Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session L37: Rheology II |
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Chair: Mona Kanso, Massachusetts Institute of Technology Room: 203AB |
Monday, November 20, 2023 8:00AM - 8:13AM |
L37.00001: Charge Regulation Modulates Polyelectrolyte Viscoelasticity J. Pedro de Souza, Jonghyun Hwang, Pia DiCenzo, Howard A Stone Polyelectrolytes exhibit unique viscoelastic responses compared to uncharged polymers owing to electrostatic interactions of charges along their backbone. While standard interpretations of polyelectrolyte viscoelasticity assume passive, fixed polyelectrolyte charge, the actual polyelectrolyte charge can depend sensitively on the solution conditions and the polyelectrolyte extension state. Clearly, the electrochemical coupling of charge adsorption reactions can lead to salt-specific, pH and salt concentration dependent rheological properties of polyelectrolyte solutions, beyond non-specific screened electrostatic interactions. In fact, some previous studies found salt-specific viscosity and relaxation times in polyelectrolyte solutions, although no quantitative model was presented to explain the observed trends. |
Monday, November 20, 2023 8:13AM - 8:26AM |
L37.00002: Recent Advances in Polymer Viscoelasticity from General Rigid Bead-Rod Theory Mona Kanso, Alan Jeffrey Giacomin, Myong Chol Pak One good way to explain the elasticity of a polymeric liquid, is to just consider the orientation distribution of the macromolecules. When exploring how macromolecular architecture affects the elasticity of a polymeric liquid, we find general rigid bead-rod theory to be both versatile and accurate. This theory sculpts macromolecules using beads and rods. Whereas beads represent points of Stokes flow resistances, the rods represent rigid separations. In this way, how the shape of the macromolecule affects its rheological behavior in suspension is determined. Our work shows the recent advances in polymer viscoelasticity using general rigid bead-rod theory, including advances applied on different viruses, including coronavirus. We calculate the rotational diffusivity of the viral suspensions, from first principles, using general rigid bead-rod theory. We do so by beading the spherical polymer, and then also by replacing each of its bulbous spikes with a single bead. We use energy minimization for the spreading and positioning of the spikes, charged identically, over the oblate or prolate capsids. We use general rigid bead-rod theory to explore the role of ellipticity on its rotational diffusivity, the transport property around which its cell attachment revolves. |
Monday, November 20, 2023 8:26AM - 8:39AM |
L37.00003: Data-driven and physics-aware microstructural modeling of flowing complex fluids Charles D Young, Patrick T Corona, Anukta Datta, Matthew E Helgeson, Michael D Graham Real flows used to process complex materials are almost always a mixture of rotational and extensional deformations that has a profound influence on the final microstructure of the material. In applications such as flexible electronics, this microstructure is key to performance. In contrast to flows generated in rheometers, real processing flows are never viscometric. Furthermore, we lack accurate first-principles models to relate flow, microstructure, and stress for many (most) complex fluids. Finally, spatially resolved microstructure measurements (i.e. scattering) are rarely available in complex flows. The present work uses new advances in experimental methodology and machine learning to circumvent these limitations. On the experimental side, we take advantage of scanning small-angle X-ray scattering (sSAXS) measurements in a fluidic four-roll mill (FFoRM). The FFoRM-sSAXS approach provides a large data set of microstructural measurements along diverse 2D Lagrangian deformation trajectories. We propose a machine learning framework in which FFoRM-sSAXS data is used to train a model which can predict the microstructural evolution of the fluid for an arbitrary deformation (velocity gradient tensor) history input. We first use autoencoders to learn a highly accurate reduced-order representation of the microstructure from scattering data. We then learn the time evolution of the microstructure in the reduced representation using a neural ODE framework that is constructed to automatically satisfy the key symmetry of microstructural evolution: material frame indifference. Finally, we learn a transformation from the state data embedded in the scattering intensity to the stress exerted on the fluid. The framework is tested with synthetic data for suspensions of Brownian rigid rods, using CFD results for flow kinematics and Brownian dynamics simulations for the microstructural evolution. |
Monday, November 20, 2023 8:39AM - 8:52AM |
L37.00004: Viscoelastic characterization of biomaterials: bridging the insights from acoustics and rheology Kausik Sarkar, Megan Anderson, Kartik V Bulusu, Michael W Plesniak, Lijie Grace Zhang The advent of tissue engineering has led to increased interest in the viscoelastic characterization of biomaterials. Gelatin methacrylate (GelMA) is a particularly promising biomaterial, largely due to its tunability, yet the impact of different preparation parameters on the material's viscoelasticity is not well understood. We characterized an array of GelMA scaffolds, fabricated by varying both GelMA concentration and ultraviolet (UV) light exposure time. Pulse-echo ultrasound techniques were used to non-invasively determine the sound speed and attenuation of the scaffolds, revealing significant dependence on GelMA concentration. Steady shear rate tests in addition to strain- and frequency-controlled oscillatory shear tests were performed using a rotational rheometer (Model: DHR-2, TA Instruments) to ascertain the levels of shear-thinning and viscoelasticity at a wide range of strain rates, oscillation frequencies, and amplitudes. The rheological tests show moduli dependence on both GelMA concentration and curing time. Together, this acoustic and rheological characterization can be used to inform the selection of GelMA scaffolds in tissue engineering applications, and this method can be used as a guide for characterizing other polymeric hydrogels. |
Monday, November 20, 2023 8:52AM - 9:05AM |
L37.00005: Predicting Extensional Behaviors of Colloidal Dispersions through Piecewise Power Law Models Naimul Hoque, Gordon Christopher Colloidal dispersions have great potential to be used as an ink for Direct ink writing 3D printing due to the ability to tune biological, mechanical, electrical, or optical properties via colloid selection, giving them a wide range of potential applications. However, such dispersions often have complicated rheological behaviors, and tuning one into a printable ink is a difficult process requiring balancing pumpability, extrudability, stability, and end use functionality. In this work, ink extrudability is characterized using the dripping on substrate method and compared to predictions derived from a piecewise power law model. |
Monday, November 20, 2023 9:05AM - 9:18AM |
L37.00006: Two-fluid rheology model for living polymer solutions Steven D Hudson, Paul Salipante, Michael Cromer What happens to wormlike micelle surfactant (living polymer) solutions at high shear rates? Applications of these fluids often require their significant shear thinning across a very wide range of shear. The viscosity and flow birefringence of surfactant solutions has been measured here across 7 decades of shear rate and 5 decades of viscosity, at temperatures ranging from 20 °C to 60 °C. In this temperature range, the resting equilibrium state of these solutions varies between well-entangled coils at low temperature and short dilute semiflexible rods at high temperature, on account of the kinetics of breaking and combination reactions. Under stress, the breaking reaction is accelerated and the average length decreases, and at high enough stress exhibits the short-dilute rod rheology. We have therefore developed a rheological model, based on a modified living-Rolie-Poly entangled-polymer rheology and a dilute reactive-rod rheology, with kinetic exchange between these states. This new model, whose parameters are determined from small-amplitude equilibrium measurements, finally accurately describes the observed non-equilibrium behavior. |
Monday, November 20, 2023 9:18AM - 9:31AM |
L37.00007: Using surface charge to control slip of yield-stress fluids at solid surfaces Elliott Sutton, Athanasios A Papaderakis, Sri Ganesh Subramanian, Robert A Dryfe, Finn Box, Claudio Pereira da Fonte, Anne Juel Many yield-stress fluids exhibit slip on solid surfaces. This significantly impacts their flow and can dramatically decrease pressure losses by reducing wall friction. Hence, promoting slip can be beneficial to reduce the energy consumption of industrial processes. It can also help to control the structure of certain products, improving their texture and taste. However, the physical origin of slip in yield-stress fluids remains poorly understood. In this talk, we demonstrate that the slip of a Carbopol microgel on a nanometrically smooth gold surface can be controlled by surface charge imposed electrochemically. When imposing negative charge at the gold surface, the formation of an electrical double layer which repels the negatively charged Carbopol network, results in a decreased yield threshold τs to overcome the adhesion of fluid particles to the wall, and a monotonic increase of the slip coefficient α. These parameters determine the increased velocity at the wall due to slip, us = α (τw - τs), where τw is the wall shear stress. We relate this charge-induced variation in slip to that observed for triboelectric coatings such as Teflon and PDMS. |
Monday, November 20, 2023 9:31AM - 9:44AM |
L37.00008: Viscoelastic bungee jetting induced by an impulsive force Kyota KAMAMOTO, Asuka Hosokawa, Yoshiyuki Tagawa This study investigated the jet behavior of viscoelastic fluids to implementation of next-generation printing technology such as three-dimensional printing. Viscoelastic fluids are used in next-generation technology and the bungee jet phenomenon that the jet returns back to the nozzle after ejection has been observed. This phenomenon is unique to viscoelastic fluids and requires clarification of the jet behavior for implementation of the next-generation printing technology. Therefore, we measured the displacement of the jet tip of the bungee jet in liquid ejection technology using impact. |
Monday, November 20, 2023 9:44AM - 9:57AM |
L37.00009: Bacteriophage Pf1 Complex Viscosity Mona Kanso, Vincenzo Calabrese, Amy Q Shen, Alan Jeffrey Giacomin, Myong Chol Pak Bacteriophages (phages) are viruses that attack bacteria, causing them to multiply. This attack requires phage orientation with respect to the bacterial receptor, a necessary condition for attachment. Since phages are not motile, they rely on their Brownian motion, and specifically its rotational components, to reorient. We focus specifically on Pf1 (the bacteriophage called pseudomonas phage Pf1), the phage about which much has been written, though whose rotational diffusivity determined from rheological measurements is not known. We compare general rigid bead-rod theory with intramacromolecular hydrodynamic interactions with our new measurements of the complex viscosity of an aqueous Pf1 suspension to arrive at the relaxation time. From this time, we get the central transport property for the Pf1 reorientation, the dimensionless rotational diffusivity, of , which differs within one order of magnitude from the fluorescence microscopy. At low frequency, we find good agreement of our theoretical predictions with both parts of our new bacteriophage Pf1 complex viscosity measurements. |
Monday, November 20, 2023 9:57AM - 10:10AM |
L37.00010: Fully synthetic mucous solutions reproduce rheological response of natural mucous Sumit Sunil Kumar, J. Brandon Mcclimon, Ilse B Nava-Medina, Adam B Braunschweig, Robert W Carpick, Sumit Sunil Kumar Mucus , a complex fluid produced by every living organism, has many essential functions including acting as an effective barrier layer in various bodily processes. The primary component of mucuses are mucins – highly glycosylated, linear polypeptides. However, a major concern with studying mucin properties is that mucus is often full of non-mucin constituents that affect the rheological response, and purifying mucus is difficult. In this study, fully synthetic mucins have been prepared and aqueous solutions of these mucins studied for comparison to the rheological response of natural mucin solutions. The purity and structural control of these synthetic mucins provide a model system where the mechanistic sources of the mucus' rheological response can be isolated and identified. Flow curves (viscosity vs. shear rate) and oscillatory measurements (storage and loss modulus vs. frequency) reveal shear thinning behavior similar to natural mucus, aging that is evocative of gelation, and a marked dependence on concentration. We will discuss the origins of these effects and their relevance for understanding mucus behavior more broadly. |
Monday, November 20, 2023 10:10AM - 10:23AM |
L37.00011: Computational rheology of a non-Newtonian fluid dripping onto a Substrate Gareth H McKinley, Konstantinos Zinelis, Thomas Abadie, Omar K Matar The Dripping-on-Substrate (DoS) technique is a conceptually-simple, but fluid dynamically complex, probe of the extensional rheology of low-viscosity, non-Newtonian fluids. In this technique, a single drop is left to flow from a syringe pump onto a partially-wettable solid substrate and stimulates the capillary-driven thinning of a liquid bridge. Monitoring the filament thinning process allows the extensional viscosity and relaxation time of the sample to be measured with a high degree of accuracy. Here, we present a computational rheology approach for understanding and optimising the operation of DoS, using an axisymmetric volume-of-fluid approach. The numerical simulations are performed with the open-source Eulerian code Basilisk in which the interface is captured accurately via an adaptively-refined grid. First, we study the effect of gravity and solid substrate wettability on the filament thinning and pinch-off. Furthermore, we examine the role of viscosity on the transition from initial inertia-capillary dynamics to the characteristic nonlinear elasto-capillary thinning of a viscoelastic fluid. We also investigate the role of polymer finite extensibility for weakly-elastic fluids and propose a fitting methodology based on the analytical solution for FENE-P fluids developed by Wagner et al. (2015) for improved determination of the relaxation time of the test fluid. Finally, we explore via simulations of DoS flow configurations the changes in the filament thinning profiles and pinch-off dynamics for strongly shear-thinning fluids such as Xanthan gum solutions. |
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