E. Bain

Nanometer-scale structure of hectorite–aniline intercalates

The inclusion of the organic guest aniline into Cu(II)-exchanged hectorite thin films has been investigated. The subsequent polymerization of aniline on the clay surface and in the intergallery regions are studied using scanning force microscopy (SFM), electron paramagnetic resonance (EPR) spectroscopy, powder x-ray diffraction (XRD), and impedance spectroscopy. EPR and XRD data show that in addition to strong polymerization of aniline on the clay surface, polymerization also occurs in the intergallery regions of the clay. Using standard lift-off techniques or razor cleaving, the exposed intergallery polyaniline is successfully imaged for the first time using noncontract SFM in phase-contrast mode. The nearly two-dimensional polymer sheets formed in these regions exhibit none of the nanometer-scale grain or bundle structure commonly associated with polyaniline synthesized using techniques such as electrochemical or vacuum deposition. The electrical response of the resulting clay-conducting polymer composi...

Analysis of peptides synthesized in the presence of SAz-1 montmorillonite and Cu2+ exchanged hectorite

We have investigated the synthesis of oligopeptides containing glycine and tyrosine in the presence of the clay minerals montmorillonite (non-exchanged, SAz-1) and Cu(2+) exchanged hectorite. In both cases, homopolymers of the two amino acids are formed, as are mixed peptides. In the case of Cu(2+) hectorite, mixed oligopeptides up to trimers are detected in small amounts. For montmorillonite, heterogeneous oligopeptides up to hexamers are detected. Our experiments indicate montmorillonite is more effective in promoting oligopeptide formation than Cu(2+) hectorite. Analysis of the oligopeptide sequences formed on the montmorillonite surfaces indicates preferential synthesis of certain Gly-Tyr sequences over others.

Scanning force microscopy and polymerization studies on cast thin films of hectorite and montmorillonite

Thin films of the smectite clays Na+ exchanged montmorillonite, Ca2+ exchanged montmorillonite, Na2+ and Cu2+ exchanged hectorite, Cu2+ exchanged sintered hectorite, and Cu2+ and Na2+ exchanged hectorite exposed to benzene, aniline, and thiophene were studied using the techniques of scanning force microscopy (SFM), electron spin resonance (ESR), and x‐ray diffraction. The microstructure of the two montmorillonite clays was markedly different, with the Ca‐montmorillonite exhibiting a sturdy, close packed array of crystallites of average dimension 0.4 μm. The Na‐montmorillonite clays consisted of smaller (0.1 μm), more poorly defined crystallites with an overall cauliflowerlike appearance. The pure Na‐hectorite and Cu‐hectorite clays exhibited large flat regions composed on interlocking platelets. Heat sintering as well as exposure to benzene resulted in measurable shifts in the platelets perpendicular to the surface for the Cu‐hectorite. It is proposed that in the sintered case these shifts are due to inte...

The formation of poly(methyl-methacrylate) on transition metal-exchanged hectorite

Abstract Hectorite clay films exchanged with Cu 2+ or Fe 3+ react with methyl-methacrylate monomer in a solventless process to form poly(methyl-methacrylate) (PMMA). Scanning force microscopy (SFM), electron spin resonance (ESR), and X-ray diffraction (XRD) are useful in studying the resulting clay/polymer composite. SFM shows that PMMA forms on the surface of both the Cu 2+ - and Fe 3+ -exchanged films. In addition, XRD shows PMMA formation in the interlayer region of the Fe 3+ -exchanged hectorite but not the interlayer region of Cu 2+ -exchanged hectorite. SFM shows that the morphology of the polymer formed on the film surface depends on: (1) the type of transition metal exchanged into the interlayer region. (2) The mode of delivery (vapor vs. liquid) of methyl-methacrylate monomer to the surface of the clay. PMMA does not form to a significant extent on or within Ca 2+ -exchanged hectorite, and ESR shows no evidence of free radical formation or reduction of the transition metals during any of the polymerization reactions. The results suggest the possibility of an unusual cationic polymerization of methyl-methacrylate to form PMMA with organic cations being stabilized by interaction with the silicate surface. The experimental results have implications for “solventless synthesis” of PMMA and other polymers.

POLYMERIZATION OF BENZENE AND ANILINE ON Cu(II)-EXCHANGED HECTORITE CLAY FILMS: A SCANNING FORCE MICROSCOPE STUDY

The technique of scanning force microscopy (SFM) was used to study the nanometer-scale structure of Cu(II)-exchanged hectorite thin films. Supporting data were also obtained from Electron Spin Resonance (ESR) and X-ray diffraction (XRD) techniques. The surfaces studied included pure Cu(II)-exchanged hectorite, Cu(II)-exchanged hectorite exposed to benzene and Cu(II)-exchanged hectorite exposed to aniline. SFM images of the unexposed Cu(II)-exchanged hectorite surface revealed a smooth surface composed of interlocking platelets. The lateral dimension of these platelets ranged from a few nm to about 1 μm. After exposure to refluxing benzene, the SFM showed that the platelets underwent vertical shifts in position. This is believed to have occurred from intercalated benzene that polymerized in the interlayer region. No SFM evidence was obtained for benzene polymerization on the surface of the hectorite. Hectorite films exposed to aniline at room temperature revealed a post-polymerization structure on the hectorite surface consisting of small polymer bundles. The diameter of these bundles was measured to be 300–3000 Å, similar to the structure seen on electropolymerized polyaniline films. Aniline polymerized on the surface of hectorite films at 180 °C revealed a structure similar to undoped n-methyl-pyrrolidinone (NMP) cast polyaniline films. In this case, the polymer bundles are only 300 Å in dimension on average. XRD and ESR data also indicated interlayer aniline polymerization in Cu(II) exchanged hectorite. Mechanistic considerations affecting these polymerization reactions are presented.

Studies on the reaction of the 5′-phosphorimidazolide of adenosine with Cu(II)-exchanged hectorite

The role of clay minerals in the prebiotic synthesis of nucleotide oligomers has received considerable attention in recent years. Scanning force microscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry are used to identify oligomers of adenylic acid formed on the clay mineral Cu(II)-exchanged hectorite in simulated prebiotic cycling experiments. Electron-spin resonance and x-ray diffraction data indicate that the monomer (5′-phosphorimidazolide of adenosine, or ImpA) penetrates into the intergallery regions of the mineral substrate, and complexes the gallery Cu(II) cations. It is postulated that polymerization of the monomer is initiated in the clay intergallery regions, producing oligomers of adenylic acid up to 8 units in length or more.

Surface Structure and Intercalative Polymerization Studies of Smectite Clay Thin Films

The microstructure of the clay minerals Cu2+ exchanged hectorite, Na+ exchanged hectorite, Na+ exchanged montmorillonite and Ca2+ exchanged montmorillonite were studied using scanning force microscopy (SFM), electron spin resonance (ESR), and x-ray diffraction. The montmorillonite films displayed the rough clay fabric commonly associated with these materials. Ca2+ montmorillonite films consisted of a porous web-like grain structure, while Na+ montmorillonite films were composed of clumps of smaller discrete grains. The lesser studied hectorite films, however, revealed many large, flat regions suitable for further SFM examination and polymerization studies. The chemical reactivity of the hectorite clays was studied by examining polymerization reactions occurring when the clays were exposed to benzene and aniline. In the case of standard Na+ exchanged hectorite, little or no reactivity was observed upon exposure to the various monomers. For the Cu2+ exchanged hectorite, large scale intergallery and surface polymerization were observed upon exposure to aniline, with intergallery polymerization observed in the case of benzene.