Testing the Derjaguin approximation for colloidal mixtures of spheres and disks.
The depletion potential between two large hard spheres due to the presence of hard disks has been derived up to first order in the number density of disks by Piech and Walz [J. Colloid Interface Sci. 232, 86 (2000)] using the Derjaguin approximation. Using the generalized Gibbs equation, we compare this depletion potential to the exact solution up to first order in density. The Derjaguin approximation turns out to be surprisingly accurate; for aspect ratios smaller than 0.25 the error is less than 1%.
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Van 't Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute, Utrecht University, Padualaan 8, 3584CH Utrecht, The Netherlands.
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