Study by EXAFS of the local structure around Si on silicene deposited on Ag(1 1 0) and Ag(1 1 1) surfaces.

The local structure around the silicon atoms of silicene deposited onto Ag(1 1 0) and Ag(1 1 1) has been determined by extended x-ray absorption fine structure spectroscopy at the silicon K-edge. This study shows that silicon atoms are not in a flat honeycomb network locally buckled, but that this structure mimics the double Si(1 1 1)-plane of crystalline silicon with almost the same first and second interatomic distances (2.35 and 3.83 Å) on a regularly buckled geometry. Moreover the results evidence silver atoms at a well-defined distance from the silicon ones, a signature for an interaction between the silicene sheet and silver atoms released from the substrate.

Pharmacist intervention reduces gastropathy risk in patients using NSAIDs.

OBJECTIVE: To establish a detection and intervention strategy in order to reduce the number of non-steroidal anti-inflammatory drug (NSAIDs) users at risk of gastropathy from receiving either inadequate or no gastroprotection. SETTING: Community Pharmacies in Valencia, Spain. METHOD: Prospective longitudinal intervention study without control group carried out by 79 Community Pharmacies. Patients over 18 who asked for any systemic NSAID were interviewed according to standard procedure. Pharmacist intervention was carried out when a patient at risk of serious NSAID-induced gastrointestinal complications due to inadequate or no gastric protection was identified. The doctor responsible was informed in order to then be able to assess the need to prescribe gastroprotection or change it if inadequate. In the case of over-the-counter (OTC) drugs, pharmacist intervention mainly involved replacing NSAIDs for safer medications. MAIN OUTCOME MEASURE: Firstly, the number of patients who had no prescribed gastroprotection or inadequate gastroprotection was determined. Pharmacist intervention then brought about changes in pharmacotherapy in this situation. RESULTS: Of the 6,965 patients who asked for NSAIDs during the study period, 3,054 (43.9%) presented NSAID gastropathy risk factors. 35.6% of the latter (1,089) were not prescribed gastroprotection or were prescribed inadequate gastroprotection. Pharmacist intervention was carried out in 1,075 of these cases. On 391 occasions such risk situations were reported to doctors, who accepted pharmacist intervention on 309 occasions (79.0%) and then either prescribed gastroprotection (77% of cases); changed it (13.9%); withdrew the NSAID (5.8%) or substituted it (3.2%). 235 Pharmacist interventions took place when dispensing OTC NSAIDs. CONCLUSION: Our strategy allowed us to identify a large number of patients who asked for NSAIDs in Community Pharmacies and who were at risk of NSAID gastropathy, as they received either inadequate gastroprotection or no gastroprotection whatsoever. Moreover, the pharmacist intervention carried out has reduced the number of these risk situations.

How confinement affects the dynamics of c60 in carbon nanopeapods.

The dynamics of confined systems is of major concern for both fundamental physics and applications. In this Letter, the dynamics of C60 fullerene molecules inside single walled carbon nanotubes is studied using inelastic neutron scattering. We identify the C60 vibrations and highlight their sensitivity to temperature. Moreover, a clear signature of rotational diffusion of the C60 is evidenced, which persists at lower temperature than in 3D bulk C60. It is discussed in terms of confinement and of reduced dimensionality of the C60 chain.

Substantial improvement of nanotube processability by freeze-drying.

As-produced carbon nanotubes often contain a fraction of impurities such as metal catalysts, inorganic supports, and carbon by-products. These impurities can be partially removed by using acidic dissolution. The resulting nanotube materials have to be dried to form a powder. The processability of nanotubes subjected to regular (thermal vaporisation) drying is particularly difficult because capillary forces pack and stick the nanotubes irreversibly, which limits their dispersability in polymeric matrices or solvents. We show that this dramatic limitation can be circumvented by using freeze-drying instead of regular-drying during nanotube purification process. In this case, the nanotubes are trapped in frozen water which is then sublimated. As a result the final powder is significantly less compact and, more important, the nanotubes can be easily dispersed with no apparent aggregates, thereby greatly enhancing their processability, e.g., they can be used to make homogeneous composites and fibers. Results from coagulation spinning from water-based dispersions of regularly-dried and freeze-dried nanotubes are compared. We also show that freeze-dried materials, in contrast to regularly-dried materials, can be dissolved in organic polar solvents using alkali-doped nanotubes. High resolution TEM and XRD analysis demonstrate that the nanotube structure and quality are not affected at the nanoscale by freeze-drying treatments.

Alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants 9. Effect of the spacer carbon number and temperature on the enthalpy of micellization.

The enthalpies of dilution of micellar solutions of several 12-s-12 dimeric surfactants of the alkanediyl-alpha,omega-bis(dodecyldi-methylammonium bromide) type, differing by the carbon number s of the alkanediyl spacer, and of dodecyltrimethylammonium bromide (DTAB) have been measured calorimetrically, in a range of concentrations extending from well below to well above the critical micelle concentration (cmc). The results permitted the determination of the enthalpy of micellization, DeltaH degrees (M), of the investigated surfactants at 25 and 35 degrees C. The values of DeltaH degrees (M) were always negative and became more negative as the temperature was increased. The plot of -DeltaH degrees (M) against s showed a shallow minimum at about s=5 and a large decrease of -DeltaH degrees (M) going from 12-2-12 to 12- 4-12. This effect has been attributed to the contribution to DeltaH degrees (M) of the hindered rotation of the dodecyl chains around the spacer C-C bond for 12-2-12. This hindrance is shown to rapidly disappear when s is increased from 2 to above 4. The specific heats of micellization, the free energies of micellization, and the entropies of micellization (DeltaS degrees (M)) have been calculated using the DeltaH degrees (M) values and the reported cmc and micelle ionization degree data for 12-s-12 surfactants and DTAB. For all surfactants the results show that TDeltaS degrees (M)>-DeltaH degrees (M), indicating an entropy-driven micellization.

Adsorption Mechanism of Conventional and Dimeric Cationic Surfactants on Silica Surface: Effect of the State of the Surface.

The aim of this study was to investigate the effect of the state of the silica surface and of the surfactant molecular structure on the adsorption of cationic surfactants onto silica. Thus, the adsorption of DTAB (dodecyltrimethylammonium bromide) and of the dimeric surfactant 12-2-12 (ethanediyl-1,2-bis(dodecyldimethylammonium bromide)) on raw silica (SiNa) and on HCl-washed silica (SiH) has been investigated under "free" system conditions. The amount of surfactant adsorbed (adsorption isotherm), the sodium ion and bromide ion concentrations and the pH in the equilibrated supernatant, and the silica particle electrophoretic mobility have been measured along the isotherms. The adsorption mechanisms of the two surfactants on the raw and washed silica are qualitatively similar. Nevertheless, important quantitative differences are observed which are all due to (i) the larger number of surface sites present at the surface of SiNa with respect to SiH and (ii) the larger ionic strength of the supernatant in SiNa/surfactant systems with respect to SiH/surfactant systems, due to the much larger amount of sodium ions released by SiNa upon surfactant binding. Thus, the amounts of surfactant adsorbed at the point of zero charge and at saturation of the silica particles, of sodium ions released by the surface and the decrease of critical micelle concentration (cmc) in the supernatant with respect to pure water are all larger for the raw silica than for the treated silica. For the four silica/surfactant systems investigated, the first adsorption step corresponds to the adsorption of individual surfactant ions on the negative sites of the silica surface. It is driven by electrostatic interactions and strongly dependent on the number of surface sites and ionic strength associated to the released ions. At the end of the first adsorption step, which is clearly seen with SiH/surfactant systems, the second adsorption step starts. This step is driven by hydrophobic interaction between surfactant alkyl chains and results in the formation of surface aggregates. The surfactant adsorption on the surface is shown to continue even after the cmc in the supernatant is reached. Copyright 1999 Academic Press.