High Concentration Polymer Solution Research Articles

Physicochemical Limitations of Capillary Models Applied to High-Concentration Polymer Solutions.

Advances in binder jet printing (BJP) require the development of new binder–powder systems, for example, to increase compatibility with better performance metal alloys or to increase the strength of parts using stronger binders. The dynamics of binder absorption are principally understood through capillary models. However, validation of these models in BJP has focused on variation of powder properties. Using a design-of-experiments approach and an optical observation method to track absorption of droplets, this study tests the influence of fluid properties on absorption time against the predictions of capillary models. Properties specific to polymeric binders, such as molecular weight and entanglement state, are also considered. Capillary models are found to be generally accurate in predicting absorption time in dilute systems; however, these predictions are not accurate for highly concentrated binder solutions. The effect of polymer entanglement becomes prevalent as the solution concentration increases, which can also potentially occur as a result of increased evaporation due to powder bed heating. Specifically, concentrated solutions close to the onset of entanglement will absorb much more slowly than predicted. Future models of BJP systems must account for the possibility of polymer entanglement throughout the absorption process. Improved models will provide a more accurate understanding of the flow and solidification of the binder in the powder, allowing faster development of new binders for improved performance in printing.

Effects of viscoelasticity on the onset of vortex shedding and forces applied on a cylinder in unsteady flow regime

The present paper aims to investigate the effect of viscoelasticity on the onset of vortex shedding of a high concentration polymer solution over a cylinder using the finite volume method for the first time. To describe the behavior of the viscoelastic fluid, mathematically, the Phan–Thien–Tanner (PTT) model is employed. The convergence problems are resolved using the rheoFoam solver developed by previous researchers based on the log-conformation method. The exact critical Reynolds number (Recr), which corresponds to the onset of vortex shedding, is estimated by implementing numerous unsteady simulations at each elasticity number (El). The Recr is also calculated at every retardation ratio (β) and elongational viscosity. The results revealed a significant impact of viscoelasticity on Recr so that the flow of a high viscosity ratio PTT becomes unstable at higher Re (at very low El) or lower Re (at higher El), compared to a Newtonian fluid. In addition, Recr decreases linearly with β according to Recr=−34.5β+46.525 and increases with extensional viscosity. It is also found that β plays a vital role in the effect of viscoelasticity on the flow parameters. The averaged drag coefficient (CD¯) and the amplitude of lift coefficient (CLmax) do not have similar behaviors for low and high β. Moreover, viscoelasticity enlarges the vortices and increases the shedding frequency. A comprehensive physical analysis of flow structures is carried out using the distribution of time-averaged stress components and pressure over the cylinder. The numerical results demonstrated the three regimes of drag reduction at El < 0.015, drag enhancement at 0.015 < E1 < 1, and a Newtonian behavior at El > 1 that is an opposite trend compared to a steady regime. The variations of CLmax with El are also similar to CD¯, but at different critical elasticity numbers (El = 0.005 and 2). It is found that the normal stress changes the drag force by the variation of pressure distribution over the cylinder, while the shear stress directly affects the drag and lift forces. In addition, the viscoelasticity decreases the size of the vortices behind the cylinder and increases their vorticity, and changes the position of maximum normal stress, which leads to drag variations. It was also concluded that the higher the elongational viscosities, the lower the shedding frequency.

Interaction between microalgae, marine snow and anionic polyacrylamide APAM at marine conditions

When an oil field ages and the pressure in the reservoir decreases, or for oil fields with heavy oil, there may be a need for enhanced oil recovery (EOR) technologies. Polymer injection is a water-based EOR method where the viscosity of the water injected for pressure support is increased by mixing with a high concentration polymer solution. In this project, the potential fate of a synthetic anionic polyacrylamide (APAM) in seawater was investigated, since these EOR polymers may enter the marine environment with the produced water (PW). The main objective of the study was to determine if the APAM will interact with cells or aggregates (marine snow) of microalgae, resulting in potential polymer transport from the euphotic zone to the seabed. Three different species of microalgae with different degree of autotrophy (autotroph, mixotroph and heterotroph) were exposed to fluorescence-tagged APAM. Attachment to algal cells or aggregates formed by active or heat-inactivated algae were analysed by fluorescence microscopy and fluorometry. Our results suggested that attachment of APAM to cells of the algal species included in his study was negligible. A carousel system with natural seawater (SW) was used for formation of algal aggregates, one of the key components of marine snow. When aggregates of the diatom Thalassiosira rotula were formed in the presence of the fluorescence-tagged APAM, and at SW temperatures relevant for the Norwegian Continental Shelf, the polymer was nearly exclusively measured in the water phase after separation from the aggregates. The aggregate measurements therefore confirmed the results from the attachment studies, and we found no evidence of accumulation of APAM in aggregates formed from algae. Marine snow from algae is therefore not expected to significantly contribute to sedimentation of APAM dissolved in the water column.

Numerical study of Phan-Thien–Tanner viscoelastic fluid flow around a two-dimensional circular cylinder at a low Reynolds number: a new classification for drag variations regimes

This study numerically investigates a low Reynolds two-dimensional flow of a viscoelastic fluid over a circular cylinder using the finite volume method. The Phan-Thien–Tanner model, as one of the most accurate non-linear models, for the first time, describes the viscoelastic behavior of a high concentration polymer solution in the flow over a cylinder in high elastic regime in Re = 10. To avoid divergence and to stabilize the numerical process in high elastic cases, the log-conformation approach proposed by previous researchers is used. The convective terms of the equations are discretized using a high-resolution scheme. The physical instability, as observed by some researchers in the creeping regime of high De flow, is very weak in the cases of this research. The numerical results of this research show both drag reduction (for the elasticity number El 0.025). Compared with the dissipative nature of viscoelastic fluid flows, the drag coefficient, resulted from the polymeric portion of stress, in the high elastic flow regime (El > 10), approached to zero due to an increase in the storing nature of viscoelastic fluid. At these elasticity numbers, the drag coefficient remains constant with El, and the material behaves like a Newtonian fluid. Compared with the shear-thinning behavior and unlike the creeping flow, the elasticity is the main cause of drag variation in most cases. Shear stress affects the drag force directly, while normal stress influences the drag force by changing the pressure distribution over the cylinder. The maximum normal stress occurs at the back of the cylinder due to the wake behind it, while in creeping flow it occurs at its half-front. Finally, the effects of elasticity number, retardation ratio and model parameters on the distribution of stress components, drag coefficient, and vortex dimensions are investigated separately, and a physical discussion is presented.

ИССЛЕДОВАНИЕ ФИЛЬТРАЦИОННЫХ И РЕОЛОГИЧЕСКИХ СВОЙСТВ ПОЛИМЕРНОГО ГЕЛЯ ДЛЯ ПОВЫШЕНИЯ НЕФТЕОТДАЧИ ПЛАСТОВ

Актуальность. Полимерное заводнение широко применяется на практике при разработке нефтяных месторождений. Высококонцентрированные растворы полимера с высокой массовой концентрацией обладают повышенной вязкоэластичностью, но с увеличением массовой концентрации полимерного раствора возникает проблема о совместимости между размером агрегата молекул полимера и размером пор в пласте. Cr3+ полимерный гель, основанный на внутримолекулярном сшивании молекул, имеет меньший размер агрегата и хорошую совместимость с пластом, поэтому очень актуальными являются исследования эффекта гелеобразования. Цель: исследование фильтрационных и реологических свойств водного геля на основе полиакриламида в присутствии ацетата хрома для повышения нефтеотдачи платов. Методы: физическое моделирование процесса нефтевытеснения и процесса фильтрации жидкости при пластовых условиях на фильтрационной установке, определение вязкости полимерного геля на вискозиметре Брукфилда DV-II, измерение размера полимерного молекулярного клубка Dh на установке Brookhaven BI-200SM, широкоугольная динамическая/статическая система рассеяния света (Brookhaven Instruments Cop., США), определение вязкоэластичности с помощью реометра Harke10. Результаты. Регулированием массовой концентрации полимерного раствора, степени минерализации воды и соотношения содержания полимера к хрому (w(П/Cr3+)) можно получить Cr3+ полимерную гелевую систему, основанную на внутримолекулярном сшивании молекул с меньшим размером молекулярной агрегации и большим фильтрационным сопротивлением. После реакции внутримолекулярного сшивания полимерного раствора, с одной стороны, вязкоэластичность системы значительно улучшается и коэффициент вытеснении нефти из пластов увеличивается. С другой стороны, реакция внутримолекулярного сшивания молекул снижает гибкость агрегатов полимерной молекулы, повышает их жесткость, ухудшает их деформируемость в процессе прохождения через поры и увеличивает задержки молекул полимера в слое с высокой проницаемостью пласта. Cr3+ полимерная гелевая система не только обладает хорошей приемистостью, но может также постепенно достигать более высокого давления нагнетания, за счет этого увеличивается коэффициент охвата пласта. В итоге коэффициент извлечения нефти с применением системы полимерного геля становится выше, чем коэффициент извлечения нефти из пласта с использованием системы полимерного раствора.

Ordered porous conjugated poly(p-phenylene)s films self-assembled through alcohol-controlled breath figure method

Because of their wide applications, the polymer porous films with regular patterned structure have attracted more and more attention. Herein, the porous films created from the poly(p-phenylene)s/CHCl3 solutions have been self-assembled in an alcohol-water mixed vapor atmosphere. The results show that the patterns of the films depend on the polymer concentration and the ratio of alcohols to water. The introduction of a small amount of alcohols can improve the regular pore patterns of the porous films. Using the mixed water/methanol droplets as soft templates, the ordered porous films can be obtained from a high-concentration polymer solution. The low-concentration polymer solution and a high ratio of alcohol to water lead to form large pores in the films. The alcohol-controlled breath figure method is a facile way to design and fabricate ordered porous films based on a conjugated polymer.

Experimental study of two-phase oil – Polymer flow in horizontal flow path

Two-phase flow inside the oil and gas wells and flow path lines is a usual occurrence in petroleum and petrochemical studies. Due to its complexity, flow transfer parameters such as hold up and pressure drop and their dependency on the flow regime maps are not well understood yet. This study is aimed at analyzing holdup for oil- water system and evaluation of this parameter by means of Image processing under different available flow regime conditions. In addition, different oil-polymer systems have been studied to evaluate the impact of polymer concentration on transport criteria. The experimental setup used for this study is consisted of a 12 m long Plexiglas pipe with an inner diameter of 30 mm. The results revealed that the only polymer solutions with polymer concentration below than 333 ppm behave as Newtonian fluids. The results showed that low concentration of polymer solution acts as drag reducing agent and reduces the amount of pressure gradient in comparison with oil – water system. Furthermore, the change in flow pattern map between oil-low concentration polymer solution and oil-high concentration polymer solution systems have been analyzed. The results showed that high concentration polymer solution not only leads to higher degrees of pressure drop but also impacts the flow pattern map and more specifically the Three-Layer flow regime cannot be observed in such flow systems. Therefore, a generalized model has been developed to define the flow regime map and the transition criteria between different flow regimes as well as pressure drop and hold up for oil – polymer systems.

Pressure Transient Behavior for Alternating Polymer Flooding in a Three-zone Composite Reservoir

Alternating polymer flooding has achieved great attractions recently in oil industry, however, the research of pressure analysis in alternating polymer flooding reservoir is rare. This work presents a numerical pressure analysis method of three-zone composite model for formation evaluation. A new numerical pressure analysis model (three-zone composite model) is established by considering diffusion, convection, shear, and inaccessible pore volume, which is based on the rheology experiments. Based on this model, the type curves are then developed and sensitivity analysis is further conducted. The type curves have seven regimes in three-zone composite model. The characteristic is the obvious upturn of pressure derivative curve in transient regime between low concentration and high concentration polymer solution. Formation parameters can be interpreted by history matching and formation evaluation can be conducted based on this model. As an important part of formation evaluation, formation damage as a result of adsorption of polymers in porous media is evaluated by comparing the interpreted permeability with the original value before polymer flooding. The field test data proves that this proposed method can accurately evaluate reservoir characteristics in alternating polymer flooding reservoirs, which emphasizes the potential application of this method in petroleum industry.

Numerical Calculation of Viscous-Elastic Fluid Flooding Residual Oil Film in the Complex Pore

In order to analyze the stress and deformation of different permeability of residual oil film in the complex pore, which are affected by the viscous-elasticity of the fluid, the hydrodynamic displacement mechanism is explored from the stand-point of hydrodynamics, that is, the residual oil film displaced by alternating injection of different concentrations of the polymer solution, viscous-elastic fluid flow equation is established in the complex pore by choosing continuity equation, motion equation and the upper convected Maxwell constitutive equation. The flow field is computed by using the method of numerical analysis. Not only the stress and deformation of residual oil film on the different permeability of micro pores, but also the analysis of the flooding mechanism of alternating injection of different concentrations of the polymer solution is got. The results show that the larger the viscous-elasticity of polymer solution is, the bigger the normal deviatoric stress acting on the residual oil film is; the distribution of normal deviatoric stress has the abrupt change. The stronger the viscous-elasticity of the polymer solution is, the bigger the horizontal stress difference acting on the residual oil film is and the more obvious the deformation is; the high-concentration polymer solution is suitable for high-permeability micro pores. Low-concentration polymer solution is suitable for medium and low-permeability micro pores. Alternating injection of polymer solution can improve Volumetric Sweep Efficiency and increase the deformation of residual oil film, which is conducive to enhancing oil recovery.

Experimental Research on the Quantitative Characterizations of Elasticity and Viscosity of Polyacrylamide Solution

Through creep-recovery and dynamic experiments, the viscoelasticity of polyacrylamide solutions (in short polymer) with different mass concentration are studied, the proportions of elastic part and viscous part in the polymer solution are calculated and the limit of mass concentration called high concentration polymer solution is given. It is indicated that the elastic part of the polymer solution increases firstly and tends to be constant with the increase in mass concentration under low external force condition. The minimum mass concentration of the polymer solution keeping constant elastic part is 1500mg/L. Under low stress and low shear rate conditions, the viscous part of the polymer solution is greater than that of elastic part; but under oil reservoir shear rate (6.283s-1) condition, the elastic part is greater than viscous part, and its elastic part increases with the increase in mass concentrations and the increment becomes smaller.

Study on Characteristics and Oil Displacement Characteristics of High Concentration Polymer System

Through laboratory experiments, viscosity stability of high concentration polymer solution was studied. Viscoelasticity of high concentration polymer was measured by HAAKE RS-150 Rheometer. The flow tests of high concentration polymer solution were carried out by utilizing artificial homogeneity cores, while the influence of injection time on displacement characteristics of high concentration polymer were studied on artificial heterogeneous cores. The results showed that high concentration polymer solution had a good stability within 15 days, but decreased significantly after 30 days. Both viscosity and elasticity of high concentration polymer are higher than the lower ones’. Because the high viscoelasticity of high concentration polymer made the flow resistance increase, resistance coefficient and residual resistance coefficient were very high. Therefore viscoelasticity of high concentration polymer could make a large improvement on chemical flooding recovery.

A modified coaxial electrospinning for preparing fibers from a high concentration polymer solution

A new process technology modified from conventional coaxial electrospinning process has been developed to prepare polymer fibers from a high concentration solution. This process involves a pure solvent concentrically surrounding polymer fluid in the spinneret. The concentric spinneret was constructed simply by inserting a metal needle through a high elastic silica gel tube. Two syringe pumps were used to drive the core polymer solution and the sheath solvent. Using polyvinylpyrrolidone (PVP) as the polymer model, which normally has an electrospinnable concentration of 10% w/v in ethanol, it was possible to electrospin 35% w/v of PVP in the same solvent, when pure N, N-dimethylacetamide (DMAc) was used as sheath fluid. The resultant fibers have a smooth surface morphology and good structural uniformity. The diameter of the fibers was 2.0±0.25 µm when the DMAc-to-polymer-solution flow rate ratio was set as 0.1. The process technology reported here opens a new window to tune the polymer fibers obtained by the electrospinning, and is useful for improving productivity of the electrospinning process.

Polymer and surface roughness effects on the drag crisis for falling spheres

. We make time resolved velocity measurements of steel spheres in free fall through liquid using a continuous ultrasound technique. We explore two different ways to induce large changes in drag on the spheres: 1) a small quantity of viscoelastic polymer added to water and 2) altering the surface of the sphere. Low concentration polymer solutions and/or a pattern of grooves in the sphere surface induce an early drag crisis, which may reduce drag by more than 50% compared to smooth spheres in pure water. On the other hand, random surface roughness and/or high concentration polymer solutions reduce drag progressively and suppress the drag crisis. We also present a qualititative argument which ties the drag reduction observed in low concentration polymer solutions to the Weissenberg number and normal stress difference.

Formation of Taylor Vortex Flow of Polymer Solutions

Laser-induced fluorescence (LIF) was applied for the flow visualization of the formation of a Taylor vortex, which occurred in the gap between two coaxial cylinders. The test fluids were tap water and glycerin 60 %wt solution as Newtonian fluids; polyacrilamide (SeparanAP-30) solutions in the concentration range of 10 to 1000ppm and polyethylene-oxide (PEO15) solutions in the range of 20 to 1000ppm were tested as non-Newtonian fluids. The Reynolds number range in the experiment was 80<Re<4.0×103. The rotating inner cylinder was accelerated under the slow condition (dRe*∕dt⩽1min−1) in order to obtain a Taylor vortex flow in stable primary mode. Flow visualization results showed that the Görtler vortices of half the number of the Taylor cells occurred in the gap when the Taylor vortex flow was formed in the primary mode. In addition, the critical Reynolds number of the polymer solutions increased, where Taylor vortices occur, because the generation of the Görtler vortices was retarded. In high concentration polymer solutions, this effect became remarkable. Measurements of steady-state Taylor cells showed that the upper and lower cells of polymer solutions became larger in wavelength than those of the Newtonian fluids. The Taylor vortex flow of non-Newtonian fluids was analyzed and the result obtained using the Giesekus model agreed with the experimental result.

Perturbed hard-sphere-chain theory modeling of vapor–liquid equilibria of high concentration polymer and coploymer systems

Perturbed hard-sphere-chain (PHSC) theory equation of state (EOS), which is based on the square-well model of Alder et al. is applied to calculate and predict the solubilities of solvents and gases in polymers and copolymer. The calculations with one temperature-independent binary parameter K 12, and the predictions with K 12=0 are performed for 29 polymer solutions and 9 copolymer mixtures. The obtained results show that this EOS can describe vapor–liquid equilibria(VLE) of high concentration polymer and copolymer solutions very well. The purely predicted results show that the equation has very good predicting potential.

Aggregation Number Determination in Aqueous Solutions of a Hydrophobically Modified Poly(ethylene oxide) by Fluorescence Probe Techniques

In this paper, we report the results of fluorescence probe studies of association in aqueous solution of a model polymer ODU, which is a C18H37 end-capped monodisperse poly(ethylene oxide) with a molecular weight of 35 000 and essentially 100% end group substitution. The main parameter of interest is the end group aggregation number NR, which we determine by the time-resolved fluorescence quenching technique using pyrene as a probe. Aiming to extend this technique to situations where the probe is not solubilized completely by the polymer micelles, which happens when the polymer concentration in a solution becomes very low, we modified the standard Poisson quenching model to account for the emission of the probe in the water phase. ODU solutions undergo phase separation at polymer concentrations between 2.1 g/L and 20 g/L. The aggregation number in a 2.1 g/L solution was found to be 23. For high concentration polymer solutions, from 3 to 17 wt %, we found that the aggregation number tends to increase with ...

Formation of concentration gradient and its application to DNA capillary electrophoresis

A new method to introduce the concentration gradient into the capillary has been developed and its application to DNA capillary electrophoresis is presented. The concentration gradient produced by mixing 5% w/v polyacrylamide-co-poly(N-dimethylacrylamide) (PAM-co-PDMA) solution and 1 × Tris/N-tris(hydroxymethyl)methyl-3-amino-propanesulfonic acid/EDTA (TT) + 5 M urea buffer was successfully achieved by using two programmable syringe pumps with strict control of dead volume, flow rate, and pressure balance. This method has the advantages of high stability, reproducibility, and versatility. The column with concentration gradient greatly improved the resolution, especially for the large DNA fragments, due to a decrease in band width broadening with time. A column containing 2—4% w/v gradient in four steps had a longer read length, shorter separation time and better resolution (after 380 base) than that of 4% w/v single concentration polymer solution. The number of steps in the gradient had almost no effect on the performance. The change in the average concentration by relocating the position of the same step gradient, i.e., a combination of different low concentration to high concentration polymer solution ratios, resulted in a different migration time, read length and resolution.

Formation of concentration gradient and its application to DNA capillary electrophoresis.

A new method to introduce the concentration gradient into the capillary has been developed and its application to DNA capillary electrophoresis is presented. The concentration gradient produced by mixing 5% w/v polyacrylamide-co-poly(N-dimethylacrylamide) (PAM-co-PDMA) solution and 1 x Tris/N-tris(hydroxymethyl)methyl-3-amino-propanesulfonic acid/EDTA (TT) + 5 M urea buffer was successfully achieved by using two programmable syringe pumps with strict control of dead volume, flow rate, and pressure balance. This method has the advantages of high stability, reproducibility, and versatility. The column with concentration gradient greatly improved the resolution, especially for the large DNA fragments, due to a decrease in band width broadening with time. A column containing 2-4% w/v gradient in four steps had a longer read length, shorter separation time and better resolution (after 380 base) than that of 4% w/v single concentration polymer solution. The number of steps in the gradient had almost no effect on the performance. The change in the average concentration by relocating the position of the same step gradient, i.e., a combination of different low concentration to high concentration polymer solution ratios, resulted in a different migration time, read length and resolution.

Comparison of Perturbed Hard-Sphere-Chain Theory with Statistical Associating Fluid Theory for Square-Well Fluids

The effect of hard-sphere-chain equations on the description of phase behavior is presented by the comparison of perturbed hard-sphere-chain (PHSC) theory with statistical associating fluid theory (SAFT) for square-well fluids. The PHSC-type equation of this work is based on the hard-sphere-chain equation of Chiew (PY−CS), the square-well fluid model of Alder et al., and the expression of Chen and Kreglewski. The PHSC-type equation has expressions similar to those of the SAFT equation. A comparison of the PHSC-type equation with the SAFT model shows that the PHSC-type equation of state presents slightly better results of pure compounds and much better vapor−liquid equilibrium results of high-concentration polymer solutions.

難水溶性薬物封入ポリ乳酸マイクロスフェアの新規調製法とその放出性

Polylactic acid (PLA) microspheres containing theophylline as a slightly soluble representative drug were prepared using the o/w emulsion in-water drying method. A high trapping efficiency was observed when polymer solution of high concentration was used and the drug/polymer weight ratio was increased. However, the particle size of the microspheres became extremely large when the high concentration polymer solution was used.Microspheres with a particle size of 88.6 μm were obtained when “ sub-emulsification” was performed with the external aqueous phase with an equal specific gravity to the polymer solution. On the other hand, the trapping efficiency of the microspheres was dependent on both the drug encapsulated in the microspheres and the particle size of microspheres.The release patterns of the drug from the microspheres showed an initial-burst release in all batches. The release rates of the drug from the microspheres prepared with the drug and polymer alone were very small. Therefore, an improvement in the drug release property of the microspheres was examined.The release rates of the drug from the microspheres increased si gnificantly depending on the amount of ethyl myristate that was incorporated as a release promoter.