The hydrophobic effect (HE) is commonly associated with the demixing of oil and water at ambient conditions and plays the leading role in determining the structure and stability of biomolecular assembly in aqueous solutions. We propose an alternative view which may also be formulated as a maximization principle: The electrostatic noise acting on water molecules is maximized under the constraint that each water molecule on average maintains as many HBs as possible. In the presence of the solute the maximized electrostatic noise is a result of nonlocal fluctuations in the labile HB network giving rise to strong correlations among at least up to four water molecules.
COBISS.SI-ID: 5094426
A two-step procedure for preparation of LiMnPO4 with small particle size (15-20 nm) and embedded in a carbon matrix is presented. The crucial point that prevents excessive particle growth is the avoidance of lithium in the first firing step, so that small Mn2P2O7 particles embedded in carbon are obtained. Because of the carbon matrix, the Mn2P2O7 particles also cannot growin the second step, which involves lithiation and heating to 700 °C in argon. The prepared LiMnPO4 shows a high theoretical capacity (up to 95% of the theoretical value) and a stable cycling ()130 mAh/g, even after 100 cyclesat 55 °C and a rate of C/20). At room temperature and using the CC-CV mode, the performance is comparable to the best result shown in the literatureso far. Finally, the performance of LiMnPO4 is briefly compared withthat of LiFePO4-
COBISS.SI-ID: 4931610
CoCrMo orthopaedic alloy was oxidized potentiostatically in various simulated physiological solutions in order to reveal differences in the composition, thickness and structure of the surface layers formed as a function of solution composition. X-ray photoelectron spectroscopy, combined with angle-resolved measurements and depth profiling, was used for the purpose. The following simulated physiological solutions were used: (1) 0.14 M NaCl, (2) simulated Hanks physiological solution containing various inorganic salts, (3) simulated Hanks physiological solution containing an aliquot of synovial fluid retrieved at a revision operation, and (4) minimum essential medium containing various inorganic salts, amino acids and vitamins. No significant differences between alloy treated in these solutions were observed after oxidation in the passive region; the oxide films are a few nanometres thick and, except in NaCl solution, contain a small amount of calcium phosphate. After oxidation at a potential in the transpassive range however, the oxide thickness increases considerably due to incorporation of cobalt and molybdenum oxides. Further, the concentration of calcium phosphate increases. The layers formed in minimum essential medium and Hanks solution containing synovial fluid comprise nitrogen and carbon containing species. The addition of synovial fluid significantly affects the behaviour in Hanks solution.
Electrochemical characteristics, composition and surface morphology of vinyltriethoxysilane (VTES) coatings on aluminum were investigated. The silane coatings were deposited chemically, by immersion in 2 and 5 % VTES, and then cured at 100 °C during 10 or 30 min. Surface morphology of VTES films was analyzed by scanning electron microscopy, while the composition was investigated by X-ray photoelectron spectroscopy. The corrosion stability of silane coatings was determined by electrochemical impedance spectroscopy in 0.03 % NaCl. The results obtained were compared with the standardized analysis in the salt spray chamber. The percentage of the corroded area was determined by optical microscopy coupled with image analysis. The influence of VTES concentration and curing time on the corrosion stability of silane films on aluminum was shown. The highest corrosion stability was obtained for silane films deposited from 5 % VTES solution with 30 min curing, while the lowest stability was determined for silane films deposited from 2 % VTES solution with 10 min curing. Surface analysis suggests that the coatings with the highest corrosion stability are related to the intensive siloxane bonding (Si–O–Si), which is favored by deposition from more concentrated VTES solution.
COBISS.SI-ID: 25969703
We have shown by means of density functional theory calculations, how typical organic corrosion inhibitors—molecules that have the ability to remarkably slow down the corrosion of metals and alloys—interact with bare surfaces of various types of metals. As representative model systems, benzimidazole and benzotriazole inhibitors on iron, copper, and aluminum surfaces have been considered. It is found that bonding depends sensitively on the type of metal. On transition metals with open d-band the inhibitor molecules can chemisorb strongly either parallel to the surface with a pronounced pi-d hybridization or perpendicularly with unsaturated N atom(s) through sigma-molecular orbitals, whereas on transition metals with fully occupied d-band and on sp-metals the molecules weakly chemisorb only with the latter mode. In addition to neutral inhibitor molecules also inhibitors in deprotonated (anionic) and protonated (cationic) forms are considered, because many corrosion inhibitors possess acidic hydrogens as well as basic heteroatoms. It is shown that the chemisorptive bonding is far the strongest for deprotonated inhibitors and, moreover, that even protonated inhibitors may chemisorb, although such bonding is characteristic of more reactive metals. However adsorbed protonated inhibitors are likely to deprotonate on all considered metals, whereas further deprotonation from neutral to deprotonated form is more likely on more reactive metals.
COBISS.SI-ID: 26199591