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Montmorillonite
Kinds of Montmorillonite Terms modified by Montmorillonite Selected AbstractsSorption of humic acids and ,-endosulfan by clay mineralsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2006Sarunya Hengpraprom Abstract Sorption of ,-endosulfan by kaolinite and montmorillonite alone and in the presence of sorbed and dissolved humic acid (HA) was investigated (pH 8 and 25°C). Three types of HA, Elliot soil HA (EHA), Peat HA (PHA), and Summit Hill HA (SHHA), were used to represent typical humic substances found in soils. For sorption of HA by either mineral, Freundlich sorption coefficient (Kf) values appeared to decrease in the order of EHA > PHA > SHHA, which followed increasing polarity (expressed as the O/C atomic ratio) and decreasing percent-carbon content. For both clays, sorption of ,-endosulfan by the HA mineral complex was greater than for sorption by the clay alone. Sorption of ,-endosulfan by the HA mineral complexes followed the same order as the Kf of the HAs (EHA > PHA > SHHA). Based on the amount of HA adsorbed by each mineral, organic carbon partition coefficients (KOC) were determined for sorption of ,-endosulfan by two of the HA mineral complexes. The value of KOC for ,-endosulfan sorption was greater for kaolinite EHA than kaolinite SHHA. However, the opposite trend was found with the montmorillonite HA complexes. Montmorillonite appeared to sorb ,-endosulfan and/or HA with higher affinity than kaolinite, which likely is due to its 2:1 layer structure and higher surface area. Sorption of endosulfan diol, a hydrolysis product, by the minerals was much less than the parent pesticide. [source] Synthesis of ,-Amino Nitriles from Carbonyl Compounds, Amines, and Trimethylsilyl Cyanide: Comparison between Catalyst-Free Conditions and the Presence of Tin Ion-Exchanged MontmorilloniteEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2010Jiacheng Wang Abstract In the absence of catalysts, the three-component, one-pot synthesis of ,-amino nitriles proceeded using various aldehydes and ketones together with amines and trimethylsilyl cyanide (TMSCN) in high yields under neat conditions at room temperature. The addition order of the reagents had a significant influence on the yields of the desired ,-amino nitriles. In contrast, when tin ion-exchanged montmorillonite (Sn-Mont), prepared by the ion-exchange of sodium montmorillonite (Na-Mont) with a tin tetrachloride solution, was used as a catalyst, the reaction rates significantly increased compared with those without catalysts, and the range of the applicable carbonyl compounds was also extended: structurally diverse aromatic, aliphatic and heteroatom-containing carbonyl compounds, including sterically hindered ketones as well as aliphatic and aromatic amines, were converted into the desired ,-amino nitriles in good to excellent yields with short reaction times under mild conditions. Sn-Mont showed a better catalytic activity than proton or other metal ion-exchanged montmorillonites, supported SnO2 catalysts and the previously reported homogeneous or heterogeneous catalysts. The recovered catalyst was reused several times without loss of catalytic performance. Along with the expansion of the interlayer space of Sn-Mont, the strong Brønsted acid and Lewis acid nature of Sn-Mont derived from protons and SnO2 nanoparticles present in the interlayers of Sn-Mont likely played important and cooperative roles in the high catalytic activity. [source] Enantioselective Aldol Reaction using Recyclable Montmorillonite-Entrapped N -(2-Thiophenesulfonyl)prolinamideADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Noriyuki Hara Abstract N -(2-Thiophenesulfonyl)prolinamide could be easily introduced into Montmorillonite by a simple ion-exchange reaction. The asymmetric aldol reactions between various isatins with acetone or acetaldehyde using a heterogeneous Montmorillonite-entrapped organocatalyst afforded products with high enantioselectivity. The catalyst was readily reusable without significant loss of catalytic activity or enantioselectivity. [source] Highly Efficient Cyanosilylation of Sterically Bulky Ketones Catalyzed by Tin Ion-Exchanged MontmorilloniteADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009Jiacheng Wang Abstract Tin ion-exchanged montmorillonite (Sn-Mont) was found to be a powerful catalyst for the cyanosilylation of aromatic and aliphatic ketones having a carbonyl group in sterically congested circumstances with cyanotrimethylsilane, giving the corresponding cyanohydrin trimethylsilyl ethers in excellent yields. [source] Polyacrylate/(carboxymethylcellulose modified montmorillonite) superabsorbent nanocomposite: Preparation and water absorbencyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Haixia Qiu Abstract Montmorillonite (MMT) was modified with carboxymethylcellulose (CMC). The X-ray diffraction (XRD) and FTIR analyses showed that the CMC chains had intercalated into the MMT sheets, and the strong chemical interaction between the ether bonds from CMC and SiO bonds from MMT was the driving force for intercalation. Polyacrylate (PAA)/modified MMT superabsorbent nanocomposites were fabricated by effectively dispersing the modified MMT in acrylic acid solution and polymerizing the acid. The superabsorbent composites were characterized by XRD, TEM, and FTIR. The influence of modified MMT, weight ratio of CMC to MMT, and modified MMT content in the nanocomposites on the water absorbency was investigated. Results showed that the introduction of pure MMT could decrease the water absorbency of the gel, but adding modified MMT could not only effectively increase the water absorbency of the gel, but also improve its water retention ability. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Ethylene polymerization behavior of Cr(III)-containing montmorillonite: Influence of chromium compoundsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2009Kazuhiro Yamamoto Abstract Montmorillonite was treated with Cr(NO3)3, Cr(acetate)3, and Cr(acac)3 to give three catalyst precursors, Cr-MMT-1, Cr-MMT-2, and Cr-MMT-3, respectively. Application of these catalysts to the ethylene polymerization reaction revealed Cr-MMT-1 to be much more reactive than the other two while the molecular weight distributions of the polymers were practically the same. Elemental analysis, XRD, and TEM measurements suggested that chromium occupied the interlayer section in Cr-MMT-1 and mostly the outer surface region for the other two catalysts. Aluminosilicate-supported Cr catalysts exhibited reactivity similar to that of Cr-MMT-2 and Cr-MMT-3. However, more of the low-molecular-weight polymer was formed. These data suggested that there is a relationship between the sites of the Cr ions and catalytic reactivity, and between supporting solid identity and molecular weight distribution of the polymer. The use of n -Bu2Mg and Et2Zn in the place of Et3Al led to lower activity but gave polymers of narrower molecular weight distribution, with more of the high-molecular-weight material. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2272,2280, 2009 [source] Gas-Phase Polymerization with Transition Metal Catalysts Supported on Montmorillonite , A Particle Morphological StudyMACROMOLECULAR SYMPOSIA, Issue 1 2009Sang-Young A. Shin Abstract This investigation focuses on the mechanism of particle fragmentation and growth when clay-supported metallocene catalysts are used to polymerize ethylene in gas-phase reactors. We supported bis(cyclopentadienyl)-zirconium dichloride (Cp2ZrCl2) on montmorillonite (MMT) pretreated with triisobutylaluminum and 10-undecence-1-ol to produce in-situ polyethylene-clay nanocomposites. During gas phase polymerization, the MMT layers were exfoliated by the growing polymer chains, starting from the openings of the clay galleries. After microtoming, the cross-section of the fragmented MMT particles showed bundles of distorted silicate layer stacks, proving that exfoliation took place during polymerization, producing an in-situ polyethylene-clay nanocomposite. Calculations of d-spacing by transmission electron microscopy (TEM) matched those measured by X-ray diffraction (XRD) analysis. [source] Properties of polypropylene/aluminum trihydroxide composites containing nanosized organoclayPOLYMER ENGINEERING & SCIENCE, Issue 12 2005Noora Ristolainen Montmorillonite is a promising substitute for aluminum trihydroxide in flame-retardant polypropylene/aluminum trihydroxide (PP/ATH) composites. Study was made of the partial substitution of organoclay for ATH in PP/ATH composites. The total concentration of filler was kept at 30 wt%. The composites were compatibilized with two types of compatibilizer: commercial maleic anhydride functionalized polypropylene (PP- g -MA) and hydroxyl-functionalized polypropylene (PP- co -OH) prepared with metallocene catalyst. The effect of compatibilization on the morphology was studied by the transmission electron microscopy and the scanning electron microscopy. Mechanical properties were characterized by tensile and impact measurements, and flammability properties with a cone calorimeter. Addition of compatibilizer and stearic acid (SA) treatment of the ATH particles contributed to the dispersion of the fillers. Both compatibilizers produced organoclay with exfoliated structure and improved adhesion between the fillers and the matrix. Toughness improved and decomposition and flammability were reduced. POLYM. ENG. SCI. 45:1568,1575, 2005. © 2005 Society of Plastics Engineers [source] Efficient Solvent-Free Oxidation of Phenols to p-Quinones with Iodic Acid on the Surface of K10 Montmorillonite.CHEMINFORM, Issue 4 2006M. M. Hashemi No abstract is available for this article. [source] A Clean and Rapid Synthesis of 5-Amino and 5-Alkoxycarbonylpyrazoles Using Montmorillonite under Acid Free Conditions.CHEMINFORM, Issue 10 2005G. Jagath Reddy Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: A Rapid and Efficient Method of Thioacetalization of Carbonyl Compounds Catalyzed by POCl3 -Montmorillonite.CHEMINFORM, Issue 48 2001Tong-Shou Jin Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Optimization of an Iron Intercalated Montmorillonite Preparation for the Removal of Arsenic at Low Concentrations,ENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 1 2007D. Masih Abstract A series of iron intercalated montmorillonites (Fe-Monts) were prepared using (i) ion exchange of native sodium and calcium ions with iron ions, (ii) base hydrolysis of inserted iron ions in montmorillonite suspension, and (iii) insertion of pre-hydrolyzed iron colloid in montmorillonite. The materials were characterized by X-ray diffraction and gas adsorption-desorption techniques. The basal d(001)-spacing and BET specific surface area increased after the intercalation of iron species in montmorillonite. Local iron structure studied by X-ray absorption fine structure (XAFS) spectroscopy showed an unsaturation of the Fe···Fe coordination number (N 2.5) of the intercalated iron species as compared to the bulk iron oxyhydroxides (N 6). The Fe-Monts were employed for arsenic removal from aqueous solutions at low concentration (0.2,16 mg/L). Among the Fe-Monts, the one prepared by the hydrolysis of inserted iron ions, was the best in performance. The saturation adsorption amount of the optimized iron-montmorillonite was 4 and 28 times higher for the removal of arsenite and arsenate, respectively, as compared to bulk iron oxyhydroxide (goethite). Compared with bulk iron oxyhydroxide, the Fe-Monts were superior for arsenate uptake and comparable for arsenite. In addition, arsenite adsorbed on the Fe-Monts was found to be oxidized to arsenate based on XAFS spectroscopy. [source] The effects of continuous and pulsed exposures of suspended clay on the survival, growth, and reproduction of Daphnia magnaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2010Sarah E. Robinson Abstract Suspended sediments are a natural component of aquatic ecosystems, but anthropogenic activity such as land development can result in significant increases, especially after rain events. Continuous exposures of suspended clay and silt have been shown to affect growth and reproduction of Cladocera, leading to a decrease in population growth rate. The mechanism of clay toxicity in these filter-feeding organisms is clogging of the gut tract, resulting in decreased food uptake and assimilation. When placed in clean water, daphnids can purge clay from their gut and recover. In many surface waters, aquatic organisms experience episodic exposures of high concentrations of suspended solids driven by rain events. However, little is known about the consequences of pulsed exposures on individuals and populations. The objective of the present study was to characterize the effects of continuous and pulsed exposures of natural and defined clays on survival, growth, and reproduction of Daphnia magna. Two defined clays, montmorillonite and kaolinite, as well as clay isolated from the Piedmont region of South Carolina, USA, were used. Continuous exposures of clays elicited a dose dependent decrease in survival. Toxicity varied depending on clay source with montmorillonite,>,natural clay,>,kaolinite. Pulsed exposures caused a decrease in survival in a 24 h exposure of 734 mg/L kaolinite. Exposure to 73.9 mg/L also caused an increase in the time to gravidity, although there was not a corresponding decrease in neonate production over 21 d. No significant effects resulted from 12 h exposures even at 730 mg/L, almost 10 times the 24-h reproductive effects concentration. This suggests that exposure duration impacted toxicity more than exposure concentration in these pulsed exposures. Environ. Toxicol. Chem. 2010;29:168,175. © 2009 SETAC [source] Kinetics of toluene sorption and desorption in Ca- and Cu-montmorillonites investigated with Fourier transform infrared spectroscopy under two different levels of humidityENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2004Yang-Hsin Shih Abstract Clays in soils or groundwater aquifer materials play roles in the sorption of organic pollutants. The intrinsic sorption kinetics of toluene in dry and humid clay films was investigated by tracking the change of infrared absorbance. Under the humid condition, similar toluene-sorbed intensities were found in Ca- and Cu-montmorillonites. However, a higher intensity of sorbed toluene was found in the Cu-form than in the Ca-form under the dry condition, which indicates a stronger interaction occurring in dry Cu-montmorillonite. The general time scale of sorption of toluene on clays is around 100 s. In both forms of montmorillonite, some portion of toluene was desorbed at an extremely slow rate under the dry condition. Some newly identified peaks were persistent against desorption from montmorillonites, suggesting the existence of irreversibly sorbed species and the possibility of toluene transformation occurring in clay systems. [source] Synthesis of ,-Amino Nitriles from Carbonyl Compounds, Amines, and Trimethylsilyl Cyanide: Comparison between Catalyst-Free Conditions and the Presence of Tin Ion-Exchanged MontmorilloniteEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2010Jiacheng Wang Abstract In the absence of catalysts, the three-component, one-pot synthesis of ,-amino nitriles proceeded using various aldehydes and ketones together with amines and trimethylsilyl cyanide (TMSCN) in high yields under neat conditions at room temperature. The addition order of the reagents had a significant influence on the yields of the desired ,-amino nitriles. In contrast, when tin ion-exchanged montmorillonite (Sn-Mont), prepared by the ion-exchange of sodium montmorillonite (Na-Mont) with a tin tetrachloride solution, was used as a catalyst, the reaction rates significantly increased compared with those without catalysts, and the range of the applicable carbonyl compounds was also extended: structurally diverse aromatic, aliphatic and heteroatom-containing carbonyl compounds, including sterically hindered ketones as well as aliphatic and aromatic amines, were converted into the desired ,-amino nitriles in good to excellent yields with short reaction times under mild conditions. Sn-Mont showed a better catalytic activity than proton or other metal ion-exchanged montmorillonites, supported SnO2 catalysts and the previously reported homogeneous or heterogeneous catalysts. The recovered catalyst was reused several times without loss of catalytic performance. Along with the expansion of the interlayer space of Sn-Mont, the strong Brønsted acid and Lewis acid nature of Sn-Mont derived from protons and SnO2 nanoparticles present in the interlayers of Sn-Mont likely played important and cooperative roles in the high catalytic activity. [source] Formation of 2,4,D complexes on montmorillonites , an ab initio molecular dynamics studyEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2007D. Tunega Summary Sorption of the anionic form of the pesticide 2,4,D (2,4,dichlorophenoxyacetic acid) on the surface of the clay mineral montmorillonite was investigated using a short-time ab initio molecular dynamics (MD) simulation at room temperature. Three different situations were modelled: sorption on a dry surface, on a hydrated surface and an intercalation between montmorillonite layers. In all three cases, the calcium cation compensates the excess negative charge of the montmorillonite layer and the negative charge of the 2,4,D anion. It was found that in all models with direct contact of the Ca2+ cation with the montmorillonite layer, the most stable position of Ca2+ is above the ditrigonal hole of the mineral layer. While in the case of a dry surface very stable bidentate binding is created between the 2,4,D anion and the Ca2+ cation, the formation of the monodentate complexes is preferred in all models that include water molecules. Hydrogen bonds formed between water molecules and the 2,4,D anion make a considerable contribution to the formation of the monodentate complexes. Tetrahedral substitutions in the montmorillonite layer have a significant effect on the formation of the complexes of any type. However, the MD simulations did not support the role of Ca2+ as a cation bridge in the adsorption mechanism. Calculations showed that hydrated 2,4,D···Ca2+ complexes are thermodynamically more stable than complexes in which the Ca2+ cation acts as a bridge to the surface. On the other hand, it is possible that phyllosilicates with a greater concentration of isomorphic substitutions (e.g. mica) will be able to form stable surface complexes with a cation bridge mechanism. [source] Effect of ionic strength and clay mineralogy on Na,Ca exchange and the SAR,ESP relationshipEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2006P. M. Kopittke Summary The relationship between sodium adsorption ratio (SAR) and exchangeable sodium percentage (ESP) for all soils has traditionally been assumed to be similar to that developed by the United States Salinity Laboratory (USSL) in 1954. However, under certain conditions, this relationship has been shown not to be constant, but to vary with both ionic strength and clay mineralogy. We conducted a detailed experiment to determine the effect of ionic strength on the Na+,Ca2+ exchange of four clay minerals (kaolinite, illite, pyrophyllite, and montmorillonite), with results related to the diffuse double-layer (DDL) model. Clays in which external exchange sites dominated (kaolinite and pyrophyllite) tended to show an overall preference for Na+, with the magnitude of this preference increasing with decreasing ESP. For these external surfaces, increases in ionic strength were found to increase preference for Na+. Although illite (2:1 non-expanding mineral) was expected to be dominated by external surfaces, this clay displayed an overall preference for Ca2+, possibly indicating the opening of quasicrystals and the formation of internal exchange surfaces. For the expanding 2:1 clay, montmorillonite, Na+,Ca2+ exchange varied due to the formation of quasicrystals (and internal exchange surfaces) from individual clay platelets. At small ionic strength and large ESP, the clay platelets dispersed and were dominated by external exchange surfaces (displaying preference for Na+). However, as ionic strength increased and ESP decreased, quasicrystals (and internal exchange surfaces) formed, and preference for Ca2+ increased. Therefore, the relationship between SAR and ESP is not constant and should be determined directly for the soil of interest. [source] Zinc ion adsorption on montmorillonite,Al hydroxide polymer systemsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2003R. P. T. Janssen Summary Clay,Al hydroxide polymers (CAlHO) can bind heavy metals effectively and may play an important role in the adsorption behaviour and metal binding capacity of soils. We studied the dependence of Al loading and pH on the adsorption of Zn on Na-saturated montmorillonite,Al hydroxide polymer systems. The available binding sites on Al hydroxide polymers (AlHO) had a very strong affinity for Zn ions. Zinc binding on the clay surface became important when the binding sites on the AlHO were nearly all occupied. The pH had a very strong effect on the Zn binding. At pH 6.6 much more Zn could be adsorbed to the AlHO than at pH 5.0. The effect of the Al:clay ratio on Zn binding was influenced by pH. At pH 6.6, Zn binding to the AlHO, expressed per mole AlHO, was independent of the Al:clay ratio, whereas at pH 5.0 this relation was dependent. This is related to the constant charge of the AlHO at pH 6.6, whereas at pH 5.0 the charge decreases with increasing Al:clay ratio. If clay,Al hydroxide polymers are present in the soil their Zn binding to the AlHO will strongly influence the availability of the Zn. [source] A study of the factors controlling the adsorption of Cr(III) on modified montmorillonitesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2001A. Bakhti Summary We have examined the way that the metallic ion Cr(III) is held by Na-montmorillonite and alumina pillared clay. We used several physico-chemical methods of analysis (X-ray powder diffraction, infrared absorption spectrometry, thermal analysis and chemical composition) to determine the structural formula of the Na-montmorillonite, and to clarify the effect of the introduction of the Al13 polycations between the clay layers on its physico-chemical and structural properties. Our results show that the strength of chromium retention increases with pH. This effect is more marked in pillared than in unpillared clays. It seems that the mechanism of fixing of the metallic cations on pillared clays is more complex than a simple cationic exchange and involves the surface groups of the pillars. In other words, chromium adsorption on pillared montmorillonite is more like adsorption on an amphoteric oxide surface (such as Al2O3) than on a non-pillared clay. Etude des facteurs contrôlant l'adsorption de Cr(III) sur des montmorillonites modifiées Résumé Nous avons examiné les possibilités de fixation de l'ion métallique Cr(III) sur une montmorillonite sodique et pontée. Les différentes analyses physico-chimiques (Rayons-X, Spectroscopie Infrarouge, Analyse Thermique Différentielle et composition chimique) ont permis d'une part, d'établir la formule structurale de l'argile sodique et d'autre part de mettre en évidence l'effet du pontage de l'argile par des polycations hydroxyaluminiques sur ses propriétés physico-chimiques et structurales. Nos résultats montrent que le pouvoir de rétention du chrome augmente avec le pH. Ce paramètre affecte davantage son comportement dans les argiles pontées. Il apparaît que le mécanisme de fixation du Cr(III) sur les argiles à piliers est différent d'un simple échange cationique. L'adsorption dans ce cas met en jeu les groupements de la surface des piliers. En d'autres termes, le mécanisme d'adsorption des cations du chrome sur une montmorillonite pontée se rapproche de l'adsorption sur une surface d'oxyde amphotère (tel que Al2O3) plutôt que l'adsorption sur une argile non pontée. [source] A flammability performance comparison between synthetic and natural clays in polystyrene nanocompositesFIRE AND MATERIALS, Issue 4 2005Alexander B. Morgan Abstract Polymer-clay nanocomposites are a newer class of flame retardant materials of interest due to their balance of mechanical, thermal and flammability properties. Much more work has been done with natural clays than with synthetic clays for nanocomposite flammability applications. There are advantages and disadvantages to both natural and synthetic clay use in a nanocomposite, and some of these, both fundamental and practical, will be discussed in this paper. To compare natural and synthetic clays in regards to polymer flammability, two clays were used. The natural clay was a US mined and refined montmorillonite, while the synthetic clay was a fluorinated synthetic mica. These two clays were used as inorganic clays for control experiments in polystyrene, and then converted into an organoclay by ion exchange with an alkyl ammonium salt. The organoclays were used to synthesize polystyrene nanocomposites by melt compounding. Each of the formulations was analysed by X-ray diffraction (XRD), thermogravimetric analysis (TGA) and transmission electron microscopy (TEM). Flammability performance was measured by cone calorimeter. The data from the experiments show that the synthetic clay does slightly better at reducing the heat release rate (HRR) than the natural clay. However, all the samples, including the inorganic clay polystyrene microcomposites, showed a decreased time to ignition, with the actual nanocomposites showing the most marked decrease. The reason for this is postulated to be related to the thermal instability of the organoclay (via the quaternary alkyl ammonium). An additional experiment using a more thermally stable organoclay showed a time to ignition identical to that of the base polymer. Finally, it was shown that while polymer-clay nanocomposites (either synthetic or natural clay based) greatly reduce the HRR of a material, making it more fire safe, they do not provide ignition resistance by themselves, at least, at practical loadings. Specifically, the cone calorimeter HRR curve data appear to support that these nanocomposites continue to burn once ignited, rather than self-extinguish. Copyright © 2004 John Wiley & Sons, Ltd. [source] Flexible Silk,Inorganic Nanocomposites: From Transparent to Highly ReflectiveADVANCED FUNCTIONAL MATERIALS, Issue 5 2010Eugenia Kharlampieva Abstract A novel type of all-natural, biocompatible, and very robust nanoscale free-standing biohybrids are reported. They are obtained by integrating a silk fibroin matrix with functional inorganic nanoplatelets using a spin-assisted layer-by-layer assembly. The organized assembly of the silk fibroin with clay (montmorillonite) nanosheets results in highly transparent nanoscale films with significantly enhanced mechanical properties, including strength, toughness, and elastic modulus, as compared to those for the pristine silk nanomaterials. Moreover, replacing clay nanoplatelets with a highly reflective Langmuir monolayer of densely packed silver nanoplates causes a similar enhancement of the mechanical properties, but in contrast to the materials above, highly reflective, mirror-like, nanoscale flexible films are created. This strategy offers a new perspective for the fabrication of robust all-natural flexible nanocomposites with exceptional mechanical properties important for biomedical applications, such as reinforced tissue engineering. On the other hand, the ability to convert silk-based nanoscale films into mirror-like biocompatible flexible films can be intriguing for prospective photonics and optical exploitation of these nanobiohybrids. [source] Analysis of adobe wall composition at the Chaves-Hummingbird Site, New Mexico, by diffuse reflectance spectrophotometryGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 8 2007William Balsam This article investigates adobe wall construction materials utilized by prehistoric inhabitants of Chaves-Hummingbird Pueblo, an ancestral Pueblo village located ,20 miles west of Albuquerque, New Mexico. The walls were constructed with native clay-rich soils some time between approximately 1275,1450 A.D. Samples were analyzed with a diffuse reflectance spectrophotometer from the near ultraviolet (NUV) through the visible (VIS) and into the near infrared (NIR) region of the electromagnetic spectrum. Cluster analysis of samples from 275 adobe walls and 36 soil locations surrounding the pueblo room blocks indicates four clusters. Comparison of typical samples from the four clusters indicates that they are very similar and are distinguished by minor variations in the three primary spectrally determined components, Na-Ca montmorillonite, bentonite, and goethite. In general, clusters correspond with room construction episodes that are discernible through patterns of wall bonding and abutment recorded during the archaeological investigation of the site. This suggests that during different phases of construction the source of the wall adobe changed. Many of the soil samples are included in wall clusters and therefore reveal a potential source of material used for adobe, adjacent soils. However, not all the soil surrounding the pueblo grouped with wall clusters indicating a preference for certain soil types and that some soils were probably unsuitable for making adobe. Therefore, diversity in spectrally identified construction materials provides insights into source locations and possible construction preferences of the site inhabitants. © 2007 Wiley Periodicals, Inc. [source] Elastic properties of dry clay mineral aggregates, suspensions and sandstonesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2003Tiziana Vanorio SUMMARY The presence of clay minerals can alter the elastic behaviour of rocks significantly. Although clay minerals are common in sedimentary formations and seismic measurements are our main tools for studying subsurface lithologies, measurements of elastic properties of clay minerals have proven difficult. Theoretical values for the bulk modulus of clay are reported between 20 and 50 GPa. The only published experimental measurement of Young's modulus in a clay mineral using atomic force acoustic microscopy (AFAM) gave a much lower value of 6.2 GPa. This study has concentrated on using independent experimental methods to measure the elastic moduli of clay minerals as functions of pressure and saturation. First, ultrasonic P - and S -wave velocities were measured as functions of hydrostatic pressure in cold-pressed clay aggregates with porosity and grain density ranging from 4 to 43 per cent and 2.13 to 2.83 g cm,3, respectively. In the second experiment, P - and S -wave velocities in clay powders were measured under uniaxial stresses compaction. In the third experiment, P -wave velocity and attenuation in a kaolinite,water suspension with clay concentrations between 0 and 60 per cent were measured at ambient conditions. Our elastic moduli measurements of kaolinite, montmorillonite and smectite are consistent for all experiments and with reported AFAM measurements on a nanometre scale. The bulk modulus values of the solid clay phase (Ks) lie between 6 and 12 GPa and shear (,s) modulus values vary between 4 and 6 GPa. A comparison is made between the accuracy of velocity prediction in shaley sandstones and clay,water and clay,sand mixtures using the values measured in this study and those from theoretical models. Using Ks= 12 GPa and ,s= 6 GPa from this study, the models give a much better prediction both of experimental velocity reduction due to increase in clay content in sandstones and velocity measurements in a kaolinite,water suspension. [source] Molecular dynamics and multiscale homogenization analysis of seepage/diffusion problem in bentonite clayINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 12 2002Y. Ichikawa Abstract A scheme combining a molecular behaviour and macro-continuum phenomenon is presented for bentonite clay, which is a key component of a barrier system for disposal and containment of hazardous wastes. On designing a disposal facility we use a macro-phenomenological model. However the existing model is not sufficiently effective. Bentonite is a microinhomogeneous material. Properties of the saturated bentonite are characterized by montmorillonite and water, called montmorillonite hydrate. Since the crystalline structure of montmorillonite determines the fundamental properties of the montmorillonite hydrate, we analyse its molecular behaviour by applying a molecular dynamics simulation to enquire into the physicochemical properties of the montmorillonite hydrate such as diffusivity of chemical species. For extending the microscopic characteristics of constituent materials to a macroscopic diffusion behaviour of the microinhomogeneous material we apply a multiscale homogenization analysis, especially in order to treat micro-level of adsorption behaviour. Copyright © 2002 John Wiley & Sons, Ltd. [source] Highly Efficient Cyanosilylation of Sterically Bulky Ketones Catalyzed by Tin Ion-Exchanged MontmorilloniteADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009Jiacheng Wang Abstract Tin ion-exchanged montmorillonite (Sn-Mont) was found to be a powerful catalyst for the cyanosilylation of aromatic and aliphatic ketones having a carbonyl group in sterically congested circumstances with cyanotrimethylsilane, giving the corresponding cyanohydrin trimethylsilyl ethers in excellent yields. [source] Synthesis of N-Heteroaryl(trifluoromethyl)hydroxyalkanoic Acid Esters by Highly Efficient Solid Acid-Catalyzed Hydroxyalkylation of Indoles and Pyrroles with Activated Trifluoromethyl KetonesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14 2005Mohammed Abid Abstract The synthesis of N-heteroaryl(trifluoromethyl)hydroxyalkanoic acid esters by solid acid-catalyzed Friedel,Crafts hydroxyalkylation of indoles and pyrroles with ethyl 3,3,3-trifluoropyruvate and ethyl 4,4,4-trifluoroacetoacetate is described. The inexpensive and readily available K-10 montmorillonite is found to be an efficient catalyst for the synthesis of a wide variety of trifluoromethylated indol-3-yl- and pyrrol-2-yl-hydroxypropionic and -butanoic acid esters. Using a series of substituted indoles and pyrroles the corresponding products were isolated in excellent yield (up to 98%) and 100% selectivity under mild experimental conditions, during very short reaction times. Beyond these, the ease of product isolation, catalyst stability and handling make this process an attractive, environmentally benign alternative for the synthesis of the target compounds. [source] Property enhancement of epoxy resins by using a combination of polyamide and montmorilloniteADVANCES IN POLYMER TECHNOLOGY, Issue 4 2007M. Bakar Abstract A bisphenol-A epoxy resin cured with triethylenetetramine was modified with the addition of a polyamide oligomer and a small amount of montmorillonite. Compositions with different amounts of modifiers were obtained and tested for their impact strength, flexural strength, and resistance to crack propagation. The latter was assessed by measuring the critical stress intensity factor in a three-point bending mode. Scanning electron microscopy was used to examine the sample fracture surfaces. It was found that the addition of 2% montmorillonite or 5% polyamide resulted in the best improvement of the impact strength and the critical stress intensity factor relative to the unmodified epoxy resin. However, the flexural strength and toughness measured under three-point bending mode was found to increase to a lesser extent. Hybrid compositions containing specific combinations of both modifier and nanofiller not only exhibited a higher impact strength and resistance to crack propagation but also displayed a synergistic effect in relation to the fracture energy. The results indicate that the improvement in mechanical properties of the epoxy resin was due to the formation of a heterogeneous morphology resulting from phase separation of the polymeric modifier. From the scanning electron microscopy and thermal analysis, it appears that the toughening may arise from chemical reactions that have taken place between the epoxy resin and the polymeric modifier, which was partially solubilized in the resin matrix. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 26:223,231, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20103 [source] The properties of reactive hot melt polyurethane adhesives modified with novel thermoplastic polyurethanesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2009Tae K. Kim Abstract A reactive hot melt adhesive (RHMA) consisting of thermoplastic polyurethane (TPU) was modified with sodium montmorillonite (Na-MMT) intercalated with poly(ethylene glycol) (PEG), and their effects on the adhesion, rheological, and mechanical properties of the RHMA were examined. The Na-MMT intercalated with PEG (Na-MMT/PEG) effectively enhanced the initial bond strength development of the RHMA, although the amounts of Na-MMT/PEG in the RHMA were less than 0.2%. The increase of the complex viscosity and pseudo-solid like behavior observed at low shear rate indicates that there are intimate interactions between the RHMA molecules and Na-MMT/PEG. The improved modulus and tensile strength of the cured RHMA film in the presence of Na-MMT/PEG demonstrates that Na-MMT/PEG effectively reinforced the RHMA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Preparation and investigation of ethylene,vinyl acetate copolymer/silicone rubber/clay nanocompositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 3 2009Shoulin Fang Abstract In this article, the combination of silicone rubber (SR) elastomer with synthetic iron montmorillonite (Fe-MMT) to form a kind of new flame-retardant system based on an ethylene,vinyl acetate (EVA) copolymer is first reported. Also, the flame retardancy of the EVA/SR/Fe-MMT hybrid are compared with that of EVA/SR/natural sodium montmorillonite. The structures of the nanocomposites were characterized with X-ray diffraction and transmission electron microscopy. Cone calorimeter tests and thermogravimetric analysis were used to evaluate the flame-retardant properties and thermal stability of the composites, respectively. In addition, tensile tests were carried out with a universal testing machine, and the morphology of the fracture surface was observed with environmental scanning electron microscopy. We found that SR/organophilic montmorillonite (Fe-OMT) was more effective in reducing the primary peak heat release rate of the nanocomposite, and the EVA/SR/Fe-OMT hybrid had a higher thermal stability in the deacetylated polymer than EVA/SR/sodium organophilic montmorillonite. Moreover, the exfoliated EVA/SR/Fe-OMT nanocomposite displayed excellent mechanical properties because of a better dispersion of Fe-OMT in the polymer matrix, and a possible mechanism is discussed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Evaluation of polymethacrylic ionomer as compatibilizers for MCPA6/clay compositesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Tongfei Wu Abstract The compatibilization effects provided by polymethacrylic ionomer (PMMA ionomer) on monomer-casting polyamide6 (MCPA6)/clay (pristine sodium montmorillonite) composites were studied in this work. The PMMA ionomer used in this study was sodium polymethacrylate ionomer (PMMA Na+ -ionomer), which is a copolymer of methyl methacrylate and sodium methacrylate, prepared using emulsion polymerization. MCPA6/clay/PMMA Na+ -ionomer composites were prepared by in situ anionic ring-opening polymerization (AROP) of ,-caprolactam (CLA). X-ray diffraction (XRD) and transmission electron microscopy (TEM) plus rheological measurement were used to characterize those composites. The results indicated that PMMA Na+ -ionomer is a good compatibilizer for this system. With increasing PMMA Na+ -ionomer content, a better dispersion of clay layers was successfully achieved in the MCPA6 matrix. Furthermore, differential scanning calorimetry (DSC) and XRD results indicated that well dispersed silicate layers limit the mobility of the MCPA6 molecule chains to crystallize, reduce the degree crystalline, and favor the formation of the ,-crystalline form of the MCPA6 matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] | ||||||||||||||||||||||||||||||||||