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Title:The effects of concentration, interaction, size distribution and shape anisotropy on rheology of colloidal mixtures
Author(s):Jiang, Tianying
Director of Research:Zukoski, Charles F.
Doctoral Committee Chair(s):Zukoski, Charles F.
Doctoral Committee Member(s):Schweizer, Kenneth S.; Higdon, Jonathan J.L.; Schroeder, Charles M.
Department / Program:Chemical & Biomolecular Engr
Discipline:Chemical Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Dynamic Arrest Transition
Binary Colloidal Mixtures
Abstract:This dissertation studies the rheological properties of dense colloidal mixtures. Particular interest is focused on the role of volume fraction and strength of interactions that lead to glass or gel formation. Variables studied include particle concentration, strength of attraction, particle size distribution, and particle shape, which have effects on dynamic arrest transitions, jamming conditions and steady flow properties of dense suspensions. A special attention is paid to changes in properties at volume fractions exceeding the dynamic arrest transitions and approaching maximum packing fractions. For mixtures of particles, dynamic state diagrams are constructed as functions of large particle volume fraction ratio and total particle volume fraction as particle interactions are varied. The main effort is focused on the system composed of spherical silica particles with different sizes (100nm-1μm) dispersed in low molecular weight polyethylene glycol (PEG) melts with molecular weight 400 and 2000. For this system we explore the impact of the polymer molecular weight on the dynamic arrest transition, linear elasticity, shear thickening, and yielding for both monomodal and bimodal particle size distributions. Data is reported showing a varied dynamic arrest transition volume fraction, weakened shear thickening behavior and augmented shear elasticity in higher molecular weight polymer melt (PEG2000) for single-component system and denoting a stronger particle-particle attraction in higher molecular weight polymer which cannot be a consequence of adsorbed polymer layer entanglement. For bimodal mixtures in PEG400, particles interact with excluded volume potentials and the dynamic arrest transition volume fraction is a non-monotonic function of large particle volume fraction ratio. The dynamic arrest volume fraction is strongly correlated with the maximum packing fraction for each mixture. The data show that rheological properties of dynamic arrested states diverge in a consistent way when approaching maximum packing fractions. When dispersed in PEG2000 where particles are attractive, the dynamic arrest volume fraction is a monotonic function of large particle volume fraction ratio, which is not correlated with maximum packing fraction. Flow properties at this condition are dominated by attractions. In a further study, the flow properties of suspensions of large (diameter~1μm) and small (diameter~300nm) polystyrene particles suspended in an aqueous electrolyte were investigated. Here two types of large particles were investigated: spheres and dumbbell shaped particles. Weak shape anisotropy of the large particles delays the dynamic arrest transition and decreases the viscoelasticity at fixed volume fractions in single-component systems, but enhances the dynamic arrests and alters the jamming conditions in binary mixtures compared to sphere mixtures with bimodal size distributions. A consistent understanding of rheology in dense suspensions is built up based on particle localization effects.
Issue Date:2013-05-24
Rights Information:Copyright 2013 Tianying Jiang
Date Available in IDEALS:2013-05-24
Date Deposited:2013-05

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