The dipole moment induced in the ion atmosphere of a macroion by application of a steady electrical field is calculated when both the applied field and the field of the macroion are small. The macroion is modeled as a rigid array of point charges in general configuration. Linearized transport and equilibrium equations are then solved analytically by Fourier transform analysis. In the absence of relative motion between macroion and solvent the moment is isotropic and proportional to the number of charges on the macroion. It varies inversely as the concentration of supporting salt. For a symmetrical salt (same charge but for sign on counterion and cohyphen;ion), the dipole moment vanishes, as the salt ions of one sign prevent polarization of the ions of opposite sign. For a general salt the moment does not vanish. If the counterion charge is the larger of the two salt ions, the induced moment is positive. It is negative if the cohyphen;ion has the larger charge. There is a clear sense in which the polarization ofcohyphen;ioncharge may be said to control this complex behavior. The polarizability tensor can be decomposed into tensors agr;Plintroduced by Fixman and Jagannathan lsqb;J. Chem. Phys.75, 4048 (1981)rsqb; and computed numerically by them for a cylindrical macroion in a nonlinear context (small applied field but macroion field of general magnitude). Comparison with their tabulated results suggests that the properties of these tensors in the range of short cylinders and large Debye lengths reflect linear behavior. When the relative motion of macroion and solvent is included in the linear analysis, the induced dipole moment becomes anisotropic (and hence, in particular, does not vanish for a symmetrical salt). The convective effect is similar to what was found by Fixman and Jagannathan.
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