RESUMEN
The SIRIUS beamline of Synchrotron SOLEIL is dedicated to X-ray scattering and spectroscopy of surfaces and interfaces, covering the tender to mid-hard X-ray range (1.1-13â keV). The beamline has hosted a wide range of experiments in the field of soft interfaces and beyond, providing various grazing-incidence techniques such as diffraction and wide-angle scattering (GIXD/GIWAXS), small-angle scattering (GISAXS) and X-ray fluorescence in total reflection (TXRF). SIRIUS also offers specific sample environments tailored for in situ complementary experiments on solid and liquid surfaces. Recently, the beamline has added compound refractive lenses associated with a transfocator, allowing for the X-ray beam to be focused down to 10â µm × 10â µm while maintaining a reasonable flux on the sample. This new feature opens up new possibilities for faster GIXD measurements at the liquid-air interface and for measurements on samples with narrow geometries.
RESUMEN
The phase diagram of the Langmuir film of diacetylene alcohol-henicosa-5,7-diyn-1-ol-is investigated by means of surface pressure versus surface area isotherms, Brewster angle microscopy, X-ray reflectivity, and grazing incident X-ray diffraction. Among the usual phases described in the generic phase diagram of small head group molecules, one observes an unexpected reversible transition from an ordered condensed phase to a disordered one upon increasing the surface pressure. We postulate that the origin of this unusual, unprecedented transition results from the competition between the interactions between the diacetylene blocks in the hydrophobic chain and the hydrogen bonds between head groups and water.
RESUMEN
The absorptivities of polydiacetylenes (PDAs) used in Langmuir films or vesicles for the development of PDA sensor films or other applications such as nonlinear optics and field-effect transistors are not known, so the polymer contents cannot be deduced from experimental spectra. Here we introduce a novel method, using nuclear reaction analysis (NRA), that allows a quantitative determination of the polymer content X proportion of monomers that have been incorporated into PDA chains. We apply it to pentacosadiynoic acid (PCDA) evaporated microcrystalline films. A calibration curve giving X as a function of the area under an absorption spectrum normalized to the monomer areal density is obtained for blue and red PCDA. The method is applicable to all kinds of films and to other PDAs, provided films with known molecular areal density are available. An example of the application to a PCDA Langmuir film is given.
RESUMEN
The dynamics of a physical gel, namely, low-molecular-mass organic gelator methyl-4,6-O-benzylidene-α-D-mannopyranoside (α-manno) in water and toluene, are probed by neutron scattering. Using high gelator concentrations, we were able to determine, on a time scale from a few picoseconds to 1 nanosecond, the number of solvent molecules that are immobilized by the rigid network formed by the gelators. We found that only a few toluene molecules per gelator participate in the network which is formed by hydrogen bonding between the gelators' sugar moieties. In water, however, the interactions leading to the gel formations are weaker, involving dipolar, hydrophobic, or π-π interactions, and hydrogen bonds are formed between the gelators and the surrounding water. Therefore, around 10 to 14 water molecules per gelator are immobilized by the presence of the network. This study shows that neutron scattering can give valuable information about the behavior of solvent confined in a molecular gel.
RESUMEN
Spectroscopic and kinetic properties of a new photochromic medium, consisting of nanocrystals of spyropyran molecules (1,3-dihydro-1,3,3,5',6',pentamethyl-spiro[2H-indole-2,2'-[2H]pyrano [3,2-b]pyridinium] iodide) embedded in an organo-silicate sol-gel film, are presented and compared to microcrystals obtained by slow evaporation of a solvent. High photoconversion efficiencies for both kinds of crystals have been observed. In microcrystals, the photomerocyanine form absorbs at 570 nm with a fading rate of 5 h, in nanocrystals the photomerocyanine form absorbs at 535 nm with a fading rate of 41 h. Therefore, the crystalline structure of nanocrystals is different from the microcrystal one.
