This article reviews viscosity modifiers, additives that increase the viscosity of lubricating oils. Viscosity modifiers are high molecular weight polymers whose functionality is derived from their ...thickening efficiency, viscosity–temperature relationship, and shear stability. There are now many different additive chemistries and architectures available, all of which have advantages and disadvantages, and affect solution viscosity through different mechanisms. Understanding these mechanisms and how they impart additive function is critical to the development of new viscosity modifiers that enable lubricants to function more efficiently over a wide range of temperatures.
I derive an exact integral expression for the ratio of shear viscosity over entropy density η/s for the massless (critical) O(N) model at large N with quartic interactions. The calculation is set up ...and performed entirely from the field theory side using a nonperturbative resummation scheme that captures all contributions to leading order in large N. In 2 + 1d, η/s is evaluated numerically at all values of the coupling. For infinite coupling, I find (η/s) ≃ 0.42 (1) × N. I show that this strong coupling result for the viscosity is universal for a large class of interacting bosonic O(N) models.
Recent advances in synchrotron sources, beamline optics and detectors are driving a renaissance in room‐temperature data collection. The underlying impetus is the recognition that conformational ...differences are observed in functionally important regions of structures determined using crystals kept at ambient as opposed to cryogenic temperature during data collection. In addition, room‐temperature measurements enable time‐resolved studies and eliminate the need to find suitable cryoprotectants. Since radiation damage limits the high‐resolution data that can be obtained from a single crystal, especially at room temperature, data are typically collected in a serial fashion using a number of crystals to spread the total dose over the entire ensemble. Several approaches have been developed over the years to efficiently exchange crystals for room‐temperature data collection. These include in situ collection in trays, chips and capillary mounts. Here, the use of a slowly flowing microscopic stream for crystal delivery is demonstrated, resulting in extremely high‐throughput delivery of crystals into the X‐ray beam. This free‐stream technology, which was originally developed for serial femtosecond crystallography at X‐ray free‐electron lasers, is here adapted to serial crystallography at synchrotrons. By embedding the crystals in a high‐viscosity carrier stream, high‐resolution room‐temperature studies can be conducted at atmospheric pressure using the unattenuated X‐ray beam, thus permitting the analysis of small or weakly scattering crystals. The high‐viscosity extrusion injector is described, as is its use to collect high‐resolution serial data from native and heavy‐atom‐derivatized lysozyme crystals at the Swiss Light Source using less than half a milligram of protein crystals. The room‐temperature serial data allow de novo structure determination. The crystal size used in this proof‐of‐principle experiment was dictated by the available flux density. However, upcoming developments in beamline optics, detectors and synchrotron sources will enable the use of true microcrystals. This high‐throughput, high‐dose‐rate methodology provides a new route to investigating the structure and dynamics of macromolecules at ambient temperature.
In recent years, chemical flooding has become significant in oilfield development. As its scope of application gets wider, choosing the proper chemical agent becomes an issue for field engineers. ...Different chemical agents have different oil displacement mechanisms, so engineers should choose the appropriate one for an oilfield application with different reservoir characteristics. The most important aspect of chemical profile-control oil-displacement technology is the selection of suitable agents for a reservoir. Petroleum engineers have considered the viscosity of a profile-control oil-displacement agent as the main technical index, and they developed salt-resistant polymers but the oilfield application results were insufficient. In this work, according to the actual need of the oilfield, the relationship between viscosity and mobility of the profile-control oil-displacement agent was studied. The results showed that the viscosity is the representation of friction, which is caused by the motion of the inner liquid layer, and it is related to the polymer molecular aggregation. Moreover, the principle of chemical profile-control oil-displacement technology is to improve the injection pressure and increase the absorption pressure difference (difference between injection pressure and absorption pressure of oil layer) of middle- and low-permeability oil layer and larger pore throat, thus realizing the goal of expanding swept volume. The mechanism of viscosity measurement and that of chemical profile-control oil-displacement are different, and there is no relationship between viscosity and oil recovery. Thus, the method of evaluating oil increasing effect by viscosity and mobility ratio (K/μ) is not logical. It was also important to achieve a good compatibility between the polymer molecular aggregation dimension and pore size so that the profile-control oil-displacement agent can be injected into a deeper area in the oil reservoir. This relationship can be evaluated by the agent transport capacity. Lastly, practice showed that irrespective of the viscosity, the profile-control oil-displacement agent could improve oil recovery if the agent is injected into the deep area in high-permeability layers.
Studying the dynamic viscosity (DV) is a key factor to determine the nanofluids’ hydrodynamic behavior (NFs). In this research, the effect of volume fraction (φ), shear rate (SR), and temperature (T) ...on the DV, and torque of SiO2 nanoparticles (NPs)/ Ethylene glycol (EG) nanofluid (NF) are studied with an artificial neural network (ANN). Different machine learning (ML) models are examined to predict the rheological properties, and then the best model is selected for prediction. The results show that the torque mostly increased linearly with the SR in all samples. The slope of this enhancing trend is higher for lower T. The Gaussian Process Regression (GPR) models with the Matérn covariance function provided the best results on both datasets to predict the DV. The correlation results provided by this method to predict the DV in terms of Pearson’s Linear Correlation Coefficient (PLCC), and Spearman’s Rank Order Correlation Coefficient (SROCC) were 0.999 and 1, respectively. R squared (R2) was 0.996 and, the Root Mean Squared Error (RMSE), and Mean Absolute Percentage Error (MAPE) values of about 0.24 and 1.61 represented the accuracy and power of this method to predict the DV values unseen data by the model. The GPR torque predictor model performed very well by providing a correlation of about 0.98 and an RMSE of about 4. Matérn covariance functions that used separate length scales per predictor with ν=3/2 (ardmatern 32) and ν=5/2 (ardmatern52) were superior to other functions. All 100 models trained on each dataset were well-trained and quite reliable. The trained models were accurate enough to be used in related applications.
Fluorescent molecular rotors (FMRs) can act as viscosity sensors in various media including subcellular organelles and microfluidic channels. In FMRs, the rotation of rotators connected to a ...fluorescent π‐conjugated bridge is suppressed by increasing environmental viscosity, resulting in increasing fluorescence (FL) intensity. In this minireview, we describe recently developed FMRs including push–pull type π‐conjugated chromophores, meso‐phenyl (borondipyrromethene) (BODIPY) derivatives, dioxaborine derivatives, cyanine derivatives, and porphyrin derivatives whose FL mechanism is viscosity‐responsive. In addition, FMR design strategies for addressing various issues (e.g., obtaining high FL contrast, internal FL references, and FL intensity‐contrast trade‐off) and their biological and microfluidic applications are also discussed.
Spinning around: This minireview discusses recently developed fluorescent molecular rotors (FMRs), which act as viscosity sensors in various media including subcellular organelles and microfluidic channels. In addition, the mechanism of viscosity‐responsive fluorescence, design strategy of FMRs for addressing remarkable issues, and their various biological and microfluidic applications, are also discussed.
Nanoparticles significantly alter the rheological properties of a polymer or monomeric resin with major effect on the further processing of the materials. In this matter, especially the influence of ...particle material and disperse properties on the viscosity is not yet understood fully, but can only be modelled to some extent empirically after extensive experimental effort. In this paper, a numerical study on an uncured monomeric epoxy resin, which is filled with boehmite nanoparticles, is presented to elucidate the working principles, which govern the rheological behavior of nanoparticulate suspensions and to simulate the suspension viscosity based on assessable material and system properties. To account for the effect of particle surface forces and hydrodynamic interactions on the rheological behavior, a resolved CFD is coupled with DEM. It can be shown that the particle interactions caused by surface forces induce velocity differences between the particles and their surrounding fluid, which result in increased drag forces and cause the additional energy dissipation during shearing. The paper points out the limits of the used simulation method and presents a correction technique with respect to the Péclet number, which broadens the range of applicability. Valuable information is gained for a future mechanistic modelling of nanoparticulate suspension viscosity by elucidating the interdependency between surface forces, shear rate and resulting drag forces on the particles.
In this study, a triangular polynomial interpolation (TPI) scheme was developed to estimate the vertical eddy viscosity coefficient (VEVC) on the basis of the Ekman model with adjoint assimilation. ...In the twin experiments, the advantages and disadvantages of estimating the VEVC using the TPI scheme under different factors are discussed. The results indicated that (1) the TPI scheme proves to be better than the cubic spline interpolation (CSI) and Cressman interpolation (CI) schemes; (2) the inversion results are more sensitive to observations from upper ocean layers than those from lower layers, and the TPI scheme is less likely to be influenced by missing data; (3) for various boundary layer depths, the inversion results of the TPI scheme remain consistent with the given distributions; (4) the inversion results can be influenced considerably by observational errors, and the TPI scheme is more resistant to noise than the CSI and CI schemes; and (5) the inversion accuracy of the TPI scheme can be improved by selecting the temporal wind stress drag coefficients. In practical experiments, the adjoint method with the TPI scheme was developed to estimate the Ekman currents by assimilating the observations from a buoy stationed in the Yellow Sea. The results showed the successful estimation of the VEVC and demonstrated that more precise current velocities can be obtained with this estimation scheme. In summary, this study provides a useful approach for the effective estimation of the VEVC.
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