Heterogeneous Electrofreezing of Super-Cooled Water on Surfaces of Pyroelectric Crystals is Triggered by Trigonal Planar Ions

Electrofreezing experiments of super-cooled water (SCW) with different ions, performed directly on the charged hemihedral faces of pyroelectric LiTaO₃ and AgI crystals, in the presence and in the absence of pyroelectric charge are reported. It is demonstrated that bicarbonate (HCO₃⁻) ions elevate the icing temperature near the positively charged faces. In contrast, the hydronium (H₃O⁺) slightly reduces the icing temperature. Molecular dynamics simulations suggest that the hydrated trigonal planar HCO₃⁻ ions self-assemble with water molecules near the surface of the AgI crystal as clusters of slightly different configuration from those of the ice-like hexagons. These clusters, however, have a tendency to serve as embryonic nuclei for ice crystallization. Consequently, we predicted and experimentally confirmed that the trigonal planar ions of NO₃⁻ and guanidinium (Gdm⁺), at appropriate concentrations, elevate the icing temperature near the positive and negative charged surfaces, respectively. On the other hand, the Cl⁻ and SO₄²⁻ ions of different configurations reduce the icing temperature.     

Als Beitrag zur Kenntnis der Reaktionen unges?ttigter Ketone

Ohne Zusammenfassung     

Ion-specific hydration effects: Extending the Poisson-Boltzmann theory

In aqueous solutions, dissolved ions interact strongly with the surrounding water and surfaces, thereby modifying solution properties in an ion-specific manner. These ion-hydration interactions can be accounted for theoretically on a mean-field level by including phenomenological terms in the free energy that correspond to the most dominant ion-specific interactions. Minimizing this free energy leads to modified Poisson-Boltzmann equations with appropriate boundary conditions. Here, we review how this strategy has been used to predict some of the ways ion-specific effects can modify the forces acting within and between charged interfaces immersed in salt solutions.     

Children’s use of realistic considerations in problem solving: some English evidence

This is the second of two papers exploring children’s responses to an extended version of a division-with-remainder problem intended to elicit general rather than particular realistic considerations during mathematical problem solving. Responses to two problems are analyzed. The first is a ‘realistically’ contextualised item drawn from national tests in England whose ambiguities have been previously discussed (Cooper, 1992); the second is a version of this problem revised to encourage a wider range of realistic responses. In Cooper and Harries (2002), the responses of children at the end of their first year of secondary schooling were analyzed. Here the responses of children at the end of their primary schooling are analyzed and compared with the previous results. It is shown that many children, given suitable encouragement, are willing and able to enter into an extended form of realistic thinking during problem solving, although the original test item renders this invisible.     

Photoabsorption spectra of CF3I and thermally dissociated CF3I near the C 1s, I 3d and F 1s ionisation thresholds

We report soft X-ray total ion yield and angular-resolved ion yield spectra of CF₃I in the C 1s, I 3d and F 1s ionisation regions, and tentatively assign the observed electronic states. Anisotropy in ion yield is observed only for the C transition, indicating that the dipole moment for this transition is parallel to the C_3v. The effusive source of CF₃I is heated to 800 K to produce a mixture of CF₃ and I, and the resulting spectra are compared to those recorded at room temperature.     

Kolloidchemische Betrachtungen auf dem Gebiet des Schellacks und Kautschuks

Zusammenfassung Es wird der Begriff Aggregation und Desaggregation erörtert. Die Aggregation entsteht durch gegenseitige Adsorption zweier oder mehrerer disperser Phasen. Die Aggregate lassen sich zu einfachen dispersen Phasen durch Peptisation desaggregieren. Die Polymerisate werden durch Peptisieren nicht depolymerisiert. Diese Erörterungen finden ihre Stütze in Beobachtungen, welche bei den Zustandsänderungen des Schellacks und des Kautschuks gemacht sind.