Search results for "small-angle X-ray scattering"
showing 10 items of 126 documents
Consolidation and protection by nanolime: recent advances for the conservation of the graffiti, Carceri dello Steri Palermo and of the 18th century l…
2014
Abstract Nanolime dispersed in 2-propanol was extensively used for the consolidation of wall paintings. The knowledge of the advances of this methodology dealing with all the possible effects associated with the nanolime new material in conservation is fundamental to assess and improve the technique. In this paper, four different dispersions of Ca(OH) 2 nanoparticles were characterised by Small Angle X-rays Scattering technique (SAXS) and Transmission Electron Microscopy (TEM) in order to achieve information on size, shape, polydispersity, agglomeration, and crystal structure (by SAED patterns) of the particles. Once characterised, the dispersions were tested in two different case studies, …
Ferroelectric polysiloxane liquid crystals with ‘de Vries’-type smectic A*–smectic C* transitions
2004
We report preliminary results of optical and small angle X-ray scattering (SAXS) experiments on the smectic A*−smectic C* transition in two ferroelectric liquid crystalline polysiloxanes. Although the optical tilt angle in the SmC* phases reaches values up to 30°, temperature-dependent SAXS measurements clearly reveal that the smectic layer spacing is basically conserved during the A*–C* transition as well as in the subsequent C* phase. Connected with the A*–C* transition we further observed a significant increase in birefringence, hence reflecting an increase of orientational order. The practical absence of layer shrinkage and the enhanced orientational ordering are consistent with the de …
Salt-induced microheterogeneities in binary liquid mixtures
2017
The salt-induced microheterogeneity (MH) formation in binary liquid mixtures is studied by small-angle x-ray scattering (SAXS) and liquid state theory. Previous experiments have shown that this phenomenon occurs for antagonistic salts, whose cations and anions prefer different components of the solvent mixture. However, so far the precise mechanism leading to the characteristic length scale of MHs has remained unclear. Here, it is shown that MHs can be generated by the competition of short-ranged interactions and long-ranged monopole-dipole interactions. The experimental SAXS patterns can be reproduced quantitatively by fitting to the derived correlation functions without assuming any speci…
Physicochemical Investigation of Lightfast AgCl and AgBr Nanoparticles Synthesized by a Novel Solid−Solid Reaction
2003
Small size AgX (X = Br, Cl) nanoparticles have been synthesized by a novel solid−solid reaction performed by mixing two dry dispersions of AgNO3 and KX nanoparticles in AOT/n-heptane solutions. UV−vis investigation ascertained that formation of nanosized particles taking place after the mixing process is fast and complete. Microcalorimetric measurements of the thermal effect coupled with the mixing process suggest the occurrence of confinement effects and adsorption of the surfactant molecules at the nanoparticle surface, hinting at formation of charged nonstoichiometric surfactant-coated nanoparticles. The analysis of SAXS spectra shows that salt-containing AOT reversed micelles are slight…
Effect of Alkali Ions on the Amorphous to Crystalline Phase Transition of Silica
2001
Abstract The effect of the addition of alkali ions to commercial amorphous silica, generally used as support for heterogeneous catalysts, has been investigated from the point of view of morphological and structural changes. Samples of alkali-doped silica were prepared by impregnation and subsequent calcination at various temperatures. The structural effect of Li, Na, K, and Cs was determined by use of techniques such as wide-angle (WAXS) and small-angle X-ray scattering (SAXS). The WAXS diffractograms, analyzed with the Rietveld method using the GSAS program, allowed qualitative and quantitative identification of the fraction of the different silica polymorphs like quartz, tridymite, and cr…
Role of the co-surfactant nature in soybean w/o microemulsions.
2008
Abstract The influence of the co-surfactant on physicochemical properties of w/o soybean oil microemulsions (MEs) has been studied. In spite of the similarity in phase diagrams, the MEs display remarkable differences when examined by electrical conductivity, dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and linear voltammetry. When different short-chain alcohols were employed as co-surfactants, together with sodium dodecyl sulfate (SDS) as surfactant, the DLS results indicated the systems to be monodisperse. Both the electrical conductivity of the MEs and the hydrodynamic radii of the droplets (RH) increased with water content while RH diminished as temperature increas…
Confinement effects on the interactions of native DNA with Cu(II)-5-triethyl ammonium methyl salicylidene orto-phenylendiiminate in C12E4 liquid crys…
2008
Confinement effects of native calf thymus DNA interacting with the complex Cu(ii)-5-(triethylammoniummethyl)salicylidene ortho-phenylendiiminate (CuL(2+)) perchlorate in tetraethylene glycol monododecyl ether (C(12)E(4)) liquid crystals have been investigated by UV absorption spectrophotometry, circular dichroism (CD) and small angle X-ray scattering (SAXS). The results indicate the occurrence of dramatic structural changes of both the DNA and the CuL(2+)-DNA system, when going from aqueous solution to C(12)E(4) liquid crystals, due to confinement constrains imposed by the closed structure of C(12)E(4) reverse micelles. Further marked departures from the behaviour observed in aqueous soluti…
Self-assembly in surfactant-based liquid mixtures: Octanoic acid/Bis(2-ethylhexyl)amine systems
2012
Abstract The physico-chemical properties of Bis(2-ethylhexyl)amine (BEEA) plus octanoic acid (OA) mixtures have been investigated by IR, SAXS, WAXS, viscosimetry, and AC complex impedance spectroscopy in the whole composition range. Mainly driven by proton transfer from the acidic OA to the basic BEEA, the formation of stoichiometrically well-defined adducts takes place in the mixtures. This causes the slowing down of molecular dynamics and the increase in charge carrier number density. Interestingly, while the pure components possess no significant conductivity (about 10−12 S cm−1 at 25 °C), their mixtures show a composition-dependent enhanced conductivity (up to about 10−5 S cm−1), i.e., …
The Allosteric Effector l-Lactate Induces a Conformational Change of 2×6-meric Lobster Hemocyanin in the Oxy State as Revealed by Small Angle X-ray S…
2001
Abstract Hemocyanins are multisubunit respiratory proteins found in many invertebrates. They bind oxygen highly cooperatively. However, not much is known about the structural basis of this behavior. We studied the influence of the physiological allosteric effectorl-lactate on the oxygenated quaternary structure of the 2×6-meric hemocyanin from the lobster Homarus americanus employing small angle x-ray scattering (SAXS). The presence of 20 mm l-lactate resulted in different scattering curves compared with those obtained in the absence of l-lactate. The distance distribution functionsp(r) indicated a more compact molecule in presence ofl-lactate, which is also reflected in a reduction of the …
X-ray study of LB multilayers of cadmium soaps in the vicinity of the break up point
1991
Temperature dependent SAXS measurements were carried out on multilayers of two different salts, cadmium palmitate (hexadecanoate) and behenate (docosanoate). The pattern characteristic of layer structure disappears at a transition temperature well below the bulk melting point in both cases. Examination by means of optical microscopy shows that the LB films break up at a temperature close to this transition. Measurements in its vicinity demonstrate that over a certain temperature range just below the transition a second set of peaks arises in the diffraction pattern. During this transition region of about 3 °C width two d-spacings for both salts were found, suggesting the simultaneous existe…