Concentrated Polymer Solutions Research Articles

Touchspinning: Mechanically drawing polyacrylonitrile nanofibers

AbstractElectrospinning is the predominant method of polymer nanofiber production, though the technique is fraught with challenges. Mechanical drawing of nanofibers is a more facile method, but most research in this area produces a small quantity of fibers, unsuitable for scale‐up applications. The touchspinner, a new device made for continuous cold‐drawing of nanofibers, has the potential to produce fiber mats comparable to electrospinning in efficiency but with fewer drawbacks. Initial studies have been performed to characterize the effect of controllable parameters on produced nanofibers. Model polymer polyacrylonitrile was spun out of N,N‐dimethylformamide into nanofibrous mats via touchspinning while varying the main process controls: solution pump speed, touchspinner rotation speed, and polymer concentration in solution. Nanofibers produced from various combinations of these parameters varied in size from 60 to 3000 nm, and optimal spinning parameters resulted in efficient production of highly aligned nanofibers. Of the three processing controls polymer concentration, and to a lesser degree rotation speed, had the highest impact on the resulting fiber diameters.

Solvability of the Non-Linearly Viscous Polymer Solutions Motion Model.

In this paper we consider the initial–boundary value problem describing the motion of weakly concentrated aqueous polymer solutions. The model involves the regularized Jaumann’s derivative in the rheological relation. Also this model is considered with non-linear viscosity. On the basis of the topological approximation approach to the study of hydrodynamics problems the existence of weak solutions is proved. Also we consider an optimal feedback control problem for this initial–boundary value problem. The existence of an optimal solution minimizing a given performance functional is proved.

Limiting Relative Permittivity "Burn-in" in Polymer Ferroelectrics via Phase Stabilization.

VDF-based polymers, such as poly(vinylidene fluoride) (PVDF) and its copolymers, are well-known ferroelectrics of interest for numerous applications, from energy storage to electrocaloric refrigeration. However, their often complex thermal phase behavior that typically leads to a low phase-stability can drastically affect the long-term dielectric properties of this materials family. Here, we demonstrate on the example of the terpolymer P(VDF-ter-TrFE-ter-CFE) (molar ratio: 64/29/7) that by limiting mass transport/segmental chain motion both during solidification and in the solid state, a drastically smaller "burn-in" in relative permittivity, εr, is observed. Indeed, εr decreases little over time and saturates rapidly at 96-97% of its initial value. Mass transport thereby is limited by using highly entangled systems via the selection of a suitable polymer solution concentration and molecular weight. In addition, rapid solvent extraction assists in reducing unwanted relaxation processes. Accordingly, increased control of the phase stability of P(VDF-ter-TrFE-ter-CFE) is gained. Moreover, pathways are opened to reliably identify processing routes for any given VDF-based polymer, with critical information being obtained from thermal analysis and rheometry data only, enabling rapid feedback to material design, including the prediction of required molecular weights without the need for complex characterization methodologies.

Rheology of stiff-chain polymer solutions

Theoretical expressions for the intrinsic viscosity, the Huggins coefficient, zero-shear viscosity, and storage and loss moduli for stiff-chain polymer solutions are reviewed. Especially, the mean-field Green function method is explained in detail to consider the intermolecular collision effect on the rheological properties of concentrated stiff-chain polymer solutions, by applying the method to monodisperse and polydisperse straight cylinders and monodisperse fuzzy cylinder models. The theoretical expressions reviewed are compared with experimental results for aqueous solutions of two rigid helical polysaccharides, schizophyllan and xanthan.

Nanofibrous polycaprolactone/chitosan membranes for preventing postsurgical tendon adhesion.

Peritendinous adhesion is considered a major postsurgical tendon complication in hand surgery. This complication could be mitigated partially through early tendon mobilization. However, development of new treatment modalities to guide tissue regeneration and to reduce postsurgical tendon adhesion has recently gained attentions. In this article, synthesis and characterization of electrospun nanofibrous membranes (NFMs) of polycaprolactone (PCL) and chitosan to form a physical barrier against cellular migration leading to tendon adhesion is presented. The mechanical properties of the NFMs are modulated to maintain high integrity during postsurgical tendon mobilization. The tensile strength of the NFMs is examined in wet and dry conditions after 1000 cyclic pull loadings. In addition, the mechanical strength of the NFMs is evaluated after a degradation period of 30 days. To obtain NFM with desired properties, concentrations of polymer solutions, operation parameters of electrospinning and the thickness of NFMs were optimized. Based on the biodegradation and mechanical evaluations, the optimum NFM was obtained for specified amounts of PCL (5wt %) + chitosan (2wt %) at an electrospinning drum speed of 400 rpm. The engineered NFM could withstand forces of 33 and 19 N before and after 1000 pull cycles that are sufficient during tendon healing process. The bonding of chitosan fibers over PCL nanofibers allowed for production of NFMs with appropriate mechanical integrity and degradation rate. In vitro cell culture tests demonstrated that PCL/chitosan could only have minor impact on decreasing fibroblast attachment over the membranes probably due to protonation of amine groups.

Influence of emulgator nature on dispersity and stability of artificial polymer suspensions based on polycarbonate and polymethyl methacrylate

Objectives. To create stable artificial polymer suspensions with a positive charge of particles based on polycarbonate and polymethyl methacrylate using cationic surfactants and organosilicon surfactants.Methods. The size of droplets and polymer suspension particles was determined by photon correlation spectroscopy (dynamic light scattering) using a Zetasizer NanoZS laser particle analyzer (Malvern, UK).Results. Domestic cationic surfactants Katamin-AB and Azol-129 were found to be capable of producing stable artificial polycarbonate and polymethyl methacrylate suspensions. Based on the polymer, the optimal surfactant concentration was 6 wt %. The effect of polymer concentration in solution on the stability and particle size of final polymer suspensions was shown. It was determined that the polymer concentration in the solution should not exceed 10%. When obtaining a highly dispersed suspension during dispersion, a higher concentration causes an increase in the viscosity of emulsions. As a result of a synergistic effect formation, we used mixtures of cationic surfactants (Katamin-AB/Azol-138 and Azol-129/Azol-138) to enhance the stability of the final polymer suspensions. The optimal surfactant ratio was 9:1. The total concentration of the mixture is 10 wt %, based on the polymer. Polymer suspensions were stabilized with each of 2:1 mixtures of cationic surfactants Katamin-AB and Azol-129 withan organosilicon surfactant U-851. The total mixture concentration was 9 wt %, based on the polymer.Conclusions. New methods of producing artificial polycarbonate and polymethyl methacrylate suspensions in the presence of domestically produced cationic surfactants, as well cationicorganosilicon surfactants mixtures, were proposed. The colloidal-chemical properties of the obtained polymer suspensions were considered. It was found that using a 2:1 mixture of cationic and organosilicon surfactants produces polymer suspensions that are stable during production and storage.

Laboratory experimental study on the binary combination flooding system in low permeability conglomerate reservoir

In view of the poor injection-production effect of low permeability conglomerate complex fault block reservoir in Xinjiang Oilfield in the late development stage of high water cut, the indoor experimental study of binary compound flooding system was carried out. By compounding the petroleum sulfonate and polymer binary system, the viscosity and morphology parameters of the binary compound flooding system were measured. The microscopic pore structure of the core in this block was analyzed by GE Phoenix Nanotom S, and four groups of experimental schemes were designed to study the oil displacement efficiency of the whole diameter core binary compound flooding system. The experimental results showed that the binary system of surfactant and polymer showed additive synergistic effect. The performance of binary compound system is less affected by polymer molecular weight and solution concentration, which meets the viscosity requirement of low permeability conglomerate for binary compound flooding system. The porosity of samples is relatively small and the connectivity between pores is relatively poor. The experimental results of physical model oil displacement efficiency show that the oil recovery can be increased by more than 17% by injecting 0.3PV 1200mg/L polymer + 0.5% (w) surfactant binary compound system.

Hydrodynamic modeling of laboratory experiments related to oil displacement with thermopolymer solution

Microscaled modeling of laboratory experiments, which needs adaptation a number of parameters of numerical model of a composite kern building, uses for the applying results of flowing laboratory experiments in sector and full hydrodynamic models of occurrences. Adaptation of parameters of numerical kern model shall be carried out at reproduction measured variables of flowing experiments. Moreover, there are uncertainties of filtration and capacitance properties related to heterogeneity of kern samples and instability of heated polymer’ displacement front. Iteration algorithm is developed and implemented in this article. Algorithm provides adapting of series synthetic hydrodynamic models of laboratory experiments. At the first adapting step the whole range of uncertainties of a series of laboratory experiments is taken into account. Minimization of number of variable parameters and model’ adaptation error realizes on all iteration steps. To increase the reliability of adaptation, the spectrum of 1D models is supplements with synthetic 3D models with stochastic distribution of heterogeneity in porosity and permeability. This process allows take processes of filtration in polymer adsorption conditions and heterogeneity of collector properties into account more fully while modeling. In addition, it can help to specify variable parameters with scaling on different numerical grids. Developed algorithm tested on heated polymer’ displacement experiments, determination of the relative phase permeability as a function of temperature. Decreased uncertainties of variable parameters, which are relative phase permeability as a function of concentration of polymer solution, residual resistance factor, dependence of the viscosity of the polymer solution on the shear rate, is the results of method’s application. Then these results transfers to the adaptation process of sector and full hydrodynamic models.

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.

The effect of surface morphology on endothelial and smooth muscle cells growth on blow-spun fibrous scaffolds

This study aimed to analyze the growth of two types of blood vessel building cells: endothelial cells (ECs) and smooth muscle cells (SMCs) on surfaces with different morphology. Two types of materials, differing in morphology, were produced by the solution blow spinning technique. One-layer materials consisted of one fibrous layer with two fibrous surfaces. Bi-layer materials consisted of one fibrous-solid layer and one fibrous layer, resulting in two different surfaces. Additionally, materials with different average fiber diameters (about 200, 500, and 900 nm) were produced for each group. It has been shown that it is possible to obtain structures with a given morphology by changing the selected process parameters (working distance and polymer solution concentration). Both morphology (solid versus fibrous) and average fiber diameter (submicron fibers versus microfibers) of scaffolds influenced the growth of ECs. However, this effect was only visible after an extended period of culture (6 days). In the case of SMCs, it was proved that the best growth of SMCs is obtained for micron fibers (with an average diameter close to 900 nm) compared to the submicron fibers (with an average diameter below 900 nm).

Origin of Apparent Slow Solvent Dynamics in Concentrated Polymer Solutions

Due to their size disparity, the dynamics of solvent molecules in concentrated polymer solutions can be faster by several orders of magnitude compared to the polymer matrix. Despite these observations, past research suggests that a fraction of the solvent contributes to the slow dynamics on the timescale of the macromolecules. By combining depolarized dynamic light scattering and molecular dynamics simulations, we show that long-lived solvent–solvent cross-correlations cause these slow solvent contributions. They originate from the energy landscape that the solute imprints onto the neighboring solvent, leading to enhanced correlations between the positions and orientations of different solvent molecules until the solute relaxes. This mechanism explains the discrepancies found between the results of techniques probing collective and single-particle dynamics, such as dielectric and nuclear magnetic resonance spectroscopy. Our findings shed new light on how solvents behave in the vicinity of macromolecules and are of relevance for materials ranging from polymer-plasticizer systems to hydrated proteins.

Quantifying Properties of Polysaccharide Solutions.

We apply a scaling theory of semidilute polymer solutions to quantify solution properties of polysaccharides such as galactomannan, chitosan, sodium carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, xanthan, apple pectin, cellulose tris(phenyl carbamate), hydroxyethyl cellulose, hydroxypropyl cellulose, sodium hyaluronate, sodium alginate, and sodium κ-carrageenan. In particular, we obtain the molar mass of the chain segment inside a correlation blob M g = B̂ 3/(3ν-1) c 1/(1-3ν) as a function of concentration c, interaction parameter B̂, and exponent ν. Parameter B̂ assumes values B̂ g, B̂ th and M 0/N A 1/3 l for exponents v = 0.588, 0.5 and 1, respectively, where M 0 is the molar mass of a repeat unit, l is the projection length of a repeat unit, and N A is the Avogadro number. In the different solution regimes, the values of the B̂-parameters are extracted from the plateaus of the normalized specific viscosity ηsp (c)/M w c 1/(3ν-1), where M w is the weight-average molecular weight of the polymer chain. The values of the B̂-parameters are used in calculations of the excluded volume v, Kuhn length b, and crossover concentrations c*, c th, and c** into a semidilute polymer solution, a solution of overlapping thermal blobs and a concentrated polymer solution, respectively. This information is summarized as a diagram of states of different polysaccharide solution regimes by implementing a v/bl 2 and c/c** representation. The scaling approach is extended to the entangled solution regime, allowing us to obtain the chain packing number, P̃ e. This completes the set of parameters {B̂ g, B̂ th, P̃ e} which uniquely describes the static and dynamic properties of a polysaccharide solution.

Kinetics of Phase Separation Polyamic Acid (PAA) Solutions with Various Precipitants

A new method with limited layer of polymeric solution was used to study the kinetics of precipitation of highly concentrated solutions of PAA in various precipitants; it allows to quickly estimate the rate of formation of the polymer membrane, adequately evaluate its morphology without membrane casting and reduce the experimental time for the preparation of a membrane with required porous structure. It was shown that the rate of precipitation of 18 wt. % PAA solution and the morphology of a layer resulting from the phase separation formed upon contact with water differ significantly in a “limited” layer and in a layer of infinite thickness. It was shown that morphology of a layer formed during phase separation of 18 wt. % PAA solution with water in the “unlimited” layer corresponds to morphology, which is formed in precipitation by 50% NMP-water solution of the same polymer solution in a “limited” layer. This supports the assumption about the strong dilution of the precipitant with a solvent when an “unlimited” layer method is used. In addition, during the investigation of the kinetics of the phase separation by water it was found that the rate of precipitation of highly concentrated polymer solution in a “limited” layer (ν = 8.3 μm/s) is significantly higher than in “unlimited” (ν = 1.7 μm/s). Using this method with “limited” layer, the kinetics of the phase separation of 18 wt. % PAA solution in aliphatic alcohols was also investigated; the rate of precipitation of the polymer solution is inversely proportional to their viscosity. Approximately twofold increase of dynamic viscosity with the chain length for each subsequent alcohol in the homologous series, the rate of precipitation of the PAA solution in them was also reduced by about 2 times

Solution Blow Spinning (SBS): A Promising Spinning System for Submicron/Nanofibre Production

Submicron/nanofibres possess great potential for application in different areas because of their amazingly high surface area-to-weight ratio. The demand for fabrication of such fibres on a huge scale is increasing with the fast improvement of nanotechnology. Traditionally, nanofibre fabrication methods have intrinsic faults, limiting their application in industry. Solution blow spinning (SBS) is a viable option for producing adaptable and conformable submicron/nanofibre mats on a variety of surfaces. The technique can be employed to produce submicron/ nanofibres with only a simple commercial airbrush, a concentrated polymer solution, and a compressed gas source. It depends on the high velocity of decompressed air that allows the rapid stretching and evaporation of the solvent from a polymeric solution jet at the outlet of the concentric nozzles system. Along with recent advancements, the importance and drawbacks of the solution blow spinning system in comparison to other methods, such as electrospinning and melt blowing, are briefly discussed. Furthermore, the mechanisms of co-axial SBS spinning and micro SBS spinning system for submicron/nanofibre fabrication are also described. Drawbacks and research challenges of SBS are also addressed in this paper.

Piezoelectric Drop‐On‐Demand Inkjet Printing of High‐Viscosity Inks

Drop‐on‐demand inkjet printing of highly viscous fluids represents a highly attractive emerging technology for advanced material deposition. The jetting of viscous inks, such as concentrated polymer solutions and nanoparticle suspensions, is a key enabling technology for many industrial applications, ranging from microelectronics to biomedicine and ceramics manufacturing. Currently available standard inkjet printers typically operate in a relatively narrow viscosity range (up to 16 mPa s), and alternative drop‐on‐demand printing techniques (such as laser‐induced forward transfer) present limited industrial applicability. In this context, the development of a piezoelectric‐driven printhead capable of jetting high‐viscosity fluids is of great interest. Herein, a prototype of such a device is presented and its performance is evaluated using model fluids at increasing viscosities. Specifically, the dependence of emitted droplets’ properties on jetting parameters is evaluated and linked to the physical characteristics of the system. In optimal conditions, piezoelectric jetting of solutions characterized by viscosities in excess of 200 cP is achieved. Finally, as an applicative example, the jetting of functional inks is attempted. A ZnO suspension and a poly(3,4‐ethylenedioxythiophene) (PEDOT) based solution are successfully jetted to demonstrate the applicability of the developed printhead to the deposition of ceramic suspensions and concentrated polymer solutions.

Data Science Guided Experiments Identify Conjugated Polymer Solution Concentration as a Key Parameter in Device Performance

Data Science Guided Experiments Identify Conjugated Polymer Solution Concentration as a Key Parameter in Device Performance

Особенности согласованного изменения сопротивления трения и профиля скорости течения в трубах при проявлении эффекта Томса

Object and purpose of research. Relationships between friction resistance coefficient and velocity distributions in the turbulent boundary layer of low-concentrated polymer solutions are investigated. These relationships are different from water because in polymer solutions the friction resistance at constant Reynolds numbers is additionally changed with solution concentrations. Materials and methods. The known experimental data on variations of the friction resistance coefficient and the velocity profiles in turbulent flows in circular tubes at changes in polymer solution concentrations. Main results. The general law of coordinated variations in friction resistance coefficient λ and flow velocity profile in the turbulent boundary layer depending on Reynolds number and polymer solution concentration. The flow models are validated, which describe the laws of velocity variations in all characteristic sections of boundary layer: laminar sublayer, buffer and logarithmic flow areas. A new non-dimensional number is introduced, which characterizes the ability of low concentrated water solutions of polymers to reduce the friction resistance. It is called the Toms effect parameter in the work. Conclusion. Results of the investigation will be useful in developing the theoretical methods for estimation of boundary layer characteristics in polymer solutions.

The shape of a falling jet formed by concentrated polymer solutions

We studied the shape of free-falling stable jets created by viscoelastic concentrated poly(acrylonitrile) solutions that were pressed out of a capillary at different outputs. The viscosity of the solutions varied by more than 1000 times, and the elasticity increased along with growing concentration. The main goal of the study was to compare theoretical predictions with experimental data. The theoretical argumentations were based on the momentum and rheological equations. We analyzed the superposition of viscoelastic, capillary, and inertial forces for fluids with different rheological properties flowing with different velocities changing more than 100 times. Although elasticity is definitely present, the Weissenberg number in all cases under study appeared less than one and, respectively, played a secondary role except for the most concentrated solution. Then we discussed the applicability of two main models based on the combination of visco-inertial and capillary-inertial forces. The best fitting and dominant input of different forces appeared dependent on the properties of the fluids and conditions of flow. At low polymer concentration, the jet profile corresponds better to the capillary-inertial model, while the visco-inertial regime of flow becomes dominant at higher velocities and highly viscous solutions. At very high concentrations (25% in our case), both of the considered models do not allow describing the complete experimental data due to the increasing role of elasticity.

Modeling to support physicochemical enhancement techniques

The article discusses ways to increase the oil recovery factor in already developed fields, special attention is paid to the methods of enhanced oil recovery. The comparative structure of oil production in Russia in the medium term is given. The experience of oil and gas companies in the application of enhanced oil recovery in the fields is analyzed and the dynamics of the growth in the use of various enhanced oil recovery in Russia is estimated. With an increase in the number of operations in the fields, the requirements for the selection of candidates inevitably increase, therefore, the work focuses on hydrodynamic modeling of physical and chemical modeling, highlights the features and disadvantages of existing simulators. The main dependences for adequate modeling during polymer flooding are given. The calculation with different concentration of polymer solution is presented, which significantly affects the water cut and further reduction of operating costs for the preparation of the produced fluid. The possibility of creating a specialized hydrodynamic simulator for low-volume chemical enhanced oil recovery is considered, since mainly simulators are applicable for chemical waterflooding and the impact is on the formation as a whole.

Polyelectrolyte complex beads of carboxymethylcellulose and chitosan: The controlled formation and improved properties

Spherical beads made of naturally derived polymers can be widely used as a promising matrix in many bio-related and safety required fields. Herein, the optimal parameters for fabrication of a core-shell bead composed of carboxymethylcellulose (CMC) and chitosan (CHI) are established based on systematic investigations on working distance, solution pH and polymer concentrations. Spherical beads will be obtained when the working distance is set as 15 cm. The beads prepared at pH 4.5 are the strongest and can resist to a force of up to 0.071 N. It will be shown that the critical concentration of polymer solutions plays important roles in determining the shape and size of beads. The observation of two new peaks at 1723 cm−1 and 1592 cm−1 in the FTIR of the prepared beads demonstrate the electrostatic interactions between CMC and CHI. With a post gentle heating (35°C), the stability of beads is significantly improved and the swelling degree in water increases to 220%.