Linear Rheology Research Articles

Health Observation of the Capital Airport South Expressway Based on Improved MT-InSAR Technology

Objectives: The Airport South Expressway in China is built in a soft soil area, which may induce great hidden danger to airport traffic safety operations. Technology or Method: A new method to improve Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) technology, based on a novel time-series InSAR deformation model and an improved parameter estimation algorithm, is proposed for soft soil expressways monitoring. The functional relationship between the deformation and the creep parameters (viscosity and elastic modulus) based on the Maxwell model in one-dimensional linear rheology replaces the traditional InSAR linear model, and the creep physical parameters can be solved simultaneously in the solution process. The least-squares method with inequality constraints (LSIC) is induced to solve the unknown parameters. In total, 19 TerraSAR-X radar satellite images covering the South Expressway were utilized to validate the proposed method. The creep parameters for each pixel along the expressways and the time series deformation sequences from January 2012 to July 2014 were obtained. Results: As the results showed, the maximum settlement along the expressway was up to 125 mm, and the accuracy verification results showed that the modeling accuracy was 1.6 mm, with an improvement of 36.0% compared to the traditional linear model; the internal accuracy of the deformation results was 11.9 mm, accounting for 1.5% of the maximum deformation. Clinical or Biological Impact: Our method can provide data support and a reference for long-term health monitoring and early warning of infrastructure and traffic operation management in poor soil regions.

Phase transitions of aqueous solutions of Pluronic F68 in the presence of Diclofenac Sodium

In recent years, advancements in bioengineering and materials science have witnessed increasing interest in synthetic polymers capable of fulfilling various applications. Owing to their distinctive properties, Pluronics can be used as nano-drug carriers, to deliver poorly water-soluble drugs, and as model systems to study colloidal science by tuning amphiphilic properties. In this work, we investigated the effect of diclofenac sodium on the self-assembly and thermoresponsive crystallization of Pluronic F68 in water solutions, by employing experimental rheology and Nuclear Magnetic Resonance (NMR). We built a complete phase diagram as a function of temperature and concentration for 45 wt% Pluronic F68 with various amounts of diclofenac sodium in water. The morphological transitions were followed as a function of temperature via linear rheology. We extrapolated the transition temperatures – identifying distinct phases – as a function of the drug concentration and proposed an empirical model for their prediction. NMR analysis provided further information on the structural characteristics of the systems, shedding light on the interactions between F68 and diclofenac sodium. Although dealing with a pharmaceutical salt, the study is focused on a colloidal system and its interaction with a binding molecule, that is of general interest for colloidal science.

Microstructural and thermodynamic characterization of wormlike micelles formed by polydisperse ionic surfactant solutions.

For industrial applications of self-assembled wormlike micelles, measurement and characterization of a micellar material's microstructure and rheology are paramount for the development and deployment of new high-performing and cost-effective formulations. Within this workflow, there are significant bottlenecks associated with experimental delays and a lack of transferability of results from one chemistry to another. In this work, we outline a process to predict microscopic and thermodynamic characteristics of wormlike micelles directly from rheological data by combining a more robust and efficient fitting algorithm with a recently published constitutive model called the Toy Shuffling model [J. D. Peterson and M. E. Cates, J. Rheol. 64, 1465-1496 (2020) and J. D. Peterson and M. E. Cates, J. Rheol. 65, 633-662 (2021)]. To support this work, linear rheology measurements were taken for 143 samples comprising a common base formulation of commercial sodium lauryl ether sulfate, cocamidopropyl betaine, and salt (NaCl). The steady state zero shear viscosity evident in linear rheology was measured in duplicate via direct steady and oscillatory shear experiments. Fitting the collected data to the model, we found trends in the microstructural and thermodynamic characteristics that agree with molecular dynamics simulations. These trends validate our new perspective on the parameters that inform the study of the relationship between chemical formulation and rheology. This work, when implemented at scale, can potentially be used to inform and test strategies for predicting self-assembled micellar structures based on chemical formulation.

Structure, Dynamics, and Rheology of Realistic Gaussian-Core Fluids: Unexpected Anomalies and Their Macromolecular Origin

We experimentally investigate the structure, dynamics, and linear rheology of dendrimer solutions as a model system of Gaussian-core fluids and ultrasoft colloids, and compare the results with those obtained by the coarse-grained approach. In the overpacked regime, particles pack in a way similar to Bernal’s celebrated plasticine model. Meanwhile, the interparticle interaction displays a counterintuitive softening under densification. Such behaviors result in transport properties remarkably different from the predictions of the simple Gaussian-core model. Particularly, we find a strong coupling between the rearrangement of interparticle configuration and intraparticle dynamics. These unexpected observations demonstrate the decisive role of intraparticle complexity in the structure and dynamics of ultrasoft colloids.

The “solvent” effect of short arms on linear and nonlinear shear rheology of entangled asymmetric star polymers

This study examines the influence of the short arms in model asymmetric 3-arm star polymers, in which the short arm is unentangled while the other two long arms are entangled, on linear and nonlinear shear rheological behavior. As increasing the short arm length of the asymmetric star polymers, the linear viscoelastic rubber plateau decreases, indicating the relaxed short arms act as “solvent” that dilute the star polymers. This idea is examined by the relationship between the plateau moduli of polymer solutions GN(φ) and the corresponding polymer melts GN(1) for entangled linear polymers, GN(φ) = GN(1)φ1+α, where φ is the volume fraction of the polymer. The “solvent” effect of the short arms is also supported by the nonlinear rheology results showing weaker damping function and larger peak strain at stress overshoot. With the above clarification of the short-arm contributions, this work provides a guidance of molecular design for tuning linear and nonlinear rheology of star polymers.

Frequency varying rheology-based fluid–structure-interactions waves in liquid-filled visco-elastic pipes

This contribution proposes a new rheology-based model for water-hammer wave propagation in visco-elastic pipes. Using a long wavelength analysis and a generalized frequency-dependent Hooke-law for the stress/strain relation, the pressure/longitudinal stress coupled wave system is derived. In this general framework, a visco-elastic Fluid–Structure Interaction (FSI) four equations model is derived by having four visco-elastic kernels associated with the non-local time response of the visco-elastic solid. The explicit dependence of these kernels with the material creep function and the pipe dimension is found. Considering a general linear visco-elastic rheology, the four visco-elastic kernels, and the corresponding creep function are explicitly derived in frequency and time-domain versus four visco-elastic parameters. For a given set of boundary conditions, a general analytical solution for the pressure/stress water hammer wave is obtained in frequency domain. The model’s predictions are successfully compared with experimental measurements as well as with other models adjusted to the same experimental data set by calibrating the model’s parameter. The proposed model can be used in many other contexts with the specific ability to distinguish the intrinsic visco-elastic rheology from the considered pipe geometry and boundary conditions.

Periodic surface loading using GRACE data for a layered viscoelastic earth model based on a direct relationship between geoid and displacement

SUMMARY Loading theory is fundamental in explaining deformation resulting from surface mass changes. Although various theoretical methods, including the classical elastic loading theory by W. E. Farrell and I. M. Longman, have been proposed, a viscoelasticity-based theory may be required to address long timescale loading problems, such as annual and interannual deformation, as well as longer timescale loading effects. In this study, we use a semi-analytical approach to simulate the continuous periodic loading deformation of a viscoelastic, spherical, layered earth model with linear rheology profiles. We provide a series of formulas in the spectral domain for the spatiotemporal displacement, which establish connections between mass, geoid and displacement solely through the utilization of complex Love numbers and Stokes coefficients, thereby circumventing the need for viscoelastic Green's function. Using our newly proposed method, we investigate the viscoelastic loading deformation caused by annual cyclic mass loading, considering both steady-state creep and additional transient creep with a wide range of viscosities. The results indicate that when utilizing steady-state viscosity values constrained by GIA data, the viscoelastic effect is not evident in the annual cyclic load deformation. However, incorporating the Burgers model with transient creep mainly constrained by post-seismic deformation influences the amplitude and phase of the annual cyclic loading, highlighting the role of rheology. Furthermore, we observe that the horizontal displacement in periodic load deformation exhibits a higher sensitivity to the viscosity of the model compared to the geoid and vertical displacement, regardless of the rheological model used.

Linear viscoelasticity, nonlinear rheology and applications of polyethylene terephthalate vitrimers

AbstractTo enhance mechanical properties and processing performance of poly(ethylene terephthalate) (PET), it was upcycled to processable PET vitrimers with different crosslinking degrees by introducing dynamic network. The thermodynamics and linear viscoelasticity of PET vitrimers were explored by non‐isothermal crystallization, isothermal sweep, frequency sweep and stress relaxation after incorporation of network. In particular, rheology experiments are sensitive to network structure and bond exchange mechanism in vitrimers. The pseudo‐master curves show that relaxation processes are composed of three characteristic regions: Rouse‐type relaxation of network strands, rubbery plateau and terminal relaxation of network, which is consistent with reversible gelation (RG) model. Two distinct (flow and chemical reaction) activation energies, are obtained by time–temperature superposition principle due to different temperature dependences of two relaxation behaviors. In addition, nonlinear rheology of PET vitrimers was investigated by extensional flow and start‐up shear at the same Weissenberg number, and obvious strain hardening behavior were observed in all vitrimers. However, vitrimers with different crosslinking density exhibited distinct strain hardening trends as increase of extensional rate, corresponding to the ductility of material. On the basis of kinetics study, self‐repairing and welding properties are further quantitatively explored for industrial applications.

Bridging Heterogeneity Dictates the Microstructure and Yielding Response of Polymer-Linked Emulsions.

Soft materials possessing tunable rheological properties are desirable in applications ranging from 3D printing to biological scaffolds. Here, we use a telechelic, triblock copolymer polystyrene-b-poly(ethylene oxide)-b-polystyrene (SEOS) to form elastic networks of polymer-linked droplets in cyclohexane-in-water emulsions. The SEOS endblocks partition into the dispersed cyclohexane droplets while the midblocks remain in the aqueous continuous phase, resulting in each chain taking on either a looping or bridging conformation. By controlling the fraction of chains that form bridges, we tune the linear elasticity of the emulsions and generate a finite yield stress. Polymers with higher molecular weight (Mw) endblocks form stronger interdroplet connections and display a higher bridging density. Beyond modifying the linear rheology, the telechelic, triblock copolymers also alter the yielding behavior and processability of the linked emulsions. We examine the yield transition of these polymer-linked emulsions through large amplitude oscillatory shear (LAOS) and probe the emulsion structure through confocal microscopy, concluding that polymers that more readily form bridges generate a strongly percolated network, whereas those that are less prone to form bridges tend to produce networks composed of weakly linked clusters of droplets. When yielded, the emulsions consisting of linked clusters break apart into individual clusters that can rearrange upon the application of further shear. By contrast, when the systems containing a more homogeneous bridging density are yielded, the system remains percolated but with reduced elasticity and bridging density. The demonstrated ability of telechelic triblock copolymers to tune not only the linear viscoelasticity of complex fluids but also their nonlinear yield transition enables the use of these polymers as versatile and robust rheological modifiers. We expect our findings to therefore aid the design of the next generation of complex fluids and soft materials.

PyDSM: GPU-accelerated rheology predictions for entangled polymers in Python

Prior studies have extensively shown that the discrete slip-link model (DSM) accurately predicts the linear and nonlinear rheology of various entangled polymer systems. The only publicly available implementation of the DSM algorithm is written in the CUDA C++ programming language. In this work we discuss the implementation of the fixed slip-link model and the clustered fixed slip-link model in Python. Our work shows that Python can also utilize GPUs for fast quantitative rheological predictions. Our simulation code, named pyDSM, allows an easy-to-read and beginner-friendly approach for users wanting to utilize the efficiency of GPU computing while also enabling an open-source Python package that can easily couple or interact with other simulation or data analysis software. We demonstrate pyDSM's versatility by implementing MUnCH, a recently published algorithm that allows estimation of the statistical uncertainty in the autocorrelations for any time series data, properly accounting for the correlation in the data. An on-the-fly version of MUnCH is applied to calculate the uncertainty in the relaxation modulus and the chain center-of-mass mean squared displacement. Moreover, the uncertainty quantification in the relaxation modulus allows propagation of error through a multi-mode Maxwell fit to determine the uncertainty in the dynamic modulus. Lastly, as an example of a novel application of the pyDSM code we calculate the re-entanglement dynamics after cessation of flow which are fundamental to the weld quality in fused-filament 3D printing. Program summaryProgram Title: pyDSM – Discrete Slip-link Model (DSM) in Python for Fast Quantitative Rheology Predictions of Entangled PolymersCPC Library link to program files:https://doi.org/10.17632/v828b9cjp9.1Developer's repository link:https://github.com/jgethier/pyDSMLicensing provisions: GPLv3Programming language: PythonNature of problem: Predicting stress relaxation in entangled polymer systems is crucial for understanding the macroscopic properties of the material. Many existing models do not capture the physics of polymer entanglements in linear, star-branched, and other entangled polymeric systems. The discrete slip-link model has been shown to predict quantitatively the rheological behavior of polymers, but only one version of the model is publicly available using CUDA C++ programming.Solution method: We implement a less-detailed version of the discrete-slip link model to predict the linear and nonlinear rheology of entangled polymers in Python. Uncertainty in the predictions is implemented with the MUnCH algorithm. We implement GPU-based calculations for fast and accurate predictions of the linear and nonlinear rheology behavior, as well as re-entanglement dynamics after cessation of flow.

Evolution of flow reversal and flow heterogeneities in high elasticity wormlike micelles (WLMs) with a yield stress

The formation and evolution of a heterogeneous flow and flow reversal are examined in highly elastic, gel-like wormlike micelles (WLMs) formed from an amphiphilic triblock poloxamer P234 in 2M NaCl. A combination of linear viscoelastic, steady shear, and creep rheology demonstrate that these WLMs have a yield stress and exhibit viscoelastic aging, similar to some soft glassy materials. Nonlinear shear rheology and rheoparticle tracking velocimetry reveal that these poloxamer WLMs undergo a period of strong elastic recoil and flow reversal after the onset of shear startup. As flow reversal subsides, a fluidized high shear rate region and a nearly immobile low shear rate region of fluid form, accompanied by wall slip and elastic instabilities. The features of this flow heterogeneity are reminiscent of those for aging yield stress fluids, where the heterogeneous flow forms during the initial stress overshoot and is sensitive to the inherent stress gradient of the flow geometry. Additionally, macroscopic bands that form transiently above a critical shear rate become “trapped” due to viscoelastic aging in the nearly immobile region. This early onset of the heterogeneous flow during the rapidly decreasing portion of the stress overshoot differs from that typically observed in shear banding WLMs and is proposed to be necessary for observing significant flow reversal. Exploring the early-time, transient behavior of this WLM gel with rheology similar to both WLM solutions and soft glassy materials provides new insights into spatially heterogeneous flows in both of these complex fluids.

Molecular structure and linear-non linear rheology relation of rice starch during milky, dough, and mature stages

Immature rice has potential to be used as healthy food. The relation between molecular structure and rheological properties was investigated. The lamellar repeating distance (8.42–8.63 nm) and crystalline thickness (4.60–4.72 nm) were not different among stages indicating a complete lamellar structure even at early stage. The relative crystallinity was higher in dough (39.62 %) than milky (36.69 %) and mature starch (35.22 %) caused by molecular structure, amylose, and amylose-lipid complex. The short amylopectin branched chains (A and B1) in dough starch were easily entangled resulted in higher Payne effect and elastic dominant. Dough starch paste exhibited higher G′Max (738 Pa) than milky (685 Pa) and mature (645 Pa) starch. In a non-linear viscoelastic regime, small strain hardening was found in milky and dough starch. Mature starch showed the highest plasticity and shear thinning at high-shear strains as the long-branched chains (B3) microstructure was disrupted, disentangled, followed by chain orientation along shear.

Introduction to viscoelasticity and plasticity, and their relation to the underlying microscopic dynamics in soft matter systems

Understanding the rheological behavior of complex fluids, and in particular its relation to the dynamics of the elementary microscopic constituents, is one of the open challenges in soft matter science. In this contribution, we give a brief introduction to linear shear rheology and passive microrheology of soft amorphous materials, and we then focus on the transition to non-linearity during oscillatory rheology tests performed on soft glassy materials. These materials exhibit solid-like properties at rest, but they display characteristics of fluids when a sufficiently large shear is applied. Significant progress in understanding such ‘fluidization’ has been recently achieved by combining rheometry with techniques capable to capture the microscopic dynamics induced by shear, and in particular by oscillatory shear. We here summarize some of these achievements, as an introduction to the field for a non-expert reader.

Jamming to unjamming: Phase transition in cyclodextrin-based emulsions mediated by sodium casein

HypothesisCyclodextrin (CD) can spontaneously build up the solid particle membrane with CD-oil inclusion complexes (ICs) by a self-assembly process. Sodium casein (SC) is expected to preferentially adsorb at the interface to transform the type of interfacial film. The high-pressure homogenization can increase interfacial contact opportunities of the components, which promote the phase transition of the interfacial film. ExperimentsWe added SC by sequential and simultaneous orders to mediate the assembly model of the CD-based films, examined the patterns in which the films adopt phase transitions to retard emulsion flocculation, and studied the physic-chemical properties of the emulsions and films from the structural arrest, interface tension, interfacial rheology, linear rheology, and nonlinear viscoelasticities through Fourier transform (FT)-rheology and Lissajous-Bowditch plots. FindingsThe interfacial and large amplitude oscillatory shear (LAOS) rheological results showed that the films changed from jammed to unjammed. We divide the unjammed films into two types: one is SC dominated liquid-like film, which is fragile and related to droplet coalescence; the other is cohesive SC-CD film, which helps droplet rearrangement and retards droplet flocculation. Our results highlight the potential of mediating phase transformation of interfacial films to improve emulsion stability.

A Generalized Mechano-statistical Transient Network Model for Unravelling the Network Topology and Elasticity of Hydrophobically Associating Multiblock Copolymers in Aqueous Solutions

In this contribution, we unravel the transient network topology and elasticity of micellar networks formed by hydrophobically associating multiblock copolymers in aqueous solutions. Unlike studies on conventional triblock copolymers bearing hydrophobic blocks as end groups, our research focuses on alternating poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) multiblock copolymers having multiple hydrophobic PPO blocks along the chain. We adopt a combinatorics approach to extend and generalize the mechano-statistical transient network model developed by Annable et al. for telechelic triblock copolymers [ Journal of Rheology, 1993, 37, 695] to multiblock copolymers. The model allows one to predict the concentration dependent elasticity of networks formed by multiblock copolymers with known molecular characteristics by using knowledge of the micellar network microstructure. The spatial distribution of the hydrophobic nodes is inferred from Small-Angle X-ray Scattering (SAXS) by converting the structure factor to the radial distribution function. The number of closely neighboring micellar cores between which an elastic bridge can be formed (nm) is calculated by spherical integration of the radial distribution function up to a distance of the radius of gyration of an intermediate soluble PEO block. Using the evolution of nm with concentration as an input for the model, the predictions show good agreement with experimental elasticity data, as inferred from the plateau modulus in linear shear rheology. The network evolves from loop-dominated, poorly elastic with cross-linking nodes with low functionality at low concentrations to bridge-dominated, highly elastic with higher node functionalities at more elevated concentrations. It is anticipated that our generalized mechano-statistical transient network model can also be used for equally spaced, multisticker associating polymers forming networks by multifunctional interactions other than micellar aggregation.

Linear and nonlinear rheology of liberase-treated breast cancer tumors.

Extracellular matrix (ECM) rigidity has been shown to increase the invasive properties of breast cancer cells, promoting transformation and metastasis through mechanotransduction. Reducing ECM stiffness via enzymatic digestion could be a promising approach to slowing breast cancer development by de-differentiation of breast cancer cells to less aggressive phenotypes and enhancing the effectiveness of existing chemotherapeutics via improved drug penetrance throughout the tumor. In this study, we examine the effects of injectable liberase (a blend of collagenase and thermolysin enzymes) treatments on the linear and nonlinear rheology of allograft 4T1 mouse mammary tumors. We perform two sets of in vivo mouse studies, in which either one or multiple treatment injections occur before the tumors are harvested for rheological analysis. The treatment groups in each study consist of a buffer control, free liberase enzyme in buffer, a thermoresponsive copolymer called LiquoGel (LQG) in buffer, and a combined, localized injection of LQG and liberase. All tumor samples exhibit gel-like linear rheological behavior with the elastic modulus significantly larger than the viscous modulus and both independent of frequency. Tumors that receive a single injection of localized liberase have significantly lower tumor volumes and lower tissue moduli at both the center and edge compared to buffer- and free liberase-injected control tumors, while tissue viscoelasticity remains relatively unaffected. Tumors injected multiple times with LQG and liberase also have lower tissue volumes but possess higher tissue moduli and lower viscoelasticities compared to the other treatment groups. We propose that a mechanotransductive mechanism could cause the formation of smaller but stiffer tumors after repeated, localized liberase injections. Large amplitude oscillatory shear (LAOS) experiments are also performed on tissues from the multiple injection study and the results are analyzed using MITlaos. LAOS analysis reveals that all 4T1 tumors from the multiple injection study exhibit nonlinear rheological behavior at high strains and strain rates. Examination of the Lissajous-Bowditch curves, Chebyshev coefficient ratios, elastic moduli, and dynamic viscosities demonstrate that the onset and type of nonlinear behavior is independent of treatment type and elastic modulus, suggesting that multiple liberase injections do not affect the nonlinear viscoelasticity of 4T1 tumors.

Adjoint Q tomography with central-frequency measurements in viscoelastic medium

SUMMARY Accurate Q (quality factor) structures can provide important constraints for characterizing subsurface hydrocarbon/water resources in exploration geophysics and interpreting tectonic evolution of the Earth in earthquake seismology. Attenuation effects on seismic amplitudes and phases can be included in forward and inverse modellings by invoking a generalized standard linear solid rheology. Compared to traditional ray-based methods, full-waveform-based adjoint tomography approach, which is based on numerical solutions of the visco-elastodynamic wave equation, has the potential to provide more accurate Q models. However, applications of adjoint Q tomography are impeded by the computational complexity of Q sensitivity kernels and by strong velocity-Q trade-offs. In this study, following the adjoint-state method, we show that the Q (P- and S-wave quality factors QP and QS) sensitivity kernels can be constructed efficiently with adjoint memory strain variables. A novel central-frequency difference misfit function is designed to reduce the trade-off artefacts for adjoint Q tomography. Compared to traditional waveform-difference misfit function, this new central-frequency approach is less sensitive to velocity variations, and thus is expected to produce fewer trade-off uncertainties. The multiparameter Hessian-vector products are calculated to quantify the resolving abilities of different misfit functions. Comparative synthetic inversion examples are provided to verify the advantages of this strategy for adjoint QP and QS tomography. We end with a 3D viscoelastic inversion example designed to simulate a distributed acoustic sensing/vertical seismic profile survey for monitoring of CO2 sequestration.

Temporal variations in plume flux: characterizing pulsations from tilted plume conduits in a rheologically complex mantle

SUMMARY Along age-progressive hotspot volcano chains, the emplacement rate of igneous material varies through time. Time-series analysis of changing emplacement rates at a range of hotspots finds that these rates vary regularly at periods of a few to several tens of millions of years, indicative of changing melt production within underlying mantle plumes. Many hotspots exhibit at least one period between ∼2 and 10 Myr, consistent with several proposed mechanisms for changing near-surface plume flux, and thus melting rate, such as small-scale convection, solitary waves and instability formation in tilted plume conduits. Here, we focus on quantifying instability growth within plumes tilted by overlying plate motion. Previous studies using fluids with constant or temperature-dependent viscosity suggest that such instabilities should not form under mantle conditions. To test this assertion, we use a modified version of the finite element code ASPECT to simulate 400 Myr of evolution of a whole-depth mantle plume rising through the transition zone and spreading beneath a moving plate. In a 2-D spherical shell geometry, ASPECT solves the conservation equations for a compressible mantle with a thermodynamically consistent treatment of phase changes in the mantle transition zone and subject to either a temperature- and depth-dependent linear rheology or a temperature-, depth- and strain-rate dependent non-linear rheology. Additionally, we examine plume evolution in a mantle subject to a range of Clapeyron slopes for the 410 km (1–4 MPa K–1) phase transitions. Results suggest that plume conduits tilted by >67° become unstable and develop instabilities that lead to initial pulses in the transition zone followed by repeated plume pulsing in the uppermost mantle. In these cases, pulse size and frequency depend strongly on the viscosity ratio between the plume and ambient upper mantle. Based upon our results and comparison with other studies, we find that the range of statistically significant periods of plume pulsing in our models (∼2–7 Myr), the predicted increase in melt flux due to each pulse (3.8–26 × 10−5 km3 km−1 yr−1), and the time estimated for a plume to tilt beyond 67° in the upper mantle (10–50 Myr) are consistent with observations at numerous hotspot tracks across the globe. We suggest that pulsing due to destabilization of tilted plume conduits may be one of several mechanisms responsible for modulating the melting rate of mantle plumes as they spread beneath the moving lithosphere.

Characterization of Nonlinear Viscoelastic Properties of Enhanced Oil Recovery Polymer Systems Using Steady-Shear Rheometry

SummaryEnhanced oil recovery (EOR) polymer systems such as hydrolyzed polyacrylamide (HPAM) solutions flowing in porous media at high fluxes were reported to cause shear-thickening, a nonlinear viscoelastic (NLVE) phenomenon. Bulk rheological studies are usually performed to characterize the viscous and viscoelastic behaviors of polymer solutions in porous media. To characterize the viscoelastic properties, oscillatory shear rheology based on linear viscoelastic (LVE) data and extensional rheology based on NLVE data have been used. Although both extensional flow and high-speed shear flow can stretch and thicken polymer solutions in a nonlinear fashion, steady-shear rheometry has been used to measure only the viscous and thinning behavior of HPAM systems. In this paper, (a) the thickening ability of HPAM polymer systems formulated with contrasting salinity and molecular weight (MW) concentration is characterized in bulk shear rheometry to analyze if the thickening in the pure shear field correlates with the thickening behavior reported in porous media and other rheometry and (b) the thickening intensity of the polymer solutions of varying salinity concentration in the bulk shear field is compared with the reported mechanical degradation effects in the literature.The shear-thickening index obtained by fitting a power-law model to thickening data in steady-shear rheograms is higher for the high-saline, high-MW low-concentration HPAM systems that have inherently higher nonlinear viscoelasticity. Furthermore, the thickening behavior observed due to salinity variation in bulk steady shear contrasts with linear oscillatory shear behavior but conforms to the thickening behavior observed in porous media and in the extensional field. This signifies that polymer-EOR researchers performing comparative studies on low-salinity and high-salinity polymer floods, and having a shear rheometer at their disposal, must look beyond linear oscillatory rheology and make use of nonlinear steady-shear rheology. There is a direct relation between the shear-thickening index of saline HPAM solutions and their mechanical degradation intensity. This paper shows that the high-speed data in steady-shear rheometry that are usually ignored in EOR literature have useful information and the notion that HPAM solutions are purely thinning in the bulk shear field needs to be reconsidered.

Correction to: Graphene oxide dispersion state in polystyrene-based composites below percolation threshold via linear melt rheology

Correction to: Graphene oxide dispersion state in polystyrene-based composites below percolation threshold via linear melt rheology