Potential Dorman

Equation (21.51) consists of two terms the first term is a weighted average of the Dorman potential i/ don and the surface potential ij/o- It should be stressed that only the first term is subject to the shielding effects of electrolytes, tending zero as the electrolyte concentration n increases, while the second term does not depend on the electrolyte concentration. In the limit of high electrolyte concentrations, all the potentials vanish and only the second term of the mobility expression remains, namely. 

Under separate headings, the nature and origin of other membrane potentials diffusion (concentration) potential adsorption (surface or interfacial) potential, distribution (outer) potential, Galvani (inner) potential, and Gouy (Dorman) potential will be considered. These potentials are... 

Another approach taken by Flory is to consider the polyelectrolyte coil xmder large ionic strength conditions as a phase subject to the conditions of the Dorman equilibrium. The coil will expand to reduce the Dorman potential, but the chain will resist due to the decreasing entropy. The coil is characterized by an effective volume, V, and the free salt concentration is c°. The condition of equilibrium is given by Morawetz as ... 

For highly porous and/or slightly charged membranes (or when the external salt concentration is much higher than the membrane fixed charge (c X, the Dorman potential can be neglected, and the membrane potential can be considered as a diffusion potential [39] ... 

The functionals can be simplified by integrating out the x,y) dimensions, parallel with the "electrode walls". Minimization of the chosen functional, with respect to the fluid particle densities then follows in the usual marmer, wherein electroneutrality is ensured via a Dorman potential. 

Hydrogels are crosslinked polymer networks with entrapped solvent. In the case of hydrogels containing polyectrolytes, in addition to solvent, ions and salt can be found in the gel as determined by the Dorman partition. This arises from the exclusion of ions of the same charge that sets a membrane potential at the gel/external electrolyte interface. 

From a survey of the literature in chemically modified electrodes [13], one can identify simple phenomenological models that have been very successful for the analysis of a particular aspect of the experimental data. Such models are, for instance, the Dorman partition model [24, 122], the Laviron [158], Albery [159] and Anson models [127] to account for the nonideal peak width, the Smith and White model for the interfacial potential distribution [129], and so on. Most of these models contain one or more adjustable parameters that give some partial information about the system. For example, the lateral interaction model proposed by Anson [127] provides a value for the lateral interactions between oxidized and reduced sites, but does not explain the origin of the interactions, neither does it predict how they depend on the experimental conditions or the polymer structure. In addition, none of these models provide information on the interfacial structure. 

Note that the whole domain (gel and solution) is solved together and thus no additional conditions prescribing the jump (e.g. obtained by the Dorman Eq. (7)) of the electric potential have to be given. In the regions outside the botmdary layers, the neutrality condition of (6) is fulfilled, i.e. A = 0. 

The situation changes in a dramatic way if salt is added to the polyelectrolyte solution. For instance, let us assume that a small amount of CINa or of any similar salt is added in cell I (or in cell If). Each CINa gives a Cle ion and a Na ion that is able to cross the membrane. The entropy of the system is larger if all the Na counter-ions are distributed as uniformly as possible, over both cells, but electrical neutrality has to be preserved. Consequently, the co-ions Cle are attracted into cell II. This is the Dorman effect. Simultaneously, the osmotic pressure diminishes in a spectacular way, and the same is true for the contact potential between the two cells. If a lot of salt was added, one would find again... 

In these experiments respiring mitochondria are observed to take up the K+ or Rb+ to give a high ratio of K+ inside to that outside and consequently a negative Ejj,. There are problems inherent in the method. The introduction of a high concentration of ion perturbs the membrane potential, and there are imcertainties concerning the contribution of the Dorman equilibrium (Eq. 8-5) to the observed ion distribution. ... 

Ray KK, Dorman S, Watson RDS. Severe hyperkalaemia due to the concomitant use of salt substitutes and ACE inhibitors in hypertension a potentially life threatening interaction. J Hum Hypertens (1999) 13, 717-20. 

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