Properties Of Polymer Solutions Research Articles

Oscillating grid turbulence in shear-thinning polymer solutions

Oscillating grid apparatuses are well known and convenient tools for the fundamental study of turbulence and its interaction with other phenomena since they allow to generate turbulence supposedly homogeneous, isotropic, and free of mean shear. They could, in particular, be used to study turbulence and mass transfer near the interface between non-Newtonian liquids and a gas, as already done in air-water situations. Although frequently used in water and Newtonian fluids, oscillating grid turbulence (OGT) generation has yet been rarely applied and never characterized in non-Newtonian media. The present work consists of a first experimental characterization of the flow properties of shear-thinning polymer (Xanthan Gum, XG) solutions stirred by an oscillating grid. Various polymer concentrations are tested for a single grid stirring condition. The dilute and semidilute entanglement concentration regimes are considered. Liquid phase velocities are measured by Particle Image Velocimetry. The existing mean flow established in the tank is described and characterized, as well as turbulence properties (intensity, decay rate, length scales, isotropy, etc.). OGT in dilute polymer solutions induces an enhanced mean flow compared to water, a similar decay behavior with yet different decay rates, and enhanced turbulence large scales and anisotropy. In the semidilute regime of XG, turbulence and mean flows are essentially damped by viscosity. The evolution of mean flow and turbulence indicators leads to the definition of several polymer concentration subregimes, within the dilute one. Critical concentrations around 20 ppm and 50 ppm are found, comparable to drag reduction characteristic concentrations.

Phase Diagram of Pinch-off Behaviors During Drop-on-Demand Inkjetting of Alginate Solutions

Viscoelastic polymer solutions have been extensively utilized in inkjet printing for a variety of biomedical applications. The pinch-off of viscoelastic jets is a key step toward the generation of droplets in inkjet printing. This complex process is governed by the interplay of four stresses, including inertial stress, capillary stress, viscous stress, and elastic stress. Depending on polymer solution properties and process conditions, four types of pinch-off phenomenon were observed during inkjetting of viscoelastic alginate solutions. In this study, material properties of alginate solutions with different concentrations have been characterized, and three dimensionless numbers (Ohnesorge number Oh, Deborah number De, and Weber number We) have been proposed to analyze different pinch-off behaviors. The phase diagram in terms of these three dimensionless numbers has been constructed to classify the regimes for different pinch-off types during inkjetting of viscoelastic alginate solutions. It is found that (1) at low De and Oh, the capillary stress is mainly balanced by the inertial stress, resulting in front pinching. (2) At medium De and low Oh, with the increase of We, the pinch-off type may change from front pinching to hybrid pinching to exit pinching. (3) At low Oh and high De, the capillary stress is mainly balanced by the elastic stress, resulting in exit pinching. (4) At high Oh and De, the viscoelastic effect is dominant. With the increase of We, middle pinching turns to be exit pinching due to the increase in the initial ligament diameter near the forming droplet.

A New Empirical Model for Viscosity of Sulfonated Polyacrylamide Polymers.

Copolymers of acrylamide with the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid—known as sulfonated polyacrylamide polymers—had been shown to produce very promising results in the enhancement of oil recovery, particularly in polymer flooding. The aim of this work is to develop an empirical model through the use of a design of experiments (DOE) approach for bulk viscosity of these copolymers as a function of polymer characteristics (i.e., sulfonation degree and molecular weight), oil reservoir conditions (i.e., temperature, formation brine salinity and hardness) and field operational variables (i.e., polymer concentration, shear rate and aging time). The data required for the non-linear regression analysis were generated from 120 planned experimental runs, which had used the Box-Behnken construct from the typical Response Surface Methodology (RSM) design. The data were collected during rheological experiments and the model that was constructed had been proven to be acceptable with the Adjusted R-Squared value of 0.9624. Apart from showing the polymer concentration as being the most important factor in the determination of polymer solution viscosity, the evaluation of the model terms as well as the Sobol sensitivity analysis had also shown a considerable interaction between the process parameters. As such, the proposed viscosity model can be suitably applied to the optimization of the polymer solution properties for the polymer flooding process and the prediction of the rheological data required for polymer flood simulators.

Ring polymer dynamics and tumbling-stretch transitions in planar mixed flows.

The properties of dilute polymer solutions are governed by the conformational dynamics of individual polymers which can be perturbed in the presence of an applied flow. Much of our understanding of dilute solutions comes from studying how flows manipulate the molecular features of polymer chains out of equilibrium, primarily focusing on linear polymer chains. Recently there has been an emerging interest in the dynamics of nonlinear architectures, particularly ring polymers, which exhibit surprising out-of-equilibrium dynamics in dilute solutions. In particular, it has been observed that hydrodynamics can couple to topology in planar elongational and shear flows, driving molecular expansion in the nonflow direction that is not observed for linear chains. In this paper, we extend our understanding of dilute ring polymer dynamics to mixed flows, which represent flow profiles intermediate between simple shear or planar elongation. We map the conformational behaviors at a number of flow geometries and strengths, demonstrating transitions between coiled, tumbling, and stretched regimes. Indeed, these observations are consistent with how linear chains respond to mixed flows. For both linear and ring polymers, we observe a marked first-order-like transition between tumbling and stretched polymers that we attribute to a dynamic energy barrier between the two states. This manifests as bimodal extension distributions in a narrow range of flow strengths and geometries, with the primary difference between rings and linear chains being the presence of molecular expansion in the vorticity direction.

Adhesion properties of poly(methylmethacrylate‐co‐n‐butylmethacrylate) copolymers in stent coatings

ABSTRACTThis work explores the adhesion properties of polymer solutions and thin coatings obtained by different‐composition poly(methylmethacrylate‐co‐n‐butylmethacrylate) copolymers. Surface wettability, work of adhesion, and work of spreading are calculated for solutions. Increasing amounts of n‐butylmethacrylate lead to higher values of work of adhesion, measured over two stent‐like flat surfaces (AISI 316L and pyrolytic carbon). The same moiety induces the solution viscosity increase and the decrease of the work of spreading and allows obtaining more homogeneous coatings. Adhesion of thin coatings is tested in dry (cross‐cut test) and wet (immersion) conditions. Adhesion tests of coatings obtained by solvent casting reflect thermodynamic parameters evaluated for solutions. Coatings show better strength in cross‐cut tests and a prolonged adhesion in wet conditions by raising the n‐butylmethacrylate fraction. The same trends are confirmed in commercial devices. In conclusion, the study of thermodynamic solution/substrate interactions can explain coating properties. The proposed approach is worthwhile to improve deposition procedures based on polymer solutions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47814.

QCN-Based Analysis for Predicting the Quality of Resulting Electrospun Nanofiber: Effect of Real-Time Transient Rheological Properties of Precursor Solution on Electrospinning.

There is a large margin between the mechanical properties and morphology of electrospun fibers required in each area. The produced fibers show a large difference depending on the external environment such as temperature, humidity, and season even in optimum concentration and same electrospinning set-up. The properties of polymer solution among the parameters are the largest determinant of the mechanical strength and diameter of electrospun fibers. Herein, the accurate predicting system in advance to electrospinning is required. In this study, we conduct a comparative study on the viscosity (measured by Brookfield rheometer) and the transient mass change and evaporation speed by our lab-made QCN in order to establish a predicting system for the quality of fiber. It was possible to measure the change of mass of the polymer solution in real-time using the lab-made QCN as well as calculating the volatility, the evaporation time of the polymer solution. The volatility of the polymer solution has a significant impact on the quality of the electrospun fiber including the diameter, uniformity, and surface topography. We compare the mass changes, viscosimetric viscosities, and the quality of corresponding fiber, and reveal the potential of QCN as a tool predicting pre-electrospinning fibers.

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.

Design of polyurethane fibers: Relation between the spinning technique and the resulting fiber topology

ABSTRACTProperties or characteristics of fibers are affected by their topology. In fact, these topologies are found to have significant impacts in the functionalities of many applications. Hence, in this study, the relations between the spinning techniques and the topology of the resulting fibers are studied with the aim to provide a guideline for future reference where fibers with certain topology can be fabricated to suit specific applications. For this purpose, polyurethane is chosen to be the raw material to fabricate the fibers due to its versatility to be applied in various fields. The surface morphology, structures, and alignments of the fibers are studied. It is found that the polymer solution properties largely influence the mechanisms in the spinning process and can significantly affect the topology of the fibers. For instance, viscous solutions enable the spinning of coiled and smooth fibers, whereas conductive solutions encourage the splaying of the solution jet which results in the spinning of straight fibers. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47706.

Study Rheological Behavior of Polymer Solution in Different-Medium-Injection-Tools.

Previous studies showed the difficulty during polymer flooding and the low producing degree for the low permeability layer. To solve the problem, Daqing, the first oil company, puts forward the polymer-separate-layer-injection-technology which separates mass and pressure in a single pipe. This technology mainly increases the control range of injection pressure of fluid by using the annular de-pressure tool, and reasonably distributes the molecular weight of the polymer injected into the thin and poor layers through the shearing of the different-medium-injection-tools. This occurs, in order to take advantage of the shearing thinning property of polymer solution and avoid the energy loss caused by the turbulent flow of polymer solution due to excessive injection rate in different injection tools. Combining rheological property of polymer and local perturbation theory, a rheological model of polymer solution in different-medium-injection-tools is derived and the maximum injection velocity is determined. The ranges of polymer viscosity in different injection tools are mainly determined by the structures of the different injection tools. However, the value of polymer viscosity is mainly determined by the concentration of polymer solution. So, the relation between the molecular weight of polymer and the permeability of layers should be firstly determined, and then the structural parameter combination of the different-medium-injection-tool should be optimized. The results of the study are important for regulating polymer injection parameters in the oilfield which enhances the oil recovery with reduced the cost.

Shear Force Fiber Spinning: Process Parameter and Polymer Solution Property Considerations.

For application of polymer nanofibers (e.g., sensors, and scaffolds to study cell behavior) it is important to control the spatial orientation of the fibers. We compare the ability to align and pattern fibers using shear force fiber spinning, i.e. contacting a drop of polymer solution with a rotating collector to mechanically draw a fiber, with electrospinning onto a rotating drum. Using polystyrene as a model system, we observe that the fiber spacing using shear force fiber spinning was more uniform than electrospinning with the rotating drum with relative standard deviations of 18% and 39%, respectively. Importantly, the approaches are complementary as the fiber spacing achieved using electrospinning with the rotating drum was ~10 microns while fiber spacing achieved using shear force fiber spinning was ~250 microns. To expand to additional polymer systems, we use polymer entanglement and capillary number. Solution properties that favor large capillary numbers (>50) prevent droplet breakup to facilitate fiber formation. Draw-down ratio was useful for determining appropriate process conditions (flow rate, rotational speed of the collector) to achieve continuous formation of fibers. These rules of thumb for considering the polymer solution properties and process parameters are expected to expand use of this platform for creating hierarchical structures of multiple fiber layers for cell scaffolds and additional applications.

How Does the Branching Effect of Macromonomer Influence the Polymerization, Structural Features, and Solution Properties of Long-Subchain Hyperbranched Polymers?

This work aims to elucidate how the branching effect of macromonomer influences the polymerization, structural features, and solution properties of ABn long-subchain hyperbranched polymers (LHPs). ...

Measurement of flow properties and mean elastic stresses of dilute polymer solutions passing through small slits

We measured pressure drops and jet thrusts of dilute (100 ppm and 10 ppm) or ultra-dilute (1 ppm) aqueous solutions of polymer in flows through slits with width of 1.0 mm, 480 μm, and 122 μm owing to investigation of flow properties of dilute polymer solution passing through a small slit. Good agreement between the experimental results of water alone and the predictions was obtained within the experimental errors. However, the dilute and ultra-dilute polymer solutions exhibited lower values. To understanding the experimental results, we estimated mean elastic stresses via jet thrust method. Moreover, we clarified that power-law relationship between mean elastic stress and mean velocity, and it corresponded to the flow properties via the pressure drops.

The Effect of Addition Silver Nanoparticles (AgNPs) onThe Rheological and Optical Properties of Polymer Solution of Poly (Vinylpyrrolidone) (PVP) Prepared in Different Solvents

In this research four samples of polymer solution of (PVP)dissolved in distilled Water (DW) and ethanol with concentrations (0.004 PVP and 0.008PVP)(mol/L) were prepared .Rheological and optical properties were studied, whereobservedin rheologicalproperties the viscosity of polymer solution of PVP increased with increasing the concentrations of polymer solution of PVP. Also the density of PVP/DW was large than the density of PVP/ethanol.In optical properties the absorbance spectra increased with the increasing the concentrations of PVP polymer solution.Fourier Transform Infrared spectroscopy (FTIR)showed the bondswhich represents the formula structural of PVP. Silver nanoparticles(AgNPs) of polymer solution of PVPwere added with concentrations (0.1,0.2 and 0.3) wt%,in rheological properties observed the viscosity in PVP/DWwas less than in case of PVP/ethanol, where this difference in viscosity value because the viscosity was depending on the attraction between the particles and on the shape and their size. In optical propertiesit was notedthe appearance peak of absorption spectra at 419nm. Fourier Transform Infrared spectroscopy (FTIR) showed that adding AgNPs of polymer solution of PVP shifted the peaks of bonds in PVP polymer.

Processing parameters for electrospinning poly(methyl methacrylate) (PMMA)/titanium isopropoxide composite in a pump-free setup

Background: Electrospinning is a technique for producing nanofibers, useful in many fields of nanotechnology. The size and morphology of the nanofibers obtained depends on the polymer solution properties, the parameters of the equipment and the conditions of the surrounding. In almost all reported electrospinning set ups, a pump ,which regulates the flow of the polymer solution, has been included as one of the requirements. In this study, the effects of solution concentration, viscosity, voltage and the distance from the tip of the syringe to the aluminum collector on the morphology and diameters of poly(methyl methacrylate)(PMMA) fibers were investigated, using a pump-free electrospinning set up. Methods: Varied PMMA concentration (50 -120 mg/mL), voltage (10-18 kV) and distance (5 – 18 cm) of electrospinning were studied and the optimum electrospinning conditions identified. PMMA/ titanium isopropoxide solution of ratio 1:2 was prepared, electrospun at optimized conditions (15 kV, 18 cm, Dichloromethane/Dimethylformamide 60:40) and the fibers obtained analyzed using a scanning electron microscope. Results: Solutions of PMMA whose concentrations were less than 50 mg/mL, produced beads on fibers, whereas those at ~ 100 mg/mL formed the best bead-free fibers of diameter 350±50 nm. The results showed a direct dependence of fiber diameter on the solution viscosity. Fibers of larger diameters were obtained when the distance from the tip of the syringe to the aluminum collector and voltage were increased but at higher distances (>18 kV) fewer fibers were collected. When the voltage was steadily increased, the fibers broadened and the diameters were non-uniform due to splaying and splitting. Increasing the distance between the pipette-tip and the collector from 10 to 18 cm resulted in reduced electric field which in turn yielded fewer fibers. Conclusions: The results obtained in a pump free set-up were comparable to those eletrospun in the presence of a pump.

Process intensification of mixing and chemical modification for polymer solutions in microreactors based on gas-liquid two-phase flow

Inert gas was introduced into a capillary microreactor for intensifying the mixing and reaction of polymer solutions. Operational ranges regarding volumetric flow rates of the gas and liquid phases deserved to be carefully selected for ensuring the process stability. Formation of side-by-side bubble flow in microreactors relevant to special properties of polymer solutions was observed with the use of high-speed camera. The gas introduction obviously promoted the mixing of polymer solutions in microreactors, and accordingly the improvement on the micromixing performance was confirmed by a diazo-coupling reaction system. Various factors such as the gas volume fraction and introduction mode affected gas-liquid two-phase flow patterns and thus the mixing efficiency in microreactors. Simplified mathematic models were developed to evaluate the shear effect and to reveal intensification mechanisms within the gas-liquid slug flow and the annular flow in microreactors. Moreover, the effectiveness of such a mixing intensification strategy for polymer solutions was further demonstrated through the sulfonation of polystyrene (PS) in the capillary microreactor.

Sustainable approach to recycle waste polystyrene to high-value submicron fibers using solution blow spinning and application towards oil-water separation

Polystyrene waste disposal is an environmental challenge and transforming it into value-added products such as submicron fibers is an attractive paradigm. In this work, we have reported a sustainable approach to deal with the twin issues of handling low-density polystyrene waste and its re-utilization. Using ethyl acetate as a cost-efficient environmentally preferable solvent, we have successfully demonstrated conversion of waste expanded polystyrene (WPS) into hydrophobic fibers via solution blow spinning technique and its application towards oil-water separation. The macroscale spray pattern analysis in combination with microscale analysis is reported as a facile tool for evaluating the effect of polymer solution properties and operating parameters on the spray morphology. Additionally, the fiber spinnability limits are identified that provide the operational parameters in which fibers without any undesirable structural features are obtained. Here, the lower fiber spinnability limits were identified as 6 wt% polymer concentration, 3 kg cm−2 gas pressure and 10 cm nozzle-to-target distance, below which excessive beads or film formation was observed. The upper fiber spinnability limits were 14 wt% polymer concentration and 5 kg cm−2 gas pressure beyond which the solution blow spinning was not feasible. Moreover, wettability studies showed the enhanced hydrophobic and superoleophilic behavior of the synthesized WPS fibrous mats with water contact angle as ∼138° and oil contact angle as ∼0°. The WPS fiber-coated membrane demonstrated a maximum separation efficiency of 97% for free oil (diesel)-water mixtures, indicating potential applications in oil recovery and treatment of oily wastewater.

Communication: A comparison between the solution properties of knotted ring and star polymers.

We computationally investigate the good solvent solution properties of knotted ring and star polymers by combining molecular dynamics (MD) simulation and path-integral calculations. We consider knotted rings having a minimal crossing number m c in the range, 0 ≤ m c ≤ 9, and star polymers having a range of f star arms, 2 ≤ f ≤ 20, attached to a common core monomer particle. After generating configurational ensembles of these polymers by MD, we use the path-integration program ZENO to calculate basic configurational properties, i.e., radius of gyration, hydrodynamic radius, intrinsic viscosity, as well as fluctuations in these properties. Our simulations indicate that the configurational properties of knotted rings and star polymers in solution show a similar decrease with increasing m c and f. Moreover, fluctuations in these properties also decrease with increasing topological complexity. Our findings should be helpful in polymer characterization and more generally for understanding the role of polymer topology in polymer material properties.

Rheological consequences of wet and dry friction in a dumbbell model with hydrodynamic interactions and internal viscosity.

The effect of fluctuating internal viscosity and hydrodynamic interactions on a range of rheological properties of dilute polymer solutions is examined using a finitely extensible dumbbell model for a polymer. Brownian dynamics simulations are used to compute both transient and steady state viscometric functions in shear flow. The results enable a careful differentiation of the influence, on rheological properties, of solvent-mediated friction from that of a dissipative mechanism that is independent of solvent viscosity. In particular, hydrodynamic interactions have a significant influence on the magnitude of the stress jump at the inception of shear flow, and on the transient viscometric functions, but a negligible effect on the steady state viscometric functions at high shear rates. Zero-shear rate viscometric functions of free-draining dumbbells remain essentially independent of the internal viscosity parameter, as predicted by the Gaussian approximation, but the inclusion of hydrodynamic interactions induces a dependence on both the hydrodynamic interaction and the internal viscosity parameter. Large values of the internal viscosity parameter lead to linear viscoelastic predictions that mimic the behavior of rigid dumbbell solutions. On the other hand, steady-shear viscometric functions at high shear rates differ in general from those for rigid dumbbells, depending crucially on the finite extensibility of the dumbbell spring.

Pseudo-laminarization effect of dilute and ultra-dilute polymer solutions on flows in narrow pipes

The properties of dilute and ultra-dilute polymer solutions flowing in a narrow pipe (inner diameter: 680, 400, and 125 μm) were evaluated experimentally by measuring the pressure drop at constant flow rate. Deionized water, silicone oil, and several aqueous solutions of polyacrylamide (PAA), polyethylene oxide (PEO), and xanthan gum (X-Gum) were used. In viscosity measurements, 100- and 10-ppm solutions exhibited non-Newtonian viscosities whereas 1-ppm solutions exhibited Newtonian viscosities. We applied a power-law model to the non-Newtonian viscosities and estimated a generalized Reynolds number. Moreover, we focused on the transition and turbulent regions because the flows being observed were through narrow pipes. For water and silicone oil, good agreement was obtained between the resultant pressure drop and the predicted value. Furthermore, the critical Reynolds number for water and silicone oil was approximately 1.8×103. In contrast, laminar flow was maintained in the transition region for the dilute and ultra-dilute polymer solutions. In the 125- μm capillary flows, the maximum critical Reynolds numbers for the ultra-dilute polymer solutions were 2.4×103 (PAA), 3.9×103 (PEO), and 3.0×103 (X-Gum). Even though ultra-dilute solutions were used, pseudo-laminarization was obtained. To understand the experimental results, we estimated the first normal stress difference. All such values were correlated with the wall shear rate. We conclude that the pseudo-laminarization can be associated with the elasticity of the polymer solutions and is typified by the appearance of strong elastic properties in small-scale flows.

(Invited) Shear-Induced Fabrication of Multiple Parallel Gel Filaments Using Aqueous Two-Phase Separation

Macroscopic structures of gel fibers have been prepared by control of the polymer solution properties and by design of the nozzle and flow path of the microfluidic device. In this research, we investigated a method to simultaneously fabricate hundreds to thousands of gel filaments simply by flowing the polymer solution inside the capillary without spinneret. An aqueous two-phase separation (ATPS) can be induced by adjusting their concentration in certain combinations of two polymers. The respective polymer concentration in each phase can be determined from the phase diagram, whereas an assembly of heterogeneous polymers generate in each phase. Hydrodynamic properties of pre-gel solution can be controlled by inducing such heterogeneous polymer assemblies. A co-axial flow double capillary was used to fabricate gel filaments, where an inner capillary (inner diameter 0.7 mm) was fixed at the insert position of an outer capillary. To induce ATPS, an ionic strength for the aqueous solution of sodium alginate (Alg) / polyethylene glycol (PEG) mixture was controlled by NaCl addition. The pre-gel Alg/PEG solution was flown as an inner flow of glass double capillaries, where a crosslinker solution (Ca2+ soln.) was flown as a sheath flow. The obtained gel was composed of multiple parallel gel filaments with a diameter of several micrometers, while a single gel without filament structure was obtained from the homogeneous solution without NaCl addition. In aqueous solution, the Alg chain has a structure with few entanglements because of its rigidity. The rigid assembly of alginate is mainly caused by guluronic acid block, that is stabilized by diaxial linkages via intramolecular hydrogen bonds. The shear stress generated by flowing the aqueous Alg solution inside the capillary cannot induce deformation of its rigid assembly, results in the single thick gel filament. By complexation with PEG, destruction of regular hydrogen bond was responsible for breaking the rigid structure of Alg. Thus, deformation of Alg/PEG assembly was enabled to elongate as the fibrous structure by the shear stress, followed by gelation in contact with Ca2+ ions at the outlet of the inner capillary. Such shear-induced deformation of the Alg/PEG assembly was studied by measuring viscoelastic properties with a spindle viscometer. Besides, Alg/PEG assembly generation in each phase was determined by size-exclusion chromatography with a multi angle light scattering detector. This presentation will discuss a simple technique for preparing multiple gel filaments simply by passing a polymer solution through a capillary.