Acid‐Base‐Equilibria at Semipermeable Membranes, their Influence on pH‐Triggered Permeabilities

Polyacrylamide gels containing potassium oxalate (sodium oxalate) are brought into contact with aqueous solutions of Pb(NO3)2, CaCl2, SrCl2 and BaCl2 respectively. The electrolyte concentrations in the gel phase and in the solutions are varied systematically. There exists a system specific characteristic concentration c̃s below which advancing precipitation zones of PbOx, CaOx, SrOx, and BaOx (Ox: oxalate) within the gel are observed. Above c̃s the precipitation zones do not grow after advancing for about 2 mm maximally. Such precipitation zones have membrane properties (e. g. Impermeability to ions forming the precipitate, osmotic property). c̃s corresponds to a supersaturation ratio of the order 103. The experiments indicate that the precipitation zones with membrane properties are generated by homogeneous nucleation. – The kinetics of formation of oxalate precipitates in cellophane skins is studied by measurements of the membrane potential as function of time. In these systems precipitate is formed by interdiffusion of two solutions containing the appropriate ions. A system specific delay time Δtdel is observed after which the precipitation zones acquire membrane properties. It is found that this time is related to the rate of formation of precipitate which is a function of the solubility product and the square of electrolyte concentration. The precipitation zone acquires membrane properties as soon as the local concentration of precipitate has reached a value of the order 10−3 mol cm−3. The existence of the characteristic concentration c̃s and of the delay time Δtdel are interpreted in terms of an absorption charge model proposed by Hirsch‐Ayalon.

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Zones of Sparingly Soluble Inorganic Salts with Membrane Properties in Gels

Choi

Newrzella

Woermann

1988

Ber Bunsenges Phys Chem

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Acid‐Base‐Titration of a System Subdivided by a Semipermeable Membrane

Schlögl

1989

Ber Bunsenges Phys Chem

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Electric Field Effects on Long Living ZEKE States

et al. 1996

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The effect of an electric field on the overall intensity of the ZEKE spectrum and on the lifetime is discussed for very long living states detected by a pulsed field ionization delayed by several microseconds or more. It is shown that the presence of a dc electrical field can shorten the very long lifetimes and that it can also reduce the overall intensity of the very long living states. The decrease in the long lifetimes of the ZEKE states is complementary to the field-induced elongation of the shorter lifetimes. The discussion is based on quantum mechanical considerations and is illustrated by detailed computational studies, for a model problem, using an effective Hamiltonian formalism for an energy range just above the lowest ionization threshold. The model allows for coupling of different Rydberg series built on different excited states of the core where the continuum corresponds to the ground state. Predissociation is not allowed for in the model Hamiltonian. The trends are in accord with the observations of Held et al. as reported in the preceding paper, and the magnitude of the measured lifetimes of the ZEKE states (dozens of microseconds) are reproduced by the computations.

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Acid‐Base‐Equilibria at Semipermeable Membranes, their Influence on pH‐Triggered Permeabilities

Cited by 5 publications

References 9 publications

Zones of Sparingly Soluble Inorganic Salts with Membrane Properties in Gels

Zones of Sparingly Soluble Inorganic Salts with Membrane Properties in Gels

Acid‐Base‐Titration of a System Subdivided by a Semipermeable Membrane

Electric Field Effects on Long Living ZEKE States

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