John Garner

Polyacrylamide from PolySciTech used in fundamental research on shear thickening/rheology

Blog Post created by John Garner on Jun 12, 2019

A fun experiment you can try at home is to mix 2 parts corn starch with 1 part water forming a colloidal suspension which flows easily under slight force but stiffens when exposed to a lot of force (shear thickening). This is a simple example of a non-Newtonian fluid (one in which the relationship between force and viscosity is not linear). Non-newtonian fluids of varying degrees of complexity have a wide array of uses both in industry and in medicine. Recently, researchers at University of Houston and Georgetown University used Polyacrylamide from PolySciTech (www.polyscitech.com) to test for the effects of colloidal attraction in non-Newtonian complex suspensions. This fundamental research holds promise for a wide variety of applications both industrial and biomedical. Read more: Park, Nayoung, Vikram Rathee, Daniel L. Blair, and Jacinta C. Conrad. "Contact Networks Enhance Shear Thickening in Attractive Colloid-Polymer Mixtures." Physical Review Letters 122, no. 22 (2019): 228003. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.228003

 

“ABSTRACT: Increased shear thinning arising due to strong attractive interactions between colloidal particles is thought to obscure shear thickening. Here, we demonstrate how moderate attractions, induced by adding a nonadsorbing polymer, can instead enhance shear thickening. We measure the rheology of colloidal suspensions at a constant particle volume fraction of ϕ = 0.40  with dilute to weakly semidilute concentrations of three polyacrylamide depletants of different molecular weights. Suspensions containing large polymer exhibit increased shear thickening and positive first normal stress differences at high shear stress, and increased heterogeneous fluctuations in the boundary stress. These results are consistent with a friction-based model for shear thickening, suggesting that the presence of large, extended polymers induces the formation of near-spanning networks of interparticle contacts.”

 

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