Isoelectric point space charge potential

It should be noted that the equilibrium conditions, Eqs. (2) and (6b), have the same form whether there is adsorbed surface charge or not. The magnitudes of (0) and Vc(0), however, will differ in these two cases because of the difference in the charge neutrality conditions, Eqs. (4) and (6a). An important consequence of the above consideration is that in the presence of adsorbed surface charge and constant x potential the space charge potentials Vs(0) and Fc(0) will not be zero at Cf/O), and in fact will not be zero at the same value of silver ion concentration in solution. The definition of isoelectric point therefore becomes ambiguous and it is necessary to define isoelectric point separately for each side of the interface corresponding to values of silver ion concentration in solution where F (0) = 0 or Fc(0) = 0. If only K (0) is measured, as in the electrophoresis experiment, the isoelectric point determined for F (0) = 0 does not ensure that Kc(0) is zero at the same time. 

Origin of Space Charge Potential and Isoelectric Point... 

From measurements of the space charge potential in solution the isoelectric point for silver chloride colloidal systems is found to be at 4... 

We might also note that for different choices of the parameter it is possible that the potential of the surface goes through zero at some finite temperature. This would be an intrinsic isoelectric point i.e., a temperature at which no space charge region exists. We shall discuss isoelectric points more fully in connection with doped crystals. 

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