Complex Rheology Research Articles

Small-scale study of Debris-Flows Interactions with a Lateral Debris Basin and Crossings: The Manival Torrent case study

Small-scale models are useful tools to study the interactions between debris flows and structures and channels. Small-scale modelling of debris flows remains however complicated because of the complex rheology and scaling challenges of these geophysical processes. An on-going study of a debris basin and the downstream channel where two fords and a bridge are located is presented in this extended abstract. The studied torrent is the Manival catchment, located near Grenoble in France. We present the catchment features, the scientific questions studied, some preliminary calibration results describing the mixtures used to model debris flows as well as results from three debris-flood and two debris-flow runs. In essence, the model highlighted that the structure enable a large share of the bedload transport to pass downstream. Debris flows can be more or equally trapped depending on their rheology which controls the surges dynamics and the deposition slope in the debris basin.

The Influence of the Surface Chemistry of Cellulose Nanocrystals on Ethyl Lauroyl Arginate Foam Stability.

Guanidine-based surfactant ethyl lauroyl arginate (LAE) and cellulose nanocrystals (CNCs) form complexes of enhanced surface activity when compared to pure surfactants. The LAE-CNC mixtures show enhanced foaming properties. The dynamic thin-film balance technique (DTFB) was used to study the morphology, drainage and rupture of LAE-CNC thin liquid films under constant driving pressure. A total of three concentrations of surfactant and the corresponding mixtures of LAE with sulfated (sCNC) and carboxylated (cCNC) cellulose nanocrystals were studied. The sCNC and cCNC suspension with LAE formed thin films, with stability increasing with surfactant concentration and with complex rheological properties. In the presence of LAE, the aggregation of CNC was observed. While the sCNC aggregates were preferentially present in the film volume with a small fraction at the surface, the cCNC aggregates, due to their higher hydrophobicity, were preferentially located at film interfaces, forming compact layers. The presence of both types of aggregates decreased the stability of the thin liquid film compared to the one for the LAE solution with the same concentration. The addition of CNC to LAE was critical for foam formation, and foam stability was in qualitative agreement with the thin films' lifetimes. The foam volume increased with the LAE concentration. However, there was an optimum surfactant concentration to achieve stable foam. In particular, the very resistant foam was obtained with cCNC suspensions that formed the interfaces with a complex structure and rheology. On the other hand, at high LAE concentrations, the aggregates of CNC may exhibit antifoaming properties.

Application of a maritime CFD code to a benchmark problem for non-Newtonian fluids: the flow around a sphere

The ship’s resistance and manoeuvrability in shallow waters can be adversely influenced by the presence of fluid mud layers on the seabed of ports and waterways. Fluid mud exhibits a complex non-Newtonian rheology that is often described using the Herschel–Bulkley model. The latter has been recently implemented in a maritime finite-volume CFD code to study the manoeuvrability of ships in the presence of muddy seabeds. In this paper, we explore the accuracy and robustness of the CFD code in simulating the flow of Herschel–Bulkley fluids, including power-law, Bingham and Newtonian fluids as particular cases. As a stepping stone towards the final maritime applications, the study is carried out on a classic benchmark problem in non-Newtonian fluid mechanics: the laminar flow around a sphere. The aim is to test the performance of the non-Newtonian solver before applying it to the more complex scenarios. Present results could also be used as reference data for future testing. Flow simulations are carried out at low Reynolds numbers in order to compare our results with an extensive collection of data from the literature. Results agree both qualitatively and quantitatively with literature. Difficulties in the convergence of the iterative solver emerged when simulating Bingham and Herschel–Bulkley flows. A simple change in the interpolation of the apparent viscosity has mitigated such difficulties. The results of this work, combined with our previous code verification exercises, suggest that the non-Newtonian solver works as intended and it can be thus employed on more complex applications.

Optimisation of a High-Throughput Model for Mucus Permeation and Nanoparticle Discrimination Using Biosimilar Mucus.

High-throughput permeation models are essential in drug development for timely screening of new drug and formulation candidates. Nevertheless, many current permeability assays fail to account for the presence of the gastrointestinal mucus layer. In this study, an optimised high-throughput mucus permeation model was developed employing a highly biorelevant mucus mimic. While mucus permeation is primarily conducted in a simple mucin solution, the complex chemistry, nanostructure and rheology of mucus is more accurately modelled by a synthetic biosimilar mucus (BSM) employing additional protein, lipid and rheology-modifying polymer components. Utilising BSM, equivalent permeation of various molecular weight fluorescein isothiocyanate-dextrans were observed, compared with native porcine jejunal mucus, confirming replication of the natural mucus permeation barrier. Furthermore, utilising synthetic BSM facilitated the analysis of free protein permeation which could not be quantified in native mucus due to concurrent proteolytic degradation. Additionally, BSM could differentiate between the permeation of poly (lactic-co-glycolic) acid nanoparticles (PLGA-NP) with varying surface chemistries (cationic, anionic and PEGylated), PEG coating density and size, which could not be achieved by a 5% mucin solution. This work confirms the importance of utilising highly biorelevant mucus mimics in permeation studies, and further development will provide an optimal method for high-throughput mucus permeation analysis.

Aggregation controlled by condensate rheology

Biomolecular condensates in living cells can exhibit a complex rheology, including viscoelastic and glassy behavior. This rheological behavior of condensates was suggested to regulate polymerization of cytoskeletal filaments and aggregation of amyloid fibrils. Here, we theoretically investigate how the rheological properties of condensates can control the formation of linear aggregates. To this end, we propose a kinetic theory for linear aggregation in coexisting phases, which accounts for the aggregate size distribution and the exchange of aggregates between inside and outside of condensates. The rheology of condensates is accounted in our model via aggregate mobilities that depend on aggregate size. We show that condensate rheology determines whether aggregates of all sizes or dominantly small aggregates are exchanged between condensate inside and outside on the timescale of aggregation. As a result, the ratio of aggregate numbers inside to outside of condensates differs significantly. Strikingly, we also find that weak variations in the rheological properties of condensates can lead to a switch-like change of the number of aggregates. These results suggest a possible physical mechanism for how living cells could control linear aggregation in a switch-like fashion through variations in condensate rheology.

Thixotropic constitutive modeling of shear banding by boundary-induced modulus gradient in lamellar gel networks

To predict the complex rheology and shear-rate inhomogeneities of lamellar gel networks, we propose a simple thixotropic constitutive model with an elastoplastic stress and a smoothly decreasing modulus near a solid boundary, motivated by the analysis of the effect of confinement and shear flow on lamellae orientation near surfaces. We show that the model qualitatively captures the important features of the lamellar gel shear rheology observed in experiments [Datta et al., J. Rheol. 64(4), 851–862 (2020)]. These include thixotropic shear thinning that is intermediate between constant viscosity and constant stress, a power-law slow creep under small constant shear stress and abrupt transition to fast creep at higher stress, as well as partial recovery of strain upon stress removal. In addition, the model correctly predicts a gap-dependent rheology and roughly predicts the amplitude dependence of storage and loss moduli in oscillatory tests despite having only a single thixotropic time constant. Most importantly, the introduction of the modulus gradient enables the model to predict the unique shear-banding phenomenon of lamellar gel networks wherein a thin, fast-shearing band exists near the boundary that widens only slowly with increased apparent shear rate until a very high rate is reached, while the bulk moves as a plug [Datta et al., J. Rheol. 64(4), 851–862 (2020)]. We discuss the influence of a lower modulus near the boundary and its possible origin in the underlying lamellar structure of the material.

Modeling the rheological behavior of crude oil–water emulsions

During crude oil extraction, crude oil is often mixed with water, leading to the formation of water-in-oil emulsions. Since these emulsions pose severe flow resistance, such as higher pressure drops, due to their complex fluid rheology, it is important to have in our arsenal a rheological constitutive model that accurately predicts their rheological response. In the present work, we propose such a model wherein the emulsions are modeled as deformable volume-preserving droplets via the use of a determinant-preserving contravariant second-rank tensor. We use the generalized bracket formalism of non-equilibrium thermodynamics to make sure that the derived model is by construction thermodynamically admissible. An additional scalar structural variable is considered to allow the prediction of a yielding point, following previous work. The predictions of the new model are shown to be in very good agreement with available experimental measurements.

How Slab Age and Width Combine to Dictate the Dynamics and Evolution of Subduction Systems: A 3‐D Spherical Study

AbstractMany of the factors expected to control the dynamics and evolution of Earth's subduction zones are under‐explored in an Earth‐like spherical geometry. Here, we simulate multi‐material free‐subduction of a complex rheology slab in a 3‐D spherical shell domain, to investigate the effect of plate age (simulated by covarying plate thickness and density) and width on the evolution of subduction systems. We find that the first‐order predictions of our spherical cases are generally consistent with existing Cartesian studies: (a) as subducting plate age increases, slabs retreat more and subduct at a shallower dip angle, due to increased bending resistance and sinking rates; and (b) wider slabs can develop along‐strike variations in trench curvature due to toroidal flow at slab edges, trending toward a “W”‐shaped trench with increasing slab width. We find, however, that these along‐strike variations are restricted to older, stronger, retreating slabs: Younger slabs that drive minimal trench motion remain relatively straight along the length of the subduction zone. We summarize our results into a regime diagram, which highlights how slab age modulates the effect of slab width, and present examples of the evolutionary history of subduction zones that are consistent with our model predictions.

Editorial: theme issue on complex rheology in biological systems

Editorial: theme issue on complex rheology in biological systems

High‐Resolution Finite Fault Slip Inversion of the 2019 Ridgecrest Earthquake Using 3D Finite Element Modeling

AbstractThe 2019 Ridgecrest earthquake sequence manifested as one of the most complex fault surface ruptures observed in California in modern times. The M6.4 foreshock and M7.1 mainshock occurred on an intricate network of orthogonal and sub‐parallel faults resulting in observable surface displacement and surface rupture captured by geodetic data. Here we present the application of a high‐resolution 3D finite element model (FEM) approach to invert for the detailed fault slip of the entire sequence using complex rheology and fused coseismic Global Navigation Satellite System (GNSS) data with Sentinel‐1 differential interferometric synthetic aperture radar and pixel offset data. The heterogeneous FEM and the fused geodetic data set of pixel offsets, interferograms, and GNSS data results in our optimal inversion solution. This preferred solution is a complex, high‐resolution non‐planar slip model of both the M6.4 and M7.1 events that features three main regions of large slip (6.9+ m), with depths ranging from 2 to 10 km. The regions of slip are bounded by the mainshock hypocenter and the mainshock aftershocks and appear to be related to spatially varying rheological properties. We successfully reproduce a localized region of observed subsidence in the northern portion of the primary fault through the inclusion of a curved fault strand with a significant dip‐slip component. The curved fault strand is the site of our maximum slip of 7.4 m at a depth of 4.2 km. The results demonstrate a robust fit from a more complete, detailed model for the entire seismogenic zone with reasonable computational cost, providing new insights into the governing rheologic and structural processes.

Evaluation of constitutive models for shear-banding wormlike micellar solutions in simple and complex flows

Wormlike micellar solutions possess complex rheology: when exposed to a flow field, the wormlike micelles may orientate, stretch, and break into smaller micelles. Entangled wormlike micellar solutions exhibit shear banding characteristics: macroscopic bands with different local viscosities are organized and stacked along the velocity gradient direction, leading to a non-monotonic flow curve in simple shear. We present a systematic analysis of four commonly used constitutive models that can predict a non-monotonic flow curve and potentially describe the rheology of entangled wormlike micellar solutions with shear-banding characteristics: the Johnson–Segalman, the Giesekus, the thixotropic viscoelastic, and the Vasquez–Cook–McKinley (VCM) models. All four constitutive models contain a stress diffusion term, to account for a smooth transition between the shear bands and ensure a uniqueness of the numerical solution. Initially, the models are fitted to shear and extensional experimental data of a shear-banding wormlike micellar solution. Subsequently, they are employed to solve three non-homogeneous flows: the Poiseuille flow in a planar channel, the flow in a cross-slot geometry, and the flow past a cylinder in a straight channel. Each of these flows exposes the wormlike micellar solution to different flow kinematics (shear, extensional, and mixed), revealing different aspects of its rheological response. The predictive capability of each model is evaluated by directly comparing the numerical results to previously published experimental data obtained from microfluidic devices with corresponding flow configurations. While all the models can describe qualitatively the characteristic features observed experimentally in the benchmark flows, such as plug-like velocity profiles and elastic instabilities, none of them yields a quantitative agreement. Based on the overall performance of the models and also accounting for their differing numerical complexity, we conclude that the Giesekus model is at present the most suitable constitutive equation for simulating shear banding wormlike micellar solutions in flows that exhibit both shear and extensional deformations. However, the quantitative mismatch between model predictions and experiments with wormlike micellar solutions demand that improved constitutive models be developed in future works. • Comparison of popular constitutive models for wormlike micellar solutions. • Evaluation of their performance in rheometric and inhomogeneous shear flows. • Investigation of their predictions in extensional flows and elastic instabilities. • The models can only make qualitative predictions.

A method to quantify time-dependent yield stress build-up in mineral slurries

Mineral slurries can have very complex rheology which may not be evident in bench-scale mixing tests. On scale-up to large industrial stirred tanks, an unexpected stagnant layer sometimes forms at the surface. We hypothesize that this occurs due to build-up of yield stress when the fluid is at rest. This behavior can cause problems on scale-up, where insufficiently mixed regions of the tank contain a much larger volume of fluid and the residence time in these regions can be much longer than at the bench scale. To study this effect, a method for continuous torque measurements was developed to quantify rest time effects at the bench scale. Nickel laterite slurries (NLS) with a broad range of solids concentration (25.2–71.8 wt%) were used to test this new method. Concentric cylinder viscometry and vane rheometry were also used to measure the behavior of the test sample. Evidence for a complex mechanism of network build-up for rest times of two minutes and longer was found. Moreover, it was found that 45 wt% is the upper limit for assuming behavior which approximates Newtonian rheology in this nickel laterite slurry sample. Solids concentration greater than 60 wt% showed rapid build-up of yield stress and thixotropic behavior. The rest time experiments validated the scale-up hypothesis. The slurry concentration at which non-Newtonian behavior appears is in accordance with other rheological investigations of nickel laterite slurries.

Slurries of complex fluids: Rheology, microstructure and fluid mechanics

<h2>Abstract</h2> Slurries of complex fluids are suspensions of non-Brownian particles in complex fluids (e.g. shear thinning, shear thickening, yield stress and viscoelastic fluids). These materials exist all around us. Examples include the following: food products, hygiene products, mine tailings, concrete, fracturing fluids, shock absorbing materials, drilling muds and muds in mudslides, lava, and numerous others. As expected from their ubiquity, non-Newtonian slurries contribute significantly to the economy both positively and negatively. Therefore, even small increases in efficiency when processing slurries of complex fluids could make significant positive economic and environmental impacts. Obviously, a thorough understanding of the rheology and fluid mechanics of these materials in natural and industrial settings is essential to improving the efficiency of production. However, this is extremely challenging due to the complex rheology of the suspending fluids, the interaction of fluid and particle phases, and multiple-body and short-range interactions of particles. My presentation will introduce an array of experimental and modelling techniques that my research team uses to investigate rheological properties and fluid dynamical behaviour of the slurries of complex fluids. The goal is to establish a continuum framework and refine it through a series of microstructure investigations. I will discuss how our recent results can be used to address and resolve mixing and pumping problems in concrete industries and to maximizing petroleum reservoir production using hydraulic fracturing processes. Finally, open questions will be disclosed, which must be answered to build a firm foundation for a long-term contribution to the area of complex suspensions.

On the determination of a generalized Darcy equation for yield stress fluid in porous media

<h2>Abstract</h2> Flows of Non-Newtonian fluids have different applications in porous media. Indeed, slurries, colloidal suspensions, emulsions, foams or heavy oil which present complex rheologies are commonly injected in porous media for various applications (Oil recovery, hydraulic fracturing, soil consolidation, etc.) Among the large number of different non-Newtonian fluids an important class of behaviour is represented by the yield-stress fluids, viz. fluids that require a minimum of stress to flow. Yield stress fluids are usually modelled as a Bingham fluid or by the Herschel-Bulkley equation. In the present work, we initially use a Lattice-Boltzmann TRT scheme to determine the flow structure in a synthetic porous medium. We then determined a generalized Darcy equation by evaluating the flow for different applied pressure drops dP. As expected, one can determine a critical pressure drop dPc below which there is no flow. Above this threshold, we observe three different flowing regimes as function of the distance to the critical pressure dP-dPc. Regime I corresponds to the situation where the fluid is flowing in only one channel. Here, the relation between flow rate and pressure drop is given by the non-Newtonian Poiseuille law. During Regime II, an increase in pressure triggers the opening of new paths. The relation between flow rate and the difference in pressure to the critical yield pressure becomes quadratic. Finally, Regime III corresponds to the situation where all the fluid is sheared. In which case one has a linear relationship between the flow rate and the applied pressure. In this presentation, we will study the crucial importance of heterogeneities in these flow regimes. In particular, we will show that even if these regimes are the consequence of disorder, some statistical laws have exponents that are independent of disorder. Finally, we will propose different models, based on the pore network, in order to better understand the origin of theses exponents and the influence of the disorder.

Rheological properties of asphalt binder modified with waste polyethylene: An interlaboratory research from the RILEM TC WMR

Significant volumes of waste materials such as plastics is generated every year worldwide with a potentially harmful impact on the environment. At the same time, the demand for asphalt modifiers has seen an increase over the year with consequent higher costs for these types of additives. Therefore, combining large amounts of available waste plastics with asphalt binder as an extender or modifier would potentially improve the paving material properties while limiting the disposed waste. While several rheological studies have been performed in the past, they were restricted to single research efforts hindering a consistent comparison among the valuable results of these investigations. For this reason, the Task Group 1 of the RILEM Technical Committee 279-WMR established a research activity with 11 international institutions to conduct interlaboratory research to evaluate the possibility of using waste polyethylene (PE) as an additive in asphalt binder. The study addressed the combined impact of PE materials and experimental conditions on the rheological properties of asphalt binder. For this purpose, conventional tests (penetration value, softening point temperature, and Fraass breaking point temperature) and the linear viscoelastic characterization using the Dynamic Shear Rheometer (DSR) were adopted. An unaged pen grade 70/100 neat binder was selected as the reference binder; PE-pellets and PE-shreds, produced from the recycled waste polyethylene materials, were used as the polymer additives. A single content (5%) of PE-pellets and PE-shreds was used to blend the PE material with the reference binder (95%) and prepare the two PE modified binders. Results indicate that the use of plastic modifiers leads to an overall higher complex shear modulus and softening point temperature while decreasing the penetration value. Higher dispersion in the results, especially in phase angles, was observed for blended binders at high temperatures. The PE modified binders exhibited poor reproducibility among laboratories and a low level of repeatability. Such a scatter in the data could result from an uneven dispersion of plastic material at high temperatures. In contrast, plastic shapes and batches appeared to have a limited impact. Three different rheological behaviors, neat binder, modified binder, and complex modified binder, were visually identified among the interlaboratory results and based on a simple statistical analysis of variance. Further analysis of the data suggested that the Glover Rowe (G-R) parameter can be used as a sensitive tool to classify the rheological behaviors of PE modified binders. Further experimental evaluation on specific testing conditions, such as measurement gaps of DSR at high temperatures, is recommended to advance the understanding of their influence on the rheological behavior of PE modified binders.

Open-source finite volume solvers for multiphase (n-phase) flows involving either Newtonian or non-Newtonian complex fluids

Two new control volume solvers multiFluidInterFoam and rheoMultiFluidInterFoam are presented for the simulation of Newtonian and non-Newtonian n-phase flows (n≥2), respectively, fully accounting for interfacial tension and contact-angle effects for each phase. The multiFluidInterFoam solver modifies certain crucial aspects of the regular multiphaseInterFoam solver provided by OpenFOAM for Newtonian flows, improving its efficiency and robustness, but most importantly improving considerably its accuracy for surface tension driven flows. The new solver uses the volume-of-fluid (VOF) method based on the MULES method and artificial interface compression for the interface capturing, in combination with a suitable continuum surface force model; i.e. the interfacial tension coefficient decomposition method is employed to treat pairings of interfacial tension between the phases. VOF smoothing is also implemented by applying a Laplacian filter on the distribution of volume fractions, and the SIMPLEC algorithm is employed for the velocity–pressure coupling. The above algorithm has also been extended with the development of the rheoMultiFluidInterFoam solver which is capable of fully taking into account complex non-Newtonian effects (e.g. yield stress, viscoelasticity, etc.) of the involved liquids. To this end, the developed solver incorporates the RheoTool toolbox (Pimenta and Alves, 2017), utilizing a wealth of constitutive equations suitable for modeling different types of fluids with complex rheology. Our solvers are tested for both the implementation of the surface tension and of the constitutive equations in a wide range of different flow setups, considering typical benchmark two-phase and three-phase flows, such as the cases of dam break with an obstacle, spreading of a floating lens, a levitating drop, and a bubble rising in an ambient fluid; flows involving Newtonian, viscoplastic and viscoelastic liquids have been considered. Comparisons against analytical solutions or previously published numerical data are performed clearly demonstrating the capability of the new solvers to efficiently and accurately simulate interfacial tension dominated three-phase flows (and n-phase flows in general) for both simple and complex liquids.

Characterization of three-dimensional fractional viscoelastic models through complex modulus analysis and polar decomposition

Soft materials such as gels, elastomers, and biological tissues have diverse applications in nature and technology due to their viscoelastic nature. These soft materials often exhibit complex rheology and display elastic and viscous characteristics when undergoing deformation. In recent years, fractional calculus has emerged as a promising tool to explain the viscoelastic behavior of soft materials. Scalar constants are primarily used to quantify viscoelastic elements such as springs and dashpots. However, in three-dimensional (3D) space, not all materials show the same elastic or viscoelastic properties in all directions, especially under elastic/viscoelastic wave propagation (or anisotropy). Though previously reported studies on viscoelastic models have explained a power-law decay of the memory functions, none of them explicitly explained the 3D complex modulus through a matrix notation. In this paper, we present a mathematical formulation that employs tensor algebra and fractional calculus to derive the 3D complex modulus of Kelvin–Voigt, Maxwell, and other arrangements of viscoelastic models. The 3D complex modulus provides information about the elastic wave propagation in a media and can be used to explain anisotropy in different viscoelastic materials. Additionally, an advanced formulation of the moduli can improve the modeling in finite element analysis of 3D viscoelastic materials where discretization is vital for studying media of asymmetric shapes. Finally, we demonstrated a polar decomposition method to visualize viscoelastic tensors using the Green–Christoffel tensor and surface plots to represent the degrees of anisotropy and viscoelasticity in the Fourier domain when the medium is probed by a time-harmonic homogeneous plane wave.

Transport of Pseudomonas aeruginosa in Polymer Solutions

Bacteria often live surrounded by polymer solutions, such as in animal respiratory, gastrointestinal, and reproductive tracts. In these systems, polymer solutions are often exposed to fluid flow, and their complex rheology can affect the transport of chemical compounds and microorganisms. Recent studies have focused on the effect of polymer solutions on the motility of bacteria in the absence of fluid flow. However, flow can be a game-changer on bacterial transport, as demonstrated by the depletion of motile bacteria from the low-shear regions and trapping in the high-shear regions in simple fluids, even for flows as simple as the Poiseuille one. Despite the relevance of polymer solutions in many bacterial habitats, the effect of their complex rheology on shear-induced trapping and bacterial transport in flow has remained unexplored. Using microfluidic experiments and numerical modeling, we studied how the shear rate and the rheological behavior of Newtonian and non-Newtonian polymer solutions affect the transport of motile, wild-type Pseudomonas aeruginosa in a Poiseuille flow. Our results show that, in Newtonian solutions, an increase in viscosity reduces bacterial depletion in the low-shear regions at the microchannel center, due to a reduction in the bacterial swimming velocity. Conversely, in the non-Newtonian solution, we observed a depletion comparable to the buffer case, despite its zero-shear viscosity being two orders of magnitude higher. In both cases, bacterial swimming and polymer fluid rheology control the magnitude of bacterial depletion and its shear-rate dependence. Our observations underscore the importance of the rheological behavior of the carrier fluid in controlling bacterial transport, in particular, close to surfaces giving rise to velocity gradients, with potential consequences on surface colonization and biofilm formation in many naturally relevant microbial habitats.

Understanding the complex rheology of human blood plasma

Blood plasma (BP) is a borderline non-Newtonian fluid. Few studies have characterized the rheology of BP and even less focused on understanding its subtle viscoelastic traits, which were only somewhat recently acknowledged. We use passive microrheology to measure the bulk response of human plasma samples under shear at body and ambient temperatures. Evidence of subdiffusive behavior in the mean-squared displacement is observed at the highest frequencies probed, which we attribute to the stress relaxation of protein molecules or chains. Jeffreys-like complex shear moduli were computed thereof. The microenvironments of albumin, fibrinogen, and gamma-globulin solutions (key plasma proteins) were probed as well. Single proteins in an aqueous buffer showed no signs of viscoelasticity within experimental resolution. Conversely, mixed together, they appear to promote the same kind of short-term elastic behavior seen in plasma. All in all, a fresh look at the shear rheology of BP is presented.

Dynamics of alternating current electric field-assisted non-Newtonian droplet formation with geometry confinement.

Recently, microfluidic techniques have been widely applied for biomaterial droplet manipulations due to their precision and efficiency. Many biosamples such as deoxyribonucleic acid and blood samples are non-Newtonian fluids with complex rheology, which brings challenges in control over them. The electric field is characterized by fast response and excellent adaptation to control microscale fluid flow. Here, we systematically investigate the alternating current electric field-assisted formation of non-Newtonian droplet in a flow-focusing microchannel with different sizes of channel orifice. The dependencies of flow conditions, microchannel geometries and electric parameters on the dynamics of non-Newtonian droplet formation are thus elucidated. An effective capacitance electric model is developed to reveal and predict the interaction between the fluid flow and the electric field. Furthermore, the flow field of non-Newtonian droplet formation is captured via the high-speed microparticle image velocimetry system. The characteristics of the regimes of droplet formation and the influences of the channel orifice are revealed quantitatively. Our work offers elaborate references to the control of non-Newtonian droplet formation, which benefits a wide range of applications in biology and chemistry.