Researchers using the XSD 12-ID-B and 8-ID-I beamlines at the APS are studying the structure, dynamic and rheology of bi-disperse suspensions of soft nanoparticles.
The team has found that dispersity in particle size has significant and unexpected effects on both the dynamics and rheology of the suspensions. The research is published in the journal Soft Matter.
Suspensions of small particles are of increasing scientific interest as model systems for studying structure, dynamics and phase transitions in atomic and molecular liquids. On imposition of pressure, thermal, or concentration fields, suspensions of micron-sized particles exhibit features such as disordered structure, jamming/glass transitions, aging and solid–liquid phase transitions traditionally found in molecular liquids. Recently, soft colloids have emerged as attractive model systems for molecular fluids because they are able to capture both excluded volume and more complex interactions in such fluids.
Yielding and flow transitions in bi-disperse suspensions of particles are studied using a model system comprised of self-suspended spherical nanoparticles. An important feature of the materials is that the nanoparticles are uniformly dispersed in the absence of a solvent. Addition of larger particles to a suspension of smaller ones is found to soften the suspensions, and in the limit of large size disparities, completely fluidizes the material. We show that these behaviors coincide with a speeding-up of de-correlation dynamics of all particles in the suspensions and are accompanied by a reduction in the energy dissipated at the yielding transition. We discuss our findings in terms of ligand-mediated jamming and un-jamming of hairy particle suspensions.
Akanksha Agrawala, Hsiu-Yu Yub, Samanvaya Srivastavaa, Snehashis Choudhurya, Suresh Narayananc and Lynden A. Archer, “Dynamics and Yielding of Binary Self-suspended Nanoparticle Fluids,” Soft Matter, Advance Article. DOI:10.1039/C5SM00639B, Published online May 29, 2015.