Dodecylammonium Ions Research Articles

PREPARATION AND PROPERTIES OF EXFOLIATED VERMICULITE-POLYAMIDE 6 NANOCOMPOSITE

Ion-exchange treatment of natural vermiculite (VER) with dodecylammonium (DDA) ions and subsequent preparation of a polyamide 6 (PA6) based nanocomposite was conducted to investigate the potential suitability of VER for use in polymer nanocomposites. In order to investigate the ion-exchange behavior, ground VER powder and DDA were treated at 60°C for 12 h, in which time the intercalation reaction was completed. DDA intercalation was rapid and complete for VER even in dilute DDA solution (0.5 mass%) at a low suspension VER concentration of 1 mass%. The VER-PA6 nanocomposite was formed via exfoliation of a DDA modified VER (DDAVER) layer. DDAVER was melt-kneaded with PA6 in a twin-screw extruder at 260°C. The morphology of the nanocomposite was characterized using X-ray diffraction and transmission electron microscopy. Measurements of the mechanical properties and methanol permeability were also carried out. The DDAVER-PA6 nanocomposite exhibits a high degree of VER exfoliation and the rigidity and gas barrier properties also appear to reflect the nanocomposite morphology. Addition of a small amount of DDAVER with 3 mass% sili- cate was sufficient to improve the rigidity, heat resistance and barrier properties of the nanocomposite.

A study of adsorption mechanism of dodecylamine on sphalerite

Long-chain primary amines are not only good collectors for silicate minerals, but, they can also float some metallic sulfides. However, the flotation mechanism of sulfide minerals using long-chain primary amines as collector is uncertain. In this paper, the flotation performance and adsorption mechanism of dodecylamine in the flotation of sphalerite was studied using micro flotation tests, zeta potential measurements, XPS analysis and FTIR measurements. The dodecylamine showed better sphalerite flotation performance over a wide pH range even at a low collector dosage. The spectroscopic data in combination with zeta potential showed that: (1) chemisorption occurred between the N atoms in dodecylammonium ions (RNH3+) and the sulfur atoms in ZnS over the pH range from 1 to 13. The molecular dodecylamines (RNH2) could also adsorb via H-bonds with other sulfur atoms; (2) the molecular dodecylamine absorbed onto the sphalerite surface may screen the electrostatic repulsion between the positive-charged head groups (−NH3+) absorbed onto the sphalerite surface, which increased the density of absorbed amine and further enhanced the surface hydrophobicity; (3) in the alkaline pH range, the dodecylamine colloidal precipitates appeared, and the zeta potential of the colloidal precipitates changed from positive to negative as the pH increased. As a result, positively charged precipitates electrostatically adsorbed onto the negatively charged sphalerite surface thus enhancing the flotation recoveries, while negatively charged precipitates inhibited sphalerite flotation.

Pickering Emulsions Prepared by Layered Niobate K4Nb6O17 Intercalated with Organic Cations and Photocatalytic Dye Decomposition in the Emulsions

We investigated emulsions stabilized with particles of layered hexaniobate, known as a semiconductor photocatalyst, and photocatalytic degradation of dyes in the emulsions. Hydrophobicity of the niobate particles was adjusted with the intercalation of alkylammonium ions into the interlayer spaces to enable emulsification in a toluene-water system. After the modification of interlayer space with hexylammonium ions, the niobate stabilized water-in-oil (w/o) emulsions in a broad composition range. Optical microscopy showed that the niobate particles covered the surfaces of emulsion droplets and played a role of emulsifying agents. The niobate particles also enabled the generation of oil-in-water (o/w) emulsions in a limited composition range. Modification with dodecylammonium ions, which turned the niobate particles more hydrophobic, only gave w/o emulsions, and the particles were located not only at the toluene-water interface but also inside the toluene continuous phase. On the other hand, interlayer modification with butylammonium ions led to the formation of o/w emulsions. When porphyrin dyes were added to the system, the cationic dye was adsorbed on niobate particles at the emulsion droplets whereas the lipophilic dye was dissolved in toluene. Upon UV irradiation, both of the dyes were degraded photocatalytically. When the cationic and lipophilic porphyrin molecules were simultaneously added to the emulsions, both of the dyes were photodecomposed nonselectively.

Adsorptive and Photocatalytic Removal of Phenol by Layered Niobates Organically Modified Through Intercalation and Silylation

Layered hexaniobate K4Nb6O17 was modified with dodecylammonium ions and octadecyltrimethoxysilane molecules, which were held in the interlayer spaces by electrostatic interactions and covalent attachment to the layers, respectively. Interlayer spacing of the niobate was expanded by incorporation of the bulky organic species. Vapor adsorption isotherms of benzene and water indicated hydrophobic interlayer microenvironments of the organically modified niobates. Both of the modified niobates fairly adsorbed phenol dissolved in water. The photocatalytic activity of hexaniobate allowed the organically modified materials to photocatalytically decompose phenol upon UV irradiation. Decomposition time courses and quantitative analysis of phenol present in the system indicated that the phenol molecules adsorbed on the niobates were preferentially degraded. XRD and IR analyses of the modified niobates indicated that the silylated niobate was more durable than the ion-exchanged sample; the former kept the structure during the photocatalytic process while the latter was partly collapsed.

Alteration of swelling clay minerals by acid activation

The bulk material of six dioctahedral and two trioctahedral swellable clay minerals was leached in H 2SO 4 and HCl at concentrations of 1.0, 5.0 and 10.0 M at 80 °C for several hours. Alteration of the clay mineral structures was dependent on the individual character of each mineral (chemical composition and initial particle size). Acid attack dissolved the octahedral sheets by interlayer and edge attack. The number of substitutions by Mg or Fe in the octahedral sheet of the clay minerals promoted the dissolution of these layers and the formation of a silica phase. The dissolution of the octahedral cations occurred in the following order: Mg > Fe > Al. The dioctahedral smectites were more stable than the trioctahedral smectites and vermiculites; the behavior of trioctahedral smectites against acid was similar to that of vermiculites. The acid activated smectites displayed still the ability to exchange cations. The obtained materials had a lower layer charge, lower CEC and higher specific surface area than the crude materials but still adsorbed very large organic cations like dodecylammonium ions. The reaction with the acid caused particle splitting within the octahedral sheet. A model of dissolution and particle splitting is proposed.

Composition-Dependent Ion-Exchange Reactivity of Potassium Lithium Titanates

Abstract The ion exchange of dodecylammonium ion was examined for two potassium lithium titanates; the titanates were K0.80Ti1.71Li0.29O3.97 prepared by a solid-state reaction at 800 °C and K0.66Ti1.73Li0.27O3.93 prepared by a solid-state reaction at 1020 °C followed by reaction with aqueous H2SO4 and subsequent annealing. A single phase intercalation compound formed successfully for K0.66Ti1.73Li0.27O3.93 (the amount of the adsorbed dodecylammonium was 2.1 mmol g−1) by reaction with an aqueous solution of dodecylammonium chloride. On the other hand, the parent titanate remained for K0.80Ti1.71Li0.29O3.97 (1.4 mmol g−1).

Synthesis, Physicochemical Characterization and MR Relaxometry of Aqueous Ferrofluids

The synthesis and characterization of ferrofluid based MR contrast agents, which offer R2* versatility beyond that of ferucarbotran, is described. Ferrofluids were formed after stabilizing magnetite cores with dodecanoic acid (a), oleic acid (b), dodecylamine (c), citric acid (d) or tartaric acid (e). Core sizes were deduced from TEM micrographs. Magnetic properties were determined by SQUID magnetometry. Hydrodynamic particle diameters were determined by dynamic light scattering measurements. Zeta potentials were measured by combining laser Doppler velocimetry and phase analysis light scattering. Iron contents were evaluated colorimetrically. MR relaxometry including R1 and R2* was conducted in vitro using homogeneous ferrofluid samples. The average core diameters of ferrofluids a, b and c equaled 9.4±2.8 nm and approximately 2 nm for ferrofluids d and e. Magnetization measurements at 300 K revealed superparamagnetic behaviour for the dried 9 nm diameter cores and paramagnetic-like behaviour for the dried cores of ferrofluids d and e. Iron contents were between 32–75 mg Fe/mL, reflecting the ferrofluids' high particle concentrations. Hydrodynamic particle diameters equaled 100–120 nm (a, b and c). For the ferrofluids a, b, d and e coated with anions, strong negative zeta potential values between −27.5 mV and −54.0 mV were determined and a positive zeta potential value of +33.5 mV was found for ferrofluid c, covered with cationic dodecylammonium ions. MR relaxometry yielded R1-values of 1.9±0.3 (a), 4.0±0.8 (b), 5.2±1.0 (c), 0.124±0.002 (d) and 0.092±0.005 s−1 mM−1 (e), and R2*-values of 856±24 (a), 729±16 (b), 922±29 (c), 1.7±0.05 (d) and 0.49±0.05 s−1 mM−1 (e). Thus, the synthesized ferrofluids reveal a broad spectrum of R2* relaxivities. As a result, the various MR contrast agents have a great potential to be used in studies dealing with malignant tissue targeting or molecular imaging.

Size-Induced Variations in Lattice Dimension, Photoluminescence, and Photocatalytic Activity of ZnO Nanorods

The synthesis and characterization of ferrofluid based MR contrast agents, which offer R2* versatility beyond that of ferucarbotran, is described. Ferrofluids were formed after stabilizing magnetite cores with dodecanoic acid (a), oleic acid (b), dodecylamine (c), citric acid (d) or tartaric acid (e). Core sizes were deduced from TEM micrographs. Magnetic properties were determined by SQUID magnetometry. Hydrodynamic particle diameters were determined by dynamic light scattering measurements. Zeta potentials were measured by combining laser Doppler velocimetry and phase analysis light scattering. Iron contents were evaluated colorimetrically. MR relaxometry including R1 and R2* was conducted in vitro using homogeneous ferrofluid samples. The average core diameters of ferrofluids a, b and c equaled 9.4 +/- 2.8 nm and approximately 2 nm for ferrofluids d and e. Magnetization measurements at 300 K revealed superparamagnetic behaviour for the dried 9 nm diameter cores and paramagnetic-like behaviour for the dried cores of ferrofluids d and e. Iron contents were between 32-75 mg Fe/mL, reflecting the ferrofluids' high particle concentrations. Hydrodynamic particle diameters equaled 100-120 nm (a, b and c). For the ferrofluids a, b, d and e coated with anions, strong negative zeta potential values between -27.5 mV and -54.0 mV were determined and a positive zeta potential value of +33.5 mV was found for ferrofluid c, covered with cationic dodecylammonium ions. MR relaxometry yielded R1-values of 1.9 +/- 0.3 (a), 4.0 +/- 0.8 (b), 5.2 +/- 1.0 (c), 0.124 +/- 0.002 (d) and 0.092 +/- 0.005 s(-1) mM(-1) (e), and R2*-values of 856 +/- 24 (a), 729 +/- 16 (b), 922 +/- 29 (c), 1.7 +/- 0.05 (d) and 0.49 +/- 0.05 s(-1) mM(-1) (e). Thus, the synthesized ferrofluids reveal a broad spectrum of R2* relaxivities. As a result, the various MR contrast agents have a great potential to be used in studies dealing with malignant tissue targeting or molecular imaging.

Dispersion of Layered Hexaniobate in Organic Solvents through Silylation and Liquid Crystalline Behavior of the Colloidal Suspension

Abstract Layered niobate K4Nb6O17 became compatible to organic solvents through grafting octadecyltrimethoxysilane onto the niobate layers. The silylated niobate was stably dispersed in chloroform and finitely swelled in toluene whereas the niobate intercalated with dodecylammonium ions was settled out in both the solvents. Colloids of the silylated niobate dispersed in chloroform exhibited lyotropic liquid crystallinity at high niobate concentrations.

Changes of organo-montmorillonite by ball-milling in water and kerosene

An experimental study has been conducted to evaluate the changes of montmorillonite under various conditions, such as different solvent (water and kerosene), intercalation by mixing and stirred ball-milling. The montmorillonite was prepared from bentonite mined in Taitung, Eastern Taiwan. The final product of exfoliated organic montmorillonite was obtained by treatment in water and kerosene systems. The XRD results show that stirred ball-milling is an effective physical operation for breaking down the size of the clay particles and facilitating the intercalation of ammonium ions. The optimum duration for stirred ball-milling was 6 h in both systems. In water the basal spacing increased gradually from 1.27 nm to 2.41 nm with dodecylammonium ions in the case of mixing and from 3.19 to 4.55 nm for dodecylammonium and hexadecylammonium ions during 2 h of ball-milling, respectively.

Illite-Smectite Mixed-Layer Minerals in the Hydrothermal Alteration of Volcanic Rocks: II. One-Dimensional HRTEM Structure Images and Formation Mechanisms

AbstractSmectite illitization was investigated in felsic volcaniclastic rocks from a drill core near the Kakkonda active geothermal system, Japan, using high-resolution transmission electron microscopy (HRTEM) that provided one-dimensional structure images of mixed-layer illite-smectite (I-S) minerals normal to [M0]. Simulated images of a rectorite-like structure revealed that smectite can be distinguished from illite in mixed-layer I-S by HRTEM if the basal spacing of smectite is larger than that of illite. The larger basal spacing of smectite, 1.3 nm under HRTEM, was obtained by intercalation of dodecylammonium ions into smectitic interlayers. In simulated and observed images normal to [hk0], tetrahedral (T) and octahedral (O) cation planes are imaged as dark lines, an illitic interlayer as a bright line, and a smectitic interlayer as a dark line sandwiched between two bright lines.The samples are from depths of 435 m (5% I; R0), 635 m (35% I; R0), 656 m (62% I; R1), and 756 m (85% I; R3) where % I is the percentage of illite layers in a sample and R is the Reichweite parameter. Sample 435 consisted mostly of smectite, and illite layers occurred, though small in amount, as M1 units (module of type 1, defined as consisting of two polar T-O-T silicate layers with one central illitic interlayer and two, half smectitic interlayers at the outermost surface; the number corresponds to that of central illitic interlayers). The M1 units were dominant and isolated and consecutive smectite layers (>2) were present in sample 635. Sample 656 consisted mostly of packets of M1 units of 1 to 5 layers containing M2 to M5 units occasionally. Isolated or consecutive smectite layers (>2) were not present in 656. Illite layers occurred almost entirely as M1 units in samples 435, 635 and 656, and the number of M1 units increased with increase in % I. Sample 756 was characterized by the presence of M2 to M10 units accompanied by smectitic interlayers at the external surface and the absence of M1 units and isolated smectite layers. The HRTEM data strongly suggest that illitization in a hydrothermal system occurs by precipitation of M1 units for mixed-layer I-S minerals up to 60% I. This does not require the presence of precursor smectite. Illitization of I-S minerals with >60% I proceeds by precipitation of various types of Mn (n ⩾ 2) units. Illite occurs only as Mn (n ⩾ 1) units throughout illitization.

New micrometer-sized monodispersed self-assembled amphiphilic polystyrene/poly( n-butyl methacrylate) composite particles of hemispherical morphology: synthesis and characterization

Uniform micron-sized polystyrene template particles surface grafted with polyvinylpyrrolidone were prepared by dispersion polymerization of styrene in alcoholic solvents in the presence of polyvinylpyrrolidone as stabilizer. Poly(acrylic acid, sodium salt) derivatized polystyrene/ poly( n-butyl methacrylate) micron-sized composite particles of hemispherical morphology and narrow size distribution were formed by a single-step swelling of the uniform polystyrene template microspheres dispersed in water with emulsion droplets of the monomer n-butyl methacrylate containing the initiator benzoyl peroxide. n-Butyl methacrylate was then polymerized at 73 °C within the template microspheres in the presence of the water-soluble monomer acrylic acid, sodium salt. The sodium ions of the poly(acrylic acid) derivatized composite particles were then replaced with dodecylammonium ions by interacting these composite particles with excess dodecylamine hydrochloride. As a result of this process the surface of the hemispherical composite particles composed of hydrophilic polyvinylpyrrolidone chains on the polystyrene phase and hydrophobic dodecyl groups on the poly(acrylic acid) derivatized poly( n-butyl methacrylate) phase. These newly formed micron-sized composite particles show amphiphilic characteristics and aggregate to form micelle-like spherical clusters. The ability to control the template polystyrene microspheres’ dimensions and various polymerization parameters may open a wide variety of self-assembled spherical and other structures composed of micron-sized particles for various fundamental and practical applications such as self-assembly processes and the formation of photonic bandgap crystals.

界面活性剤水溶液中での微粒子‐気泡間相互作用力の直接測定

In many industrial processes, surfactants are used to control the dispersion and coagulation of particles in aqueous solutions. Especially, surfactants have critical effects in flotation separation. To investigate the effects of surfactants to the surface force between bubble and particle, which is critical for the particle recovery in flotation, we conducted direct measurements of the interaction forces between a spherical silica particle and an air bubble in dodecylamine hydrochloride (DAH) solution using atomic force microscope. Interaction forces were measured between the particle attached on the top of AFM probe and bubble generated on the flat surface.When a hydrophilic silica particle was used, electrostatic force was observed at large separation distance on approach of the silica and the bubble. Then long-range attractive force acted between the surfaces even when DAH concentration was low. The range of attractive force includes the penetration distance of particle into the bubble. The relation between the floatability of silica particle in batch column flotation and the interaction force was discussed.On the other hand, when the hydrophobized silica was used, the range of attractive force became short with the increase of DAH concentration. The repulsive force before attraction became very strong at high DAH concentration. The origin of the strong repulsive force is assumed to be the steric force between adsorbed dodecylammonium ions. These interaction forces cause the depression of the particle in flotation.

EVA/clay nanocomposite by solution blending: Effect of aluminosilicate layers on mechanical and thermal properties

Ethylene vinyl acetate (EVA)/clay nanocomposites were synthesized by blending a solution of ethylene vinyl acetate copolymer containing 12% vinyl acetate abbreviated as EVA-12 in toluene and dispersion of dodecyl ammonium ion intercalated montmorillonite (12Me-MMT) inN,N-dimethyl acetamide (DMAc). X-ray patterns of sodium montmorillonite (Na+-MMT) and 12Me-MMT exhibited d001 peak at 2θ?=7.4° and 2θ?=5.6° respectively; that is, the interlayer spacing of MMT increased by about 0.39 nm due to intercalation of dodecyl ammonium ions. The XRD trace of EVA showed no peak in the angular range of 3–10° (2θ). In the XRD patterns of EVA/clay hybrids with clay content up to 6 wt% the basal reflection peak of 12Me-MMT was absent, leading to the formation of delaminated configuration of the composites. When the 12Me-MMT content was 8 wt% in the EVA-12 matrix, the hybrid revealed a peak at about 2θ?=5.6°, owing to the aggregation of aluminosilicate layers. Transmission electron microscopic photograph exhibited that an average size of 12–15 nm clay layers were randomly and homogeneously dispersed in the polymer matrix, which led to the formation of nanocomposite with delaminated configuration. The formation of delaminated nanocomposites was manifested through the enhancement of mechanical properties and thermal stability, e.g. tensile strength of an hybrid containing only 2 wt% 12Me-MMT was enhanced by about 36% as compared with neat EVA-12.

Synthesis and characterization of organosoluble, thermoplastic elastomer/clay nanocomposites

AbstractWe synthesized organosoluble, thermoplastic elastomer/clay nanocomposites by making a jelly like solution of ethylene vinyl acetate containing 28% vinyl acetate (EVA‐28) and blending it with organomodified montmorillonite. Sodium montmorillonite (Na+‐MMT) was made organophilic by the intercalation of dodecyl ammonium ions. X‐ray diffraction patterns of Na+‐MMT and its corresponding organomodified dodecyl ammonium ion intercalated montmorillonite (12Me‐MMT) showed an increase in the interlayer spacing from 11.94 to 15.78 Å. However, X‐ray diffraction patterns of the thermoplastic elastomer and its hybrids with organomodified clay contents up to 6 wt % exhibited the disappearance of basal reflection peaks within an angle range of 3–10°, supporting the formation of a delaminated configuration. A hybrid containing 8 wt % 12Me‐MMT revealed a small hump within an angle range of 5–6° because of the aggregation of silicate layers in the EVA‐28 matrix. A transmission electron microscopy image of the same hybrid showed 3–5‐nm 12Me‐MMT particles dispersed in the thermoplastic elastomer matrix; that is, it led to the formation of nanocomposites or molecular‐level composites with a delaminated configuration. The formation of nanocomposites was reflected through the unexpected improvement of thermal and mechanical properties; for example, the tensile strength of a nanocomposite containing only 4 wt % organophilic clay was doubled in comparison with that of pure EVA‐28, and the thermal stability of the same nanocomposite was higher by about 34 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2065–2072, 2002

EFFECTS OF SHEAR AND THERMAL HISTORY ON THE MICROSTRUCTURE OF SOLUTION POLYMERIZED POLY(METHYL METHACRYLATE)–CLAY COMPOSITES

Poly(methyl methacrylate)–clay composites were synthesized through free-radical solution polymerization of methyl methacrylate in the presence of clay that was preintercalated with dodecylammonium or hexadecyltrimethylammonium ions. Neither the diffraction peak from the (001) plane nor the 00l reflections for the (001) plane were observed during x-ray characterization, showing that the clay particles were greatly expanded (i.e., exfoliated) in the reaction products, due to the presence of large quantities of polymer between the clay layers. Syntheses carried out with high clay loadings resulted in reductions in the weight and number-average molecular weights and increases in the polydispersities of the polymers, caused by chain transfer to active sites on the surface of the clay. It was found that heat and shear, during subsequent processing of the reaction products, resulted in reordering of the microstructure through narrowing of the clay galleries with the partial exclusion of the polymer. The final interlayer spacings were determined by the orientation and lengths of the preintercalated alkylammonium ions. It was concluded that the exfoliated structure created during polymerization was unstable under the processing conditions and, consequently, reordered into a more stable form.

Long-Range Hydrophobic Forces between Mica Surfaces in Dodecylammonium Chloride Solutions in the Presence of Dodecanol

Hydrophobic forces were measured using a Mark IV surface force apparatus with mica surfaces in equilibrium with dodecylamine hydrochloride (DAHCl) solutions at pH 5.7. With DAHCl alone, only “short-range” hydrophobic forces were observed with decay lengths of 1.3 nm. In the presence of dodecanol, long-range hydrophobic forces were observed with the decay length as large as 9.0 nm, which represents the strongest ever recorded hydrophobic force with soluble single-chain surfactants. The appearance of the long-range hydrophobic forces in the presence of neutral surfactants can be attributed to thecoadsorptionmechanism, by which a close-packed mixed monolayer of dodecylammonium ions and dodecanol is formed on the mica surface. The decay lengths of the hydrophobic forces obtained in the present work and reported in the literature have been plotted vs advancing water contact angles (θa). The results show that long-range hydrophobic forces appear at θa≥ 90°, which may be attributed to the formation of domains of close-packed hydrocarbon chains. These domains may have large dipole moments (or charges), which correlate with those of the opposing surface to give rise to long-range hydrophobic forces. The domains may also serve as sites for microscopic cavitation, as the local contact angle may exceed 90° and thereby satisfy the thermodynamic requirement for cavitation.

Long-Range Hydrophobic Forces between Mica Surfaces in Alkaline Dodecylammonium Chloride Solutions

A Mark IV surface force apparatus was used to measure forces between mica surfaces in dodecylamine hydrochloride (DAHCl) solutions. At pH 5.7, only “short-range” hydrophobic forces with decay lengths of approximately 1.3 nm were observed. At pH 9.5, however, a long-range hydrophobic force with a decay length of 5.5 nm was observed due to the coadsorption of dodecylammonium ions and dodecylamine, which increases the packing density of hydrocarbon chains on the mica surface. At pH 10.1, no significant hydrophobic forces are observed above 2 × 10−5MDAHCl possibly due to the formation of phase-separated amine on the surface. This concentration is 50 times below that of bulk precipitation. Furthermore, the force curves obtained at pH 10.1 exhibit repulsive steric forces at separation distances below 30 nm, which may provide an evidence for the existence of preprecipitation complexes on the surface. The pH at which the long-range hydrophobic force appears corresponds to the pH where the flotation of quartz reaches a maximum, suggesting that long-range hydrophobic forces may be required for good flotation.

Application of Extended DLVO Theory

Abstract Using a Mark IV surface force apparatus, adsorption of dodecylamine hydrochloride has been studied at pH 5.7 in the presence and absence of octanol. With amine alone, the repulsive forces between mica surfaces are reduced due to charge neutralization and attractive hydrophobic force; however, the latter is of relatively short range with decay lengths in the range of 1.2-1.4 nm. In the presence of amine and octanol, long-range hydrophobic forces are observed, the largest decay length being 6.8 nm. The appearance of the long-range hydrophobic force in the presence of octanol may be attributed to the coadsorption of the neutral surfactant in the monolayer of dodecylammonium ions on mica. The increased hydrophobic force due to the coadsorption of octanol is also manifested by the improved floatability of silica in dodecylamine solutions.

Charge Heterogeneity and Nanostructure of 2:1 Layer Silicates by High-Resolution Transmission Electron Microscopy

AbstractSeveral soil and reference smectites and vermiculites and one reference illite were examined by high-resolution transmission electron microscopy (HRTEM) to decipher the nanostructure and layer charge heterogeneity in these minerals. HRTEM results were compared with those obtained from powder X-ray diffraction (XRD) analysis. Samples were either exchanged with Na+ ions followed by equilibration with a very dilute solution of NaCl in a pressure membrane apparatus at 316 hPa (pF = 2.5) to see the effect of hydration and applied pressure on layer organization, or exchanged with dodecylammonium ions to see the expansion behavior. Oriented samples were embedded in a low viscosity resin and cut approximately 500 Å thick perpendicular to d(001) using an ultramicrotome fitted with a diamond knife. In general, Na-saturated soil clays possessed crystallites that were thinner (c-direction) and shorter (ab-direction) as compared with reference clays. In all cases, samples treated with dodecylammonium chloride exhibited nanostructures that were more disintegrated as compared with Na-saturated samples. In a soil vermiculite, dodecylammonium ion exchange showed frayed edges indicating the initiation of mica transformation to vermiculite from edge toward core. In a reference vermiculite (Transvaal) treated with dodecylammonium ions, in addition to completely expanded crystallites, a regular interstratification between expanded vermiculite and mica (phlogopite) layers was clearly observed in some crystallites. Such nanostructural details were not detected by XRD. HRTEM of the Na-treated illite showed thick crystallites having 10 Å layer separations, whereas the dodecylammonium-exchanged illite showed three types of layers with different degrees of expansion indicating charge heterogeneity in illite: 1) unexpanded (10 Å, highest charge) crystallites; 2) expanded high-charge vermiculite-like (24 Å) crystallites; and 3) occasionally expanded high-charge vermiculite-like (24 Å) layers interspersed in the matrix of 10Å crystallites.