Anders Sand

Influence of colloidal interactions on pigment coating layer structure formation.

The consolidation of pigment coating layers was simulated using a three-dimensional particle dynamics model. The model included hydrodynamic interactions as well as colloidal force models and the Brownian motion. The impact of various colloidal model parameters on the z-direction solids profile development and coating layer thickness was investigated. Also, the influence of continuous (liquid) phase viscosity was tested. Particle systems resembling a polydisperse ground calcium carbonate (GCC) distribution were studied. Results show that a lower particle surface potential on pigments increased the thickness of the coating layer, while the electrostatic double layer thickness influenced the internal coating structure. An increased viscosity of the continuous phase slowed the consolidation down, but did not have a significant impact on the final microstructure. The work contributes to the understanding of the influence of colloidal system properties on the consolidation and structure development of coating layers. The results may aid in the understanding of the impact of chemical additives on coating layer structure formation.

A particle motion model for the study of consolidation phenomena

Abstract A three-dimensional method is described for simulating the dynamics of low particle Reynolds number colloidal suspensions at high solids content. The method is based on modified Stokesian dynamics and includes hydrodynamic interactions, colloidal interactions, steric interparticle forces from polymers and the Brownian motion. A free surface model, containing hydrodynamic and surface tension components, is also described. The applicability of the method ranges over a wide variety of particle systems, but in this work is tailored for the simulation of paper coatings. The particle suspension is represented by spherical rigid bodies of a given size distribution that are suspended in a Newtonian liquid. Numerical simulations performed using this technique enable the study of microscopic scale mechanisms, the characterisation of particle system constituents, an appreciation on microstructure development in time and the evaluation of macroscopic level properties of particle suspensions or consolidating systems. The method is evaluated in a number of test cases to illustrate its functionality and provide examples on the potential of its use in the simulation of paper coatings.