Determination of the rheological properties of aqueous solutions of branched PEO‐PPO‐PEO copolymers. Confrontation with small‐angle neutron scattering studies.

The physico‐chemical properties of Tetronic^® 908 in aqueous solution have been explored on a wide range of temperature and concentration. This system presents interesting rheological properties depending on the polymer concentration in solution, and temperature. For weight percentage p comprised between 5% and 20%, the viscosity of the solution passes through a maximum. Small angle neutron scattering experiments show that the increase in the viscosity is due to the progressive aggregation of the chains. For higher weight percentages, the viscosity of the system diverges and the mixture becomes “gel‐like”. SANS studies of the same solution indicate that the micelles are organized in a cubic structure. We have developed a model which suitably describes the SANS curves of the system in the region where micelles are formed. It allows the calculation of several parameters (volume fraction of the micelles, size, composition). The evolution of these parameters with temperature and polymer concentration is detailed. Comparisons with models of literature are discussed.     

On Optimal Error Bounds for Derivatives of Interpolating Splines on a Uniform Partition

Based on Peano kernel technique, explicit error bounds (optimal for the highest order derivative) are proved for the derivatives of cardinal spline interpolation (interpolating at the knots for odd degree splines and at the midpoints between two knots for even degree splines). The results are based on a new representation of the Peano kernels and on a thorough investigation of their zero distributions. The bounds are given in terms of Euler–Frobenius polynomials and their zeros.     

Temperature and field dependence of stress induced leakage currents in very thin (<5 nm) gate oxides

We have studied the electric field and temperature dependence of stress induced leakage currents that appear in 3.8 and 4.7 nm thick SiO₂ oxides of metal oxide semiconductor structures after Fowler–Nordheim (FN) electron injections from the poly-Si gate and localized hot-hole injections from the p-Si substrate. Constant voltage or constant current stressing modes were used, which did not produce any difference in stress induced leakage currents (SILC) increase. A Schottky law apparently fits the field dependence of such currents in 4.7 nm samples, but the slope found in 3.8 nm thick oxides disagrees with the theoretical prediction. Moreover, the field dependence of the thermal activation energy found is much less than the Schottky prediction, which rules out the possibility of a thermoionic process to fully explain such currents in our samples. We show that a direct tunneling law, modified to account for a mechanism assisted by stress induced baricentric neutral defects, does correctly fit the oxide field dependence of these currents and is consistent with the observed thermal activation energy.     

Molecular orbitals and photoelectron spectra of some titanium(IV) organometallic compounds

The photoelectron spectra of some titanium(IV) organometallic compounds are reported, and the data and the bonding in the compounds are discussed with the aid of extended CNDO/2 calculations.     

Reduction—complexation des sulfures de phosphines par les fer-carbonyles

1-Phenyl-3,4-dimethylphosphole (L) yields the classic σ complex LFe(CO)₄ with Fe₂(CO)₉ and the unsual σ,π complex LFe₂(CO)₇ with Fe₃(CO)₁₂, whereas 1-t-butyl-3,4-dimethylphosphole (L′) with Fe₃(CO)₁₂ yields L′Fe₂(CO)₆ which belongs to a type already described in the literature. With Fe₂(CO)₉ at 85°C, the phosphole sulfide LS yields the two σ and σ,π complexes directly by reduction—complexation. This Fe₂(CO)₉ reduction—complexation process works only with phosphole and phospholene sulfides. However, with Fe(CO)₅ in great excess at 150°C, a general phosphine sulfide reduction—complexation procedure takes place. A study of the displacement of 1-phenyl-3,4-dimethyl-3-phospholene (L″) from its σ complex L″Fe(CO)₄ by trimethylphosphite has shown that L″ has a greater complexing ability toward iron than the phosphite, contrary to what could be expected from the work of Tolman on nickel complexes.