Rheological Properties Of Polymer Solutions Research Articles

An Investigation of the Factors Influencing the High Temperature Rheology of Polymers

Introduction: Nowadays, polymers, as an important application material in drilling engineering, have obvious advantages in solving the rock-carrying problem at the bottom of deep wells, and improving the drilling speed due to their excellent viscosity enhancement effect. Method: In this study, the effects of polymer type, concentration, shear time, electrolyte, and clay on the rheological properties of polymer solutions at high temperature and high pressure were investigated using a Fann 50SL rheometer. The experimental results showed that, except for the polymer additive amount and clay, the increase in shear time and the amount of salt both led to a decrease in the viscosity of the polymer solution, with 190°C as the critical temperature above which the viscosity decreased significantly. Results: The polymer solution containing formate showed higher viscosity retention during heating and then cooling compared to chlorides. The presence of clay enhances the reticulation of polymer molecules in the blend, which facilitates the carrying of rock cuttings at high temperatures. In addition, regression analyses showed that the increase in temperature resulted in an enhanced tendency for the polymer solution to evolve from a pseudoplastic to a Newtonian type. Conclusion: This research provides theoretical basis and data support for developing high-temperature polymers and formulating high-temperature drilling fluid systems.

Rheological properties of polymer solutions and ways to improve the efficiency of development of high-viscosity oil fields in Uzbekistan

The results of experimental research on studying the filtration properties of polymer solutions and the mechanism of the displacement process in porous medium were presented in this article. The methodology of experimental studies in a specially designed laboratory setup is given. In the present work the rheological properties of polymer K-9 are considered. At the same time, the relaxation time of viscoelastic particles of K-9 polymer filtered in porous medium is experimentally found. Also, the results of experimental studies on oil displacement of fields with high content of asphaltene-resinous substances by polymer solutions on artificially created reservoir models to determine the optimal concentration of polymer solution and the size of the rim with the purpose of increasing oil recovery. Experimental studies on displacement of high-viscosity oils with a thickened water rim established that this method gives the greatest increase in water-free and ultimate oil recovery of reservoirs, within the range of change in the concentration of polymer solution 0.2-0.4%, with the size of the rim more than 70% of the oil saturated volume of the reservoir. Studies on displacement of high-viscosity oils by polymer solutions show that the use of this method of increasing oil recovery factor in practice is not always economically feasible, because of the need to ensure high injection pressures and high concentration of expensive polymer solution.

Phase behavior of colloidal nanoparticles and their enhancement effect on the rheological properties of polymer solutions and gels.

The interaction between nanoparticles and polymers has been of great interest in colloidal theory and novel materials. For example, the properties of polyacrylamide solutions and gels, which are usually used for conformance control and water shut-off in oilfields, can be improved with the addition of nanoparticles. This underlying mechanism and its applicability are investigated in this paper. A strong relationship between the phase behaviors of nanoparticles in polymer solutions and their enhancement effect on the rheology of the nanocomposite polymer solutions and gels was observed. Experiment results showed that the stability of nanoparticles was dependent on several factors, including pH, salinity, and polymer type. At neutral pH conditions, the tendency of the aggregation of nanoparticles was strengthened upon increasing the salinity, polymer concentration, and electronegativity of the polymers. Rheological measurements showed that nanoparticles could improve the viscosity of polymer solutions or the fracture stress of gels only if nanoparticles were aggregated in the corresponding systems. In addition, these rheological parameters significantly increased with increasing salinity and nanoparticle concentration. As a result, the mobility ratio of polymer solutions may be increased several times by the addition of nanoparticles. Referring to the gels, their rupture pressure gradient in the ideal model was also found to increase with nanoparticle concentration. In particular, if the nanoparticle concentration was sufficiently high (reaching 2%), the formed gels would not be destroyed by the injected water, but rather functionally act as a porous medium for permeation.

Parameter estimation on polymer solutions with fractional viscoelastic model

The rheological properties of polymer solutions are extremely complex and it leads to a specific power-law behavior in response to creep experiments, which can not be better characterized by the classical viscoelastic constitutive models. The renowned viscoelastic fluid models with fractional derivatives have shown astonishing advantages in characterizing the broad relaxation process of the multiple materials with power-law response behavior. In this paper, we use the fractional Maxwell constitutive model to simulate the power-law responses for several polymer solutions through experimental measuring, and better fitting results than classical models can be found.

ПОЛИМЕРЛІ ЕРІТІНДІЛЕРДІҢ РЕОЛОГИЯЛЫҚ ҚАСИЕТТЕРІН ЗЕРТТЕУ

Annotation. The long-term operation of the deposit, the alternation of reservoir zones with high and degraded filtration and capacitance properties due to the heterogeneity of the reservoir, the deformation of the development system due to downtime and inactivity of wells predetermined the selective movement of water through the most permeable layers. As practice shows, the widespread use of traditional flooding technology does not ensure the effective production of residual reserves from low-permeable and highly watered formations. Therefore, increasing the degree of oil extraction from the depths of the developed fields using effective methods of active impact on water-oil-saturated formations is an important scientific and technical task facing the oilmen of the republic. One of the most effective and promising methods of stabilizing oil production is physics-chemical technologies based on the use of injection of polymer compositions. The main purpose of injection of polymer compositions is to equalize the heterogeneity of productive layers by reducing the mobility of the displacing agent in highly conductive interlayers and increasing the coverage of the reservoir by flooding both in power and in stretch. As is known, the effectiveness of the use of technologies based on polymer solutions depends on their good selective filterability into zones with high water saturation, which allows creating water-insulating screens in the desired direction and to a sufficient depth. It is known that the effective use of polymer solutions depends on the influence of various factors: molecular weight, polymer concentration in solution, filtration rates, reservoir permeability, as well as such an important parameter as the rheological properties of polymer solutions. The study of the rheological properties of polymer solutions allows us to substantiate and propose for practical implementation effective integrated technologies for increasing oil recovery during the operation of the oil fields under consideration. In this work, the rheological properties of polyacrylamide, physical parameters, taking into account their physics-chemical properties, are studied. The influence of mineralization and water hardness on polymer solutions is considered. The issues of mechanical destruction of polymers have been studied. The degree of mechanical destruction of the polymer is estimated based on the results of the study of the rheological properties of the polymer sample.

Effect of Rheological Properties of Polymer Solution on Polymer Flooding Characteristics.

Polymer flooding is an appropriate enhanced oil recovery (EOR) process that can increase macroscopic sweep efficiency. We examined two polymeric superpushers at different salinities (10,000 and 42,000 ppm of NaCl and 18,000 ppm of CaCl2) and temperatures (30 to 75 °C) as polymer-flooding agents for the EOR process. Rheological and thixotropic tests were attempted to find shear viscosity change when the polymer solutions were introduced under different salinity and temperatures, followed by describing the rheological behavior with the two most common rheological models used for polymer solutions, and then a quadratic model with Design-Expert to detect the effective parameters. Core flooding tests were conducted afterward to determine the final proposed fluid. An increase in the concentration of monovalent ions and the addition of divalent ions adversely affected both types of polymers used, which was similar to the effects of a temperature increase. The Flopaam 3630S at 1000 ppm has more stability under harsh conditions and enables 22% and 38% oil recovery in carbonate and sandstone core rocks, respectively. Consequently, Flopaam 3630S can be the perfect polymer agent for different chemical flooding procedures in high-salinity oil reservoirs.

Dissipative particle dynamics simulations for biological systems: From protein structures to cell mechanics

<p indent="0mm">Dissipative particle dynamics (DPD) is a mesoscopic coarse-grained simulation method developed in recent years, which is an important method for studying the dynamic behaviors of soft matter and complex fluids. In this method, each DPD particle represents a coarse-grained virtual cluster of a set of atoms or groups of matter. The position and momentum of the DPD particle are updated in a continuous phase but spaced at discrete time steps. The coarse-grained DPD particles are subject to simplified pairwise interacting conservative, dissipative, and random forces. Especially, the dissipative force and random force in the DPD method act as a heat sink and a source, respectively, and the combined effect of these two forces act as a thermostat, which conserves momentum and thus provides the correct description of hydrodynamic interactions for the model system. In addition, a common choice of the soft repulsion for the conservative force allows using larger integration time steps in DPD simulations than that usually allowed in classical molecular dynamics (MD) simulations. Hence, compared with the MD method, the computational cost of the DPD simulation is significantly reduced due to the smaller number of modeled particles and the larger computational time step, enabling the simulations of the static and dynamic behaviors of complex fluids and soft matter systems at physically attractive length scale and time scale. Moreover, the particle-based framework of the DPD method enables people to easily incorporate additional physical features into the model systems and extend its application to complex systems. For these reasons, the DPD method and its extension have been successfully applied to numerous soft matter and complex fluid systems such as oil/water/surfactant systems, chemical morphology, microscopic morphology, phase separation, as well as dynamics and rheological properties of polymer solutions and colloidal suspensions. In this paper, we first introduce the theoretical formulation and parameterization of the DPD method. Then, we review recent advances in DPD modeling of biological systems, focusing on its applications at the molecular and cellular scales. At the molecular scale, we highlight examples of successful simulations of the protein structures and their interactions, the structure and dynamics of amphiphilic lipid molecule membranes (e.g., the self-assembly of lipid molecules, the structure and properties of lipid membranes, the fusion of lipid membranes, and the budding and fission of lipid membranes), the interaction of lipid membranes with protein molecules, and the interaction of nanoparticles with lipid membranes; at the cellular scale, we focus on the DPD modeling of blood cell flow and blood rheological behaviors in the blood microcirculatory systems, including the shape deformation and flow dynamics of red blood cells, the margination and adhesion dynamics of white blood cells, the margination and aggregation behaviors of platelets, the hemorheological behavior of blood flow, as well as the separation of circulating tumor cells from blood flow using microfluidic devices. Additionally, we compare the advantages and disadvantages of the microscale blood flow simulations between the continuum-based methods and particle-based methods, including the DPD method. Finally, we briefly present the development trends and application prospects of DPD modeling in biological systems.

Effect of Composition and Viscosity of Spinning Solution on Ultrafiltration Properties of Polyphenylene Sulfone Hollow-Fiber Membranes.

In this work, PPSUs with different molecular weights were synthesized for the development of highly permeable ultrafiltration hollow fiber membranes for the first time. The MW of the synthesized polymers was controlled by varying the monomers molar ratio within 1:1-1.15 under the same synthesis conditions. Based on the study of the rheological properties of polymer solutions, a high molecular weight PPSU (MW 102,000 g/mol) was chosen for the formation of hollow fiber membranes. The addition of PEG400 to the spinning solution led to an increase in viscosity, which makes it possible to work in the region of lower PPSU concentrations (18-20 wt. %) and to form membranes with a less dense porous structure. With the addition of PEG400 to the spinning solution, the membrane permeance increased sharply by more than two orders of magnitude (from 0.2 to 96 L/m2 h bar). At the same time, the membranes had high rejection coefficients (99.9%) of Blue Dextran model filtered substance (MW = 69,000 g/mol).

Interactions between polymers and flows in macro and micro length scales.

Polymer solution with large molecular weights show scale dependent nonlinear behavior. The dynamics of such polymer solution in a meter length scale are very different from those in a micrometer length scale. To clarify this scale dependent behavior, we have conducted several experiments that focus on interactions between polymers and flows in multiple length scales [1Hidema R. Suzuki H. Hisamatsu S. Komoda Y. Furukawa H. Effects of the extensional rate on two-dimensional turbulence of semi-dilute polymer solution flows.Rheol. Acta. 2013; 52: 949https://doi.org/10.1007/s00397-013-0733-3Crossref Scopus (13) Google Scholar, 2Hidema R. Suzuki H. Hisamatsu S. Komoda Y. Characteristic scales of two-dimensional turbulence in polymer solutions.AICHE J. 2014; 60: 1854https://doi.org/10.1002/aic.14364Crossref Scopus (15) Google Scholar, 3Hidema R. Murao I. Komoda Y. Suzuki H. Effects of the extensional rheological properties of polymer solutions on vortex shedding and turbulence characteristics in a two-dimensional turbulent flow.J. Non-Newtonian Fluid Mech. 2018; 254: 1https://doi.org/10.1016/j.jnnfm.2018.02.001Crossref Scopus (12) Google Scholar, 4Hidema R. Fukushima K. Yoshida R. Suzuki H. Vortex deformation and turbulent energy of polymer solution in a two-dimensional turbulent flow.J. Non-Newtonian Fluid Mech. 2020; 285104385https://doi.org/10.1016/j.jnnfm.2020.104385Crossref Scopus (3) Google Scholar, 5Fukushima K. Kishi H. Suzuki H. Hidema R. Modification of turbulence caused by cationic surfactant wormlike micellar structures in two-dimensional turbulent flow.J. Fluid Mech. 2022; 933: A9https://doi.org/10.1017/jfm.2021.1058Crossref Scopus (1) Google Scholar, 6Hidema R. Hayashi S. Suzuki Hiroshi Drag force of polyethyleneglycol in flow measured by a scanning probe microscope.Phys. Rev. Fluids. 2019; 4074201https://doi.org/10.1103/PhysRevFluids.4.074201Crossref Scopus (2) Google Scholar, 7Hidema Ruri Fujito Ken-ya Suzuki Hiroshi Drag force of polyethyleneglycol in flows of polymer solutions measured by a scanning probe microscope.Soft Matter. 2022; 18: 455https://doi.org/10.1039/D1SM01305JCrossref PubMed Google Scholar].In the first part of this talk, I will highlight characteristic vortex deformation and energy transfer caused by polymers in a two-dimensional turbulent flow [1Hidema R. Suzuki H. Hisamatsu S. Komoda Y. Furukawa H. Effects of the extensional rate on two-dimensional turbulence of semi-dilute polymer solution flows.Rheol. Acta. 2013; 52: 949https://doi.org/10.1007/s00397-013-0733-3Crossref Scopus (13) Google Scholar, 2Hidema R. Suzuki H. Hisamatsu S. Komoda Y. Characteristic scales of two-dimensional turbulence in polymer solutions.AICHE J. 2014; 60: 1854https://doi.org/10.1002/aic.14364Crossref Scopus (15) Google Scholar, 3Hidema R. Murao I. Komoda Y. Suzuki H. Effects of the extensional rheological properties of polymer solutions on vortex shedding and turbulence characteristics in a two-dimensional turbulent flow.J. Non-Newtonian Fluid Mech. 2018; 254: 1https://doi.org/10.1016/j.jnnfm.2018.02.001Crossref Scopus (12) Google Scholar, 4Hidema R. Fukushima K. Yoshida R. Suzuki H. Vortex deformation and turbulent energy of polymer solution in a two-dimensional turbulent flow.J. Non-Newtonian Fluid Mech. 2020; 285104385https://doi.org/10.1016/j.jnnfm.2020.104385Crossref Scopus (3) Google Scholar, 5Fukushima K. Kishi H. Suzuki H. Hidema R. Modification of turbulence caused by cationic surfactant wormlike micellar structures in two-dimensional turbulent flow.J. Fluid Mech. 2022; 933: A9https://doi.org/10.1017/jfm.2021.1058Crossref Scopus (1) Google Scholar]. The effects of the extensional rheological properties of polyethylene oxide solutions were focused to understand the vortex deformation in turbulent flow and turbulent statistics of the polymer solution. In the polymer solution, although the turbulent energy production was virtually zero, a characteristic peak appeared in turbulent energy. The results imply the extension and relaxation of polymers affect the energy transfer.In the second part, I will introduce a method to measure the drag force due to synthetic polymers in flowing fluids by using a scanning probe microscope [[6]Hidema R. Hayashi S. Suzuki Hiroshi Drag force of polyethyleneglycol in flow measured by a scanning probe microscope.Phys. Rev. Fluids. 2019; 4074201https://doi.org/10.1103/PhysRevFluids.4.074201Crossref Scopus (2) Google Scholar,[7]Hidema Ruri Fujito Ken-ya Suzuki Hiroshi Drag force of polyethyleneglycol in flows of polymer solutions measured by a scanning probe microscope.Soft Matter. 2022; 18: 455https://doi.org/10.1039/D1SM01305JCrossref PubMed Google Scholar]. The conformation of polymers attached to the cantilever probe was predicted, and the drag force due to the deformed polymers in a flow was calculated. The drag forces obtained by model calculations were compared to the force detected by experiments, and found to be reasonably close.

Engineering network entanglement of functionalized graphene oxide/poly(acrylamide) nanocomposites for enhanced oil recovery

Hydroxyl-functionalized graphene oxide (OGO) was prepared from graphene oxide (GO) modified by diethanolamine (DEOA) to promote the interaction between nano sheets and polymer molecules. Three OGO samples with different GO to DEOA ratios, and an acrylamide-based polymer (PM) were synthesized. The nanoparticle and polymer hybrid systems were prepared using GO or OGO suspension into PM solution. The interaction strength investigation indicated that the hybrid system had two kinds of hydrogen bonds, one is between amide groups on polymer and the other is between amide groups on polymer and hydroxyl groups on nanosheets, and there was a competition for them. As a result, a proper surface hydroxyl density is critical to form a suitable molecular network for improving the hybrid property under harsh condition. The rheological properties of PM solution and these hybrid systems were studied, and the results showed that the introduction of OGO obviously improved the salt-resistance and temperature-tolerance of PM solution. The results from oil displacement experiments showed that the enhanced oil recovery ratio jumped to 20.9% for PM/OGO system, while it was only 13.8% for PM solution.

Effect of Fiber on Rheological Properties and Flow Behavior of Polymer Completion Fluids.

The application of fiber in the completion fluid can improve the rheological properties of the completion fluid and the plugging quality of the production layer by the completion fluid and reduce the damage of the filtrate to the reservoir formation. However, there are few studies on the influence of fibers on the rheological properties of completion fluids and the flow behavior in pores. In this paper, plant fiber, mineral fiber, and synthetic fiber are discussed. Carbon fiber, bamboo fiber, polypropylene fiber, and polyester fiber are selected as research objects. The dependence of the rheological property of polymer solution on fiber type, fiber concentration, temperature, and shear rate is evaluated. The evaluation is carried out by observing the microscopic state of the fiber through a microscope and a scanning electron microscope, testing the rheological property parameters of the fiber with an OFITE 900 rheological tester, and fitting with the Herschel–Bulkley model. The results show that polypropylene fiber and carbon fiber have the best dispersion in polymer solution. The higher the fiber content, the greater the influence of fiber on the rheological properties of the solution. Compared with the other three fibers, carbon fiber has the greatest influence on the rheological properties of polymer solution. When the temperature is lower than 70 °C, the influence of the fiber on the rheological properties of the solution is not affected by the temperature. When the temperature exceeds 70 °C, the carbon fiber and polypropylene fiber are affected by the temperature, and the viscosity of the polymer solution is increased. The flow behavior of fiber suspensions in pores varies with the flow factor n. Carbon fiber suspensions are most conducive to the transition of polymer solution to plate laminar flow, which can improve the bearing capacity of plugging materials.

Vortex deformation and turbulent energy of polymer solution in a two-dimensional turbulent flow

An experimental study was performed to investigate the effects of the extensional rheological properties of polymer solutions on vortex deformation in turbulent flow and turbulent statistics. To focus on the extensional properties, a self-standing two-dimensional (2D) turbulent flow was used as an experimental setup, and the flow was observed through interference patterns and particle image velocimetry (PIV). Vortex shedding and the resulting deformation in the 2D flow were categorized into three types. The vortex flow regime was defined by the shedding frequency and relaxation time of the polymer solution. Turbulent energy was suppressed by polymer additives; however, a characteristic peak reappeared with increasing concentration. The results imply that the characteristic turbulent energy peak is influenced by the relaxation process of the extended polymers in the flow.

Effects of rheological properties on heat transfer enhancements by elastic instability in von-Karman swirling flow

Elastic instability is proposed as a promising method to intensify heat transfer under very low Reynolds number conditions. However, the onset of elastic instability and its influence on heat transfer is highly dependent on the rheological properties of polymer solution, which has not been revealed. By varying polymer concentration, sucrose proportion and the degree of salinity, the heat transfer performance due to the variations of rheology is investigated in a swirling flow configuration between parallel plates. The results indicate that both the increase of polymer concentration and the reduction of the salinity can induce elastic instability easily, leading to a better heat transfer performance when the swirling velocity is fixed. However, the salinity effects become weakened as the swirling velocity continually increases and the maximum enhancement becomes independent on salinity. In particular, the heat transfer performance based on pure elastic instability shows larger enhancement than that of inertial-elastic instability at low Reynolds number.

Effects of salinity on the onset of elastic turbulence in swirling flow and curvilinear microchannels

Elastic turbulence, which is sensitive to geometry and polymer rheology, has shown great potential for improving the performance of mixing, heat transfer, and even oil recovery. Recent studies showed the importance of the rheological properties of polymer solutions on the onset of elastic turbulence. However, variations of rheological properties based on polymer sensitivities such as salinity and its corresponding effects on the elastic turbulence have not been revealed. This work investigated systematically the effects of salinity on the onset of elastic turbulence in both swirling flow and curvilinear microchannels. The variations of statistical properties, such as probability distribution functions (PDFs) and power spectral density of injected power (PSD), were analyzed for characterization. The onset conditions of elastic turbulence are postponed by high salinity, which is consistent with the mixing performance in a curvilinear microchannel. A salinity independent power-law exponent at a value of −4.3 is observed in a fully developed elastic regime for all polymer solutions. Particularly, the diffusion of fluorescein at a low flow rate in the microchannel is possible due to the existence of a steady secondary flow before the onset of elastic instability.

ВЛИЯНИЕ МИНЕРАЛИЗАЦИИ ПЛАСТОВЫХ ВОД НА ФИЗИКО-ХИМИЧЕСКИЕ И ФИЛЬТРАЦИОННЫЕ ХАРАКТЕРИСТИКИ ПОЛИМЕРНЫХ РАСТВОРОВ И ГЕЛЕЙ ДЛЯ ПОВЫШЕНИЯ НЕФТЕОТДАЧИ ПЛАСТОВ

Актуальность. В последние годы технологии полимерного заводнения широко применяются при эксплуатации нефтяных и газовых месторождений, особенно на поздних стадиях разработки месторождений. Однако при эксплуатации коллекторов с повышенной температурой более 70–80 °С и высокой степенью минерализации пластовых вод многие полимерные нефтевытесняющие агенты подвергаются быстрой деструкции, что приводит к снижению уровня добычи углеводородного сырья. В связи с этим одной из важных проблем является создание и разработка термо- и солеустойчивых полимерных материалов и композиций на их основе для повышения добычи углеводородного сырья на нефтяных и газовых месторождениях. Цель: исследование влияния минерализации пластовых вод на физико-химические и фильтрационные характеристики полимерных растворов и гелей для повышения нефтеотдачи пластов. Методы. Определение вязкости растворов полимера и полимерного геля проводили на вискозиметре Брукфилда DV-II, форму и размеры частиц полимеров и полимерного геля изучали на сканирующем электронном микроскопе марки Hitachi S-400N, измерение размеров полимерного молекулярного клубка Dh определяли на установке Brookhaven BI-200SM, широкоугольная динамическая/статическая система рассеяния света (Brookhaven Instruments Cop., США), физическое моделирование процесса фильтрации жидкости при пластовых условиях проводили на фильтрационной установке, определение вязкоэластичности и реологических свойств полимерных растворов и гелей изучали с помощью реометра Harke 10. Результаты. Степень минерализации пластовой воды оказывает значительное влияние на вязкость растворов полимеров. В связи с тем, что в частично деминерализованной воде предварительно были удалены ионы кальция и магния, полимеры обладают хорошей растворимостью и способностью увеличения вязкости растворов. С увеличением концентрации вытесняющего агента вязкость растворов возрастает. Деструктивное воздействие солей пластовых вод на полимеры вызывает значительное снижение вязкости растворов вытесняющих агентов. Из-за высокой степени минерализации частично деминерализованной воды большое количество ионов хлористого натрия окружают молекулярный скелет полимера вытесняющего агента. Макромолекулы полимера П-1 имеют преимущественно двухмерную сетевую структуру. Макромолекулы полимеров П-2 и П-3 имеют преимущественно пространственную трехмерную сетевую структуру, в которой некоторые полимерные молекулярные цепи разорваны и сетевая структура полимеров является дефектной. По сравнению с полимером П-3, трехмерная сетевая структура полимерного молекулярного агрегата П-4 имеет более четкое пространственное строение. Из сравнения физико-химических свойств полимеров П-1, П-2 и П-3 следует, что коэффициент сопротивления и коэффициент остаточного сопротивления для полимера П-1 больше, чем для полимеров П-2 и П-3. Это связано с тем, что молекулы солеустойчивого полимера П-1 образуют агрегаты сетевой структуры вследствие межмолекулярной ассоциации, которая приводит к плохой совместимости с порами керна, а коэффициент сопротивления и коэффициент остаточного сопротивления для полимера П-4 наибольшие за счет того, что в реакционной полимерной смеси прошли реакции внутримолекулярного сшивания молекул полимера и катионов Cr3+, которые привели к значительному увеличению удерживания раствора полимера, фильтрационного сопротивления, давления нагнетания и к повышению нефтеотдачи пластов.

Elucidating the Effects of Metal Complexation on Morphological and Rheological Properties of Polymer Solutions by a Dissipative Particle Dynamics Model

When a salt is added to a polymer solution, metal cations may coordinate with polymer ligands forming interchain and intrachain links. Metal coordination leads to drastic changes of polymer morphology, formation of clusters, and, ultimately, a sol–gel transition that affect the solution rheology. Although metal coordination is ubiquitous in polymeric systems, the physical mechanisms of coordination-induced morphological and rheological changes are still poorly understood due to the multiscale nature of this phenomenon. Here, we propose a coarse-grained dissipative particle dynamics (DPD) model to study morphological and rheological properties of concentrated solutions of polymers in the presence of multivalent cations that can coordinate the polymer ligands. The coordinating metal is introduced as a 3D complex of planar, tetrahedral, or octahedral geometry with the central DPD bead representing the metal cation surrounded at the vertices by either four or six dummy beads representing coordination sites, s...

Study on rheological properties of CMC/Eu-Tb solutions with different concentrations

The rheological properties of polymer solution are sensitive to variations in the polymer structure. Carboxymethyl cellulose (CMC) aqueous solution has been used in many fields, such as food, medicine and paper industry. In this paper, the effects of different concentrations (2% - 6%) of CMC/Eu-Tb on their rheological properties were investigeted, including steady-state flow and viscoelastic response. The results show that, the viscosity of CMC/Eu-Tb is lower than that of CMC, at the same concentrations; the products solutions present a nearly Newtonian behavior at the low concentrations (2% - 3%); while at the higher concentrations (4% - 6%), the products solutions present a pseudoplastic behavior; shear-thinning behavior is due to the polymer chains unravel under the action of flow and the molecular chains are oriented in the flow direction. The results also show that the viscosity of the solutions decreases with increasing temperature. Dynamic rheological tests show that CMC/Eu-Tb has viscoelasticity in the concentrations of 2% - 6%. At lower concentrations, the elastic modulus G′ is slightly higher than the viscous modulus G″, and as the concentrations increase, the elastic modulus G′ is significantly higher than the viscous modulus G″. It means that at the lower solution concentrations, the solutions tend to be less elastic and easier to flow. Most of the energies are lost through the viscous flow. As the solution concentrations increase, the solutions tend to be more elastic, and the system tends to form a gel.

Effects of the extensional rheological properties of polymer solutions on vortex shedding and turbulence characteristics in a two-dimensional turbulent flow

An experimental study was performed to investigate the relationship between the extensional rheological properties of polymer solutions and vortex deformation in turbulent flow. Polyethyleneoxide as a flexible polymer and hydroxypropyl cellulose as a rigid polymer are added to two-dimensional (2D) turbulent flow. Specifically, 2D flow is advantageous as it examines the effect of the extensional rheological properties of polymers on the flow. In the study, 2D turbulent flow and vortex shedding in 2D turbulent flow were observed using interference patterns and particle image velocimetry (PIV). Power spectrum of the 2D flow images and 2D turbulence statistics calculated by PIV analysis indicated that there are three flow regimes of vortex shedding in the 2D turbulent flow of the polymer solution. The vortex shedding in the 2D flow was categorized into three types, and this was affected by the relaxation time of the polymer solutions.

The effect of poly (lactic-co-glycolic) acid composition on the mechanical properties of electrospun fibrous mats

The aim of this study was to investigate the influence of polymer molecular structure on the electrospinnability and mechanical properties of electrospun fibrous mats (EFMs). Polymers with similar molecular weight but different composition ratios (lactic acid (LA) and glycolic acid (GA)) were dissolved in binary mixtures of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF). The intrinsic viscosity and rheological properties of polymer solutions were investigated prior to electrospinning. The morphology and mechanical properties of the resulting EFMs were characterized by scanning electron microscope (SEM) and dynamic mechanical analysis (DMA). Sufficiently high inter-molecular interactions were found to be a prerequisite to ensure the formation of fibers in the electrospinning process, regardless the polymer composition. The higher the amount of GA in the polymer composition, the more ordered and entangled molecules were formed after electrospinning from the solution in THF-DMF, which resulted in higher Young’s modulus and tensile strength of the EFMs. In conclusion, this study shows that the mechanical properties of EFMs, which depend on the polymer molecule-solvent affinity, can be predicted by the inter-molecular interactions in the starting polymer solutions and over the drying process of electrospinning.

高分子の伸長粘度および配向性が二次元流れの渦形成に与える影響

Addition of a little amount of high-molecular-weight polymers in a Newtonian fluid reduces turbulent intensity, which causes the drag reduction in a pipe flow. When the drag reduction occurs in a flow, vortices generated in the flow deform. In this study, in order to understand the vortex formation and vortex deformation in turbulent flows affected by extensional rheological properties of polymer solution, we have observed the vortices in two-dimensional turbulence. Polyethylene oxide and hydroxypropylcellulose were used as polymers that have different extensional rheological properties. We investigated how the relaxation time of the polymer solution that is related to the extensional viscosity of the solution affected the vortex shedding in two-dimensional flow.