Monolayers of mono-, di-, tri-, and tetraalkylammonium cations of varying chain length (C 4 , C 8 , and C 18 ) were self-assembled on montmorillonite platelets. The structure and chain dynamics of these SAMs were probed by infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). Depending on the cross-sectional area, the available area/cation, and the alkyl chain length, the molecules adopt a two-dimensional order or a disordered state at ambient temperatures. Short alkyl chains lie flat, disordered on the substrate surface as long as there is enough space. With increasing volume of the organic layer between two silicate layers facing each other, the chains force the layers to enlarge their basal-plane spacing but remain disordered. At a certain length and number of chains, the molecules adopt an ordered state due to increasing chain interactions and packing density. To minimize their conformational entropy and maximize their packing density, the chains attached to platelets facing each other interdigitate. The average molecular axis in the organic thin film is inclined to the montmorillonite surface normal by an angle, which depends on the packing environment and the geometry of the molecules. In the ordered state, the alkyl chains preferentially assume an all-trans conformation. With increasing temperature, conformational transformation of the chains takes place, leading to a dynamically disordered phase (liquidlike). Although the translational freedom of the chains is restricted by the electrostatic binding of the headgroups to the substrate, the conformational transformation leads to chains with random conformation and destroys the two-dimensional order. The phase transition manifests itself in an increase in basal-plane spacing as well as in IR absorption frequency and carbon resonance shifts accompanied by an entropy change. The density of the organic ultrathin film confined between two silicate layers seems to decrease on heating across the phase transition, leading to an increase in volume and consequently in the organic layer thickness and in d-spacing, respectively. The basal-plane spacing of 3C18 and 4C18 is appreciably larger than that of C18 and 2C18, which is advantageous for exfoliation in the synthesis of polymer nanocomposites.

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Generally, the abundance of 03 centres (silicon vacancy) and E'I centres (oxygen vacancy) in agate is remarkably higher than in quartz. The high defect density in agates points to rapid growth of silica from a strongly supersaturated solution probably with a noncrystalline precursor.CL microscopy reveals internal structures and zoning in agates and quartz incrustations which clearly differ from those discernible by conventional polarizing microscopy. The CL spectra of agates differ from those of quartz from crystalline rocks. At least three broad emission bands were detected in the CL spectra: a blue band of low intensity, a yellow band at about 580 nm, and an intense red band at 650 nm. The CL emission at 650 nm shows some relations to the hydroxyl or alkali content and the abundance of O 3-centres and E' 1 centres. The emission intensity increases during electron bombardement due to the conversion of different precursors (e.g. -Si-O-H, --Si-O-Na groups) into hole centres. Another conspicuous feature in the CL spectra of agates is the existence of a yellow emission band centred at around 580 nm. The predominance of the yellow CL emission band and the high concentration of E' 1 centres are typical for agates of acidic volcanics and are indicative of a close relationship between the two.

Paramagnetic defects in natural, irradiated (2 kGy, 60 CO, 295 K) and etched (40% HF, 30 min, 295 K) sampies of quartz grains (grain size < 0.16 mm) from quartz-sand deposits in Weferlingen, Haltern and Frechen (Germany) were investigated by EPR at 9.5 GHz and at 20, 70, and 295 K. In all sampies [AI04jO, [TiOJLi+jO, [Ti041H+jO, [Ti04j-, and Fe3+ paramagnetic centres were detected. Generally, y-irradiation caused a transformation of diamagnetic precursor centres into these paramagnetic centres, resulting in an increase of the EPR intensity of up to five times. Sampies from Weferlingen have similar trace-element contents and show only minor differences in the abundance of paramagnetic centres. In contrast, the abundance of paramagnetic centres in quartz from the different deposits may differ significantly, especially Fe3+, [AI04jO and [Ti04/Li+jO centres in the y-irradiated quartz sampIes. The high concentrations of [AI04jO and [Ti04/Li+jO centres in the Weferlingen quartz sampies reflect higher amounts of igneous quartz than in the other deposits investigated. These differences in quartz composition were confirmed by cathodoluminescence microscopy. Etching of quartz sampIes with hydrofluoric acid (ca. 30% loss of mass) followed by further EPR measurement revealed that AI centres generally show a more or less homogeneous distribution pattern, whereas no Fe centres were left in quartz after etching. This indicates that Fe centres are concentrated in the outer rim of the quartz grains.

This paper reports the results of the first geomechanical laboratory experiments carried out on the polluted submarine clayey sediments of the Mar Piccolo in Taranto (South of Italy). The study had to face with extreme difficulties for the very soft consistency of the sediments and the contaminants. The mineralogy, composition and physical properties of the sediments were analysed, along with their compression and shearing behaviour. The investigation involved sediments up to about 20 m below the seafloor, along three vertical profiles in the most polluted area of the Mar Piccolo, facing the Italian Navy Arsenal. The experimental results were used to derive a preliminary geotechnical model of the site, necessary for the selection and design of the most sustainable in situ mitigation solutions. Moreover, the experimental data reveal that the clayey sediments of the most polluted top layer do not follow the classical geotechnical correlations for normally consolidated deposits. This seems to open interesting perspectives about the effects of pollutants on the geotechnical behaviour of the investigated sediments.