Viscosity Of Polymer Solutions Research Articles

Macroscopic Viscosity of Polymer Solutions from the Nanoscale Analysis.

The effective viscosity in polymer solutions probed by diffusion of nanoparticles depends on their size. It is a well-defined function of the probe size, the radius of gyration, mesh size (correlation length), activation energy, and its parameters. As the nanoparticle’s size exceeds the radius of gyration of polymer coils, the effective viscosity approaches its macroscopic limiting value. Here, we apply the equation for effective viscosity in the macroscopic limit to the following polymer solutions: hydroxypropyl cellulose (HPC) in water, polymethylmethacrylate (PMMA) in toluene, and polyacrylonitrile (PAN) in dimethyl sulfoxide (DMSO). We compare them with previous data for PEG/PEO in water and PDMS in ethyl acetate. We determine polymer parameters from the measurements of the macroscopic viscosity in a wide range of average polymer molecular weights (24–300 kg/mol), temperatures (283–303 K), and concentrations (0.005–1.000 g/cm3). In addition, the polydispersity of polymers is taken into account in the appropriate molecular weight averaging functions. We provide the model applicable for the study of nanoscale probe diffusion in polymer solutions and macroscopic characterization of different polymer materials via rheological measurements.

An analytical tool to forecast horizontal well injectivity in viscous oil polymer floods

Injection rate is a key factor for successful polymer floods of viscous oil reservoirs. Injectivity during polymer flooding is lower compared to waterflooding due to the viscosity of polymer solution. Accurate estimation of injection rate/pressure build-up due to polymer injection is essential to evaluation and design of polymer flood projects. Typically, a short-term polymer injectivity test is performed on a single well, but it is hard to extrapolate future behavior of polymer injectivity because the tests are often too short. Reservoir simulation can be used to forecast injectivity, but the grid size and radial flow often affect the calculated injectivity. Analytical methods provide simple and quick ways to estimate injectivity using realistic reservoir conditions. The goal of this work is to develop an analytical tool and demonstrate its applicability by comparison with field data. An analytical solution is developed for the injectivity of horizontal wells in polymer floods in viscous oil reservoirs. The analytical solution is validated by comparing it to a numerical field-scale box model simulation. The pressure profiles are calculated using spreadsheets and compared against the data from several fields with increasing degrees of complexity. In each case, the analytical-spreadsheet method provides close matches of injection pressure data. This analytical tool can be used for preliminary design of polymer floods before getting into more complex and time-consuming reservoir simulations. • Developed an analytical solution for injectivity in viscous oil polymer floods. • Compared the analytical solution to numerical simulation with grid refinement. • Compared analytical solution to field data from 5 wells. • Novel tool to design and optimize polymer floods in viscous oil reservoirs.

Microscopic experimental study on the sweep and displacement efficiencies in heterogeneous heavy oil reservoirs

Oil recovery is closely related to the sweep and displacement efficiencies in oil reservoirs. Therefore, several measures have been devised to enhance oil recovery based on these two factors. In heterogeneous heavy oil reservoirs, expansion of the swept volume of medium- and low-permeability layers is a suitable approach for enhancing oil recovery. However, the oil displacement efficiency is also an important factor. With regard to enhancing oil recovery, the selection of displacement agents will depend on whether the sweep efficiency or displacement efficiency is to be adjusted and on how these factors can be controlled to maximise the increase in oil recovery. In this study, the pixel method is used to distinguish between the sweep efficiency and displacement efficiency, and the joint effect of these factors is analysed. A heterogeneous microscopic model is used to conduct oil displacement experiments using polymer solutions with different viscosities and surfactant–polymer systems with similar viscosities and different interfacial tensions. The results indicate that under heterogeneous conditions, increasing the viscosity of the polymer solution leads to a slight expansion in the swept volume and an increase in the oil displacement efficiency in the low-permeability area; however, the overall sweep efficiency remains almost unchanged. There is a critical point for sweep efficiency: under the experimental conditions, when the oil viscosity is 305 mPa s, the critical viscosity of the polymer solution is 125 mPa s, and when the oil viscosity is 1050 mPa s, the critical value is 205 mPa s. When the viscosity of polymer solution reaches the critical value, for the surfactant–polymer system, a reduction in the oil–water interfacial tension has the same effect as a substantial increase in the polymer solution viscosity; moreover, the joint effect of the sweep efficiency and displacement efficiency can be enhanced. Therefore, for heterogeneous heavy oil reservoirs, the focus should be on improving oil displacement efficiency under certain sweep conditions rather than on expanding the swept volume. The findings of this study can help for better understanding of the selection of displacements agent in heterogeneous heavy oil reservoirs for enhanced oil recovery.

Disentangling Nano- and Macroscopic Viscosities of Aqueous Polymer Solutions Using a Fluorescent Molecular Rotor.

The macroscopic viscosity of polymer solutions in general differs strongly from the viscosity at the nanometer scale, and the relation between the two can be complicated. To investigate this relation, we use a fluorescent molecular rotor that probes the local viscosity of its molecular environment. For a range of chain lengths and concentrations, the dependence of the fluorescence on the macroscopic viscosity is well described by the classical Förster–Hoffmann (FH) equation, but the value of the FH exponent depends on the polymer chain length. We show that all data can be collapsed onto a master curve by plotting the fluorescence versus polymer concentration, which we explain in terms of the characteristic mesh size of the polymer solution. Using known scaling laws for polymers then allows us to quantitatively explain the relation between the FH exponent and the polymer chain length, allowing us to link the nano- to the macroviscosity.

Optimization of zero-shear viscosity for HPAM-Polystyrene microspheres formulations through experimental design approach

In this work, the reinforcing effects of polystyrene microspheres in a hydrolyzed polyacrylamide (HPAM) matrix was studied. The experimental design approach was used to optimize the rheological behavior of the HPAM polymer. The effects of three important parameters, including the size of the polystyrene microspheres, their concentration, and the test temperature on the zero-shear viscosity of HPAM polymer solutions were considered. The results showed that the size of the microspheres and test temperature were the most influential factors simultaneously. Moreover, the optimal zero-shear viscosity, at 20 °C, was predicted to be at microspheres concentration of 50 ppm and microspheres size of 1000 nm. The results showed close agreement between the predicted results by the RSM method and those obtained experimentally.

Influence Factors on Viscosity Loss of Injection System in A Test Area

As the first ASP flooding test in the transitional zone, it was put into pre polymer flooding in October 2018. However, the viscosity of single well cannot meet the design requirements at the initial stage of production. In view of the viscosity loss of polymer solution in the process of surface injection, by investigating the concentrated viscosity of each node of polymer injection process and single well injected outside the station, this paper analyzed the field test data and water quality report, found out the key links affecting the viscosity of polymer solution, and proposed various technical measures to reduce the viscosity loss. It is found that the viscosity loss is mainly formed after the mixing of polymer mother liquor and high-pressure sewage, and it is concluded that the main reason is the influence of injected water quality. Based on the analysis of salinity, bacterial content and iron ion in water quality, it is found in this paper that the viscosity of polymer injection increases by 40% when a fresh water pipeline is laid and the waste water is diluted on site.

Investigating the Transition between Polymer Melts and Solutions in Nonlinear Elongational Flow

The Doi–Edwards tube model, coupled with relaxation mechanisms, such as reptation, contour length fluctuation, and constraint release, allows us to quantitatively predict the linear viscoelastic properties of entangled polymers. However, for nonlinear elongational flows, large discrepancies between theoretical predictions based on the tube model and experimental results still persist today. This is in particular obvious for the experimentally observed strong qualitative differences in extensional flow of entangled polystyrene (PS) melts and solutions despite having the same number of entanglements and exhibiting the same linear viscoelastic behavior. The cause of this non-universality is often attributed either to a monomeric friction reduction or to an interchain pressure effect. In this work, we investigate the changes in extensional flow behavior going from polymer solutions to the melt state. For this purpose, we measure with a filament stretching rheometer the nonlinear extensional responses of differently long PS chains, both in the melt state and diluted in short-chain matrices of the same polymer at varying concentrations. These concentrations have been chosen sufficiently high, such that the chains stay entangled. This allows us to discuss the influence of concentration and molar mass on the steady-state elongational viscosity to highlight scaling relations. The purpose of the present work is to conduct well-defined experiments to further investigate how the steady extensional viscosity of polymer solutions and blends varies with the concentration and with the molecular weight of the chains.

Improved Calculation of Wellblock Pressures for Numerical Simulation of Non-Newtonian Polymer Injection

Summary The viability of any enhanced-oil-recovery project depends on the ability to inject the displacing fluid at an economic rate. This is typically evaluated using finite-volume numerical simulation. These simulators calculate injectivity using the Peaceman method (Peaceman 1978), which assumes that flow is Newtonian. Most polymer solutions exhibit some degree of non-Newtonian behavior resulting in a changing polymer viscosity with distance from the injection well. For shear-thinning polymer solutions, conventional simulations can overpredict injection-well bottomhole pressure (BHP) by several hundred psi, unless a computationally costly local grid refinement is used in the near-wellbore region. We show theoretically and numerically that the Peaceman pressure-equivalent radius, based on Darcy flow, is not correct when fluids are shear thinning, and derive an analytical expression for calculating the correct radius. The expression does not depend on any particular functional relationship between polymer-solution viscosity and velocity. We test it using the relationship described by the Meter equation (Meter and Bird 1964) and the Cannella et al. (1988) correlation. Numerical tests indicate that the solution provides a significant improvement in the accuracy of BHP calculations for conventional numerical simulation, reducing or removing the need for expensive local grid refinement around the well when simulating the injection of fluids with shear-thinning non-Newtonian rheology.

Dynamics of the sub-ambient gelation and shearing of solutions of P3HT and P3HT blends towards active layer formation in bulk heterojunction organic solar cells.

Organic solar cells (OSCs) containing an active layer consisting of a nanostructured blend of a conjugated polymer like poly(3-hexylthiophene) (P3HT) and an electron acceptor have the potential of competing against silicon-based photovoltaic panels. However, this potential is largely unfulfilled first due to interrelated production and stability issues of organic solar cells and second due to the unscalable nature of the generally employed spin coating process used for the fabrication of organic solar cells. Furthermore, alternatives to spin coating, especially relying on continuous polymer processing methods like extrusion and coating, cannot be readily applied due to the typically low shear viscosity and elasticity of polymer solutions making up the active layer. Recently, He et al. have reported that the gelation of P3HT with [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM) under sub-ambient conditions can provide a new route to the processing of the active layers of bulk heterojunction solar cells. Furthermore, increases in power conversion efficiencies (PCEs) of the P3HT/PC60BM active layer were determined to be possible under certain shearing and thermal histories of the P3HT/PC60BM gels. Here oscillatory and steady torsional flows were used to investigate the gel formation dynamics of P3HT with a recently proposed non-fullerene acceptor o-IDTBR under sub-ambient conditions and compared with the gelation behavior of P3HT/PC60BM blends. The rheological material functions as well as the gel strengths defined on the basis of linear viscoelastic material functions, characterized via small-amplitude oscillatory shearing, were observed to be functions of the P3HT and o-IDTBR concentrations, the solvent used and the shearing conditions. Overall, the P3HT gels which formed upon quenching to sub-zero temperatures were found to be stable during small-amplitude oscillatory shear (linear viscoelastic range) but broke down even at the relatively low shear rates associated with steady torsional flows, suggesting that the shearing conditions used during the processing of gels of P3HT and blends of P3HT with small molecule acceptors can alter the gel structure, possibly leading to changes in the resulting active layer performance.

Comparison of equilibrium techniques for the viscosity calculation from DPD simulations.

Dissipative Particle Dynamics (DPD) is a powerful mesoscopic modelling technique that is routinely used to predict complex fluid morphology and structural properties. While its ability to quickly scan the conformational space is well known, it is unclear if DPD can correctly calculate the viscosity of complex fluids. In this work, we estimate the viscosity of several unentangled polymer solutions using both the Einstein and Green-Kubo formulas. For this purpose, an Einstein relation is derived analogous to the revised Green-Kubo formula suggested by Jung and Schmid, J. Chem. Phys., 2016, 144, 204104. We show that the DPD simulations reproduce the dynamical behaviour predicted by the theory irrespectively of the values of the conservative and friction parameters used and estimate a Schmidt number compatible to that of a fluid system. Moreover, we observe that the Einstein method requires shorter trajectories to achieve the same statistical accuracy as the Green-Kubo formula. This work shows that DPD can confidently be used to calculate the viscosity of complex fluids and that the statistical accuracy of short trajectories can be improved by using our revised Einstein formula.

Synthesis and characterization PVA electro-spun nanofibers containing encapsulated vitamin C in chitosan microspheres

This paper reported vitamin C (VC) encapsulated chitosan (CS) microspheres cross-linked in the presence of two cross-linking agents, sodium tripolyphosphate (STPP) and Tween 80, for controlled release of VC. Furthermore, the effect of the crosslinking agent was described. The obtained micro and nanocapsules were evaluated by loading efficiency, scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and in vitro release studies. Encapsulation efficiency was calculated. FTIR and XRD revealed the dispersion and stability of VC after encapsulation in the CS matrix. Using Tween 80, as a crosslinking agent, encapsulation was completely done, which is related to the larger number of hydroxyl groups of Tween, causing the formation of extensive hydrogen bonding with CS and VC. The release of VC from these microspheres was sustained and affected by the volume of cross-linking agent added. Finally, the release of VC from STPP-chitosan and Tween-chitosan microspheres followed Fick’s law of diffusion. By loading encapsulated VC in PVA, electrospun nanofibers obtained without beading defect, also conductivity, and viscosity of PVA polymer solution were measured. SEM and EDX results indicated that inorganic particle size was of the nano-order with uniform distribution and dispersion and the release of VC from PVA nanofibers was characterized.

Effect of salt-resistant monomers on viscosity of modified polymers based on the hydrolyzed poly-acrylamide (HPAM): A molecular dynamics study

In this work, the viscosity and the aggregation behavior of partially hydrolyzed poly-acrylamide (HPAM), 2-acryloylamino-2-methyl-1-propanesulfonic acid (AMPS) and acrylamide-N-vinypyrrolidone (AM-NVP) in aqueous solution and salt solutions were investigated by molecular dynamics simulation. The results show that: (i) The order of the viscosity of different polymer solutions is AMPS > HPAM > AM-NVP. With the aggregation and curling of the polymer chains, a spatial network structure among the polymer chains is formed by the occurrence of the intermolecular and intramolecular cross-links through hydrogen bonds, increasing the rigidity of polymer chains. Simultaneously, due to the number of electronegative atoms and steric stabilization, the order of the number of hydrogen bonds in three polymer solutions is AMPS> HPAM> AM-NVP. (ii) The synergistic stabilizing effects of the surrounding cations around different monomers in three polymers can increase the viscosities of three systems, and negatively charged groups tend to be transfer from the inside of polymer chains to the outside of the chains because of the electrostatic attraction, reducing the electrostatic repulsion and maintaining the number of hydrogen bonds. (iii) Different ions (Na+, Mg2+, Ca2+, Cl−) have different effects on the groups of three polymers. For COO− and SO3− groups, Mg2+ basically cannot enter the hydration layer around the groups, while Na+ and Ca2+ can enter the hydration layer of both groups and tend to be distributed between two oxygen atoms. Moreover, Mg2+ and Ca2+ ions have the main influence on the C5H9NO group.

In-line monitoring alternatives of polymer solution viscosity in EOR process

La inyección de polímeros es un método de recobro mejorado utilizado en el mundo como tecnología exitosa, sin embargo, uno de los principales problemas es la sensibilidad de las soluciones poliméricas a la degradación por esfuerzos de corte. En ese sentido, el monitoreo de la viscosidad en tiempo real permite la toma de decisiones rápida durante la operación, con el fin de asegurar un proceso eficiente y así el incremento en el factor de recobro. En este trabajo se analizaron diferentes viscosímetros in-line para el monitoreo en tiempo real de la viscosidad de soluciones poliméricas. Adicionalmente, se realizó un análisis económico de los viscosímetros técnicamente factibles y disponibles mediante un sondeo de mercado, los cuales se compararon con la metodología de monitoreo empleada actualmente en Ecopetrol S.A.

Stability, flocculation, and rheological behavior of silica suspension-augmented polyacrylamide and the possibility to improve polymer flooding functionality

In this study, the characterization and rheological behavior of silica suspensions in aqueous/polymeric media are investigated. The variation of silica nanoparticles size and concentration, polymer molecular weight and concentration, pH, valency, and concentration of electrolytes are considered for this purpose. The findings show that bridging flocculation of dispersed silica nanoparticle-augmented polymer solution increases with nanoparticle concentration, nanoparticle diameter, the charge of electrolyte, and electrolyte concentration. In contrast, it decreases with an increase in pH and polymer concentration. Also, the intrinsic shear viscosity of aqueous polymer solution increases with molecular weight, unlike the behavior of polymer solution in the presence of silica nanoparticles. The shear viscosity and the rate of bridging flocculation of the silica nanoparticle-augmented polymer solution primarily increase until it reaches a maximum and finally decreases with further increasing polymer molecular weight. In polymer high molecular weight and high concentration, the repulsion due to steric stabilization overcomes the interaction between two adsorbed polymer chains resulting in a stable form of suspension. By utilizing the proper conditions, core flooding experiments are designed and implemented to enhance the hydrolyzed polyacrylamide polymer flooding efficiency. Around 20–52% higher recovery was obtained for the silica nanoparticle-augmented polymer solutions with respect to the polymer flooding.

Plate reader microrheology

In this work, we report the development of a simplified method to perform microrheology to rapidly assess soft materials. This approach uses fluorescence polarization and a plate reader format to measure the rotational diffusion of nanoparticles within a sample of interest. We have established that this technique can be used to characterize a range of soft materials based on the rotational diffusion of nanoparticles in materials with viscosities exceeding 100 cP. Using these fluorescence polarization-based measurements, we describe formalism that enables the estimation of viscosity in polymer solutions and gels composed of polyethylene glycol, hyaluronic acid, and Matrigel after accounting for the length-scale dependent effects of the polymer environment on the nanoparticle rotational diffusion. Using this analysis, we show that the plate reader microrheology measurements of viscosity are in reasonable agreement with traditional particle tracking microrheology. The use of a plate reader format allows this approach to be higher throughput, less technically challenging, and more widely accessible than standard macro- and micro-rheological methods, making it available to non-experts. This approach has potential applications in clinical settings where conventional rheological equipment may not be available to rapidly characterize patient-derived samples.

Phase Equilibrium and Morphology of High-Molecular Condensation Structures in Three- and Four-Component Systems

Using the method of diffusion enrichment with a nonsolvent of polymer solutions in mixed solvents, porous structures are obtained and their structural characteristics are determined. Quasi-binary state diagrams of two four-component systems were obtained. Viscosities of polymer solutions in mixed solvents were measured. The dependences of the reduced viscosity on the polymer concentration are obtained. The slopes ratio and the characteristic viscosities are determined. It is shown that the properties of structural elements ([η] and tgα) of solutions differ significantly depending on the composition of the mixed solvent, and that the positions of the regions of heterogeneity in the quasi-binary phase diagrams for the systems under study correspond to these differences. It is shown that significant differences in the sizes of pores and their proportions in the area of ​​the flat section of the structure correspond to the differences in the constitutional diagrams and the degree of nonequilibrium of the structures, which was qualitatively estimated from the value of [η]. The results indicate that the performed viscometric measurements provide useful information in studying the modification of the morphology of condensation structures by changing the composition of the mixed solvent.

Influence of PVA Molecular Weight and Concentration on Electrospinnability of Birch Bark Extract-Loaded Nanofibrous Scaffolds Intended for Enhanced Wound Healing.

Triterpenes from the outer bark of birch (TE) are known for various pharmacological effects including enhanced wound healing. Apart from an already authorized oleogel, electrospun nanofiber mats containing these triterpenes in a polyvinyl alcohol (PVA) matrix appear to be an advantageous application form. The effects of PVA molecular weight and concentration on the fiber morphology have been investigated. Three different molecular weights of PVA ranging from 67 to 186 kDa were used. The concentration of PVA was varied from 5 to 20 wt%. Polymer solutions were blended with colloidal dispersions of birch bark extract at a weight ratio of 60:40 (wt.%). The estimated viscosity of polymer solutions was directly linked to their concentration and molecular weight. In addition, both pure and blended solutions showed viscoelastic properties with a dominant viscous response in the bulk. Fiber morphology was confirmed using scanning electron microscopy (SEM). Both polymer concentration and molecular weight were found to be significant factors affecting the diameter of the fibers. Fiber diameter increased with a higher molecular weight and polymer concentration as more uniform fibers were obtained using PVA of higher molecular weight (146–186 kDa). In vitro drug release and ex vivo permeation studies indicated a faster drug release of betulin from electrospun scaffolds with lower PVA molecular weight. Our research suggests that the fabricated TE-loaded PVA electrospun dressings represent potential delivery systems of TE for wound care applications.

Investigation into mobility control mechanisms by polymer flooding in offshore high-permeable heavy oil reservoir

ABSTRACT The systematic understanding of the mobility control of polymer solution in porous media is conducive to the engineering application and development of polymer flooding technology. In this paper, two kinds of polymers (partially hydrolyzed polyacrylamide (HPAM) and MJ-10 (a hydrophobically associating polyacrylamide, HAPAM)) with different adsorption characteristics were used to build a solution system with different performance characteristics. And run a series of viscosity measurement, residual resistance factor (RRF) measurement and oil displacement experiments on man-made sand packs. The results show that the viscosity and residual resistance coefficient of polymer solution can enhance its fluidity control. The higher the viscosity of solution, the higher the RRF, and the higher the displacement efficiency. The solution system HM3 can make full use of the solution characteristics of the two polymers to obtain a moderate solution viscosity and residual resistance coefficient. Compared with a single solution H2 and M2, it can increase the oil recovery by 5% in the low permeability layer. The compound application of polymer solution will be a development direction of polymer flooding in the future.

Efficient Oil Removal of Polymer Flooding Produced Sewerage Using Super-Hydrophobic Mesh Filtration Method

During the past 20 years, polymer flooding has become a successful enhanced oil recovery (EOR) technique for mature reservoirs with high water cut and recovery percent around the world. However, the high bulk viscosity of polymer solutions could slow down the separation rate of the crude oil emulsion and make it difficult to treat the produced fluid. Consequently, the efficient removal of oil from the polymer flooding produced sewerage has still drawn significant concern. In this research, a high flux super-hydrophobic copper mesh was prepared using two-stage processes to treat the sewerage from polymer flooding. The surface of the super-hydrophobic mesh was characterized using various techniques including scanning electron microscope (SEM), OCA 20-contact angle goniometer, etc. Accordingly, the static contact angle of the super-hydrophobic copper mesh reached up to 165°. Moreover, the performances of the mesh were systematically evaluated under different internal and external factors such as oil to water volume ratio, polymer concentration, shear rate, and pH. The corresponding configuration and separation mechanisms are further explained in detail. The prepared superhydrophobic mesh can be a potential candidate for sewerage with both a polymer solution and crude oil.

Improving the Viscosity of Polymer Solutions Prepared with Sewage through Bio-competitive Exclusion in Shengli Oilfield

This paper summarized and analyzed the research and application of biocompetitive exclusion technique to remove sulfides produced in wastewater and inhibit SRB from producing new sulfides to mitigate the loss of viscosity of polymer solutions prepared with sewage water in the Shengli Oilfield. The results indicated that by adding a regulator can activate NR-SOB and RB in sewage water, which inhibit SRB activity and prevent them for producing new sulfides by competing for nutrient substrates and living space. The inhibition of SRB leads to improved polymer solution viscosity and high viscosity stability.