Two-phase Polymer Research Articles

Bi2S3/poly(vinylidene fluoride) composite with high dielectric constant and unusual low dielectric loss based on preferentially oriented fillers

In this work, a novel two-phase ferroelectric polymer composite, consisting of semiconducting bismuth sulfide nanorods and a poly(vinylidene fluoride) matrix, was fabricated by a sequence of casting, hot-stretching and hot-pressing techniques.

Activation of the Electrical Conductivity on Non-conductive MWCNT-filled Plastic Moldings by Laser Processing

Two-phase polymer blends consisting of a polypropylene matrix and dispersed polycarbonate particles containing multi-walled carbon nanotubes (MWCNTs) have been injection molded. The obtained plastic moldings were patterned by laser treatment. The initially non-conductive molded plastic parts became electrically conductive in the treated areas after the laser treatment. Structures with line resistances of as low as 1.5 kΩ/cm-1 were created on the surface of the parts. The dependency of the reachable resistance values on the parameters of the laser treatment, the material composition (the mass fraction of MWCNT in the polymer blend 3wt%.5wt%) as well as the injection molding parameters were investigated.

Spectroscopically tracking charge separation in polymer : fullerene blends with a three-phase morphology

Transient absorption spectroscopy reveals that the superior performance of three-versus two-phase polymer : fullerene blends is associated with hole migration from intermixed to pure polymer phases.

Solvent-free ring opening polymerization of ε-caprolactone and electrical properties of polycaprolactone blended BiFeO3nanocomposites

A novel two-phase polymer nanocomposite comprising polycaprolactone (PCL) and nanocrystalline multiferroic BiFeO3(BFO NPs) has been fabricated by a simple casting technique.

A finite volume method for a two-phase multicomponent polymer flooding

Multicomponent polymer flooding used in enhanced oil recovery is governed by a system of coupled non-strictly hyperbolic conservation laws. In the presence of gravity, the flux functions need not be monotone and hence designing Godunov type upwind schemes is difficult and computationally expensive. To overcome this difficulty, we use the basic idea of discontinuous flux to reduce the coupled system into an uncoupled system of scalar conservation laws with discontinuous coefficients. For these scalar equations we use the DFLU flux developed in [5] to construct a second order scheme. The scheme is shown to satisfy a maximum principle and the performance of the scheme is shown on both one and two dimensional test problems.

5CN05 partitioning in an aqueous two-phase system: A new approach to the solubilization of hydrophobic drugs

Liquid–liquid extraction for the purification of molecules has been central to many advances in the pharmaceutical industry. These processes were developed based on the property that some polymer and/or micellar solutions present to separate into a concentrated phase and a diluted phase. Based on the differences in the physical and chemical environments of the two coexisting phases, and since both phases contain approximately 60–90% of water, liquid–liquid extraction provides a powerful alternative to both extract and solubilize a molecule. This paper examines the partition behavior of the synthetic drug, 2-[(3,4-dichlorine-benzylidene)-amino]-5,6-dihydro-4H-cyclopenta[b]thiophene-3-carbonitrile (5CN05), in an aqueous two-phase polymer system (ATPPS) and also in an aqueous two-phase micellar system (ATPMS). The results showed that both systems are favorable for extraction the 5CN05 drug high partition coefficient values (K5CN05>200) and yield (Y5CN05>99.48%) in the concentrated phase were achieved with the systems. However, the ATPPS generated a partition coefficient (K5CN05) higher than the one obtained with ATPMS. The results suggest that both processes may be used for the extraction and concentration of molecules with hydrophobic characteristics, such as 5CN05. They also provide an optimal environment for the solubilization of such molecules, allowing for greater efficiency when purifying many classes of drugs.

Ag+-ion conducting Nano-Composite Polymer Electrolytes (NCPEs): Synthesis, characterization and all-solid-battery studies

Ag+-ion conducting Nano Composite Polymer Electrolyte (NCPE) films: [90PEO: 10AgCF3SO3]+xAl2O3, where x=0.5, 1, 1.5, 2, 3, 4, 5wt.(%), have been prepared by a completely dry hot-press technique in place of the traditional solution-cast method. NCPE film, basically a two-phase organic composite polymer electrolyte, has been synthesized using Solid Polymer Electrolyte (SPE) composition: [90PEO: 10AgCF3SO3], identified as one of the high conducting films with room temperature (300K) ionic conductivity (σrt)~7.12×10−7S/cm and having superior mechanical flexibility, as 1st-phase host and nano-particles (size<50nm) of an insulating/inert filler material Al2O3 as 2nd-phase dispersoid. Filler particle concentration dependent conductivity measurements revealed NCPE film: [(90PEO: 10AgCF3SO3)+3Al2O3] as Optimum Conducting Composition (OCC) with σrt~2.57×10−6S/cm. A conductivity enhancement of more than 3-fold could be achieved in SPE as a consequence of dispersal of Al2O3 nano-particles. Also, NCPE OCC film physically appeared relatively more stable/flexible as compared to SPE host film. The characterization of ion transport properties in SPE host and NCPE OCC films has been done in terms of ionic conductivity (σ) and total ionic (tion)/cation (t+) transference numbers. These ionic parameters have been evaluated experimentally using different ac/dc techniques. The temperature dependent conductivity has also been studied and the activation energy (Ea) was computed by liner least square fitting of Arrhenius plot. The material characterization was done by analyzing X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) responses on the film samples. All-Solid-State batteries in the cell configuration Ag (anode)//NCPE OCC film//(I2+C+NCPE) (cathode) have been fabricated and the cell-potential discharge performances have been studied under varying load conditions. An Open Circuit Voltage (OCV)~0.56V was obtained. Some important cell parameters have been evaluated from the cell potential discharge profiles. The battery performed quite satisfactorily especially under low current drain states.

Novel Method for Characterizing Single-Phase Polymer Flooding

Summary Polymer flooding has been used to enhance oil production and reduce water cut for a long time. However, there are still many fundamental challenges in characterizing the multiphase-fluid flow, even the single-phase-fluid flow, associated with polymer flooding. For example, it is difficult to measure and calculate two-phase polymer solution/oil relative permeability. One of the difficulties comes from the non-Newtonian and time-dependent properties of polymer solutions; another comes from the change in absolute permeability caused by the adsorption of polymer on rock surfaces. Almost all the methods for computing relative permeability are based on the assumption that the absolute permeability is constant. It may be helpful to further understand the mechanisms and develop more-reliable methods for calculating two-phase polymer solution/oil relative permeability by investigating single-phase polymer flooding more profoundly. In this study, a new method has been developed to calculate the pseudopermeability during single-phase polymer flooding. The non-Newtonian property of the polymer solutions was considered in the new method. Polymer-flooding experiments with different concentrations of polymers were designed and conducted to study the single-phase flow of polymer solution in rocks with different permeabilities. The values of the pseudopermeability of single-phase polymer flooding were then calculated with the method. It has been found that the relationships between the pseudopermeability and the reciprocal of shear rate were linear. The polymer-flooding pseudopermeability extrapolated at the infinite shear rate was close to the brine-flooding permeability after polymer injections in many cases.

Influence of empty space and internal stresses on dielectric strength in two-phase polymer

In the present work, a study on the dependence of the Dielectric Strength (DS) as a function of the empty space and the internal stresses into polymer samples has been performed. The empty space was measured by means of positron annihilation lifetime spectroscopy. The internal stresses into the polymer matrix, due to the appearance of the crystalline zones, were determined by applying the inclusion theory results to the dynamic mechanical analysis measurements. Attention to the effect of the chain movement on the electrical breakdown process has been paid. The study has been performed at a mesoscopic scale with the aim of demonstrating the influence of the thermal, mechanical or electrical stresses on the chains movement and their effect on the dielectric breakdown phenomenon. It has been verified that, DS is a function of the empty space into the sample and also of the internal stresses acting at the polymer chains, which result from the crystalline state promoted by chemicrystallization. The empty space decrease and the internal stresses act overlapped against the electrical force operating on the polymer chains. It is deduced from the work, that the precursor phenomenon for the electrical breakdown is the bend of polymer chains, prior to the onset of their collective movement promoted by the electrical forces.

The influence of multiscale fillers reinforcement into impact resistance and energy absorption properties of polyamide 6 and polypropylene nanocomposite structures

Three-phase composites (thermoplastic polymer, glass-fibres and nano-particles) were investigated as an alternative to two-phase (polymer and glass-fibres) composites. The effect of matrix and reinforcement material on the energy absorption capabilities of composite structures was studied in details in this paper. Dynamic and quasi-static axial collapse of conical structures was conducted using a high energy drop tower, as well as Instron universal testing machine. The impact event was recorded using a high-speed camera and the fracture surface was investigated with scanning electron microscopy (SEM). Attention was directed towards the relation between micro and macro fracture process with crack propagation mechanism and energy absorbed by the structure. The obtained results indicated an important influence of filler and matrix material on the energy absorption capabilities of the polymer composites. A significant increase in specific energy absorption (SEA) was observed in polyamide 6 (PA6) reinforced with nano-silica particles and glass-spheres, whereas addition of montmorillonite (MMT) caused a decrease in that property. On the other hand, very little influence of the secondary reinforcement on the energy absorption capabilities of polypropylene (PP) composites was found.

Dinitrogen fixation is restricted to the terminal heterocysts in the invasive cyanobacterium Cylindrospermopsis raciborskii CS-505.

The toxin producing nitrogen-fixing heterocystous freshwater cyanobacterium Cylindrospermopsis raciborskii recently radiated from its endemic tropical environment into sub-tropical and temperate regions, a radiation likely to be favored by its ability to fix dinitrogen (diazotrophy). Although most heterocystous cyanobacteria differentiate regularly spaced intercalary heterocysts along their trichomes when combined nitrogen sources are depleted, C. raciborskii differentiates only two terminal heterocysts (one at each trichome end) that can reach >100 vegetative cells each. Here we investigated whether these terminal heterocysts are the exclusive sites for dinitrogen fixation in C. raciborskii. The highest nitrogenase activity and NifH biosynthesis (western-blot) were restricted to the light phase of a 12/12 light/dark cycle. Separation of heterocysts and vegetative cells (sonication and two-phase aqueous polymer partitioning) demonstrated that the terminal heterocysts are the sole sites for nifH expression (RT-PCR) and NifH biosynthesis. The latter finding was verified by the exclusive localization of nitrogenase in the terminal heterocysts of intact trichomes (immunogold-transmission electron microscopy and in situ immunofluorescence-light microscopy). These results suggest that the terminal heterocysts provide the combined nitrogen required by the often long trichomes (>100 vegetative cells). Our data also suggests that the terminal-heterocyst phenotype in C. raciborskii may be explained by the lack of a patL ortholog. These data help identify mechanisms by which C. raciborskii and other terminal heterocyst-forming cyanobacteria successfully inhabit environments depleted in combined nitrogen.

Core-scale simulation of polymer flow through porous media

The behavior of partially hydrolyzed polyacrylamide (HPAM) polymer solutions in porous media is more complicated than what the bulk rheology might suggest. In addition, HPAM polymers exposed to high frontal velocities during corefloods display shear thickening and degradation characteristics. Recently developed models have displayed the capacity to accurately predict numerical values for the apparent viscosity behavior of HPAM polymers in the shear thickening and degradation flow regimes without in-depth data from coreflood experiments. The ability to simulate this polymer behavior is valuable when selecting effective polymer flood designs for field applications. This work aimed to determine whether or not a commercially available simulator could accurately simulate single- and two-phase polymer coreflood experimental results conducted for a range of injection rates. The adherence to physically realistic input values with respect to experimentally derived parameters was of primary importance during the development of the models. In the single-phase simulations, the shear thinning, shear thickening, and degradation flow regimes were successfully modeled, but numerical issues arose for the highest injection rates corresponding to the polymer degradation flow regime. Analytical models developed to predict porous medium apparent viscosities were used with appropriate adjustments of the permeability reduction factor RRF to history match core-scale experimental pressure drop data. In the two-phase polymer flood in a water-wet porous medium, the modeled polymer behavior spanned from the shear thinning to the shear thickening flow regimes, but did not include any polymer degradation data. With this model, both the pressures and cumulative oil production were successfully matched. Ultimately, understanding, modeling and predicting the polymer behavior on a core-scale under various flow conditions will improve the ability to design polymer floods on the field scale.

Investigation of species transport in a gas diffusion layer of a polymer electrolyte membrane fuel cell through two-phase modelling

A two-phase polymer electrolyte membrane fuel cell model has been developed to investigate transport of species in a gas diffusion layer taking into account effects of liquid water saturation. A set of governing equations for mass, momentum, species concentration involving oxygen, hydrogen, water vapour and liquid water together with electrochemical reaction equations have been solved under computational fluid dynamics technique. The effects of presence of liquid water on the effective diffusivity of species have been investigated. A thorough comparison study of liquid water saturation model using power law with various exponential factors and a percolation based model has been carried out. The simulation results show that the power law model with exponential factor of 2 provides a good representation of species diffusivity and produces much closer agreement with experimental cell voltage, while the percolation based model produces overprediction of cell voltage. The effects of isotropic and anisotropic permeability of gas diffusion layer have also been studied and the simulated results show that the high isotropic permeability or a combination of high in-plane and low through-plane permeability results in higher performance of a polymer electrolyte membrane fuel cell. The fuel cell performance significantly deteriorates with low in-plane and high through-plane permeability of gas diffusion layer.

Highly-Tunable Polymer/Carbon Nanotubes Systems: Preserving Dispersion Architecture in Solid Composites via Rapid Microfiltration.

This research presents a new fabrication method for tailoring polymer/carbon nanotube (CNT) nanostructures with controlled architecture and composition. The CNTs are finely dispersed in polymeric latex, that is, polyacrylate, via ultrasonication, followed by a microfiltration process. The latter step allows preserving the homogeneous dispersion structure in the resulting solid nanocomposite. The combination of microfiltration and proper choice of the polymer latex, particle size, and composition allows the design of complex nanostructures with tunable properties, for example, porosity and mechanical properties. An important attribute of this methodology is the ability to tailor any desired composition of polymer-CNT systems, that is, nanotube content can practically vary anywhere between 0 to 100 wt %. Thus, for the first time, a given polymer/CNT system is studied over the entire CNTs composition, resembling two-phase polymer blends. The polyacrylate in these systems exhibits a structural transition from a continuous matrix (nanocomposite) to segregated domains dispersed within a porous CNTs network. An analogy of this structural transition to phase inversion phenomena in two-phase polymer blends is suggested. The resulting polyacrylate/CNT layers exhibit a percolation threshold as low as 0.04 wt %. Additionally, these nanomaterials show low total reflectance values throughout the visible, NIR and SWIR spectrum at a CNT content as low as 1 wt %, demonstrating their potential applicability for optical devices.

Numerical analysis on performances of polymer electrolyte membrane fuel cells with various cathode flow channel geometries

This paper investigated numerically the effect of cathode channel shapes on the local transport characteristics and cell performance by using a three-dimensional, two-phase, and non-isothermal polymer electrolyte membrane (PEM) fuel cell model. The cells with triangle, trapezoid, and semicircle channels were examined using that with rectangular channel as comparison basis. At high operating voltages, the cells with various channel shapes would have similar performance. However, at low operating voltages, the fuel cell performance would follow: triangle > semicircle > trapezoid > rectangular channel. Analyses of the local transport phenomena in the cell indicate that triangle, trapezoid, and semicircle channel designs increase remarkably flow velocity of reactant, enhancing liquid water removal and oxygen utilization. Thus, these designs increase the limiting current density and improve the cell performance relative to rectangular channel design.

The Influence of Channel Wettability on Two-Phase Flow and Polymer Electrolyte Membrane Fuel Cell Performance

Water management is one of the critical issues affecting polymer electrolyte membrane fuel cell (PEMFC) performance, durability and cost. Modifying the surface wettability of flow field channels in PEMFC can improve the water management and fuel cell performance. In present work, an ex-situ investigation of the effects of channels with different surface wettability on the two phase-flow characteristics has been conducted. Horizontal graphite channel (slightly hydrophobic) and other four channels coated with polytetrafluoroethylene (PTFE) (hydrophobic), silica/Polydimethylsiloxane (PDMS) (super-hydrophobic), silica/PDMS at the bottom wall but with the side walls being raw graphite (combined surface wettability channel), and silica coated channel (superhydrophilic), are tested and visualized at room temperature and atmospheric pressure. Pressure drop measurements and two-phase flow visualization using high speed camera have been performed. Super-hydrophobic channel has shown desirable positive effect on the two-phase flow and on the PEMFC's performance compared with the other channels, especially at high current densities.

Concentration Dependence of the Interfacial Tension for Aqueous Two-Phase Polymer Solutions of Dextran and Polyethylene Glycol

We studied the interfacial tension between coexisting phases of aqueous solutions of dextran and polyethylene glycol. First, we characterized the phase diagram of the system and located the binodal. Second, the tie lines between the coexisting phases were determined using a method that only requires measuring the density of the coexisting phases. The interfacial tension was then measured by a spinning drop tensiometer over a broad range of polymer concentrations close to and above the critical point. In this range, the interfacial tension increases by 4 orders of magnitude with increasing polymer concentration. The scaling exponents of the interfacial tension, the correlation length, and order parameters were evaluated and showed a crossover behavior depending on the distance to the critical concentration. The scaling exponent of the interfacial tension attains the value 1.50 ± 0.01 further away from the critical point, in good agreement with mean field theory, but the increased value 1.67 ± 0.10 closer to this point, which disagrees with the Ising value 1.26. We discuss possible reasons for this discrepancy. The composition and density differences between the two coexisting phases, which may be taken as two possible order parameters, showed the expected crossover from mean field behavior to Ising model behavior as the critical point is approached. The crossover behavior of aqueous two-phase polymer solutions with increasing concentration is similar to that of polymer solutions undergoing phase separation induced by lowering the temperature.

Lipid membranes in contact with aqueous phases of polymer solutions

In this highlight, we describe recent developments in research on lipid vesicles encapsulating aqueous two-phase polymer solutions. Special emphasis is given on the morphological changes of the vesicles and the membrane transformations induced by the phase separation process, and on the interactions of the lipid bilayers with the phases. These interactions lead to a variety of interesting wetting phenomena and to the formation of membrane nanotubes. Future directions and possible developments in this research field are also discussed.

Studies on effective thermal conductivity of particle-reinforced polymeric flexible mould material composites

Due to poor thermal conductivity of conventional flexible polymeric mould materials, the solidification of (wax/plastic) patterns in soft tooling (ST) process takes a longer time. This problem can be solved by increasing the effective thermal conductivity of mould materials through (high thermal conductive) particle reinforcement. Therefore in this study, the equivalent thermal conductivities (ETCs) of particle-reinforced polymeric mould materials, namely silicone rubber and polyurethane are experimentally observed using hot disc technique. Findings show that not only the amount of filler content and type of filler material, but also particle size has significant influence on the effective thermal conductivity of polymer and it starts increasing drastically at 20–30 per cent volume fraction of filler content. To predict the cooling time in ST process, it is important to have an appropriate model of ETC. In this study, a new method is proposed based on a genetic algorithm fuzzy (GA-fuzzy) approach to model the effective thermal conductivity of a two-phase particle-reinforced polymer composites (PCs). The effectiveness of the model is extensively tested in comparison with various empirical expressions reported in literature based on the experimental measurements. It has been found that the model based on GA-fuzzy approach not only outperforms the existing models, but also possesses a generic one applicable to a wide range of two-phase particle-reinforced PCs.

Affinity of PIP-aquaporins to sterol-enriched domains in plasma membrane of the cells of etiolated pea seedlings

The hypothesis that sterol-enriched domains represent sites of preferred localization of PIP-aquaporins was tested in experiments on plasma membranes isolated from cells of etiolated pea (Pisum sativum L.) seedlings. Plasma membranes were isolated from microsomes by the partition in the aqueous two-phase polymer system and separated into vesicle fractions of different buoyant density by flotation in discontinuous OptiPrep gradient. Two types of plasma membrane preparations were used: one was treated with cold 1% Triton X-100 and the other was not. In untreated preparations, three populations of plasma membrane vesicles were obtained, while in the case of treated preparations, fractions of detergent-resistant membranes (DRM) and solubilized membrane proteins were obtained. In all membrane fractions collected after OptiPrep flotation, the amounts of proteins, sterols, and PIP-aquaporins were determined. The highest sterol content was detected in the membrane fraction with buoyant density 1.098 g/cm3 and in the DRM fraction (1.146 g/cm3). These fractions contained much more PIP-aquaporins than the other ones. Phase state of the lipid bilayer was determined by measuring generalized polarization excitation of fluorescence (GPEX) of laurdan incorporated into the membranes of different fractions. It was revealed that the lipid bilayer of the membranes with density of 1.098 g/cm3 had a higher extent of ordering than that of the fractions with density of ∼1.146 g/cm3. The results indicated that uppermost local concentrations of PIP-aquaporins were associated with tightly packed sterol-enriched domains. Moreover, upon solubilization of plasma membrane with Triton X-100, PIP-aquaporins mainly resided in DRM, thus exhibiting a high affinity to sterols.