Trimethylammonium Ions Research Articles

Mechanical properties, flammability and char morphology of epoxy resin/montmorillonite nanocomposites

Epoxy resin/montmorillonite nanocomposites were obtained via in-situ intercalative polymerization. Na-montmorillonites modified with octadecyl, hexadecyl and dodecyl trimethylammonium, benzyl triethylammonium and tetramethylammonium ions were used in diglycidyl ether of bisphenol-A epoxy resin. Montmorillonites modified with long alkyl ammonium ions yielded intercalated nanocomposites whereas those with benzyl or very short alkyl ammonium ions gave phase separated microcomposites. Significant improvements in flexural strength and stiffness were obtained, especially at a low clay mineral level of 0.5 mass% with octadecyl trimethylammonium ions. Fracture toughness values double that of neat epoxy resin could be reached together with improved stiffness and strength by nanocomposite formation. The largest improvement in fracture toughness was also obtained by octadecyl trimethylammonium montmorillonite. Regarding flexural strength and fracture toughness, optimum clay mineral levels were assessed as 0.5 mass% for intercalated nanocomposites. Flammability was evaluated by oxygen index measurements with varying clay mineral level and surface modification. Largest improvement, i.e. from 20.9% to 23.2%, was attained with 2 mass% dodecyl trimethylammonium montmorillonite containing epoxy resin. Basal spacings in char residues of oxygen index tests were around 1.3 nm, irrespective of the montmorillonite content, type of modification and oxygen index performance.

Adsorption of herbicides 2,4-D and acetochlor on inorganic–organic bentonites

Inorganic–organic bentonites were prepared by co-adsorption of cetyl trimethylammonium (CTMA) ions onto bentonites intercalated by poly(hydroxo aluminum) or poly(hydroxo iron) cations. The inorganic–organic bentonites adsorbed much more anionic herbicide 2,4-D than the inorganic and organic bentonites. For bentonites modified with poly(hydroxo iron) and CTMA ions, the enhancement may be attributed not only to the van der Waals interaction between 2,4-D and the organic cations, but also to the strong bonding of 2,4-D on the inorganic cations, which was confirmed by desorption studies, XRD measurements and FTIR analysis. The inorganic–organic bentonites did not show higher adsorption of acetochlor compared to the organo-bentonite. For such a nonionic herbicide, the van der Waals interaction dominated the adsorption, and the inorganic modification did not make an obvious contribution to the adsorption.

Separation of surfactant modified smectite from bentonite by delamination

Smectite modified with cetyl trimethylammonium ions was separated from a mixture of organobentonite and unreacted pristine clay mineral through delamination in nitrobenzene. On delamination and restacking the layer structure remained intact though the basal spacing of the organomontmorillonite decreased slightly due to changes in the organization of the alkyl chains of the surfactant within the interlayer space of the clay mineral.

A comparative study of UV active silane-grafted and ion-exchanged organo-clay for application in photocurable urethane acrylate nano- and micro-composites

A number of urethane acrylate nano- and micro-composites have been developed using both ion exchange and silane grafting chemistry. The organically modified clays which were used contained either methacrylate or acrylate functionalities which were capable of reacting with the acrylate groups in the urethane acrylate matrix. [2-(Acryloyloxy)ethyl]trimethyl-ammonium ion (AOETMA) or [2-(methacryloyloxy)ethyl]trimethylammonium ion (MAOTMA) were exchanged onto montmorillonite (MMT) as shown by an increase in the inter-gallery spacing of the MMT. Silane grafting was undertaken using [3-(acryloxy)propyl]dimethylmethoxysilane (APDMMS) or [3-(methacryloxy)propyl]dimethylmethoxysilane (MAPDMMS) and also showed an increase in inter-gallery spacing. The structures of the resulting urethane acrylate composites were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) and showed predominantly intercalated structures with some exfoliation (more evident in the silane-grafted systems). Dynamical mechanical thermal analysis (DMTA) showed a more significant increase in effective crosslink density (as measured from the plateau of the rubbery modulus) in the composites containing the reactive clays as compared to the unmodified clay, supporting the concept that the acrylate and methacrylate functionalities of the modified clays had reacted with the matrix. Other thermal and mechanical properties were also evaluated.

Lipid imaging by gold cluster time-of-flight secondary ion mass spectrometry: application to Duchenne muscular dystrophy

Imaging with time-of-flight secondary ion mass spectrometry (TOF-SIMS) has expanded very rapidly with the development of gold cluster ion sources (Au(3+)). It is now possible to acquire ion density maps (ion images) on a tissue section without any treatment and with a lateral resolution of few micrometers. In this article, we have taken advantage of this technique to study the degeneration/regeneration process in muscles of a Duchenne muscular dystrophy model mouse. Specific distribution of different lipid classes (fatty acids, triglycerides, phospholipids, tocopherol, coenzyme Q9, and cholesterol) allows us to distinguish three different regions on a mouse leg section: one is destroyed, another is degenerating (oxidative stress and deregulation of the phosphoinositol cycle), and the last one is stable. TOF-SIMS imaging shows the ability to localize directly on a tissue section a great number of lipid compounds that reflect the state of the cellular metabolism.

Water-soluble pentasulfonatocalix[5]arene: selective recognition of ditopic trimethylammonium cations by a triple non-covalent interaction

The inclusion of tetramethylammonium and ditopic trimethylammonium cations by the water-soluble pentasulfonatocalix[5]arene 1 has been studied at neutral pH by 1H NMR and compared with the homologous tetrasulfonatocalix[4]arene 2 . Unlike host 2 , host 1 selectively binds the ditopic trimethylammonium ions by three different non-covalent interactions. Remarkably the flexible host 1 exhibits both more efficiency and selectivity in the complexation of ditopic methylammonium ions with respect to similar more preorganised calix[4]arene receptors.

Solubilization of Phenol in an Intercalated Surfactant Bilayer

Solubilization of phenol molecules in an intercalated surfactant bilayer, formed within the galleries of an inorganic layered solid, {CdPS_3}, is reported. The bilayer, formed by grafting of cetyl trimethylammonium (CTA) ions to the internal surface of {CdPS_3}, functionlizes the surface, converting it from a hydrophilic to a hydrophobic surface. The CTA ions being devoid of functional groups, the interaction between the guest phenol molecules and the methylene chains of the bilayer are dispersive in nature. It is shown that there are two phases of the phenol-solubilized intercalated bilayer, distinguishable by their interlayer lattice spacing and corresponding to solubilized phenol to intercalated CTA ion concentration ratios less than 0.5 and greater. The presence of the guest phenol, which is rotationally mobile, induces conformational disorder in the methylene chains of the intercalated bilayer. The nature and extent of conformational disorder have been studied using infrared and Raman vibrational spectroscopy and {^{13}C CP-MAS NMR} spectroscopy. Conformational disorder in the two phases of the phenol-solubilized bilayer is different, and the observed differences in the interlayer lattice spacings have been related to differences in the nature of conformational disorder.

Dynamics of methylene chains in an intercalated surfactant bilayer by solid-state NMR spectroscopy

Two complementary solid-state NMR techniques – variable contact time cross-polarization magic angle spinning (VCT CPMAS) and 2D wide-line separation (2D WISE) spectroscopy have been used to probe the dynamics of methylene chains in an intercalated surfactant bilayer, formed within the galleries of layered cadmium thiophosphate by the insertion of cetyl trimethyl ammonium ions. A gradient of conformational mobilities is observed in the intercalated bilayer; the cationic heads are immobile while the terminal methylenes of the surfactant tail undergo rapid motion. In the crystalline salt, the gradient is reversed, the tails are stationary and the heads mobile.

A synthetic receptor for choline and carnitine.

A synthetic receptor is described with the appropriate shape and size for alkylated trimethylammonium ions such as choline and carnitine. The structure features a deep, concave binding site, lined with aromatic walls that provide cation-pi interactions between host and guest. Molecular mechanic calculations suggest that the host's shape is maintained through intermolecular hydrogen bonding with DMSO solvent molecules. The cavity is too small to accommodate larger ions. Choline and carnitine are recognized and bound with high affinity even though no complementary charges are involved in the process.

Preparation and Characterization of Macroporous Silicate Films

A straightforward procedure for engineering porosity in thin silicate films has been demonstrated. Macroporous silicate films were fabricated by doping a silica sol prepared from the acid-catalyzed condensation of tetramethoxysilane with polystyrene latex spheres of diameter ranging from 0.3 to 1 μm. After film formation, the polystyrene spheres are etched out the film using chloroform so that the pores are completely exposed on both top and bottom surfaces of the film. The size and distribution of pores in the film and the extent at which the pores are accessible to species in solution were characterized using atomic force microscopy (AFM) and electrochemical methods. AFM reveals that the pores are uniform in size with dimensions defined by the diameter of the particles. The number density of pores in the silica surface was varied from 10 to 150 pores/100 μm2 by controlling the concentration of microspheres in the sol. Cyclic voltammetry with probe compounds (ruthenium hexaammine, potassium ferricyanide, ferrocene methanol, and ferrocenylmethyl trimethylammonium ion) shows that the extent of pore penetration is a strong function of the ionic charge of the redox probe and the size of the pores.

Hydrocarbon chain conformation in an intercalated surfactant monolayer and bilayer

Cetyl trimethyl ammonium (CTA) ions have been confined within galleries of layered CdPS3 at two different grafting densities. Low grafting densities are obtained on direct intercalation of CTA ions into CdPS3 to give Cd0.93PS3(CTA)0.14. Intercalation occurs with a lattice expansion of 4.8 A with the interlamellar surfactant ion lying flat forming a monolayer. Intercalation at higher grafting densities was effected by a two-step ion-exchange process to give Cd0.83PS3(CTA)0.34, with a lattice expansion of 26.5 A. At higher grafting densities the interlamellar surfactant ions adopt a tilted bilayer structure.13C NMR and orientation-dependent IR vibrational spectroscopy on single crystals have been used to probe the conformation and orientation of the methylene ‘tail’ of the intercalated surfactant in the two phases. In the monolayer phase, the confined methylene chain adopts an essentially all-trans conformation with most of the trans chain aligned parallel to the gallery walls. On lowering the temperature, molecular plane aligns parallel, so that the methylene chain lies flat, rigid and aligned to the confining surface. In the bilayer phase, most bonds in the methylene chain are in trans conformation. It is possible to identify specific conformational sequences containing a gauche bond, in the interior and termini of the intercalated methylene. These high energy conformers disappear on cooling leaving all fifteen methylene units of the intercalated cetyl trimethyl ammonium ion in trans conformational registry at 40 K.

Clay-based formulations of metolachlor with reduced leaching

The current research in herbicide application aims to develop formulations that reduce leaching of the herbicide to deep layers of the soil and to concentrate its biological activity at the top layers. Adsorption of metolachlor on clay minerals, their organic derivatives or pillared forms provides the best possibility to develop slow-release formulations. Metolachlor is a selective pre-emergence herbicide widely used in irrigated crops to control annual weeds. It is adsorbed by bentonites and montmorillonites, but the amount adsorbed strongly depends on the type of bentonite and possible pretreatment reactions. Wyoming bentonites adsorbed considerable amounts of metolachlor but other bentonites did not bind this herbicide. An acid-activated pillared montmorillonite was also an effective adsorbent of metolachlor. Modification of this sample by preadsorbing different amounts of benzyl trimethylammonium ions did not influence the level of herbicide adsorption. The biological efficiency of the formulations was tested with bioassay soil columns. Slow-release formulations could be prepared with raw bentonites and the acid-activated pillared montmorillonite. A formulation, prepared by adsorbing metolachlor from aqueous solution on the acid-activated pillared montmorillonite, showed high herbicide activity at the top 10 cm, and did not diffuse significantly to greater depths. This formulation should allow a better weed control than the commercial formulations.

Electrochemical characteristics of viologen carboxylic acid derivatives assembled onto Au electrode as a synthetic receptor for electron-rich compounds

Electrochemical characterization in monolayer assemblies formed by covalent linkage of synthesized 1,1′-[1,4-phenylenebis(methylene)]bis(2-carboxyethyl)-4,4′-bipyridium (PBB) to cystamine, chemisorbed onto gold electrodes, were examined. The surface coverage of PBB corresponded to Γ=2.4×10 −10 mol cm −2. The equilibrium binding constants of charge–transfer complexes formed by the receptor, resulting in a redox-active monolayer surface with five aromatic compounds (tiron, hydroquinone sulfonic acid, and three kinds of ferrocene derivative) and sodium hexachloroiridate (III), were measured in aqueous media using the differential pulse voltammetric method. The values obtained from tiron were K o=330 000 M −1 of PBB 4+-modified electrode and K r=4200 M −1 of PBB 2+-modified electrode. Furthermore K o values of the three kinds of ferrocene derivative were increased in order of negative charge number. The coulomb force between host and guest was influenced by host–guest interaction. On the other hand, the value obtained from monocationic (ferrocenylmethyl) trimethylammonium ion repulsed positively charged PBB-modified electrode was K r/ K o=0.019. The reduction of tetracationic PBB to dicationic one decreased the π-acceptor character of the receptor PBB-modified electrode.

Entrapping pesticides by coagulating smectites

Highly delaminated montmorillonite (from Wyoming) with a high specific surface area when dispersed in water was used as an adsorbent of the hydrophobic herbicide metolachlor. The montmorillonite was coagulated with Na +, Ca 2+, Al 3+ and benzyl trimethylammonium ions. Ca 2+ and Al 3+ screened the surface charges and the adsorption of metolachlor was strongly enhanced by the interaction of metolachlor with the hydrophobic siloxane oxygen atoms and the water molecules of the hydration shell of the interlayer cations. With increasing salt concentration the mechanism changed from a cooperative adsorption process on a heterogeneous surface (S-type isotherm) to adsorption on a homogeneous surface (L-type). Coagulation with Ca 2+ and Al 3+ increased the amounts of metolachlor adsorbed from 14–41% (Na +) to 57–86% (Ca 2+) and 67–91% (Al 3+). The light microscopic images revealed that increasing amounts of metolachlor changed the band-type network into spherical “potato-like” aggregates. The enhanced herbicide adsorption hydrophobized the particles that crowded together to form spherical aggregates. Entrapping the herbicide molecules in clay mineral aggregates—either band-type networks or spherical aggregates—offers a useful tool in creating leaching-resistant herbicide formulations.

Conformation of Methylene Chains in an Intercalated Surfactant Bilayer

Infrared and Raman spectroscopy have been used to establish the conformation and orientation of the methylene “tail” of cetyl trimethylammonium ions intercalated in an inorganic layered host, $CdPS_{3}$. Intercalation, effected by a two-step ion-exchange process leading to the formation of $Cd_{0.83}$$PS_{3}$ $(CTA)_{0.34}$, occurs with a lattice dilation of 26.5 \AA with the surfactant ions within the galleries adopting a bilayer structure. The frequencies of the conformationally sensitive methylene stretching modes in the infrared and Raman spectra indicate that a majority of the bonds in the methylene chain are in a trans conformation. The methylene chains are tilted with respect to the inorganic layer. The tilt angle as determined from orientation-dependent infrared spectra is \sim $35^0$. Although the population of gauche conformers is low, it has been possible to identify specific conformational sequences containing a gauche bond, in the interior and termini of the intercalated methylene chains, by their characteristic frequencies in the infrared spectrum. These high-energy conformers, except for the ones at the chain end, disappear on cooling, leaving on average all 15 methylene units of the intercalated cetyl trimethylammonium ion in trans conformational registry at 40 K. The terminal gauche defects are significant in preventing interdigitation of the low-density intercalated surfactant bilayer.

A glass capillary ultramicroelectrode with an electrokinetic sampling ability.

A glass capillary ultramicroelectrode (tip diameter approximately 1.2 microm) having an electrokinetic sampling ability is described. It is composed of a pulled glass capillary filled with an inner solution and three internal electrodes (Pt working and counter electrodes and an Ag/AgCl reference electrode). The voltammetric response of the capillary electrode is based on electrokinetic transport of analyte ions from the sample solution into the inner solution across the conical tip. It was found that the electrophoretic migration of analytes at the conical tip is faster than electroosmotic flow, enabling electrokinetic transport of analyte ions into the inner solution of the electrode. By using [Fe(CN)6]4- and (ferrocenylmethyl)trimethylammonium (FcTMA+) ions as model analytes, differential pulse voltammetric responses of the capillary electrode were investigated in terms of tip diameter of the capillary, sampling voltage, sampling time, detection limit and selectivity. The magnitude of the response depends on the size and charge of analyte ions. With a capillary electrode having a approximately 1.2-microm tip diameter, which minimizes non-selective diffusional entry of analytes, the response after 1 h sampling at +1.7 V is linearly related to [Fe(CN)6]4- concentration in the range of 0.50-5.0 mM with the detection limit of 30 microM. Application of a potential of the same sign as that of the analyte ion forces the analyte to move out from the electrode to the solution, enabling reuse of the same capillary electrode. The charge-selective detection of analytes with the capillary electrode is demonstrated for [Fe(CN)6]4- in the presence of FcTMA+.

Conformation of an Alkane Chain in Confined Geometry: Cetyl Trimethyl Ammonium Ion Intercalated in Layered CdPS3

Cetyl trimethylammonium (CTA) ions have been confined at low grafting densities within the galleries of layered CdPS3 by an ion-exchange intercalation reaction to give Cd0.93PS3(CTA)0.14. Intercalation occurs with a lattice expansion of 4.8 A with the methylene “tail” of the intercalated surfactant lying closer to the walls of the galleries, rather than in the center. 13C NMR and orientation-dependent IR vibrational spectroscopy of single crystals of the intercalated Cd0.93PS3(CTA)0.14 have been used to probe the conformation and orientation of the methylene tail of the isolated, interlamellar surfactant ions. We find that the confined methylene chain adopts an essentially all-trans conformation, even in the absence of intermolecular interactions, with a large section of the molecular plane of the trans chain aligned parallel to the walls of the galleries. Upon lowering of the temperature, increasingly larger sections of the molecular plane align parallel, so that the methylene chain lies flat, rigid, and...

Effect of Colloidal Particle Size on Catalytic Activity of Anion Exchange Gels

Cross-linked anion exchange latexes 20, 150, and 1200 nm in diameter were prepared via microemulsion, emulsion, and dispersion copolymerization, respectively, of vinylbenzyl chloride, styrene, and divinylbenzene followed by treatment with trimethylamine or tributylamine. As catalysts for the unimolecular decarboxylation of 6-nitrobenzisoxazole-1-carboxylate (1) the tributylammonium ion latexes were much more active than the trimethylammonium ion latexes. There were only small differences in the rates of decarboxylation in the three different tributylammonium ion latexes, and first-order kinetics were found at all relative concentrations of ion exchange sites and 1 in the 20 and 150 nm particle dispersions. Retardation of the rate both early and late in the reaction using a low concentration of the 1200 nm particles is attributed to slow mass transfer of 1 from solution to the particle surface and to competitive inhibition by the product ion.

Influence of Organic and Inorganic Salts on the Coagulation of Montmorillonite Dispersions

AbstractThe colloidal state (stable, coagulated, or gel-like) and the rheological properties of Na-rich montmorillonite (Wyoming) dispersions are strongly influenced by organic cations. This effect is shown for homologous organic cations: alkyl trimethylammonium ions, paraquat, diquat, alkyl bispyridinium ions, and the triphenylmethane dyes crystal violet, methyl green, and tris (tri-methylammonium phenyl) methane chloride. The critical coagulation concentrations, cK, are small (often < 1 mmol/L) because the cations are enriched in the Stern layer and influence the solvent structure near the surface. The strong adsorption of the counterions at the clay-mineral surface causes cK values to increase with the solid content. Charge reversal (recharging) of the particles was observed with the longer chain alkyl trimethyl-ammonium ions, dodecyl bispyridinium ions, and crystal violet. Other cations reduced the electrophoretic mobility to zero but positive particle charges were not observed.The plastic viscosity increased sharply at the critical coagulation concentration and showed a minimum slightly below cK, which was caused by the electroviscous effect. Yield values were developed at concentrations above cK. In most cases, yield values reached a plateau where the amount of organic cations was ∼0.5 mmol/g, i.e., about half of the cation-exchange capacity. The cK values decreased with increasing hydrophobicity of homologous compounds, but the yield value showed maxima at intermediate chain lengths. The yield value of several 0.5% dispersions was high, e.g., dodecyl trimethylammonium ions, 71 Pa; paraquat, 100 Pa; diquat, 42 Pa; hexyl bispyridinium ions, 53 Pa (vs. Ca2+, 0.2 Pa; Al3+, 0.7 Pa). The storage modulus as a function of the number of organic cations changed in a similar way as the yield value, and high values were observed (e.g., dodecyl trimethylammonium ions, hexyl bispyridinium ions: 1000 Pa, paraquat: >4000 Pa). Thus, dispersions with high viscosity, yield value, and pronounced viscoelasticity are obtained by coagulating Na-rich montmorillonite dispersions with organic cations.

Trimethylammonium Nickel(II) Chloride Dihydrate

catena-Poly[trimethylammonium [diaquanickel(II)-di-μ-chloro] chloride], [(CH3)3NH][NiCl2(H2O)2]Cl, is built up by infinite chains of Cl-edge-sharing trans-[NiCl4(H2O)2] octahedra separated by trimethylammonium cations and discrete Cl− anions. The compound is isostructural with the Co and Mn compounds, with negligible modifications caused by the difference of the ionic radii of the metal ions. The crystal structure is stabilized by hydrogen bonds between the discrete Cl− ions and the water molecules and also between the trimethylammonium ions and the water molecules.