lamellar spaces. Results of the fitting analyses show that eight or nine pairs of low- and high-index layers typically contribute to the observed reflectivity in live cells, whereas six or seven pairs of low- and high-index layers typically contribute to the reflectivity in chemically fixed cells. The reflectin-containing, high-index lamellae of live cells have a refractive index proportional to the peak reflectivity, with an average of 1.405 ± 0.012 and a maximum around 1.44, while the reflectin-containing lamellae in fixed tissue have a refractive index of 1.413 ± 0.015 suggesting a slight increase of refractive index in the process of fixation. As expected, incremental changes in refractive index contribute to the greatest incremental changes in reflectivity for those Bragg stacks with the most layers. The excursions in dimensions required to tune the measured reflected wavelength from 675 (red) to 425 nm (blue) are a decrease from ca 150 to 80 nm for the high-index lamellae and from ca 120 to 50 nm for the low-index inter-lamellar spaces. Fixation-induced dimensional changes also are quantified, leading us to suggest that further microspectrophotometric analyses of this iridocyte system can be used as a model system to quantify the effects of various methods of tissue fixation. The microspectrophotometry technique described can be expected to provide deeper insights into the molecular and physical mechanisms governing other biophotonically active cells and structures.

Compressibility behaviour of bentonite and organically modified bentonite slurry

Bentonite in slurry walls needs to be amended with organo-clay to control the migration of organic contaminants. Consolidation behaviour of the slurry is important because it will reduce the total effective stress owing to mobilisation of frictional force between the side wall of the trench and the slurry. Compressibility of the slurry of bentonite is expected to undergo significant changes owing to amendment with organo-clay and according to the nature of the fluid. Standard one-dimensional consolidation tests were carried out on slurries of bentonite, organo-clay and their mixtures by remoulding them to their respective liquid limit consistency with water as well as fluids of low polarity, such as carbon tetrachloride, and inundating with different fluids. Organo-clay and its mixture with bentonite when moulded with water exhibit lower compressibility than bentonite in any pore fluid, but their compressibility increases when moulded with carbon tetrachloride and inundated with the same fluid. These changes in the compressibility of bentonite amended with organo-clay are explained by particle rearrangements, changes in the development of the diffuse double layer and contribution from the water adsorbed in the inter-lamellar space of the clay.

Amoebic gill disease due to Paramoeba perurans in ballan wrasse (Labrus bergylta)

Ballan wrasse (Labrus bergylta) is cultured for the use as cleaner fish in Atlantic salmon farms. A low level of mortality was experienced in ballan wrasse broodstock tanks during spawning. Examined moribund and clinically healthy fish showed patchy gill lesions characteristic of amoebic gill disease (AGD). Microscopy on wet preparations from gill patches showed large numbers of amoebae. Histology revealed pathology characteristic for AGD, such as extensive hyperplasia, bridging of lamellae and forming of interlamellar spaces. Lesions were associated with amoebae, resembling Paramoeba spp. Molecular studies on both gill samples and gill-derived amoeba-cultures showed the presence of Paramoeba perurans. These observations show that cultured ballan wrasse may host P. perurans infections. Since this observation suggests that ballan wrasse may be infected with P. perurans also in nature, the possible role of wrasses in the epizootiology of AGD in salmonid aquaculture needs to be examined.

Additive potentials of Zingiber officinale on the aflatoxin secreted in wastemould feed fed to Clarias gariepinus (burchell, 1822)

The growth and pathological effect of aflatoxin in waste-mould feeds fed to juvenile Clarias gariepinus and the additive nature of Zingiber officinale was studied. Clarias gariepinus juveniles (58.19±1.8 g) were distributed at the rate of 10 per happa net in earthen ponds. There were 5 Treatments with 3 replicates – control diet TRT 1 (Good feed, without mould), TRT 2 (Mould feed only), TRT 3 (60 g of Z. officinale + 1 kg of mould feed), TRT 4 (30 g of Z. officinale + 1 kg of mould feed), and TRT5 (10 g of Z. officinale + 1 kg of mould feed). The fish were fed to satiation at 5% body weight twice per day for 8 weeks (56 days) and the fish growth parameters measured. There was significant increase (P&lt;0.05) in mean weight gain of TRT 1, TRT 3, and TRT 4 compare to TRT 2 and TRT 5. The experimental fish at TRT1, TRT 3, TRT 4 and TRT 5 were significantly different (P&lt;0.05) compared to TRT 2 in weight gain, protein efficiency ratio (PER), feed conversion ratio (FCR), and specific growth rate (SGR). The gills and liver of the control group (TRT1) of fish appeared with single layer of epithelial cells covering the secondary lamellae and uniform distribution of the hepatocytes respectively. In the TRT 2 and TRT 5, there was haemorrhage of the capillaries in the interlamellar space of the gills. Kidney of the fish in the TRT 1, TRT 3 and TRT 4 had normal glomeruli which are not the same with the TRT 2 and TRT 5. These findings showed that Z. officinale has the capacity to suppress the toxic effects of the aflatoxin (secondary metabolites) secreted by the mould feeds on the growth and vital organs of C. gariepinus. © 2013 International Formulae Group. All rights reserved.Keywords: Aflatoxin, Clarias gariepinus, mould feed, Zingiber officinale, treatments.

Ag/lamellar hosts composites: a route to morphology-controllable synthesis of Ag nanoparticles

An easy and novel routine are reported for the preparation of metallic silver nanoparticles (AgNPs) with controlled morphology, using Na+–magadiite swelled with hexadecyltrimethylammonium bromide (CTA+–magadiite) and a layered aluminophosphate with kanemite-type structure modified with n-dodecylammonium and n-butylammonium (but,dod-AlPO-kan) as hosts. For the preparation of the metallic AgNPs (Ag0) in the interlamellar space, the CTA+–magadiite and but,dod-AlPO-kan hosts were dispersed in N,N-dimethylformamide (DMF) solution with different AgNO3 concentrations. DMF acts as reducing agent of Ag+ ions leading to nanoparticles with disk-like morphology of magadiite silicate; these were characterized by TEM and UV–Vis spectroscopy. On the other hand, the AgNPs are intercalated in but,dod-AlPO-kan showing spherical-like morphology. The UV–Vis spectra of the nanocomposites based on Ag0 and magadiite silicate show bands at 565 nm that can be attributed to Ag0 nanodisks. The Ag-but,dod-AlPO-kan-based nanocomposites present a band at 422 nm attributed to the surface plasmon resonance of Ag0 nanospheres. The results of transmission electron microscopy agree very well with XRD and UV–Vis analysis, indicating the formation of AgNPs with different morphologies using the two kinds of lamellar materials. The magadiite host has an important role in the synthesis of Ag nanodisks, because it controls the growth of nanoparticles inside the interlayer region with disk-like morphology due the high interlayer interactions of the silicate, leading to the growth of nanoparticles in only two directions (xy plane). On the other hand, when but,dod-AlPO-kan is used a sphere-like morphology is preferred due the best accommodation of AgNPs between the layers of aluminophosphate host.

Quantitative XRD analysis of the dehydration–hydration performance of (Na+, Cs+) exchanged smectite

The clay mineral membrane is increasingly used, as a natural geological barrier, in wastewater treatment. The variation of the environmental condition (T, P, RH, etc.) induces probably several change on the materials structure. This work aims at characterizing the link between dehydration–hydration behavior, charge location, and the ionic radius, in the case of dioctahedral smectites, exchanged with Na+ and Cs+ cation, which are occurred from industrial waste. A natural montmorillonite and beidellite, with different charge location (respectively, dioctahedral and trioctahedral), are selected. The exchange process is directed using Na+ and Cs+ cations. The hydration hysteresis is investigated “in situ” as a function of relative humidity condition rates. All samples are studied using quantitative X-ray diffraction (XRD) analysis. This method allows us to determine the structural parameters obtained from the theoretical mixed layer structure used to fit experimental XRD patterns. For both Na+ and/or Cs+ exchangeable cations, an increase in hydration heterogeneity degree for the tetrahedral substituted smectite layer is noted and the position of exchangeable Cs+ cation induce a homogeneous hydration trend which is interpreted by a new interlamellar space organization.

Long-Distance Water Exchange within Dense Clay Sediments Probed by Two-Time 2H Stimulated Echo NMR Spectroscopy

Two-time correlation functions are measured by deuterium (2H) NMR spectroscopy to probe the long-distance mobility of water molecules strongly confined within dense clay sediments. As checked by 2H NMR multiquantum relaxation measurements, these strongly confined water molecules satisfy the two main requirements for a successful use of that experimental procedure, i.e., slow exchange of the water molecule between its various confining environments and slow modulation of the nuclear couplings responsible for its NMR relaxation. The exchange time scale detected by the attenuation of the two-time 2H NMR stimulated echo is 3 orders of magnitude larger than the average residence time of the water molecules within the interlamellar space of individual clay platelets. Finally, numerical simulations are used to illustrate the impact of local heterogeneities of the clay orientation on the attenuation of the two-time correlation function.

Microstructural investigation of calcium montmorillonite

AbstractBentonite clay is planned to form a part of deep-geological repositories of spent nuclear fuel in several countries. The extremely long operation time of the repository requires an indepth understanding of the structure and properties of used materials. In this work the microstructure of a simplified system of Ca-montmorillonite is investigated using a set of complementary methods: X-ray diffraction, small angle X-ray scattering, nuclear magnetic resonance, transmission electron microscopy and ion exclusion. The paper presents experimental results obtained from compacted, water saturated samples in the dry density range 0.6–1.5 g/cm3. It can be observed that different methods yield similar quantification of water present in the interlamellar space. Combined results support the multiple porosity concept of the bentonite structure.