(734j) Combined Numerical and Experimental Study of Shear-Induced Aggregation Using Thermo-Responsive Polymer Nanoparticles

José Francisco Wilson (wilsonj@vscht.cz), Miroslav Soos (soosm@vscht.cz).

University of Chemistry and Technology Prague, Technicka 5, 16628 Prague 6, CZECH REPUBLI

Abstract

The properties of fractal aggregates depend mainly on the method of preparation and the material of the nano-particles used as building block. The method of the preparation influences the structure of the aggregates as well as the strength of the formed nano-material. In this work, fractal aggregates, were prepared by aggregation of polymeric primary nano-particles in a colloidal suspension. The stability of the suspension was compromised by addition of salt with concentration higher than the critical coagulation concentration (CCC) of the used polymer. The nano-particles structure consisted of a core composed by polymethyl methacrylate and a soft shell composed by combination of polymethyl methacrylate and polybutylacrylate. Due to significantly different glass transition temperature (Tg) of these polymers, the core act as a hard sphere, while the presence of polybutylacrylate in the shell gives the surface a soft character. By varying the system temperature, different softness of the particles were tested during aggregation experiments.

To further investigate the micromechanical behavior and kinetics of the micro clusters during aggregation and breakage, a numerical study was pursued using an in-house code including a novel interaction model that describes non-contact forces, adhesion as well as elastic, plastic and viscous deformation. Using the experimental data, the interaction model was calibrated and validated. The numerical model is capable to reproduce the increase of temperature in the experiments by decreasing the softness of the particles through a stiffness parameter during plastic deformation. The results showed a good agreement between experiments and simulations in terms of size and strength of the micro clusters for different temperatures and stirring speeds.

Keywords: Discrete Element Method (DEM), aggregation, nanoparticles, polymers, contact model, adhesion, plastic deformation, aggregation and breakup.