SHEAR MODULUS TITRATION IN CRYSTALLINE COLLOIDAL SUSPENSIONS

We present the first direct experimental access to the actual surface charge number Z of colloidal particles under conditions of strong elec trostatic interaction. We further calculate a renormalized charge numb er Z(Z) using the modified DLVO approximation and the dependence of t he shear modulus G(Z) on the concentration of neutral electrolyte n(s ). The excellent agreement of predicted and measured values provides a n experimental verification of the renormalization concept under varia tion of the salt concentration. The link between the true surface char ge number and experimental results via Z is extended to the conductiv ity sigma(Z). On the basis of the number of dissociable surface group s N and numerical solutions of the nonlinearized Poisson-Boltzmann equ ation we further provide a qualitative model for incomplete dissociati on under conditions of overlapping double layers. (C) 1995 Academic Pr ess, Inc.