MULTIION NERNST DISTRIBUTION POTENTIAL EQUATIONS - INTERFACIAL POTENTIALS AT EQUILIBRIUM LIQUID LIQUID AND MEMBRANE INTERFACES

This paper presents analyses of practical cases of multi-ion Nernst distribution potential equations, and gives tables of interfacial potential difference (pd) expressions. The form of pd expressions for mixtures of partitioning ions within the window is emphasized. The topic of blocking is investigated and the whole range of behavior, from simple salt distribution Nernst distribution potentials to blocked interfaces that obey the more familiar Nernst-Donnan equation, is covered. The relation between the two limits, through Donnan exclusion and Donnan failure, is shown. Examples of model systems are calculated and illustrated. The notion of a "potential window" and conditions for establishment of the window using strongly and weakly partitioning salts are indicated. The problem of defining reference partitioning species to establish a reference pd and an ideally non-polarizable interface is emphasized. Likewise, the conditions for an ideally polarizable liquid/liquid interface are mentioned. A new concept of "repartitioning" is explained to interpret effects of foreign, "inert" salt partitioning on a reference pd. Equilibrium, not steady state, pds at single non-classical interfaces are discussed here, but single interface systems are inevitably part of larger two-interface or three-interface systems. Factors determining rates of development of pds and some connections between equilibrium single interface and steady state total membrane potential differences are considered to explain a result, viz., steady state membrane pds, comprising two interfacial pds and intervening diffusion-migration pd, often have the same mathematical form as single equilibrium interfacial pds, but contain mobilities or diffusion coefficients as multiplying factors.