Understanding colloidal charge renormalization from surface chemistry: Experiment and theory

Abstract

In this paper we report on the charging behavior of latex particles in aqueous suspensions. We use static light scattering and acid-base titrations as complementary techniques to observe both effective and bare particle charges. Acid-base titrations'at various ionic strengths provide the pH dependent charging curves. The surface chemical parameters (dissociation constant of the acidic carboxylic groups, total density of ionizable sites and Stem capacitance) are determined from tits of a Stem layer model to the titration data. We find strong evidence that the dissociation of protons is the only specific adsorption process. Effective particle charges are determined by tits of integral equation calculations of the polydisperse static structure factor to the static light scattering data. A generalization of the Poisson-Boltzmann cell model including the dissociation of the acidic surface groups and the autodissociation of water is used to predict effective particle charges from the surface chemical parameters determined by the titration experiments. We find that the light scattering data are best described by a model where a small fraction of the ionizable surface sites are sulfate groups which are completely dissociated at moderate pH. These effective charges are comparable to the predictions by a basic cell model where charge regulation is absent. 0 I994 American Institute of Physics.

The charge of glass and silica surfaces

“…For some of the aforementioned interaction measurements [12,17] this approach is appropriate, in other cases it may provide a very rough upper limit for the surface charge. If, on the other hand, the counterions due to the charged surfaces give a non-negligible contribution to the overall ionic strength, they have to be considered explicitly, for instance within a cell model [26,27]. Here, we concentrate on the former case of "high salt" and adopt the Basic Stern model [28], which has been shown to accurately describe titration data [29] obtained in the this regime for nominally nonporous, fully hydrated silica particles [24,25].…”

Charge renormalization, effective interactions, and thermodynamics of deionized colloidal suspensions

“…The inflection point in the running effective charge of the macroion has been identified as another sensible boundary between free and bound counterions [36]. Yet another fruitful approach is to fit the effective one-component model (with a screened-Coulomb pair potential) to either the static structure factor measured in lightscattering experiments [14] or the pair distribution function computed in simulations of the primitive model [19,20,21,22,23]. A useful comparison of various criteria for defining effective charges is provided in ref.…”

“…Similar ideas were subsequently applied to colloidal suspensions by Alexander et al [13], who demonstrated that strong association of counterions can significantly renormalize spherical macroion charges. Numerous experimental studies of deionized aqueous suspensions of highly charged spherical latex particles [14,15,16,17], integral-equation calculations [18], and simulation studies of the primitive model [19,20,21,22,23] have since confirmed the effective charge as a physically important parameter in the one-component model of colloidal suspensions.…”

Nonlinear Poisson-Boltzmann theory of a Wigner-Seitz model for swollen clays

“…It should be stressed that counterion condensation is a well-defined concept only within the cylindrical geometry of an infinite, uniformly charged thin rod [9,10]. In all other geometries, effective valences Z ef f can only be defined within some phenomenological convention [11,12]. In the case of spherical charge-stabilised colloids some recent direct measurements of the effective pair potential between polyions in the bulk of a suspension point to the validity of the functional form and range of the DLVO potential, provided Z ef f is considered to be an adjustable parameter, varying within a physically reasonable range [13].…”