HPL-2011-108Computational and Experimental Study of Colloidal Stability of CuPc Aqueous Dispersions
Yan Zhao, Hou T. Ng, Eric Hanson, Jiannan Dong, David S. Corti, and Elias I. Franses
Abstract: Dispersions of copper phthalocyanine (CuPc) pigments are commonly used in digital printing. Their colloidal stability is essential for fulfilling desirable shelf life and achieving good printing performance. In order to understand the role of electrostatic and van der Waals forces in their stability, a combined computational and experimental study has been performed to investigate the stability of the CuPc aqueous dispersions. The Hamaker constant was calculated with a novel combination of an ab initio and an empirical methodology (J. Chem. Theory Comput., 2010, 6 (2), pp 491?498) to address the van der Waals attractions between the pigment particles. The calculated Hamaker constant was then employed in the DLVO (Derjaguin-Landau-Verwey-Overbeek) equation for dispersion stability simulation. The predictions allow comparisons with experimental colloidal stability study of CuPc aqueous dispersions (Langmuir, 2010, 26 (10), pp 6995?7006)). The effect of a nonionic surfactant on the dispersion stability of CuPc particles was taken into consideration. The experimental dispersion stability ratio (W) was determined from dynamic light scattering (DLS) data and based on the Rayleigh-Debye-Gans (RDG) scattering theory. The adsorption isotherms show that the adsorption density increases with increasing equilibrium concentration of surfactant up to the cmc, and then reaches a plateau. Desorption tests were conducted to determine the reversibility or irreversibility of adsorption. Preliminary results suggest that a portion of the surfactant adsorbs irreversibly. The comparisons reveal that electrostatic forces play a significant role in the dispersion stabilization.
External Posting Date: July 21, 2011 [Abstract]. Approved for External Publication - External Copyright Consideration
Internal Posting Date: July 21, 2011 [Fulltext]