Approach to Estimation of Hamaker Constant as Taking Hofmeister Effects into Account

The Hamaker constant is an important material parameter for both the description of particle interaction and the prediction of colloidal stability. Existing methods based on the classic Derjaguin-Landau-Verwey-Overbeek theory ignore the Hofmeister effects and would derive flawed results. In this article, approaches to the g estimation of the Hamaker constant with and without consideration of the Hofmeister effects were, respectively, suggested, where the Hamaker constant was obtained on the basis of the mathematic relationship between electrostatic repulsive and van der Waals attractive interaction at the critical coagulation concentration (CCC) by using the dynamic light scattering technique. It indicated that the montmorillonite particles aggregation kinetics in the presence of Li+, K+, and Cs+ exhibited remarkable Hofmeister effects and the CCC values show: Li+ (277.2 mM) > K+ ( + (80.3 mM) > Cs+ (27.2 mM). Without consideration of Hofmeister effects, completely distinct Hamaker constants for the same material were obtained from aggregation kinetics of the three cations (6.70, 17.4, and 35.7 X 10(-20) J for Li+, K+, and Cs+ system, respectively). Obviously, it is unacceptable because the obtained Hamaker constant values should be the same for the same montmorillonite. In contrast, by taking the Hofmeister effects into account, consistent Hamaker constants (6.20, 6.09, and 6.75 X 10 -20 J for Li+, K+ and Cs+ system, respectively) could be derived and reached in good agreement with results reported in the literature. Our study proved that Hofmeister effects deeply affect the solid/liquid interface process of nano-/microsized particles and only by taking the Hofmeister effects into account could we get the reliable Hamaker constant and correctly describe particle interaction.