Showing papers on "Clay minerals published in 1997"

Synthesis and properties of polyimide-clay hybrid films

Abstract: Polyimide-clay hybrid films with four different sizes of clay minerals have been synthesized to investigate the effect of the size of clay minerals to the properties of the hybrids. Hectrite, saponite, montmorillonite, and synthetic mica were used as clay minerals. Those clays consist of stacked silicate sheets about 460 A (hectrite), 1650 A (saponite), 2180 A (montmorillonite), and 12300 A (synthetic mica) in length, 10 A in thickness. The longer the length of clay mineral was, the more effectively properties of polyimide were improved. In the case of polyimide-mica hybrid, only 2 wt % addition of synthetic mica brought permeability coefficients of water vapor to value less than one-tenth of that of ordinary unfilled polyimide, and thermal expansion coefficient was lowered at the level of 60% of the original one. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2289–2294, 1997

Reactions of boron with soils

Abstract: Boron is an essential micronutrient for plants, but the range between deficient and toxic B concentration is smaller than for any other nutrient element. Plants respond directly to the activity of B in soil solution and only indirectly to B adsorbed on soil constituents. Soil factors affecting availability of B to plants are: pH, texture, moisture, temperature, organic matter and clay mineralogy. Boron adsorbing surfaces in soils are: aluminium and iron oxides, magnesium hydroxide, clay minerals, calcium carbonate, and organic matter. Boron adsorption reactions can be described empirically using the Langmuir adsorption isotherm equation, the Freundlich adsorption isotherm equation, and the phenomenological Keren model. Chemical models such as the constant capacitance model, the triple layer model, and the Stern VSC-VSP model can describe B adsorption over changing conditions of solution pH and B concentration. Boron desorption reactions often exhibit hysteresis. The rate of B desorption can be described using the first order rate equation, the Elovich reaction rate equation, and the power function equation.

Molecular Dynamics Modeling of Clay Minerals. 1. Gibbsite, Kaolinite, Pyrophyllite, and Beidellite

Abstract: A molecular dynamics model for clays and the oxide minerals is desirable for studying the kinetics and thermodynamics of adsorption processes. To this end, a valence force field for aluminous, dioctahedral clay minerals was developed. Novel aspects of this development include the bending potential for octahedral O−Al−O angles, which uses a quartic polynomial to create a double-well potential with minima at both 90° and 180°. Also, atomic point charges were derived from comparisons of ab initio molecular electrostatic potentials with X-ray diffraction-based deformation electron densities. Isothermal−isobaric molecular dynamics simulations of quartz, gibbsite, kaolinite, and pyrophyllite were used to refine the potential energy parameters. The resultant force field reproduced all the major structural parameters of these minerals to within 1% of their experimentally determined values. Transferability of the force field to simulations of adsorption onto clay mineral surfaces was tested through simulations of ...

Binding of Fluoroquinolone Carboxylic Acid Derivatives to Clay Minerals

Abstract: Large quantities of fluoroquinolone carboxylic acid (FQCA) derivatives are applied as antibacterial agents in large-scale animal husbandry. Important quantities are transported to agricultural areas by means of liquid manure. The binding of FQCA derivatives to clay minerals and their sorption by five soils from different geographic areas were investigated. Sorption was studied in batch experiments using radioactive labeled enrofloxacin (Baytril), decarboxylated enrofloxacin, ciprofloxacin (Cyprobay), levofloxacin (Oxaldin), and a fluorochloroquinolone carboxylic acid derivative. More than 90% (KD = 260−5612) of the applied enrofloxacin adsorbed on the different soils. The other chemicals showed a similar adsorption (KD = 285−496) on a German soil except the decarboxylated enrofloxacin (KD = 7.7). At clay minerals enrofloxacin was adsorbed >98%. X-ray diffraction analysis showed that the adsorption at the clay mineral montmorillonite occurred between the layers, resulting in an expansion of the spacing. Mi...

ADSORPTION OF 137Cs ON MONTMORILLONITE AND ILLITE: EFFECT OF CHARGE COMPENSATING CATION, IONIC STRENGTH, CONCENTRATION OF Cs, K AND FULVIC ACID

Abstract: A thorough understanding of the capacity of clay minerals to adsorb radiocesium is essential in order to predict the fate of this pollutant in the environment and to interpret routine measurements, such as desorbability. We have investigated the adsorption of radiocesium onto 2 contrasting reference clay minerals in dilute suspensions after a 2-h contact period. The results have been expressed as the distribution coefficient, Kd, or the selectivity coefficient, Kc. The adsorption properties have been studied with respect to various parameters: nature of the charge compensating cation, ionic strength, concentration of Cs, concentration of K and concentration of a soil-extracted fulvic acid. A Freundlich isotherm has been found to fit experimental data well for levels of adsorbed cesium in the range 10−7 to 1 mol kg−1. Evidence of surface heterogeneity is discussed, but it was not possible to deduce the exchange capacities of the groups of exchange sites with differing affinities for Cs, which are thought to exist in illites. The concentration dependence of adsorption upon montmorillonite is postulated to arise from a modification of the exchange complex with increasing presence of Cs, rather than from heterogeneity of exchange sites. Increasing ionic strength caused a decrease in the relative affinity for a trace amount of cesium on both minerals, although mass action led to a fall in Kd. This is thought to indicate a high covalent interaction between Cs and the clay surface. Potassium caused a smaller decrease in adsorption than stable Cs, which suggests that neither K nor NH4 plays a decisive role in the immobilization of radiocesium by clay minerals. There was a small decrease in adsorption upon addition of soil organic matter, which may contribute to the poor fixation capacity observed for some soils with a high organic matter content.

Bonding between polyacrylamide and clay mineral surfaces

Abstract: The objectives of this research were to determine the effects of clay mineralogy on the efficacy of cationic and anionic polyacrylamides (PAM) as flocculents for dispersed clays and to evaluate bonding mechanisms between clay mineral surfaces and both cationic and anionic PAM. A relative floccul

The Possible Role of Nannobacteria (Dwarf Bacteria) in Clay-Mineral Diagenesis and the Importance of Careful Sample Preparation in High-Magnification SEM Study

Abstract: Bacterial textures are present on clay minerals in Oligocene Frio Formation sandstones from the subsurface of the Corpus Christi area, Texas. In shallower samples, beads 0.05-0.1 µm in diameter rim the clay flakes; at greater depths these beads become more abundant and eventually are perched on the ends of clay filaments of the same diameter. We believe that the beads are nannobacteria (dwarf forms) that have precipitated or transformed the clay minerals during burial of the sediments. Rosettes of chlorite also contain, after HCl etching, rows of 0.1 µm bodies. In contrast, kaolinite shows no evidence of bacterial precipitation. We review other examples of bacterially precipitated clay minerals. A danger present in interpretation of our earlier work (and much work of other ) is the development of nannobacteria-looking artifacts caused by gold coating times in excess of one minute; we strongly recommend a 30-second coating time. Bacterial growth of clay minerals may be a very important process both in the surface and subsurface.

The structure of the kaolinite minerals — a FT-Raman study

Abstract: The Fourier transform Raman spectra of the kaolinite minerals have been measured in the 50–3800 cm−1 region using near infrared spectroscopy. Kaolinites are characterized by remarkably intense bands in the 120–145 cm−1 region. These bands, attributed to the O-Si-O and O-Al-O symmetric bending modes, are both polymorph and orientation dependent. The 200–1200 cm−1 spectral range is a finger-print region for clay minerals and each kaolinite clay has its own characteristic spectrum. The structure of clays is fundamentally determined by the position of hydroxyl groups. Fourier-transform Raman spectroscopy readily enables the hydroxyl stretching region to be examined allowing identification of the component bands. The advantages of FT-Raman spectroscopy are shown to enhance the study of the kaolinite structure.

Weathering of chlorite to a low-charge expandable mineral in a spodosol on the apennine mountains, Italy

Abstract: The clay fraction of a Spodosol and its parent rock in the Apennlne mountains of central Italy were studied by powder X-ray diffraction (XRD) and infrared (IR) spectroscopy, to evaluate the possibility of transformation of chlorite into low-charge expandable minerals. Results indicated that the main phyl- losilicate in the rock was a slightly weathered trioctahedral chlorite, rich in both Mg and Fe. together with dioctahedral mica and minor amounts of kaolinite. In the BC horizon, chlorite has undergone partial transformation into 2 vermiculitic components, in 1 of which the interlayer could be removed by hot Na-citrate treatment: the presence of a regular interstratified mineral (high-charge corrensite) was also observed. Further changes in the structure of chlorite were detected in the Bsl horizon, becoming more evident towards the soil surface. The first stage of weathering of chlorite involved Fe oxidation and partial expulsion of Mg from the hydroxide sheet, followed by deposition of A1 in the interlayer space. Iron is also removed from the interlayer sheet, possibly remaining, in the oxidized state, in the 2:1 octahedral sheet, and so contributing to the lowering of layer charge and transformation to a dioctahedral structure. When approaching the surface, A1 removal from the interlayers is enhanced by complexing agents, and further charge reduction leads to the formation of 2:1 minerals with a smectite nature. Illite. because ot its low content in the soil clay fraction, contributes marginally to this weathering sequence, forming the high charged expandable component observed in the Bhs horizon. At the soil surface, a randomly inter- stratified vermiculite/illite was detected, which probably originated from K fixation by the higher-charged expandable minerals. This study of weathering in a natural soil strongly supports the hypothesis, previ- ously ascertained by laboratory experiments, that chlorite can transform into a low-charge expandable mineral.

Soils and sediments : mineralogy and geochemistry

Abstract: From the contents: Clay Minerals in Weathered Rock Materials and in Soils Calcareous Epigenetic Replacement ("Epigenic") in Soils and Calcrete Formation Laterites and Bauxites Geochemical Processes in Tropical Landscapes: Role of the Soil Covers Evolution of Lateritic Manganese Deposits The Lateritic Nickel-Ore Deposits The Behavior of Gold in the Lateritic Alterosphere Comparative Ecology of Two Semi-Arid Regions: the Brazilian Sertao and the African Sahel Importance of the Pore Structures During the Weathering Process of Stones in Monuments Continental Silicifications: A Review Clay Minerals, Paleoweathering, Paleolandscapes and Climatic Sequences: The Paleogene Continental Deposits in France On the Genesis of Sedimentary Apatite and Phosphate-Rich Sediments Clay Mineral Sedimentation in the Ocean Revisited Isotopic Dating Methods of Sdimentary Minerals for Stratigraphic Purpose Concomitant Alteration of Clay Minerals and Organic Matter During Burial Diagenesis.

Origin and classification of coastal plain kaolins, Southeastern USA, and the role of groundwater and microbial action

Abstract: Along the inner Coastal Plain, kaolinite-metahalloysite-rich, neritic muds of Cretaceous-Eo- cene age have undergone intense postdepositional alteration in the recharge area of the regional ground- water system. Weathering processes have had the following profound effects on the original sediments: 1) strong compositional and textural modification of both clay and non-clay minerals; 2) whitening of the originally darker sediments by partial removal of organic matter, Fe and Mn; and 3) recrystallization of kaolinite and metahalloysite, most conspicuous where there are coarse stacks and vermiforms. Where the combination of initial sediment composition and alteration intensity was most favorable, these changes have produced important deposits of commercial quality, which now sustain the world's largest kaolin production district. The earliest change was partial sequestration of iron as sulfide and concurrent destruc- tion of some organic matter, mediated by sulfate-reducing bacteria. Subsequent weathering resulted in gradual leaching of alkalies, alkaline earths, iron and silica, and attendant nucleation and growth of minerals compatible with the compositional changes. The existence of several closely spaced erosional unconformities, separated by neritic sediments, is proof that weathering conditions commonly changed at a given site, in response to changes in thickness or lithology of the overlying rocks. Dsyoxic ---) ~-- oxic reversals modified both the rate and kind of alteration. ("Dysoxic" refers to molecular oxygen concen- tration too low to be toxic to anaerobes or cause abiotic oxidation; less extreme than "anoxic".) Kaolins were produced partly by slower dysoxic weathering in saturated groundwater zones but mainly by more rapid oxic weathering in unsaturated zones, where bauxites also locally formed. Gradual transformation of some sediments to kaolin rarely began and ended in the same epoch. At several places most of the kaolinization (see "Definitions") took place during Recent time, tens of millions of years after deposition of the sediments. Since the kaolins resulted from postdepositional alteration rather than sedimentary processes, they are better referred to as "Coastal Plain" rather than "sedimentary" kaolins.

Laser Raman spectroscopy of varnished basalt and implications for in situ measurements of Martian rocks

Abstract: Earth-based and orbital spectroscopy and Viking Lander data strongly suggest that rocks on Mars are coated with indurated dust deposits. Rock coatings will influence mineralogical measurements to be acquired in situ from Mars rovers and other surface missions, in that most techniques will detect the coatings and/or coatings plus underlying minerals. In this paper, we present results of experiments on varnished basalt cobbles from the Lunar Crater Volcanic Field, Nevada, using laser Raman spectroscopic microprobe measurements obtained with a 514.5 nm Ar+ laser and irradiation spot sizes from 1 to 20 μm. Measurements from thin sections and fresh, unprepared rock surfaces clearly allow identification of igneous minerals. Varnish spectra acquired from thin sections as well as from unprepared exterior rock surfaces typically show broad peaks consistent with the fine-grained nature of varnish and the dominance of manganese oxide and clay minerals. Several areas also show sharp Raman peaks due to phosphates and anatase, indicative of the heterogeneity of varnish deposits. Raman spectra taken through varnished rock surfaces reveal the mineralogy of coatings (where varnish is >15 μm in thickness) and a combination of coatings and igneous minerals in areas with thinner varnish. Given the abundance of rock coatings observed at the Viking and Pathfinder landing sites, results indicate that techniques such as Raman spectroscopy (and any others with comparable penetration depths) will sample some combination of coatings and underlying rock materials. The ability to make many in situ measurements across samples, coupled with the ability to expose fresh rock surfaces, will be needed to unambiguously characterize both the coatings and the rocks on Mars from future landers and/or rovers.

Wettability contrasts in kaolinite and illite clays; characterization by infrared and X-ray absorption spectroscopies

Abstract: A reservoir rock is a porous geological formation in contact with 2 liquids, brine and oil. An improved knowledge of rock wettability is of primary importance to estimate the amount of crude oil in underground resources. The petroleum industries have observed that wettability contrasts in sedimentary reservoir rocks are largely correlated to the presence of clays, illite and/or kaolinite in the rocks' intergranular space. More precisely, the grain surfaces of illite show a preference for brine. Kaolinite preferentially adsorbs oil, which imparts its hydrophobic characteristics to the mineral surface. Using X-ray absorption spectroscopy (XAS) and Fourier transform infrared (FTIR) spectroscopy, we studied the adsorption process of asphaltenes in the presence of water at the microscopic level. We demonstrate experimentally that the wettability contrasts observed in kaolinite and illite are related to structural differences between these 2 clays, and we show the role of the grain surface hydroxyls. With clay materials, the purity of the samples is the most important limitation of the quantitative use of extended X-ray absorption fine structure (EX-AFS).

Iodide, caesium and strontium adsorption by organophilic vermiculite

Abstract: A B S T R A C T: Distribution coefficients and isotherms for the adsorption of radioiodide, caesium and strontium ions (125I-, 134Cs+ and 85Sr2+) were determined in untreated vermiculite and in vermiculite treated with the chloride salt of hexadecylpyridinium (HDPy+). Experimental data reveal that some of the alkylammonium ions were incorporated as HDPyCI ion pairs into the vermiculite. The fraction of ion pairs adsorbed is reflected by an increase in distribution coefficients with increasing saturation levels. Consequently, a considerable part of the iodide adsorption could be attributed to an anion exchange process. At smaller amounts of Cs § and Sr z+ adsorbed, distribution coefficients of the modified clay mineral are significantly reduced in comparison with the original material. These differences are less pronounced when greater amounts of cations are adsorbed. Generally, larger distribution coefficients were found for the Cs + compared with the Sr z§ ion in the untreated and modified samples. Soils represent an important filter and buffer system for many cations and anions. Generally, their sorption properties are determined by the contents and compositions of clay minerals and humic substances. A great part of the soil organic matter is associated with clay minerals forming organomineral complexes (Greenland, 1965) which are of pronounced importance with respect to element transport and/or retention and to aggregate stability. Clay minerals also interact with organic cations. The replacement of inorganic cations by alkylammonium ions causes considerable modification in the hydration and swelling properties of the clays. Research in this area has significantly increased the

A study of organo-hectorite clay crystallization

Abstract: A method has been developed to synthesize organo-hectorite clays directly from a Mg-silicate gel containing organic or organometallic molecules that are expected to be incorporated within the interlayer space Complete crystallization occurs upon aqueous reflux for 48 h The progress of clay layer formation was monitored by X-ray powder diffraction (XRD), differential thermal gravimetry (DTG), and infrared (IR) spectroscopy Evidence of clay XRD peaks occurs after just 4 h of hydrothermal treatment, and Mg(OH)2 is no longer observable after 14 h Observable changes in DTG and IR occur at about this time as well Warren line-shape analysis of the 110 reflection indicates that when growth is complete the clay lamellae are on average ∼50% and 25% of the size of natural hectorites and montmorillonites, respectively The N2 BET surface areas for all materials are also compared Small angle neutron scattering shows that addition of tetraethyl ammonium (TEA) ions does not alter the structural integrity over that of the purely inorganic form of Li-hectorite, but that use of a cationic polymer does significantly alter the microstructure The effect of temperature is critical, for at room temperature only the layered Mg hydroxide mineral brucite crystallizes unless very long time scales are used The crystallizations carried out at room temperature show that clay will form after about 3 months, but that the presence of organics (at least TEA) acts to hinder this process greatly The role of the organic molecules on silicate clay layer formation is compared with the role of organics in zeolite synthesis

Sodicity and Clay Type: Influence on Decomposition of Added Organic Matter

Abstract: Sodicity and clay type influence the decomposition of organic matter, and hence its accumulation in soil. In this study, the interaction of these two factors was examined. Two soils were prepared by mixing sand (57%) and silt (28%), separated from one soil, with clay (15%) separated from two soils. One clay type (Urrbrae) was composed mostly of illite and kaolimite, with a mean particle diameter of 1050 nm. The other (Claremont) was composed of smectite-dominated materials, with a mean diameter of 104 nm. The prepared soils were brought to different values of exchangeable sodium percentage (ESP) by equilibration with solutions having sodium adsorption ratios (SAR) between 0 and 30. Pea (Pisum sativum L.) straw was added at 50 g kg−1 soil, and the samples were incubated moist. After 67 d, cumulative mineralization of C was 16% greater in the soils with Urrbrae clay than in those with Claremont clay. Sodicity had a slight negative effect on mineralization, but its interaction with clay type was not significant. Differences in the mineralization of C with time and between treatments were reflected in the chemical nature of the remaining C, as determined by 13C nuclear magnetic resonance (NMR) spectroscopy. The greater the loss of C, the lower the proportion of O-alkyl C relative to other types of C. An implication of the findings is that, following a large addition of organic matter to a sodic soil, retention of organic C would not be improved by a prior reduction in ESP, irrespective of clay mineralogy.

Quantitative Aspects of Weathering and Neoformation in Selected Costa Rican Volcanic Soils

Abstract: Gains and losses of major elements in eight soil profiles developed on volcanic parent material in the perhumid tropical Atlantic lowland of Costa Rica were calculated from total element contents, assuming Ti to be immobile. Initially soil formation (0-500 yr) in Tropopsamments involves dilation of the sandy deposits by incorporation of organic matter and formation of structure and biopores, without detectable gains or losses of elements. In 2000- to 5000-yr-old sandy Hapludands, primary minerals are still abundant, but up to 20% of the mineral soil consists of x-ray amorphous materials. Dilation continues and losses of Mg, Ca, Na, and K, and to a lesser degree Si, become measurable. Within 18 000 yr, a Melanudand develops, which is depleted of primary minerals and especially volcanic glass in the fine-earth fraction. A mixture of short-range order material, metal-humus complexes, and gibbsite and kaolin minerals dominate its upper horizon, while gibbsite, halloysite, and short-range order material are the most important secondary minerals at greater depths. Dilation of the soil mass prevails in the A horizon, while collapse has occurred in the B horizon. The Melanudand has lost considerable amounts of mobile elements: 50 to 85% of Si, Mg, Ca, Na, and K have been leached from the fine-earth fraction. Within 125 000 yr, a Haploperox has formed (thought to have formed from Andisols); it is strongly collapsed and is dominated by gibbsite, kaolin minerals, and Fe (hydr) oxides. The upper meters are devoid of primary minerals except for small opaques. Under the prevailing environmental conditions, weathering and neoformation of primary volcanic minerals lead to almost complete dissolution and leaching of basic cations, probably within 20 000 to 50 000 yr. The Si and P mineral reserves are depleted considerably, but part is still present after such long time periods.

Geochemistry of Cu, Co, Ni, Zn, Cd and Cr in the surficial sediments of a tropical estuary, southwest coast of India: a granulometric approach

Abstract: Geochemical characteristics of six trace metals – Cu, Co, Ni, Zn, Cd and Cr – in the bulk sediment and sand, silt and clay fractions of a tropical estuary on the southwest coast of India have been studied and discussed. In bulk sediment, the trace metal concentration is controlled mainly by the textural composition of the sample. Mud, sandy mud and sandy silt register higher concentrations of trace metals than that in sand-dominant sediments. The granulometric partitioning studies also re-affirmed the role of particle size in enriching the trace metals. The silt and clay fractions exhibit 7–8 times the enrichment of Cu and Cd compared to that in sand. The enrichment factors of Zn, Cr, Ni and Co in the silt and clay fractions, compared to that in sand, are 5–6, 4–5, 2–5 and 2–3 times, respectively. The trace metals in the sand fraction, particularly Ni and Cr, exhibit strong positive correlation with the heavy mineral content of the samples. It clearly indicates a heavy mineral pathway to the trace metals in the sand fraction. Cu and Co in silt and clay fractions exhibit a marked decrease towards the high saline zones of the estuary. This is attributed to the desorption of Cu and Co from particulate phases during estuarine mixing. Contrary to Cu and Co, the content of Zn in the clay fraction shows a marginal increase towards the estuarine mouth. This could be explained by the influx of Zn-rich contaminant discharges from Zn-smelting industries located slightly north of the estuarine mouth. The released Zn will effectively be held in the lattices of the clay mineral montmorillonite, which also exhibits a marked increase towards the estuarine mouth. The anomalously high values of Cd in some places of the Central Vembanad estuary is attributed to the local pollution.

Characterization of Colloids Mobilized from Southeastern Coastal Plain Sediments

Abstract: Two subsurface samples representing highly weathered sediments of the Upper Coastal Plain (Aiken, SC) that differed in Fe-oxide content (7.3 vs 35.9 g Fe kg -1 ) were evaluated in terms of mobile colloid generation in response to changes in solution composition. In repacked columns, the two sediments were leached (∼0.72 m d -1 Darcy velocity) with either 0.001 N NaCI or CaCl 2 solutions for 10 pore volumes followed by 10 pore volumes of deionized water. Bulk clay mineralogy from the two samples and suspensions generated in the column studies was characterized by energy dispersive X-ray analysis (EDXA) using a field-emission scanning electron microscope (SEM). SEM results were confirmed by selected-area electron diffraction (SAED) and EDXA in a transmission electron microscope. In column experiments, the sample lower in Fe oxide displayed increased effluent turbidity that coincided with a decrease in effluent pH during injection of the CaCl 2 solutions. In contrast, no effluentturbiditywas observed during the leaching of NaCl solutions. The sample higher in iron oxide displayed greater effluent turbidity from the onset of leaching that decreased over the duration of injection for both the CaCl 2 and NaCl solutions. Colloids generated from both materials displayed positive electrophoretic mobilities, confirming the importance of iron oxides in controlling dispersion and surface charge properties of the mobile colloids. Minor differences in the clay mineralogy (i.e., iron oxide/kaolinite content) between the samples were reflected in both their sensitivity to pore-solution composition and the relative degree of dispersion observed for each sample. Electron microscopy, EDXA, and thermal gravimetric analysis (TGA) confirmed that the mobile colloids consisted mainly of submicron sized Al-rich goethite, with lesser amounts of kaolinite,the predominate layer silicate of the bulk sediments, and varying amounts of crandallite.

Surfactant Adsorption on a Clay Mineral: Application of Radiation Scattering

Abstract: Aqueous mixtures of the synthetic clay mineral Laponite and cetyltrimethylammonium bromide (CTAB) in dilute suspension have been investigated by small-angle neutron scattering (SANS) and dynamic light scattering (DLS). The SANS intensity pattern from the suspension of the pure clay is consistent with that from disks or platelets with diameters of about 30 nm. After addition of CTAB to the clay suspensions, CTAB adsorbs on the face of the clay platelets by cationic exchange and the resulting complex contains excess CTAB in an amount corresponding to about four multiples of the clay's cation exchange capacity (CEC). Contrast matching by isotopic substitution in the solvent indicates that the CTAB/clay complex retains a disk morphology, even if the CTAB in the aqueous medium is in considerable excess. Analyses of the DLS data are interpreted to indicate two possible stable clay platelet configurations in the suspensionsfree clay platelets or clay platelets with CTAB adsorbed in an amount above the CEC and pr...