Comparison of colloidal effective charges from different experiments

We present measurements of effective charges in de-ionized aqueous suspensions of highly charged spherical latex colloids. For crystalline ordered samples the shear modulus G was measured using torsional resonance spectroscopy. It increases with increasing particle number density n. From fits of theoretical expressions based on a Debye-Huckel-type pair interaction potential, an effective charge Z(G)* was derived. On the other hand the effectively transported charge Z(sigma)(*) was determined from the n dependence of the suspension conductivity. Both effective charges are independent of n within experimental error. For most species they scale with the ratio of radius to Bjerrum length. For all species, however, Z(sigma)* is found to be systematically larger than Z(G)* by some 40%. (C) 2002 American Institute of Physics.