Homogeneous Polymer Solutions Research Articles

Additive Manufacturing of Poly(phenylene Sulfide) Aerogels via Simultaneous Material Extrusion and Thermally Induced Phase Separation.

Additive manufacturing (AM) of aerogels increases the achievable geometric complexity, and affords fabrication of hierarchically porous structures. In this work, a custom heated material extrusion (MEX) device prints aerogels of poly(phenylene sulfide) (PPS), an engineering thermoplastic, via in situ thermally induced phase separation (TIPS). First, pre-prepared solid gel inks are dissolved at high temperatures in the heated extruder barrel to form a homogeneous polymer solution. Solutions are then extruded onto a room-temperature substrate, where printed roads maintain their bead shape and rapidly solidify via TIPS, thus enabling layer-wise MEX AM. Printed gels are converted to aerogels via postprocessing solvent exchange and freeze-drying. This work explores the effect of ink composition on printed aerogel morphology and thermomechanical properties. Scanning electron microscopy micrographs reveal complex hierarchical microstructures that are compositionally dependent. Printed aerogels demonstrate tailorable porosities (50.0-74.8%) and densities (0.345-0.684g cm-3), which align well with cast aerogel analogs. Differential scanning calorimetry thermograms indicate printed aerogels are highly crystalline (≈43%), suggesting that printing does not inhibit the solidification process occurring during TIPS (polymer crystallization). Uniaxial compression testing reveals that compositionally dependent microstructure governs aerogel mechanical behavior, with compressive moduli ranging from 33.0 to 106.5MPa.

High‐performance heterocyclic para‐aramid aerogels for selective dye adsorption and thermal insulation applications

AbstractThe high‐performance polymer para‐aramid (PPTA) is discovered to gel too soon during the polymerization process, resulting in poor processing performance. In this work, a homogeneous polymer solution containing heterocyclic para‐aramid (HPPTA) was successfully synthesized by introducing 2,4‐aminophenyl‐5‐aminobenzimidazole groups into the molecular chains of PPTA, and then HPPTA aerogel was prepared using a supercritical drying technique that took advantage of the HPPTA solution's excellent property of slow gelation. When the HPPTA polymer mass fraction was 1 wt%, the aerogel had the lowest density of 0.086 g cm−3 with a BET specific surface area of 376.59 m2 g−1. The HPPTA‐2 aerogel had better adsorption performance for anionic dye methyl orange, with a maximum adsorption capacity of 319.47 mol g−1; however, its adsorption capacity for cationic dye methylene blue and neutral dye dimethyl yellow was very low, at only 19.68 and 0 mol g−1, respectively. The selective adsorption ability of HPPTA aerogel made it a simple and scalable platform for removing anionic dyes from water solutions. Furthermore, the HPPTA aerogel has outstanding thermal properties for thermal insulation applications in severe environments due to the synergistic effect of the 3D porous structure inside the aerogel and the exceptional thermal stability of the HPPTA.

Terpyridine-Induced Folding of Anisotropic Polyphosphoester Platelets.

The folding of macromolecules is of great importance in nature. Also in synthetic polymer chemistry, single-chain nanoparticles, i.e. folding synthetic macromolecules, are a current research topic to mimic protein folding and to generate well-defined structures. Here, we present the "folding" of anisotropic polymer platelets to further mimic natural folding processes on the (sub)micrometer scale. We report on the synthesis of terpyridine-functionalized long-chain polyphosphoesters by acyclic diene metathesis polymerization that can crystallize in dilute solution into anisotropic polymer crystal platelets. As the terpyridine units are expelled to the platelet surface, terpyridine-metal interactions could be induced by adding nickel(II) bis(acetylacetonate) (Ni(acac)2) to the platelet dispersion in ethyl acetate. These polymer crystals were "folded" to homogeneous nanoparticles with a wrinkled structure, which were visualized by transmission electron microscopy (TEM). The size and size distribution of the obtained assemblies could be altered by varying the concentration of Ni(acac)2. In contrast, no wrinkled structures but rather intrachain cross-linking was observed, when Ni(acac)2 was added to the homogeneous polymer solution before crystallization. We believe that this concept of "folding" anisotropic polymer platelets will further enhance the control of morphologies on (sub)micrometer particles and might be useful for catalysis or separation.

Redox-Responsive Colloidal Particles Based on Coordination Polymers Incorporating Viologen Units.

Colloidal particles based on supramolecular polymers are emerging as promising functional materials because of their intrinsic dynamic features and the possibility of stimuli responsivity. In this work, ≈200 nm self-assembled redox-responsive colloidal particles made of 1D-coordination polymers were readily prepared. In these metallopolymers, organic entities made of bis(viologen) groups covalently associated with terpyridine units are spontaneously bridged by Zn2+ cations through the formation of coordination bonds. The properties of these particles were analyzed and their redox activities investigated. Upon reduction of the viologen units, the formation of π-dimers between the reduced viologen moieties was demonstrated by spectroscopic experiments. It was shown that intermolecular π-dimers (i.e., between different polymer chains) that do not exist in homogeneous polymer solutions were, nevertheless, formed in the particle's structure because of the effects of confinement. The presence of these π-dimers allows stabilization of the charge in the colloids.

On the Use of the Coaxial Cylinders Equivalence for the Measurement of Viscosity in Complex Non-Viscometric, Rotational Geometries

The rheology of macroscopic particle suspensions is relevant in many industrial applications, such as cement-based suspensions, synthetic and natural drilling fluids. Rheological measurements for these complex, heterogeneous systems are complicated by a double effect of particle size. On the one hand, the smallest characteristic length of the measuring geometry must be larger than the particle size. On the other hand, large particles are prone to sediment, thus calling for the use of rotational tools that are able to keep the suspension as homogeneous as possible. As a consequence, standard viscometric rotational rheometry cannot be used and complex flow geometries are to be implemented. In this way, however, the flow becomes non-viscometric, thus requiring the development of approximate methods to translate the torque vs. rotation speed raw data, which constitute the rheometer output, into viscosity vs. shear rate curves. In this work the Couette analogy methodology is used to establish the above equivalence in the case of two complex, commercial geometries, namely, a double helical ribbon tool and a square-shaped stirrer, which are recommended for the study of relatively large size suspensions. The methodology is based on the concept of the reduction of the complex geometry to an equivalent coaxial cylinder geometry, thus determining a quantitative correspondence between the non-standard situation and the well-known Couette-like conditions. The Couette analogy has been used first to determine the calibration constants of the non-standard geometry by using a Newtonian oil of known viscosity. The constants have been subsequently used to determine the viscosity curves of two non-Newtonian, shear thinning fluids, namely a homogeneous polymer solution and two heterogeneous concentrated suspensions. The results show that the procedure yields a good agreement between the viscosity curves obtained by the reduction method and those measured by a standard viscometric Couette geometry. The calibration constants obtained in this work from the coaxial cylinder analogy are also compared with those provided by the manufacturer, indicating that the calibration can improve the accuracy of the rheometer output.

Synthesis, in-situ membrane preparation, and good gas permselectivity of insoluble poly(substituted acetylene)s loosely cross-linked with short and soft siloxane and silanol linkages

Insoluble but membrane-formable poly(substituted acetylene)s loosely cross-linked by short and soft Si–O–Si and SiOH---(OH)Si linkages have been synthesized from the corresponding monomers having one or two SiOH groups. These monomers have been polymerized in homogeneous systems to produce homogeneous polymer solutions in toluene. The resulting solutions were cast on polytetrafuluoroethylene sheets followed by evaporation of the solvent to give tough and flexible membranes which were completely insoluble. The membranes showed good oxygen and carbon oxide permselectivity and their plots in PO2 vs PO2/PN2 graph exceeded the 1991 Robeson's upper bound and very close to the 2008 Robeson's upper bound. The excellent selectivity are caused by enhancement of diffusion selectivity by the soft network structure which can create small pores (i.e., ultramicro pores) based on the short linkages. No drop in permeability may be due to the soft Si–O–Si and SiOH---(OH)Si linkages. In addition no change in PO2 and PO2/PN2 by aging was observed.

Rheological Issues of Phase Change Materials Obtained by the Complex Coacervation of Butyl Stearate in Poly Methyl Methacrylate Membranes

The research started from the fact that the coacervation process represents the process of formation of macromolecular aggregates after separation from the phase that takes place in a homogeneous polymer solution as a result of the addition of a non-solvent. This process is very complex, and takes place in several stages of emulsification technology. The first step of the research created a sample through an encapsulation process of complex coacervation, followed by the creation of three different samples with specific emulsification technologies. Each resulting sample and step of emulsification went through rheological analysis, including the development of evolutions of the complex viscosity, loss module and respective storage module. When we analyzed the rheological properties of each sample at different emulsification stages, we reached the conclusion that, at the moment when the polymerization reaction develops the methyl methacrylate (MMA), the loss modules of the samples were stronger than the storage modules. In this context, the emulsification technology strongly influenced the process of forming the polymethyl methacrylate (PMMA) layer over the butyl stearate particles. In addition, in order to obtain the corresponding microcapsules, it was preferable for the butyl stearate particles covered with MMA to be vigorously stirred in a short period of time, under 250 s, because after that the polymerization process of the MMA on the surface of the particles begins. When producing microcapsules, it is very important that the whole process of emulsification be accompanied by rigorous stirring.

Evaluation of pH- responsive poly(styrene-co-maleic acid) copolymer nanoparticles for the encapsulation and pH- dependent release of ketoprofen and tocopherol model drugs

The pH- induced intelligent drug release ability of poly(styrene-co-maleic acid) copolymer nanoparticles (SMA NPs; d = 22.4 ± 3.1 nm) is presented using poorly water soluble ketoprofen (KETO) and α-Tocopherol (TP) model drugs. Increasing styrene content of the copolymer led to lower surface charge (from −28.4 to −15.0 meq/100 g) and the different styrene/maleic acid ratio (SMA#1: 1:2; SMA#2: 2:1 and SMA#3: 3:1) influences the pH- dependent solubility properties. Because of the polyanionic nature, homogeneous polymer solution was obtained at higher pH, while at lower pH nanoparticles were formed. The corresponding cut- off pH values showed increasing tendency with increasing hydrophobicity (pH = 3.12, 4.22 and 5.44 for SMA#1, 2 and 3, respectively).Next the hydrophobic, non- water soluble KETO and TP drug cores were coated with SMA#2 shell. The polymer-stabilized drug particles provided stable dispersion in aqueous environment, i.e. the prepared polymer shell increased the water dispersibility of the initial hydrophobic drugs. According to the experiments the release of low crystallinity KETO drug was almost complete at physiological pH (=7.40), while at acidic pH the released amount of model drug was only about 30%. Similar kinetic release profile was obtained in the case of more hydrophobic TP drug without charged groups and it indicates that the drug release was primarily controlled by the pH- responsive polymer particles instead of the pH- dependent solubility of the model drug. The prepared NPs could be useful in all areas where the alkaline pH value causes problems, for example in the case of female genital diseases of fungal origin.

Effect of the solvent viscosity on pure electro-osmotic flow of viscoelastic fluids

In this work the fully-developed steady channel flow of the homogeneous polymer solution studied in [4] is revisited and a completely new analytical solution is proposed which is devoid of the limitations of the previous solution (β3ɛDeκ2≤2/27), i.e., it is valid for the complete range of the rheological parameters. The viscoelastic fluid is described by the simplified Phan–Thien and Tanner model with linear stress coefficient function for the polymer contribution plus a Newtonian solvent. The solution is also valid if the polymer contribution is described by the finitely extensive non-linear elastic model with the Peterlin approximation for the average spring force (FENE-P model).

Electrical Characterization of PVdF based Proton Conducting Polymer Gel Electrolytes

Background: Polymer gel electrolytes have attracted much intention due to their high ionic conductivity (10-2 - 10-3 S/cm) along with other suitable properties like good thermal stability, compatibility with electrode materials, easy workability, wider control of properties etc. These materials are also called smart materials due to their practical applications in various devices like high energy power devices, electrochromic devices, supercapacitors, devices for Infra-red systems etc. This paper mainly discusses the enhancement of an ionic conductivity with the addition of polymer. No appreciable change in conductivity of gel electrolytes has been observed with temperature, which makes them suitable for device applications. Methods: Liquid electrolytes were prepared by dissolving orto-nitro benzoic acid (o- NBA) in the ternary mixture of ethylene carbonate (EC), propylene carbonate (PC), and dimethylacetamide (DMA) (in 2:2:1 volume ratio). The homogeneous polymer solution of PVdF in acetone is prepared and then added to the liquid electrolyte along with continuous stirring. Polymer gel electrolytes are obtained after the evaporation of acetone. Ionic conductivity of liquid and polymer gel electrolytes is measured by HP4284A precision LCR meter (having frequency range from 20Hz-1MHz) using complex impedance spectroscopy. Results: The conductivity of liquid electrolytes increases by two orders of magnitude with an addition of ortho-nitro benzoic acid (10-6 to 10-4 S/cm) and maximum room temperature conductivity of 1.46 x 10-4 S/cm has been obtained at 2M concentration of o-NBA in ternary mixture of EC, PC and DMA. The conductivity of electrolytes increases with the addition of polymer and maximum conductivity of 5.91 x 10-4 S/cm has been obtained at room temperature. The increase in conductivity has been explained by using “Breathing Polymer Chain Model”. Ionic transference number was calculated and it was found out to be nearly 1, which suggests that gel electrolyte is principally ionic conductor. Conclusion: Maximum conductivity of 5.91 x 10-4 S/cm at room temperature has been observed for gel electrolyte containing 2M ortho-nitrobenzoic acid in EC:PC:DMA (2:2:1) with 8 wt% PVdF. The conductivity of polymer gel electrolytes has been found to increase with the addition of PVdF concentration. The conductivity of gel electrolytes is found to be higher than that of liquid electrolytes at all PVdF concentrations i.e. σ(gel) > σ(liquid). The increase in conductivity has been found to depend upon the concentration of acid, dissociation constant of acid and concentration of PVdF used. No appreciable change in conductivity of gel electrolytes has been observed with temperature, which make them suitable for device applications. Ionic transference number measurements suggest that these electrolytes are principally ionic conductors. Keywords: Conductivity, dimethylacetamide, ethylene carbonate, gel, transference number.

Study the cooperative motion of long-chain polyelectrolyte in presence of small globular protein

We study in this paper the effect of small globular protein on the dynamic properties of long-chain NaPSS in semidilute regime using Dynamic Light Scattering and viscometry in three phases respecting the pH of the medium. The scaling concept of the heterogeneous system is compared with the De Gennes argument for homogeneous polymer solutions. The results showed a positive and negative deviations to the De Gennes approach of the correlation length scale of mixture defined by (cc*)δ. The macroscopic viscosity of protein and the potential electrostatic interaction are taken as principal factors affecting the cooperative motion of blobs. δ was discussed as the parameter responsible for the conformational change of polyelectrolyte chain subunit within blob. The theoretical analysis of the electrostatic interaction between protein and subunit gave one possible solution relating the deviation δ to the dimensionless coupling constant u as δ~uu+1 and δ~−13uu+1 for a swollen and shrunk subunit, respectively. A good accordance of experimental values of δ to theoretical approach was found.

Grid and subgrid-scale interactions in viscoelastic turbulent flow and implications for modelling

ABSTRACTUsing direct numerical simulations of turbulent plane channel flow of homogeneous polymer solutions, described by the Finitely Extensible Nonlinear Elastic-Peterlin (FENE-P) rheological constitutive model, a-priori analyses of the filtered momentum and FENE-P constitutive equations are performed. The influence of the polymer additives on the subgrid-scale (SGS) energy is evaluated by comparing the Newtonian and the viscoelastic flows, and a severe suppression of SGS stresses and energy is observed in the viscoelastic flow. All the terms of the transport equation of the SGS kinetic energy for FENE-P fluids are analysed, and an approximated version of this equation for use in future large eddy simulation closures is suggested. The terms responsible for kinetic energy transfer between grid-scale (GS) and SGS energy (split into forward/backward energy transfer) are evaluated in the presence of polymers. It is observed that the probability and intensity of forward scatter events tend to decrease in the presence of polymers.

DEVOLOPMENT OF COMPOSITION AND TECHNOLOGY OF EYE MEDICINAL FILMS WITH ALOE EXTRACT

Drugs which stimulate cornea regeneration are an obligatory component of the inflammatory diseases and injuries of eyes treatment. Nowadays the choice for these drugs is not diverse. A search for new prolonged medical drugs in dosage forms of eye films with Aloe extract with germicide and regenerative properties is prospective nowadays. A choice for additive substances for production of eye films with Aloe extract and working out of an optimal extraction technology was the purpose of the study. Materials and methods. The work involved: Aloe liquid extract, methylcellulose (MC), polyvin-ylpyrrolidone (PVP), carboxymethylcellulose (CMC), glycerol plasticiser, polyethylene-400. Humidity of ophthalmic drug films was determined with a gravimetric method; films dimensions: thickness, length and width in mm were measured with calipers; pH of the aqueous solution in films was determined potentiometrically. Results and discussion. A satisfactory appearance (uniformity, goodgap from the substrate, the absence of cracks and ruptures, elasticity and film thickness) was the criterion for selection of film formers at the initial stage. Based on the requirements for ocular dosage forms, the films included sodium tetraborate buffer solution, which provided stability during preparation and use. Based on the study of literature data the selected samples were administered with 10% of aloe liquid extract. Prepared homogeneous transparent polymer solutions were cast on glass petri dish, pretreated with ethyl alcohol layer with a thickness of 5 mm. Drying of the film mass was done at room temperature to a residual humidity of 5%. As the result of the studies we have chosen films with film former of methylcellulose. Plates were strong, elastic, homogeneous, without gaps transparencies odorless, 0.035 mm thick. The obtained films were carved oval shape with a scalpel 4.0 mm in width and 9 mm diameter. Conclusions. 1. We have designed an optimal structure and technology of ocular medicinal films with Aloe extract. 2. Based on the analysis of the data we have found that the worked out base fulfills all the physical, chemical, and technological parameters.

A Reynolds stress model for turbulent flow of homogeneous polymer solutions

Using a priori analyses of direct numerical simulation (DNS) data, a Reynolds stress model (RSM) is developed to account for the influence of polymer additives on turbulent flow over a wide range of flow conditions. The Finitely Extensible Nonlinear Elastic-Peterlin (FENE-P) rheological constitutive model is utilized to evaluate the polymer contribution to the stress tensor. Thirteen DNS data sets are used to analyze the budgets of elastic stress–velocity gradient correlations as well as Reynolds stress and dissipation transport. Closures are developed in the framework of the RSM model for all the required unknown and non-linear terms. The polymer stresses, velocity profiles, turbulent flow statistics and the percentage of friction drag reduction predicted by the RSM model are in good agreement with present and those obtained from independent DNS data over a wide range of rheological and flow parameters.

Preparation, surface morphology, and optical properties of indium(III) oxide nanoparticles by thermolysis of indium–poly(vinyl alcohol) coordination polymer

First report on the preparation of well-dispersed, indium(III) oxide (In2O3) nanoparticles with 22–35 nm size by polymer thermolysis is presented. Indium–poly(vinyl alcohol) (PVA) coordination polymer films were prepared by ‘solution casting technique’ from the homogeneous aqueous solution of coordination polymer prepared using PVA and indium(III) nitrate as starting materials; subsequently the films were calcined at 550 °C to yield In2O3 nanoparticles. Both indium–PVA coordination polymer that served as the precursor and the titled nanoparticles were characterized by Fourier transform-infrared spectroscopy, photoluminescence (PL), powder X-ray diffraction (XRD), transmission electron microscopy, and thermal analysis. Room temperature PL spectra of the prepared indium oxide nanoparticles showed intense blue emissions around 360, 410 and 430 nm, characteristic of indium oxide nanoparticles due to oxygen vacancies. The lower energy PL emission decreases with an increase of indium(III) content in the precursor. The size of the nanoparticles calculated from line broadening of XRD pattern (cubic; JCPDS: 06-0416) was found to be around 24 nm. The average particle size of the synthesized nanoparticles increased with metal ion content in the precursor coordination polymer.

Inertio-elastic instability of non shear-banding wormlike micelles

Homogeneous polymer solutions are well known to exhibit viscoelastic flow instabilities: purely elastic when inertia is negligible and inertio-elastic otherwise. Recently, shear-banding wormlike micelle solutions were also discovered to follow a similar phenomenology. In the shear-banding regime, inertia is usually negligible so only purely elastic flows have been reported. Here, we investigate a non-shear-banding solution where inertia becomes significant, leading to flow patterns akin to the inertio-elastic regime of dilute polymer solutions. We show that the instability follows a supercritical bifurcation and we investigate the structure of the inertio-elastic vortices that develop above the onset.

Optimizing carbon nanotube-reinforced polysulfone ultrafiltration membranes through carboxylic acid functionalization

Multiwalled carbon nanotubes (CNTs) carboxylated to varying weight percentages were added to polysulfone membranes. The degree to which the CNTs were retained within the membrane during membrane production, operation and cleaning was examined as a function of the extent of CNT carboxylation. The effects of CNTs on polymeric membranes – increases in tensile strength, changes in surface hydrophilicity, and changes in membrane permeability – were evaluated as a function of CNT carboxylation, which was found to be coupled to CNT retention within the membrane. It was found that CNTs functionalized to a higher degree form more homogeneous polymer solutions, which lead to greater improvements in the aforementioned membrane characteristics. However, CNTs functionalized to a higher degree were also found to more-readily leave the membrane during immersion precipitation and membrane cleaning. Therefore, a balance was discovered between the benefits associated with increased dispersibility and hydrophilicity, and the disadvantages associated with decreased retention, increased leaching, and decreased strength of CNTs with greater carboxylation.

Controlled assembly of graphene oxide nanosheets within one-dimensional polymer nanostructure

We have demonstrated that the location and distribution of graphene oxide nanosheets (GONs) confined in 1D polymer composites were readily controlled depending on the processing conditions of electrospinning such as the types of polymers and the solvents used for the fabrication. The uniform bead-free poly(vinyl alcohol) (PVA)/GON composite nanofibers (NFs) even at high GON loading were obtained from the homogeneous polymer solutions attributable to the favorable interactions, as elucidated by spectroscopic data, thereby showing significant enhancement of their physical properties. The GONs were localized in the surface regions of the PVA-NFs due to the rapid convective evaporation of the water molecules, with concomitant aggregation into several sheets (<10 layers). In contrast, the co-continuous internal morphology of PVA/GON-NFs was constructed using less-volatile, polar dimethylformamide (DMF) solvents. Furthermore, the GONs were uniformly distributed in the more compatible polymer matrices such as polyacrylonitrile (PAN) and polystyrene (PS). Therefore, the distribution of GONs in 1D nanofibers was governed by the kinetics of solvent evaporation and the interaction with the polymer matrices.

Solvent entropy and coarse-graining of polymer lattice models

The self- and mutual-avoiding walk used in conventional lattice models for polymeric systems requires that all lattice sites, polymer segments, and solvent molecules (unoccupied lattice sites) have the same volume. This incorrectly accounts for the solvent entropy (i.e., the size ratio between the polymer segments and solvent molecules), and also limits the coarse-graining capability of such models, where the invariant degree of polymerization controlling the system fluctuations is too small (thus exaggerating the system fluctuations) compared to that in most experiments. Here we show how to properly account for the solvent entropy in the recently proposed lattice models with multiple occupancy of lattice sites [Q. Wang, Soft Matter, 2009, 5, 4564], and present a quantitative coarse-graining strategy which ensures that both the solvent entropy and the fluctuations in the original systems are properly accounted for using such lattice models. Although proposed in the context of homogeneous polymer solutions, our strategy is equally applicable to inhomogeneous systems such as polymer brushes immersed in a small-molecule solvent, where quantitative agreement with experimental results can be achieved without any adjustable parameters.

Influence of the Polymer Content in the Preparation of Polymeric Membranes

This work aims to evaluate the effect of polymer content in the preparation of membranes obtained from polyamide 6/national clay nanocomposites. The polymeric membranes were produced varying the polymer content at 20 and 22% and using the technique of precipitation by immersion, which consists of three main steps: preparation a homogeneous polymer solution, scattering the solution on a surface forming a film of determined thickness and finally formation of polymeric structure of membrane by separation phases the system. The obtained results by scanning electron microscopy (SEM) indicated that the content of polymer changes the pore formation, the distribution and density, thereby obtaining membranes with different pore sizes, and it was possible to observe that the higher the polymer content, the lower will the pore diameter and more thicker will be the selective membrane layer.