= Debye screening of colloid repulsion
{c}
{title2=$\kappa^2=2ne^2/(\epsilon k_BT)$}
For a symmetric monovalent reservoir with <number density> $n$ of each species, linearizing Poisson-Boltzmann theory gives the displayed inverse screening length. A planar potential decays exponentially; a spherical far field also has a geometrical inverse-distance factor. Increasing salt reduces the range of repulsion. Fixed surface potential, fixed charge and charge regulation need not give identical interaction amplitudes.
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