Approximate analytic expression for the electrophoretic mobility of a spherical colloidal particle

An approximate analytic expression for the electrophoretic mobility of a spherical colloidal particle in a symmetrical electrolyte solution is obtained, This mobility expression, which is correct to the order of the third power of the zeta -potential of the particle, considerably improves Henry's mobility formula (Proc, R, Sec. London Ser. A 133, 106(1931)) and has a much simpler form than similar mobility formulas expressed in powers of zeta derived by Overbeek (Kolloid-Beihefte 54, 287 (1943)) and by Booth (Proc, R, Sec. London Ser. A 203, 514 (1950)), Comparison with the exact computer calculation by O'Brien and White (J, Chem, Sec. Faraday Trans. 2 74, 1607 (1978)) shows that the obtained mobility formula is an excellent approximation, especially for small kappaa (where kappa is the Debye-Huckel parameter and a is the particle radius) in which region no other simple analytic mobility formulas are available than Henry's formula, which is correct to order zeta and is applicable only fair low zeta. (C) 2001 Academic Press.