Dorman equilibrium

When two coexisting phases are subjected to the condition that one or several of the ionic components cannot pass from one phase to the other, a particular type of equilibrium is set up, called a Dorman equilibrium. This type of ionic equilibrium is unique for ionic absorbents containing a fixed ion, and the isotherm describing such equilibria differs from the established Langmuir Freundlich and Bru-nauer, Emmett, and Teller types which are found for neutral species. 

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. ... 

This equilibrium is called the Dorman equilibrium. As a consequence of the requirement for electroneutrality, it follows that the total concentration of sodium ions outside the pores is equal to the concentration of chloride ions outside the pores. Also, inside the pores, the total concentration of sodium ions is equal to the concentration of the ion-exchange groups and the concentration of chloride ions. Equation (12.9) then becomes... 

For a polyelectrol3de gel, the charge interactions can be further added into the total chemical potentials according to Dorman equilibrium (Dorman and Guggenheim 1932), and one can obtain... 

Selective permeability of the capsule wall can lead to the establishment of a concentration gradient even for permeable solutes. Indeed, the presence of charged polymers exclusively either inside or outside the capsule contributes according to Dorman equilibrium in the distribution of all ions for which the shell is permeable. As a result, the small ions - including H and OH - may have a concentration gradient across the capsule wall, which can reach 4-5 pH units [45]. 

Reverse osmosis can be used for the separation of ions om an aqueous solution. Neutral membranes are mainly used for such processes and the transport of ions is determined by their solubility and diffusivity in the membrane (as expressed by the solute permeability coefficient, see eq V 162). The driving force for ion transport is the concentration difference, but if charged membranes or ion-exchange membranes are used instead of neutral membranes ion transport is also affected by the presence of the fixed charge. Teoreil [45] and Meyer and Sievers [46] have used a fixed charge theory to describe ionic transport through these type of systems. This theory is based on two principles the Nemst-Planck equation and Dorman equilibrium. 

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 ... 

Outstanding contributions in the field of colloidal chemlstiy have been made ty many other scientists, notabty Freundlich (phenomenon of adsorption). Donnan (Dorman equilibrium) Svedberg (sedimentation) and Einstein. 

Membrane potential (MP) gives information on the effective fixed charge associated with the bulk membrane phase, Dorman equilibrium between the membrane, and the adjacent solution, and the relative flow of ion through the membrane (ion transport number). 

Takashima Wet al (1997) Mechanochemoelectrical effect of polyaniline. Synth Met 85 1395 1396 Takashima W, Hayasi BC, Kaneto K (2007) Force detection with Dorman equilibrium in polypyrrole film. Electrochem Cormntm 9(8) 2056 2061... 

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