Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session ZC25: Suspensions: Rheology II |
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Chair: Jeffrey Morris, City College of New York Room: 251 C |
Tuesday, November 26, 2024 12:50PM - 1:03PM |
ZC25.00001: Rheology and Flow Visualization of Temperature-Responsive Volume-Phase Transition Microgels and their Implications in Geothermal Systems Aaron Baxter, Danni Tang, Adam Jacob Hawkins, Uli B Wiesner, Patrick Fulton, Jefferson W Tester, Frederic Blanc, Sarah Hormozi Geothermal energy remains a largely untapped indigenous resource for nations across the globe to increase their energy security and simultaneously reduce their carbon footprint. The introduction of enhanced geothermal systems has amplified the potential for geothermal extraction in previously overlooked regions, but also presents significant uncertainty with the inherent risk of premature thermal breakthrough. Previous simulations have suggested a temperature-responsive change in aperture to redirect flow around flow paths which are prematurely drained of their thermal energy can significantly boost system efficiency and life expectancy. Volume-phase transition microgels present a real world implementation of this change in aperture through their ability to reversibly swell and shrink in response to temperature changes. Rheometry combined with visualization techniques are performed to understand the microstructure, macro-rheological properties, velocity, and volume fraction. Particularly, we will show how yield stress varies as a function of volume fraction of soft hydrogels and temperature. |
Tuesday, November 26, 2024 1:03PM - 1:16PM |
ZC25.00002: The role of rolling friction in the rheology of a dense suspension of rings Jonathan Lalieu, Donald Lyle Koch, Sarah Hormozi Suspensions of rigid particles in viscous liquids are common in wide-ranging contexts (e.g., mudslides, drug delivery), and very few involve spherical solid particles. However, the effect of particle shape is often neglected when modeling dense suspensions. To address this knowledge gap, we argue that studying the rheological behavior of dense suspensions of non-Brownian rings provides a platform for understanding the striking role of shape in establishing nonlinear rheology. For these ring-shaped particles, a geometric resistance to rotation is introduced between the particles in the form of a rolling friction coefficient that can be tuned and is proportional to their aspect ratio. We report on the experimental investigation of a dense suspension of non-Brownian, square cross-section ring-shaped particles of controlled mean diameter and aspect ratio that we design and mass-produce through a photolithography technique. We use a microfluidic device to show that, in the absence of density difference between the particles and solvent, the rings have a preferred alignment with their neighbors and with the flow. Our rheological characterization shows a yield stress due to many particle contacts at low shear rates, whereas, at high shear rates, we observe a shear-independent viscosity diverging at a jamming volume fraction smaller than that of spherical particles. |
Tuesday, November 26, 2024 1:16PM - 1:29PM |
ZC25.00003: Abstract Withdrawn
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Tuesday, November 26, 2024 1:29PM - 1:42PM |
ZC25.00004: ABSTRACT WITHDRAWN
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Tuesday, November 26, 2024 1:42PM - 1:55PM |
ZC25.00005: A comprehensive rheological study of thermally activated suspensions of polymer-grafted silica nanoparticles Sotoodeh Rassouli, Mehryar Jannesari Ghomsheh, Nyalaliska W Utomo, Lynden Archer, Donald Lyle Koch, Sarah Hormozi This experimental study reveals the broad range of interesting rheological characteristics of suspensions of covalently grafted poly(ethylene glycol) methyl ether (mPEG) polymers on silica nanoparticles in the presence of a secondary solvent. The rheology of this system is governed by Brownian motion of the core particles and polymer-brush induced interactions. At small core volume fractions, these suspensions exhibit Newtonian rheology with a viscosity that increases with volume fraction similar to other well-studied low-Peclet number Brownian suspensions. With increasing the shear rate and particle concentration, the suspensions begin to shear thin as the hydrodynamic stresses are sufficient to drive overlap between the polymer brushes of neighboring particles. At large core volume fractions, these systems exhibit soft glassy rheology. In this case, the system has an apparent yield stress which we attribute to the free energy barrier arising as the mixture of solvent and tethered polymers tries to fill the interstices between a deformed array of cores. We measure the apparent yield stress in the polymer grafted suspension and observe the history dependent rheology occurring as thermal fluctuations aid their yielding. We also investigate the effect of changing the synthetic parameters (e.g.: grafting density, core volume fraction, solvent molecular weight, etc.) on the apparent yield stress of this class of materials. |
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