Behavior Of Polymer Solutions Research Articles

Capillary electrophoresis investigation on equilibrium between polymer-related and surfactant-related species in aqueous polymer-surfactant solutions

It was inferred from aqueous solution behavior of nonionic polymers and anionic surfactants that the formation of charged polymer-bound surfactant micelle above critical aggregation concentration (cac) and the formation of free surfactant micelle beyond polymer saturation point (psp), but there was still a lack of direct experimental evidence for the considered equilibrium chemical species. Three modes of capillary electrophoresis are applied in this paper to study the complexation between nonionic polymers, polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG), and sodium dodecylbenzenesulfonate (SDBS) by successfully distinguishing the imaginary charged polymer-bound SDBS micelle from nonionic polymer and SDBS molecule. Perhaps even more important, it is the action of SDBS as both a main surfactant and a UV probe that makes the free surfactant micelle emerged in electropherogram beyond psp, and thus makes it possible for the first time to provide the equilibrium relationship of the polymer-related and the surfactant-related species in the concentration regions divided into by cac and psp.

Direct observation of DNA dynamics in semidilute solutions in extensional flow

The dynamic behavior of semidilute polymer solutions is governed by an interplay between solvent quality, concentration, molecular weight, and flow type. Semidilute solutions are characterized by large fluctuations in polymer concentration, wherein polymer coils interpenetrate but may not be topologically entangled at equilibrium. In nonequilibrium flows, it is generally thought that polymer chains can “self-entangle” in semidilute solutions, thereby leading to entanglements in solutions that are nominally unentangled at equilibrium. Despite recent progress in the field, we still lack a complete molecular-level understanding of the dynamics of polymer chains in semidilute solutions. In this work, we use single molecule techniques to investigate the dynamics of dilute and semidilute solutions of λ-phage deoxyribonucleic acid in planar extensional flow, including polymer relaxation from high stretch, transient stretching dynamics in step-strain experiments, and steady-state stretching in flow. Our results are consistent with a power-law scaling of the longest polymer relaxation time τ∼(c/c*)0.48 in semidilute solutions, where c is the polymer concentration and c* is the overlap concentration. Based on these results, an effective excluded volume exponent ν ≈ 0.56 was found, which is in good agreement with recent bulk rheological experiments. We further studied the nonequilibrium stretching dynamics of semidilute polymer solutions, including transient (1 c*) and steady-state (0.2 c* and 1 c*) stretching dynamics in planar extensional flow using an automated microfluidic trap. Our results show that polymer stretching dynamics in semidilute solutions is a strong function of concentration. In particular, a decrease in transient polymer stretch in semidilute solutions at moderate Weissenberg number (Wi) compared to dilute solutions is observed. Moreover, our experiments reveal a milder coil-to-stretch transition for semidilute polymer solutions at 0.2 c* and 1 c* compared to dilute solutions. Interestingly, a unique set of molecular conformations during the transient stretching process for single polymers in semidilute solutions is observed, which suggests transient stretching pathways for polymer chains in semidilute solutions are qualitatively different compared to dilute solutions due to intermolecular interactions. Taken together, this work provides a molecular framework for understanding the nonequilibrium stretching dynamics of semidilute solutions in strong flows.

Thermo-Responsive Complexes of c-Myc Antisense Oligonucleotide with Block Copolymer of Poly(OEGMA) and Quaternized Poly(4-Vinylpyridine).

Solution behavior of thermo-responsive polymers and their complexes with biological macromolecules may be affected by environmental conditions, such as the concentration of macromolecular components, pH, ion concentration, etc. Therefore, a thermo-responsive polymer and its complexes should be characterized in detail to observe their responses against possible environments under physiological conditions before biological applications. To briefly indicate this important issue, thermo-responsive block copolymer of quaternized poly(4-vinylpyridine) and poly(oligoethyleneglycol methyl ether methacrylate) as a potential nonviral vector has been synthesized. Polyelectrolyte complexes of this copolymer with the antisense oligonucleotide of c-Myc oncogene are also thermo-responsive but, have lower LCST (lower critical solution temperature) values compared to individual copolymer. LCST values of complexes decrease with molar ratio of macromolecular components and presence of salt. Dilution of solutions also affects solution behavior of complexes and causes a significant decrease in size and an increase in LCST, which indicates possible effects of severe dilutions in the blood stream.

Continuous Thermodynamics of Polydisperse Polymer/Solvent Systems: Polystyrene/Cyclohexane and Polystyrene/Methyl Acetate Mixtures

Various types of liquid–liquid equilibrium of polydisperse polymer solutions, including upper critical solution temperature (UCST), both UCST and lower critical solution temperature (LCST), and closed loop miscibility, are investigated. Determination of the cloud-point curves for polydisperse polystyrene (PS)/cyclohexane and PS/methyl acetate systems is conducted by thermal optical analysis. In addition, the molecular weight distribution of polydisperse PS is determined by a gel permeation chromatography technique. To describe the phase equilibria of polydisperse polymer solutions, a continuous thermodynamic approach is incorporated into the incompressible lattice model. This appropriately describes the characteristic phase behaviors of polydisperse polymer solutions, and the calculated results show good agreement with the experimental data.

An Investigation of Polymer Adsorption in Porous Media Using Pore Network Modelling

Polymer injection in hydrocarbon reservoirs has been of great interest in petroleum engineering as an enhanced oil recovery method. In order to have a reliable injection plan, an accurate estimation of polymer behaviour is required to control the fluid flow in porous media. However, it is difficult to calculate the flow properties of polymer solutions—known as non-Newtonian fluids—in porous media, due to variable viscosity at different shear rates. Adsorption of polymer molecules onto the rock surface decreases the available cross-sectional area of polymer solution, therefore at a constant rate, the shear rate increases. As a result, it is important to investigate how polymer adsorption can affect the polymer solution flow behaviour in porous media. Moreover, prior to any polymer injection plan, the amount of adsorbed polymer should be calculated, due to the high cost of polymers. In the present study, pore network modelling was used to investigate the effect of polymer adsorption on flow behaviour of polymer solutions in porous media. To achieve this goal, a simple pore was constructed to adequately represent the real structure of the porous medium. It was then validated by simulation of Newtonian fluid flow in the network and comparison of the calculated flow properties with the experimental data. After validation, the pore network was used for simulation of non-Newtonian fluid flow in porous media. The experimental apparent viscosity of non-Newtonian fluid was used for verification of the procedure and the developed network. The apparent viscosity of non-Newtonian was calculated successfully using macroscopic properties of the rock sample and measured bulk properties of non-Newtonian fluid. The effect of polymer adsorption on calculation of non-Newtonian fluid apparent viscosity was then investigated. It was shown that the polymer adsorption process plays an important role in calculation of polymer solution apparent viscosity. The results reveal that polymer adsorption cannot be neglected, especially in near well-bore areas where the adsorption is high. Finally, the effect of wettability in calculating the total amount of adsorbed polymer volume was studied. The results suggest that neglecting the rock’s wettability can result in an overestimation or underestimation of the amount of adsorbed polymer.

Tailoring the hierarchical porous structure within polyethersulfone/cellulose nanosheets mixed matrix membrane to achieve efficient dye/salt mixture fractionation

Mixed matrix concept using cellulose nanosheets (CNs) and polyethersulfone was employed to fabricate hierarchical porous membrane with potential application for efficient dye/salt mixture fractionation. To this end, CNs was extracted by acid hydrolysis of alpha cellulose and incorporated in polyethersulfone casting solutions at four concentration levels. After that, membranes were manufactured by typical nonsolvent induced phase separation method. Effect of CNs incorporation on thermodynamic stability and phase separation behavior of polymer solution was investigated by construction of phase diagram. In addition, the obtained flat-sheet membranes characteristics including surface morphology, cross-section structure, thermal decomposition, porosity, pore size and pure water flux, were investigated. CNs filled membranes were also evaluated for fractionation of direct dye/NaCl binary mixture. Results reveal that, two stages of phase separation process are observed in CNs filled solution, in which the early stage can initiate with lower water content. This leads to fabrication of more porous membranes with longer finger-like cavities which were confirmed by FESEM analysis of the membranes. Results of TGA reveal that, two weight loss steps forms during decomposition process of CNs filled membranes. It was also observed that addition of 1.5 wt.% CNs into polymer solution increases water permeability from 20 to 90 L/m2 h. Application of 1.5 wt.% CNs filled membranes for fractionation of binary mixture containing direct red 23 (1 g/l) and NaCl (40 g/l) revealed that dye rejection and salt penetration percentages of obtained membranes are 98 % and 97 % respectively. Results confirm the potential of CNs filled membrane as a novel and promising approach for highly efficient fractionation of salt/dye mixtures, owning to its fabrication simplicity and perfect structural features.

Cation-Induced Hydration Effects Cause Lower Critical Solution Temperature Behavior in Protein Solutions.

The phase behavior of protein solutions is important for numerous phenomena in biology and soft matter. We report a lower critical solution temperature (LCST) phase behavior of aqueous solutions of a globular protein induced by multivalent metal ions around physiological temperatures. The LCST behavior manifests itself via a liquid-liquid phase separation of the protein-salt solution upon heating. Isothermal titration calorimetry and zeta-potential measurements indicate that here cation-protein binding is an endothermic, entropy-driven process. We offer a mechanistic explanation of the LCST. First, cations bind to protein surface groups driven by entropy changes of hydration water. Second, the bound cations bridge to other protein molecules, inducing an entropy-driven attraction causing the LCST. Our findings have general implications for condensation, LCST, and hydration behavior of (bio)polymer solutions as well as the understanding of biological effects of (heavy) metal ions and their hydration.

A simple and effective boundary model in nonequilibrium molecular dynamics method

We propose a simple and effective boundary model in a nonequilibrium molecular dynamics (NEMD) simulation to study the out-of-equilibrium dynamics of polymer fluids. The present boundary model can effectively weaken the depletion effect and the slip effect near the boundary, and remove the unwanted heat instantly. The validity of the boundary model is checked by investigating the flow behavior of dilute polymer solution driven by an external force. Reasonable density distributions of both polymer and solvent particles, velocity profiles of the solvent and temperature profiles of the system are obtained. Furthermore, the studied polymer chain shows a cross-streaming migration towards center of the tube, which is consistent with that predicted in previous literatures. These numerical results give powerful evidences for the validity of the present boundary model. Besides, the boundary model can also be used in other flows in addition to the Poiseuille flow.

Study on Flow Parameters Measurement Experiment of Polymer Solution in Porous Media

Due to the complexity of porous media and viscoelasticity of polymer solution, the flow behavior of polymer solution in porous media is more complex than that in the rheometer, and the flow regular pattern of polymer solution in porous media directly affects the formulation of polymer flooding projects. This paper designs experiment on flow parameters measurement of polymer solution (partially hydrolyzed polyacrylamide) in porous media, and the regular pattern of influence on resistance factor, residual resistance factor and flow viscosity in porous media caused by core permeability, polymer concentration, polymer molecular weight and polymer injection rate was given. The followings are the results: even for the same batch core with similar parameters, due to reasons such as natural fractures which could lead to comparatively large difference of core parameters between the same batch of core, thus in order to ensure the reliability of experiment data, it is necessary to detect core quality before core flooding experiment. Core end effect has significant effect on the results of core flooding experiment, it suggests that we should eliminate the effect of core end effect when carry out core flooding experiment, otherwise it is difficult to obtain valid experiment data. There exists a critical polymer concentration, when polymer concentration is lower than critical concentration, resistance factor is basically equal to apparent viscosity; when polymer concentration is higher than critical concentration, resistance factor is far less than apparent viscosity and the difference value increases with the increase of polymer concentration. Flow viscosity of polymer solution in porous media is far less than apparent viscosity in the rheometer and when polymer concentration increases, the increase extent of flow viscosity is far less than the increase of apparent viscosity. Results of this research are of great importance for enhancing flooding effect and guiding oilfield production.

Numerical investigation of spinneret geometric effect on spinning dynamics of dry‐jet wet‐spinning of cellulose/[BMIM]Cl solution

ABSTRACTIn this study, the effect of spinneret geometry, including the entrance angle α of the entrance channel, the length Ls, and the diameter D0 of the exit channel, on the spinning dynamics of dry‐jet wet‐spinning of cellulose/1‐butyl‐3‐methylimidazolium chloride ([BMIM]Cl) solution was simulated by using finite element method. Based on the mathematical model of dry‐jet wet‐spinning established in our previous work (Xia et al., Cellulose 2015, 22, 1963) the radial and axial profiles of velocity, pressure, and shear rate in the spinneret and the profiles of diameter, temperature, and tensile stress in the air‐gap region were obtained. From the simulated profiles, the effect of spinneret geometric parameters on the flow behavior and the pressure drop of polymer solution in the spinneret and the die‐swell ratio near the spinneret was discussed. The entrance angle α of the entrance channel mainly influences the flow behavior of polymer solution in the spinneret and the die‐swell effect near the spinneret. As the decrease of the entrance angle α of the entrance channel, the vortices in the spinneret could be removed and the die‐swell ratio decreases. The increase of the length Ls of the exit channel results in the increase of pressure drop in the spinneret and the decrease of the die‐swell ratio. It is also found that the increase of the diameter D0 of the exit channel reduces the flow velocity of polymer solution and decreases the pressure drop in the spinneret at a constant mass flow rate. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43962.

Characterizing the Role of Clay and Silica Nanoparticles in Enhanced Heavy Oil Recovery During Polymer Flooding

Polymer flooding as one of the most effective methods for enhancing oil recovery has a significant effect on tertiary production of reservoirs with poor vertical sweep efficiencies and those which are extremely heterogeneous. Water-soluble polymers are used to both increase the viscosity of water and decrease the mobility ratio of the displaced and displacing fluids. However, due to high amount of polymer adsorption, presence of divalent cations and mechanical degradation, polymer molecules may lose their properties. Hence it is necessary to further improve the displacement effectiveness of polymer flooding. Despite the fact that several ways have been suggested to enhance the performance of polymer flooding, application of nanoparticles in the improvement of rheological properties of the polymer solution used in enhanced oil recovery has not been reported previously and is still an ongoing subject. This paper investigates the effects of nanoparticles on flow behavior of polymer solution in porous media by employing both experimental studies and numerical simulations. The simulation model first is validated against well-controlled laboratory experiment to have reliable predictions of the full-field implementations. The results show that the amount of polymer adsorption and viscosity of polymer solution will improve when the clay or silica nanoparticles is present in the injectant, and accordingly, the cumulative oil recovery and breakthrough time will be bettered. The result of sensitivity analysis demonstrates that polymer molecules are more degradable during polymer flooding compared to nanoparticles-assisted polymer flooding. Based on the validated model, 3D simulations of nanoparticles-assisted polymer field pilot were performed and the results revealed that the cumulative oil recovery, water cut and breakthrough time will improve when the injectant has some dispersed nanoparticles.

The coalescence of polystyrene in correlated binary solvents

ABSTRACTThe solution behavior of solvophobic polymers is crucial to the development of polymer coatings and polymeric drug delivery vehicles. In this article, the role of dipolar interactions is investigated in the solvophobic coalescence of polystyrene in binary correlated polar solvent mixtures. A simple model for coalescence thermodynamics is derived from correlations between thermally rotating dipole moments in the solvent. The stabilizing correlations lost to the solvent due to a solute's presence give rise to a driving force for the coalescence of solutes. This stabilization is offset by the entropy of mixing that favors the dispersion of solutes. Predictions are compared to the measured point of coalescence of polystyrene in acetone when different alcohols are titrated. The model is shown to capture this point of coalescence and conformation for a variety of systems. Our results suggest the significant property determining the solubility of nonpolar polymers in a polar liquid is a free energy resulting from attractive dispersion interactions between thermally rotating solvent dipole moments. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 948–955

Visualizing phase transition behavior of dilute stimuli responsive polymer solutions via Mueller matrix polarimetry.

Probing volume phase transition behavior of superdiluted polymer solutions both micro- and macroscopically still persists as an outstanding challenge. In this regard, we have explored 4 × 4 spectral Mueller matrix measurement and its inverse analysis for excavating the microarchitectural facts about stimuli responsiveness of "smart" polymers. Phase separation behavior of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) and pH responsive poly(N,N-(dimethylamino)ethyl methacrylate) (PDMAEMA) and their copolymers were analyzed in terms of Mueller matrix derived polarization parameters, namely, depolarization (Δ), diattenuation (d), and linear retardance (δ). The Δ, d, and δ parameters provided useful information on both macro- and microstructural alterations during the phase separation. Additionally, the two step action ((i) breakage of polymer-water hydrogen bonding and (ii) polymer-polymer aggregation) at the molecular microenvironment during the cloud point generation was successfully probed via these parameters. It is demonstrated that, in comparison to the present techniques available for assessing the hydrophobic-hydrophilic switch over of simple stimuli-responsive polymers, Mueller matrix polarimetry offers an important advantage requiring a few hundred times dilute polymer solution (0.01 mg/mL, 1.1-1.4 μM) at a low-volume format.

Prediction of Sanchez‐Lacombe equation of state characteristic parameters for plus fractions

Sanchez‐Lacombe is one of the main polymeric equations of state that is used to predict thermodynamic properties of polymer solutions. Due to the similarity of the physical behaviour of polymer solutions and black oil, Sanchez‐Lacombe is also recommended to predict the liquid density of hydrocarbon fluids. In conventional thermodynamic equations of state, each component of the fluid is specified with some characteristic parameters such as the acentric factor, critical temperature, and critical pressure. Similarly, in the Sanchez‐Lacombe equation of state each component has some characteristic parameters which are obtained for pure components. Since there are no correlations for plus fractions (unknown fractions), the aim of this study is to present empirical correlations to predict the characteristic parameters of plus fractions based on experimental data. These empirical correlations are then used so that the Sanchez‐Lacombe equation of state can be applied to determine the liquid phase density of hydrocarbon fluids.

Controlled synthesis of amino-acid based tadpole-shaped organic/inorganic hybrid polymers and their self-assembly in aqueous media

Synthesis, characterization and solution behavior of tadpole-shaped amphiphilic polymers with hydrophobic polyhedral oligomeric silsesquioxane (POSS) chain-end and hydrophilic main-chain having leucine pendants were investigated. Reversible addition-fragmentation chain transfer (RAFT) polymerization technique was employed to polymerize tert-butyloxycarbonyl-l-leucine methacryloyloxyethyl ester (Boc-Leu-HEMA) in the presence of POSS based RAFT agent. The POSS content and molecular weight of polymers could be controlled while maintaining a narrow molecular weight distribution (<1.3). Glass transition temperature (Tg) of tadpole shaped polymers (TSP) increased with increasing content of POSS moiety in the polymer matrix. Circular dichroism (CD) spectroscopy confirmed that the POSS moiety did not perturb the higher ordered secondary conformation of TSP, attained due to the presence of pendent chiral leucine moiety. Expulsion of side chain Boc groups produced pH responsive amphiphilic cationic polymers, which exhibited self-assembly in aqueous medium, confirmed by dynamic light scattering (DLS) and field-emission scanning electron microscopy (FE-SEM). The aggregation behavior of POSS end-capped polymeric nanoparticles was further investigated through nile red encapsulation as a hydrophobic probe in aqueous medium.

Nonlinear electro-osmosis of dilute non-adsorbing polymer solutions with low ionic strength.

Nonlinear electro-osmotic behaviour of dilute non-adsorbing polymer solutions with low salinity is investigated using Brownian dynamics simulations and a kinetic theory. In the Brownian simulations, the hydrodynamic interaction between the polymers and a no-slip wall is considered using the Rotne-Prager approximation of the Blake tensor. In a plug flow under a sufficiently strong applied electric field, the polymer migrates toward the bulk, forming a depletion layer thicker than the equilibrium one. Consequently, the electro-osmotic mobility increases nonlinearly with increasing electric field and becomes saturated. This nonlinear mobility does not depend qualitatively on the details of the rheological properties of the polymer solution. Analytical calculations using the kinetic theory for the same system quantitatively reproduce the results of the Brownian dynamics simulation well.

A multi-species exchange model for fully fluctuating polymer field theory simulations.

Field-theoretic models have been used extensively to study the phase behavior of inhomogeneous polymer melts and solutions, both in self-consistent mean-field calculations and in numerical simulations of the full theory capturing composition fluctuations. The models commonly used can be grouped into two categories, namely, species models and exchange models. Species models involve integrations of functionals that explicitly depend on fields originating both from species density operators and their conjugate chemical potential fields. In contrast, exchange models retain only linear combinations of the chemical potential fields. In the two-component case, development of exchange models has been instrumental in enabling stable complex Langevin (CL) simulations of the full complex-valued theory. No comparable stable CL approach has yet been established for field theories of the species type. Here, we introduce an extension of the exchange model to an arbitrary number of components, namely, the multi-species exchange (MSE) model, which greatly expands the classes of soft material systems that can be accessed by the complex Langevin simulation technique. We demonstrate the stability and accuracy of the MSE-CL sampling approach using numerical simulations of triblock and tetrablock terpolymer melts, and tetrablock quaterpolymer melts. This method should enable studies of a wide range of fluctuation phenomena in multiblock/multi-species polymer blends and composites.

Structural analysis of telechelic polymer solution using dissipative particle dynamics simulations

A telechelic polymer is an amphiphilic polymer that can form micellar structures when dissolved in water. A telechelic polymer solution shows viscoelastic behaviour owing to the formation of characteristic networks, i.e. loops, bridges and dangling chains. For industrial purposes, telechelic polymers have many applications as thickening agents, such as in paints and cosmetics. Thus, it is desirable to predict and control the rheological properties of telechelic polymers. However, detailed studies at the molecular level have not yet been performed. In this study, I use the dissipative particle dynamics (DPD) method to investigate the relationship between the characteristic structural properties and the molecular structure in telechelic polymer solutions. I show that the morphology of telechelic polymer solutions depends on the concentration and chain length, the distribution of the end-to-end distance, the mean square end-to-end distance, the mean square radius of gyration and the time-averaged mean square displacement. Although an effect of entanglement is important for properties of polymer melts, the polymer chain composed of DPD particles cannot reproduce it. Therefore, I compare telechelic polymer solutions with and without the segmental repulsive potential (SRP), which can simulate the effect of entanglement in DPD simulations. The results indicate that it is necessary to include the SRP in DPD simulations to correctly analyse the behaviour of telechelic polymer solutions.

An electrorheological investigation of PVB solutions in connection with their electrospinning qualities

During the process of electrostatic spinning, the rheological behaviour of polymer solutions is significantly influenced by the presence of an external electric field. The aim of this contribution is to find a correlation between the electrorheological characteristics of polyvinylbutyral (PVB) solutions and their electrostatic spinnability. When exposed to an external electric field, PVB solutions with either poor or good solvents respond in different ways. It was shown that the complex viscosity ratio ηE*/η0* (where ηE* and η0* represent complex viscosities of a solution in the presence and absence of an external electric field, respectively) can serve as an indicator as to whether a chosen material is a potential candidate for acceptable electrospinning. This occurs when the ratio ηE*/η0* increases with increasing electric field strength, i.e., when poor solvents are applied. The possible changes to the physical and chemical properties of PVB solutions were investigated using SEM, FTIR, DSC, 13C- and 1H-NMR techniques.

High-frequency rheological characterization of homogeneous polymer films with the quartz crystal microbalance.

We utilize quartz crystal resonators operating at multiple resonant harmonics to measure the high-frequency rheological properties of materials with a broad range of viscoelastic properties. The technique is demonstrated with poly(t-butyl acrylate) films in the vicinity of the calorimetrically determined glass transition and with rubbery polyisoprene films. The technique is a noncontact technique that can be used to quantify the temperature or time-dependent viscoelastic response in homogeneous films with thicknesses in the micrometer range. This work complements the ability of the resonators to quantify the viscoelastic behavior of viscoelastic polymer solutions and simple Newtonian liquids. For each material we obtain the density-shear modulus product and the viscoelastic phase angle at frequencies of 5 and 15 MHz. A standardized analysis protocol is described that enables this information to be obtained reliably and accurately. The polyisoprene data are found to be in good agreement with measurements obtained by dynamic mechanical analysis using extrapolated temperature shift factors.