Montmorillonite Layered Silicates Research Articles

Silacrown Ethers-Clay Intercalation Materials: Application in Potentiometric Sensors for Detection of Alkali-Ions

Abstract Dimethylsila-14-crown-5 (DMS14C5) and dimethylsila-17-crown-6 (DMS17C6) macrocyclic polyethers have been intercalated into montmorillonite layered silicates containing Li+, Na+ or K+ cations as exchangeable cations. XRD and FTIR spectroscopy offer information on the disposition of the macrocycle in the interlayer and accommodation of cations within the cavity of the polyoxyethylene ligand. 13C and 23Na solid-state NMR spectroscopy provides information about the replacement of water molecules from the hydration shell of interlayer cations by the macrocyclic ligand and confirms differences in the interactions depending on the nature of the ligand. The resulting montmorillonite intercalation materials were tested as active phase of PVC electrodes for the development of potentiometric sensors, in a preliminary attempt to evaluate their electrochemical response towards alkali-metal ions in solution.

Orderly Arranged NLO Materials Based on Chromophore-Containing Dendrons on Exfoliated Layered Templates

Three chromophore-containing dendrons were intercalated into montmorillonite layered silicates via an ion-exchange process. Enlarged d spacings ranging from 50 to 126 A were achieved for these novel organoclays. After the organoclays were blended with a polyimide, the steric bulkiness of the dendrons and the interaction between dendron and polyimide resulted in an ordered morphology. The orderly arranged nanocomposites were characterized by a UV-visible spectrophotometer, a variable-temperature infrared spectrometer, and electro-optical modulation. The dendrons in layered silicates were capable of undergoing a critical conformational change into an ordered structure, indicated by the drastic changes of interlayer distances at certain packing densities. Electro-optical coefficients increased sharply from 0 to 6 pm/V while the conformational change occurred. Furthermore, the addition of a polyimide capable of interaction-induced orientation was found to exert an enhancing effect on the degree of the noncentrosymmetric alignment.

Investigation of Polybutylene Succinate-co-Adipate (PBSA)/Montmorillonite Layered Silicate (MLS) Melt-Processed Nanocomposites

Biodegradable nanocomposites were prepared with polybutylene succinate adipate (PBSA) and three organically modified montmorillonite layered silicates (MLSs) by melt-extrusion methods at three screw speeds (20, 40, and 60 rpm) to determine the interaction and properties of the polymer/MLS nanocomposites. The samples were evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) to determine the level of MLS interaction with PBSA. All formulations formed varying degrees of intercalation regardless of the modification of the MLS or the variation of the screw speed upon melt processing. Differential scanning calorimetry (DSC) experiments did not reveal significant differences in melt temperature or glass transition temperature of PBSA. Dynamic mechanical analysis did display improved modulus values as a function of temperature with some of the nanocomposite formulations processed at different screw speeds. Extensive biodegradation tests were performed and determined that the nanoparticles did not hinder biodegradation in soil. Toxicity tests also were performed and all samples proved to be nontoxic.

Surfactant concentration effects on amorphous PETG–montmorillonite layered silicate (MLS) nanocomposite films

AbstractImprovements in the dispersion of montmorillonite layered silicates (MLS) have centered on appropriate surfactant treatment of the MLS, to ensure chemical interaction with the polymer material. Here, polyethylene terephthalate glycol (PETG) nanocomposites made with two MLS cation exchanged with dimethyl dihydrogenated tallow quaternary ammonium at two concentrations, 95 (MLS‐95) and 125 meq (100 g)−1 (MLS‐125), were investigated. The host MLS had a cation exchange capacity (CEC) around 92 meq (100 g)−1. The effect of exchanging past the CEC was studied with respect to the dispersion, glass transition and mechanical properties. Films were extruded on a single‐screw extruder with a film die attached. X‐ray diffraction (XRD) and optical transmission measurements indicated that increasing surfactant concentration changed the dispersion from intercalated to immiscible. The differences in the dispersion were related to the inherent degradation temperature of the MLS treated with the different surfactant concentrations, relative to the processing temperature. The over‐exchanged MLS (MLS‐125) suffered more surfactant degradation leading to an immiscible dispersion and narrower XRD peaks reflected a higher degree of ordering. In contrast, the XRD peaks of the MLS‐95 nanocomposites had increased breadth indicating decreased ordering. MLS orientation, however, did not influence birefringence measured by polarized Fourier‐transform infrared spectroscopy (FTIR). All nanocomposites showed no significant changes in the glass transition temperatures. Copyright © 2005 Society of Chemical Industry

Magnetism and nuclear magnetic resonance of hectorite and montmorillonite layered silicates

The temperature and magnetic-field (H) dependencies of the bulk dc magnetization (M) and the M∕H ratio of montmorillonite (MMT), hectorite (HCT), and synthetic mica-montmorillonite (SMMT) clays have been measured and compared with the signal intensity of H1 and Si29 nuclear magnetic resonance (NMR) spectra. MMT exhibits Langevin paramagnetism with an effective magnetic moment of 5.5±0.1μB per Fe ion whereas SMMT has diamagnetic properties. At 300K, M∕H of HCT measured in a magnetic field of H⩽1kOe is larger than that of MMT, whereas in a field of 50kOe, the inverse situation is observed. The difference arises because the magnetization of HCT is dominated by a contribution from ferromagneticlike impurities. The H1 and Si29 NMR signals of MMT are broadened beyond detectability due to the paramagnetic effect. Although HCT contains ferromagneticlike components that result in a large M∕H in low field, it yields H1 and Si29 NMR spectra with signal intensities similar to those of diamagnetic SMMT. Our data highlight that the quality of the NMR spectra is not related to the low-field magnetic susceptibility but to the bulk magnetization in the high magnetic field used for NMR.

Nylon-6 and Montmorillonite-Layered Silicate (MLS) Nanocomposites

Reducing the high gas permeability of plastic packaging is of serious concern for a variety of applications in food packaging and microelectronics arena. In the development of high altitude scientific balloons, the potential for unmanned mission success is critically related to the improvement in helium barrier capability. Separately, the introduction of expandable smectite clays, such as montmorillonites, into polymers has resulted in improved barrier properties. Here we investigate the mechanical properties and helium permeability of dispersed montmorillonite-layered silicates (MLS) in nylon-6 nanocomposite films. A 20 wt% MLS in nylon-6 master batch was prepared in a twin-screw extruder and then mixed with nylon to produce nylon MLS nanocomposites with MLS content ranging from 1 to 5% for testing. The nylon nanocomposites were extruded into films. A highly exfoliated dispersion in different films was determined using X-ray diffraction. Nylon-6 nanocomposites showed formation of -crystalline form, which was absent in neat nylon-6. Differential Scanning Calorimetry (DSC) confirmed the crystallinity change and the role of MLS as an additional nucleation contributor. The glass transition and mechanical properties were related to the nucleation capabilities of MLS. Increase in the degree and type of crystallinity together with tortuous path development due to exfoliated dispersion were the primary reasons behind the improvement in gas barrier properties of exfoliated nylon-6 nanocomposites.

Epoxy + montmorillonite nanocomposite: Effect of composition on reaction kinetics

AbstractThe objective of this investigation is to determine the effects of montmorillonite layered silicates on the curing kinetics of an epoxy resin. Differential scanning calorimetry was used to probe the changes in reactivity due to the presence of montmorillonite and due to the diamine hardener. The enthalpy of polymerization was strongly affected at compositions greater than 5% (wt) montmorillonite for epoxy + montmorillonite reactions. On introduction of the hardener, epoxy + amine kinetics dominate the reaction for all compositions except for a montmorillonite concentration of 2.5 wt%. X‐ray diffraction was used to determine if the reacted system was exfoliated. The results show a strong montmorillonite composition dependence on the exfoliated state. Transmission electron microscopy of the cured epoxies confirmed a mixed intercalated and exfoliated dispersion at compositions having montmorillonite greater than 2.5 wt%.