Dynamic solubility limits in nanosized olivine LiFePO4

Because of its stability, nanosized olivine LiFePO(4) opens the door toward high-power Li-ion battery technology for large-scale applications as required for plug-in hybrid vehicles. Here, we reveal that the thermodynamics of first-order phase transitions in nanoinsertion materials is distinctly different from bulk materials as demonstrated by the decreasing miscibility gap that appears to be strongly dependent on the overall composition in LiFePO(4). In contrast to our common thermodynamic knowledge, that dictates solubility limits to be independent of the overall composition, combined neutron and X-ray diffraction reveals strongly varying solubility limits below particle sizes of 35 nm. A rationale is found based on modeling of the diffuse interface. Size confinement of the lithium concentration gradient, which exists at the phase boundary, competes with the in bulk energetically favorable compositions. Consequently, temperature and size diagrams of nanomaterials require complete reconsideration, being strongly dependent on the overall composition. This is vital knowledge for the future nanoarchitecturing of superior energy storage devices as the performance will heavily depend on the disclosed nanoionic properties.     

P-stable Obrechkoff methods of arbitrary order for second-order differential equations

Following the ideas of Ananthakrishnaiah we develop a family of P-stable Obrechkoff methods of arbitrary even order. The coefficients of these methods follow from a recursive algorithm. It is also shown that the stability functions of the thus obtained methods can be expressed as Padé approximants of the exponential function with a complex argument. A numerical example is given to illustrate the performance of the methods.     

Energy transport in plasma etching of nanoporous dielectric materials

A Monte Carlo routine was developed to simulate the motion and energetics of ions in the pores of a xerogel material under plasma etching conditions. The simulation included the effects of an applied electric field and input conditions for the pore as a function of pressure and applied voltage in the plasma reactor. We were interested in the ion energy in a pore, the ion penetration depth and the effect of ion energy on etching.At low pressures the nanoporous material etches faster than dense silicon dioxide. This is to be expected given the decrease in density and increase in surface area that arises due to the porosity. However, as the pressure is increased, the etch rate decreases dramatically and, eventually, the dense oxide may etch faster than the porous material. CHF₃ was used as the etchant gas and, for this gas, we believe this behavior to be controlled by the ion energy and energy transport in the pores of the xerogel material. As the pressure in the plasma reactor is increased, the incoming ions switch over from etching activation to polymerisation activation. This agrees with the observed crossover in etch rate seen experimentally and with the cessation in etching as pressure is increased. The switch is affected by pore roughness and correlates with the average ion energy in the pore.     

Addition–substitution competition in liquid-phase chlorinations

The rate constants of liquid-phase hydrogen abstraction by chlorine atoms from 1,2-C₂H₄Cl₂ relative to those of addition to C₂HCl₃ and to C₂Cl₄ and to that of hydrogen abstraction from cyclohexane have been measured between 250 and 345°K. Assuming a zero activation energy for the addition reactions permits one to calculate the corresponding values for the liquid-phase hydrogen abstraction from the chlorinated ethanes. These values are discussed and compared with the gas-phase data.     

Hydrogen-bond quenching of photodecarbonylation in the solid state and recovery of reactivity by co-crystallization

Intermolecular H-bonding between C=O (ketone) and HO (4'-hydroxyphenyl) quenches photodecarbonylation of 2,2,4,4-tetramethyl-1,3-di(4'-hydroxyphenyl)acetone 1 in the crystalline solid state, its reactivity is recovered by co-crystallization with the small organic molecule 4,4'-bicyclohexanone.     

Single-crystal-to-single-crystal E-->Z and Z-->E isomerizations of 3-chloroacrylic acid within the nanocavities of a supramolecular framework

Single-crystal-to-single-crystal E-->Z and Z-->E photo-isomerizations of 3-chloroacrylic acid (HClA) take place with full retention of the crystal lattice in the framework cavities of the supramolecular crystals CECR.HClA.2MeOH.1.5H(2)O (CECR = C-ethylcalix[4] resorcinarene); their progress has been monitored as the reaction proceeds.     

Preservation of the injectivity of the Gauss map for general projections

Let X be a smooth irreducible quasi-projective variety of dimension n in P ^N with N ≥ 2n + 2. Let γ be its Gauss map, let be the embedding obtained from the general projection in P ^N and let γ′ be its Gauss map. We say that the general projection preserves the injectivity of the Gauss map if γ(Q) ≠ γ(Q′) implies γ′(Q) ≠ γ′ (Q′). We prove that this property holds in the following cases: N≥ 3n + 1; N ≥ 3n with n ≥ 2; N ≥ 3n−1 with n ≥ 4 and X does not contain a linear (n−1)-space. In case N = 3n−1 and X does contain a linear (n−1)-space (such smooth varieties exist) then the general projection does not preserver the injectivity of the Gauss map. This shows that there does not exist a straightforward kind of Bertini theorem for properties related to the Gauss map. The author is affiliated with the University at Leuven as a research fellow. This paper belongs to the FWO-project G.0318.06.     

Effects of surface curvature and surface chemistry on the structure and activity of proteins adsorbed in nanopores

The interactions of proteins with the surface of cylindrical nanopores are systematically investigated to elucidate how surface curvature and surface chemistry affect the conformation and activity of confined proteins in an aqueous, buffered environment. Two globular proteins, lysozyme and myoglobin, with different catalytic functions, were used as model proteins to analyze structural changes in proteins after adsorption on ordered mesoporous silica SBA-15 and propyl-functionalized SBA-15 (C(3)SBA-15) with carefully controlled pore size. Liquid phase ATR-FTIR spectroscopy was used to study the amide I and II bands of the adsorbed proteins. The amide I bands showed that the secondary structures of free and adsorbed protein molecules differ, and that the secondary structure of the adsorbed protein is influenced by the local geometry as well as by the surface chemistry of the nanopores. The conformation of the adsorbed proteins inside the nanopores of SBA-15 and C(3)SBA-15 is strongly correlated with the local geometry and the surface properties of the nanoporous materials, which results in different catalytic activities. Adsorption by electrostatic interaction of proteins in nanopores of an optimal size provides a favorably confining and protecting environment, which may lead to considerably enhanced structural stability and catalytic activity.     

Time-resolved Laue diffraction of excited species at atomic resolution: 100 ps single-pulse diffraction of the excited state of the organometallic complex Rh2(μ-PNP)2(PNP)2·BPh4

The polychromatic Laue technique has been applied in 100 ps delay synchrotron pump-probe experiments of the triplet excited state of a Rh(I) dinuclear complex. The observed contraction of the Rh-Rh distance of 0.154 (13) ? is less than predicted by a series of theoretical calculations, a difference attributed to the constraining effect of the crystal lattice.