Study of the peak effect phenomenon in single crystals of 2H-NbSe2

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability effects and pinning.     

Solvation forces in asymmetrically charged electrolytes

Density functional theories of solvation forces in charged fluids which self-consistently include the effects of finitesized ions are extended to treat asymmetrically charged electrolytes. For a given electrolyte concentration both the electric potential and the solvation force between charged surfaces are seen to deviate from the results of the classical DLVO theory more markedly for asymmetrically charged electrolytes than for a 1 : 1 electrolyte.     

Phase coexistence overlap induced by steric interactions

Novel phase diagram calculations, in which the two phase-separated regions of polymer stabilized colloidal suspensions overlap under certain constraints of the reduction in the range of the steric interaction with increasing temperature, are presented. A phase diagram displaying liquid-vapour, liquid-solid and vapour-solid coexistence with two triple points, but no critical points is shown to exist in qualitative agreement with observations.     

Shaping Solid-State Supramolecular Cavities: Chemically Induced Accordionlike Movement of gamma-Zirconium Phosphate Containing Polyethylenoxide Pillars

The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space.     

Forces between surfaces in electrolyte solutions

Density functional theories of solvation forces in charged fluids are extended to treat electrolytes consisting of finitesized ions and neutral solvent particles. The resulting forces display pronounced oscillations whose magnitude is a strong function of the bulk density of the neutral species.     

A perturbation approach to the density functional theory of adsorption

A modified treatment of an exact density functional theory for non-uniform fluids due to Saam and Ebner is presented and a perturbation method of solution is proposed which avoids the need for a local density approximation. For hard-core fluids near a hard wall the equation for the equilibrium density reduces tothe wall-particle version of the RHNC approximation.