Journal of Colloid and Interface Science 280 (2004) 264–275 www.elsevier.com/locate/jcis The shear viscosity of polyampholyte (gelatin) stabilized colloidal dispersions Lakshmi-narasimhan Krishnamurthy a , Eric C. Weigert a , Norman J. Wagner a,∗ , David C. Boris b a Center for Molecular and Engineering Thermodynamics, Department of Chemical Engineering, University of Delaware, Newark, DE 19716, USA b Coating Formulation Technology, Kodak Research Laboratory, Rochester, NY 14650, USA Received 22 March 2004; accepted 23 July 2004 Available online 26 August 2004 Abstract A micromechanical model for the zero shear viscosity of polyampholyte-stabilized colloidal dispersions based on the osmotic overlap potential is proposed and tested against model system measurements. This model relates the shear viscosity of polyampholyte-stabilized colloidal dispersions to the oncotic pressure of polyampholyte solutions through an interparticle potential and an effective hard-sphere scaling. The results of viscosity calculations based on independently measured parameters compare favorably to experimental measurements on model, silica dispersions stabilized with adsorbed photographic grade gelatin. The results support a direct link between the capacity of polyampholytes and polyelectrolytes to stabilize dispersions and control dispersion viscosity and their solution oncotic pressure. The model is also demonstrated to provide a master curve for literature data for the zero shear viscosity of polyampholyte stabilized colloidal dispersions.  2004 Elsevier Inc. All rights reserved. Keywords: Rheology; Gelatin; Polyampholyte; Colloidal stability; Electrosteric; Osmotic pressure; Tertiary electroviscous effect 1. Introduction The colloidal stability imparted by polyampholytes through steric stabilization is of fundamental importance in industries ranging from photography to pharmaceuti- cals [1,2]. The adsorption of polyampholytes on colloidal surfaces provides stability and affects the thermodynamic properties and flow behavior of these suspensions [3]. A thorough understanding of the microscopic colloidal forces imparted by adsorbed polyampholytes is necessary to accurately predict the stability characteristics and flow be- havior of these complexes [4–6]. This understanding will aid in the design and formulation of polyampholyte and poly- electrolyte stabilized colloidal and nanoparticle dispersions. Gelatin, a polyampholyte of biological origin, is well- suited for stabilizing dispersions of charged colloids due to features such as hydrophobic and hydrophilic moieties, its * Corresponding author. E-mail address: wagner@che.udel.edu (N.J. Wagner). ability to structure in solution, and its charge distribution, which can be controlled by pH and added salts [7,8]. These complementary properties present on a single molecule pro- vide multiple mechanisms for adsorption onto a wide variety of surfaces, which leads to a complex stability and flow be- havior for general mixtures of colloids and gelatin across broad ranges of solution properties. Of primary interest here are dispersions stabilized by gelatin adsorption, in contrast to those exhibiting bridging or depletion flocculation. It is generally postulated that the stability and rheology of these suspensions are dominated by the electrosteric repulsion arising from overlap of the adsorbed gelatin layers [2]. As the adsorbed layer proper- ties, in turn, depend on the electrochemical properties of the solution, the rheological response to the change in so- lution conditions is amplified by this nontrivial coupling of the electrochemical properties of the solution (salt, pH) and the adsorbed layer architecture, the so called “tertiary- electroviscous effect” [7,9]. The flow behavior of colloidal systems stabilized by gelatin has been studied and correlated to the properties of 0021-9797/$ – see front matter  2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2004.07.039