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We have prepared and analyzed thin film structures formed by polyethylenimine and alkyltrimethylammonium bromide (CnTAB) surfactants at the air/water interface, using both surface and bulk sensitive techniques. In initial experiments it was observed that hexagonal arrays of rodlike micelles surrounded by the polymer were formed at the solution surface, with the principal axis of the micelles running parallel to the surface. In the studies reported here, the formation of these ordered mesostructured films was identified as being kinetically but not thermodynamically favored, with some of the systems examined showing a loss of structure from their neutron reflectometry profiles with time. The polymer was used in both an as-diluted state (with a small net positive charge) and a neutral state, through the addition of sodium hydroxide to the solution. The primary interaction in these systems was found to be that of a neutral polymer with a cationic surfactant; however, by modifying the charge on the polymer it is possible to alter the distance between micelles by up to 6 Å without destroying the structure of the films. Analysis of the bulk solution with small-angle neutron scattering showed that the micelles in solution are elliptical rather than rod-shaped, and so the assembly of the hexagonal mesostructure occurs at the air/water interface rather than adsorbing to the interface from the bulk.

Abstract: The gold outcrops employed by the ancient kingdom of Tartessos, settled in the SW of the Iberian Peninsula from ca. 10th to the 6th century BC, for the Aliseda treasure manufacture, has been discovered. This paper reports on the finding of collected gold nuggets, more than 80 units up to 218 g, in an ancient mining area located in Casas de Pedro (Extremadura, SW of Spain). The comparative physical-chemical analyses between these gold nuggets picked at present and the archaeological gold collected in 1920, have been performed by microscopy, X-ray diffraction (XRD), thermoluminescence (TL), X-ray photoelectron spectrometry (XPS) and electron microprobe analyses (EMPA). Pieces of Aliseda treasure and the picked gold nuggets show a highly homogeneous chemical composition of trace elements namely: As 0.01%, S 0.02%, Bi 0.35%, Fe 0.016%, Ag 0.8%, Sb 0.05% and Te 0.04%. The small difference between both gold samples is only of 0.2% extra copper in Aliseda due to an anthropogenic addition of a silver-copper mixture during a second firing of the jewel to weld ornamental spheres.

Off-specular X-ray reflectivity measurements were carried out to follow the in situ development of surfactant-templated silica thin films at the air−water interface under conditions of controlled relative humidity and temperature, using an enclosed sample cell designed for this purpose. The results suggest a strong dependence of formation time and growth mechanism on ambient conditions. Thin films were synthesized at the air−water interface using cetyltrimethylammonium bromide (CTAB, 0.075 M) and a silica precursor, tetramethoxysilane (TMOS, 0.29−0.80 M) in an acidic medium. The studied humidity range was from 50 to 100%, the temperature was between 25 and 40 °C, and the TMOS/CTAB molar ratio was between 3.3 and 10.7. We observed that high humidity slows down the growth process due to lack of evaporation. However, increasing the temperature results in a decrease in the film-formation time. We proposed a formation mechanism for film growth as a consequence of phase separation, organic array assembly, and silica polymerization.