The effects of particle shape, size, and interaction on colloidal glasses and gels

colloids;rheology;suspensions;shape anisotropy;glasses;Gels

Kramb, Ryan C.

关键词: colloids;    rheology;    suspensions;    shape anisotropy;    glasses;    Gels;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/18295/Kramb_Ryan.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Using multiple step seeded emulsion polymerization reactions, colloid particles of tunable shape are synthesized from polystyrene. In all, four particle shapes are studied referred to as spheres (S), heteronuclear dicolloids (hDC), symmetric homonuclear dicolloids (sDC), and tricolloids (TC). Two size ranges of particles are studied with approximate diameters in the range of 200-300nm and 1.1-1.3μm. The solvent ionic strength is varied from 10^-3M to 1M resulting in particle interaction potentials that range from repulsive to attractive. The effect of anisotropic shape is found to increase the glass transition volume fraction (phi_g) in good agreement with activated naïve Mode Coupling Theory (nMCT) calculations. Differences in fg and the linear elastic modulus (G_0’) due to particle shape can be understood in terms of the Random Close Packed volumefraction (phi_RCP) for each shape; phi_RCP−pih_g is a constant. In addition, a reentrant phasediagram is found for S and sDC particles with a maximum in the fluid state volume fraction found at weakly attractive interaction potential, in agreement well withtheoretical calculations. Nonlinear rheology and yielding behavior of repulsive and attractive spheres and anisotropic particles are examined and understood in terms of barriers constraining motion. The barriers are due to interparticle bonds or cages constraining translational or rotational motion. Yield stress has similar volume fractiondependence as G_0’ and a similar framework is used to understand differences due to particle shape and interaction. For larger particles, the effects of shape and interaction are studied with respect to dynamic yielding and shear thickening. The dynamic yield stress is found to increase with volume fraction while the stress at thickening is constant. The intersection of these indicates a possible jamming point below phi_RCP.