Zeta Potential and the Electric Double Layer

When a charged colloid is placed in solution, the particle surface will influence the distribution of any ions in the surrounding fluid. Take, for 

FIGURE 5.17 The electric double layer, comprised of the Stern layer and the diffuse layer, is defined by the charge distribution around a charged colloidal particle in an ionic solution. 

Although charge distributions on complex particles such as proteins or other anisotropic particle shapes can occur, most particles can be approximated as spherically symmetrical with a uniform charge distribution. In this case, we can use the Henry equation to extract information about the particle  

p is defined as the electrophoretic mobility (particle velocity/ applied electric field) of a particle of radius a. C is the zeta potential, and q is the viscosity of the suspending solution./(A ), a) is Henry s function and depends on the Debye length (see Section 5.5.2). This variable represents the thickness of the electric double layer. 

In everyday measurements, estimates for Henry s function can be used to simplify analysis of the zeta potential. If the Debye length is small 

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