Importance of the Induced Dipole

1 through 2.7.3 have focused on permanent dipoles, p. As with neutrals, ions in an electric field develop an induced dipole, Pi , controlled by molecular (here ionic) polarizability. Then the total dipole, pt, is the vector sum of p and Pin. Except for homogeneous spheres (e.g., atomic ions), the polarizability and thus Pin are direction-dependent according to the polarizability tensor. For homogeneous nonspherical species, off-axis matrix elements are null and Pin is collinear with E but pin depends on the direction of E the polarizability becomes anisotropic. In general, ions are 

In many cases, pm is negligible compared to p. An example is typical proteins with sufficient p for ahgnment under reasonable FAIMS conditions (2.7.3). For macromolecules, one can estimate p-y based on the dielectric susceptibility of bulk material ( yi)  

FIGURE 2.32 Dynamic shape factor (a term for the relative cross section common in aerosol science) measured using DMA for PSL dimers with spheres of various diameters, as labeled. (From Zelenyuk, A., Imre, D., Aerosol Sci. TechnoL, 41, 112, 2007.) 

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