Phase Behavior Of Polymer Blends Research Articles

Promoted liquid-liquid phase separation of PEO/PS blends with very low LiTFSI fraction

Studies on phase behavior of polymer blends with lithium salts can provide a theoretical basis for developing solid polymer electrolytes in lithium-ion battery. In this paper, the liquid-liquid phase separation of PEO/PS/LiTFSI system is characterized by small angle neutron scattering (SANS) and small angle laser light scattering (SALLS). A combination of the Debye-Bueche equation and Ornstein-Zernike scattering function is employed to fit the SANS data in the homogeneous state. The thermodynamic parameters, including the forward scattering intensity I0, correlation length ξ, spinodal temperature Ts, effective interaction parameter χeff and cloud point boundaries, are obtained. The cloud point temperatures increase with LiTFSI concentration, especially at the low PEO fractions. We conclude that even a small amount of lithium salt enhances the liquid-liquid phase separation of PEO/PS blends significantly, and the effect of electrostatic interaction increases with temperature.

Mesoscale Morphologies of Nafion-Based Blend Membranes by Dissipative Particle Dynamics

Polymer electrolyte membrane (PEM) composed of polymer or polymer blend is a vital element in PEM fuel cell that allows proton transport and serves as a barrier between fuel and oxygen. Understanding the microscopic phase behavior in polymer blends is very crucial to design alternative cost-effective proton-conducting materials. In this study, the mesoscale morphologies of Nafion/poly(1-vinyl-1,2,4-triazole) (Nafion-PVTri) and Nafion/poly(vinyl phosphonic acid) (Nafion-PVPA) blend membranes were studied by dissipative particle dynamics (DPD) simulation technique. Simulation results indicate that both blend membranes can form a phase-separated microstructure due to the different hydrophobic and hydrophilic character of different polymer chains and different segments in the same polymer chain. There is a strong, attractive interaction between the phosphonic acid and sulfonic acid groups and a very strong repulsive interaction between the fluorinated and phosphonic acid groups in the Nafion-PVPA blend membrane. By increasing the PVPA content in the blend membrane, the PVPA clusters’ size gradually increases and forms a continuous phase. On the other hand, repulsive interaction between fluorinated and triazole units in the Nafion-PVTri blend is not very strong compared to the Nafion-PVPA blend, which results in different phase behavior in Nafion-PVTri blend membrane. This relatively lower repulsive interaction causes Nafion-PVTri blend membrane to have non-continuous phases regardless of the composition.

Miscibility characterization of zein/methacrylic acid copolymer composite films and plasticization effects

Composite films have gained interest for producing films with optimal properties, without the need of chemical modification. Miscibility of components in the film is important for attaining reproducible and consistent film properties. This study used several techniques, i.e. differential scanning calorimetry, Fourier transform infrared spectroscopy and Raman spectroscopy to understand the degree of miscibility of components and its impact on morphology and mechanical properties of the composite film prepared by casting the blend of zein and methacrylic acid copolymer (Eudragit® L100-55). The effects of composition and plasticization by triethyl citrate and polyethylene glycol 1000 were explored. The results demonstrate the miscibility of zein and methacrylic acid copolymer at a molecular level; and the phase behavior of polymer blends is modified by plasticization. Polyethylene glycol 1000 is more compatible with the polymer blend. Its plasticization effect is associated with an increase in β-sheets. Understanding the miscibility between the plasticizer and the polymer blend allows the ability to predict and control mechanical properties of the zein/methacrylic acid copolymer composite film, in particular when the plasticizer level is changed.

Morphing Simulations Reveal Architecture Effects on Polymer Miscibility

The Flory–Huggins interaction parameter χ quantifies the excess free energy of mixing unlike species and governs phase behavior in polymer blends and block copolymers. Chain architecture affects ho...

Thermodynamics of Associative Polymer Blends

We report on a theoretical study of the phase behavior of polymer blends with hydrogen-bonding (HB) groups using the mean-field approximation. The hydrogen bonds are modeled as saturable bonds. We ...

Phase transition of block copolymer/homopolymer binary blends under 2D confinement

Constraints imposed by nanometer scale confinement lead to the changes in bulk equilibrium behavior of block copolymers (BCPs). Cylindrical pores with diameter corresponding to the equivalent length of several copolymer chains have been employed to investigate the influence of two-dimensional (2D) confinement on the behavior of BCPs. Herein, we reported the microdomain transition behavior of block copolymer/homopolymer (AB/A) binary blends in cylindrical confinement. Lamellae forming poly(styrene-b-butadiene) (PS-b-PBD) and PS homopolymers (hPS) were drawn into the pores of anodized aluminum oxide (AAO) and isolated by selective etching of the AAO templates. Concentric ring morphologies of neat PS-b-PBD in the cylindrical confinement varied with on the addition of hPS. Given the volume fraction of homopolymers, the phase behavior of polymer blends was dependent on the molecular weight of homopolymers. When the ratio between the molecular weight of hPS and PS block was much lower than unity (α«1) (i.e., wet brush regime), the concentric ring structure was transformed into helical or spherical structure depending on the volume fraction of hPS. For α≈1 (i.e., dry brush regime), additional hPS chains were localized at the center of concentric ring where the entropic penalty of copolymer chains induced by confinement is maximized. Over the capability of hPS in the BCP domains in radial axis, the phase transition into microemulsions occurred in the dry brush regime. In both wet and dry brush regimes, the effect of hPS on the phase transition of BCP was significantly enhanced in the nanoscale 2D confinement compared to the bulk state due to the loss of conformational entropy of polymer chains.

Deuterated Polymers for Probing Phase Separation Using Infrared Microspectroscopy

Infrared (IR) microspectroscopy has the capacity to determine the extent of phase separation in polymer blends. However, a major limitation in the use of this technique has been its reliance on overlapping peaks in the IR spectra to differentiate between polymers of similar chemical compositions in blends. The objective of this study was to evaluate the suitability of deuteration of one mixture component to separate infrared (IR) absorption bands and provide image contrast in phase separated materials. Deuteration of poly(3-hydroxyoctanoate) (PHO) was achieved via microbial biosynthesis using deuterated substrates, and the characteristic C-D stretching vibrations provided distinct signals completely separated from the C-H signals of protonated poly(3-hydroxybutyrate) (PHB). Phase separation was observed in 50:50 (% w/w) blends as domains up to 100 μm through the film cross sections, consistent with earlier reports of phase separation observed by scanning electron microscopy (SEM) of freeze-fractured protonated polymer blends. The presence of deuterated phases throughout the film suggests there is some miscibility at smaller length scales, which increased with increasing PHB content. These investigations indicate that biodeuteration combined with IR microspectroscopy represents a useful tool for mapping the phase behavior of polymer blends.

Phase behavior of polymer blends with reversible crosslinks—A self-consistent field theory study

Abstract

Polymer equations of state derived from molecular simulation

This work characterizes fluid equations of state for many common polymers from small oligomers to the infinite chain limit. The methodology applies the formalism of discontinuous molecular dynamics (DMD) and thermodynamic perturbation theory (TPT) previously developed for polyethylene [1,2]. Oligomers with each structure are simulated for a series of molecular weights varying from the monomer to roughly 1100g/mol. Each oligomer is simulated at 21 densities to interpolate the reference and perturbation contributions to the equation of state. Plotting the perturbation term vs. density for a polymer series leads to an asymptotic inference in the long chain limit. Interpolation functions are then developed to characterize the polymer at any molecular weight. The polymers characterized include polyethyleneoxide, polylacticacid, polypropylene, polyisoprene, and polystyrene.The characterizations are compared to the result of Wertheim's theory of polymerization to show how individual monomer structure lead distinctive behavior. Given these characterizations, it is straightforward to predict phase behavior of polymer blends and solutions that can be tested by experiment and targeted molecular simulations at specific compositions.

Miscible and Core−Sheath PS/PVME Fibers by Electrospinning

We demonstrate that miscible and phase-separated fibers of the blend between polystyrene (PS) and poly(vinyl methyl ether) (PVME) can be electrospun by appropriate selection of the solvent. Solutions in benzene allow preparing miscible fibers with composition ranging from pure PS to PS/PVME 70/30. Results indicate that the rapid solvent evaporation during electrospinning has no significant influence on the phase behavior of polymer blends when the system is miscible throughout the ternary phase diagram. On the other hand, fibers electrospun from chloroform solutions show a clear phase separation because of a closed immiscibility loop. They are nevertheless highly malleable, in contrast with the brittle films obtained by solution casting. The confinement and solvent evaporation kinetic lead to a core−sheath structure, with the interior composed of the PS-rich phase and the surface highly enriched in PVME, as opposed to microdomains in cast films. The shell can be extracted rapidly and efficiently by a 10 s treatment in water, converting the mat from fully wettable to highly hydrophobic.

Modeling of thermodynamic behavior of PVT properties and cloud point temperatures of polymer blends and polymer blend + carbon dioxide systems using non-cubic equations of state

In recent years, many factors influencing phase behavior of polymer blends have been studied because of their widely technological importance, as a simple method of formulating new materials with tailored properties which make them suitable for a variety of applications. This work has three main goals which were reached by using the Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) and the Sanchez–Lacombe (SL) non-cubic equations of state (EoS), which in previous works have shown their ability to handle long chain and associating interactions. First, both equations of state were tested with the correlation of the specific volumes of pure blends (PBD/PS, PPO/PS, PVME/PS, PEO/PES) and the prediction of the specific volumes for blends; second, the modeling of blend miscibilities in the liquid–liquid equilibria (LLE) of PBD/PS, PPG/PEGE, PVME/PS, PEO/PES, and PnPMA/PS blends; third, the modeling of the phase behavior of PS/PVME blends at various compositions in the presence of CO 2. PC-SAFT and SL pure-component parameters were regressed by fitting pure-component data of real substances (liquid pressure–volume–temperature, PVT, data for polymers and vapor pressure and saturated liquid molar volume for CO 2) and the fluid phase behavior of blend systems were simulated fitting one binary interaction parameter ( k ij ) by regression of experimental data using the modified likelihood maximum method. Results were compared with experimental data obtained from literature and an excellent agreement was obtained with both EoS, which were also capable of predicting the fluid phase behavior corresponding to the critical solution temperatures (LCST: lower critical solution temperature, UCST: upper critical solution temperature) of blends.

Bicontinuous Polymeric Microemulsions from Polydisperse Diblock Copolymers

Polymeric bicontinuous microemulsions are thermodynamically stable structures typically formed by ternary blends of immiscible A and B homopolymers and a macromolecular surfactant such as an AB diblock copolymer. Investigations of these bicontinuous morphologies have largely focused on model systems in which all components have narrow molecular weight distributions. Here we probe the effects of AB diblock polydispersity in ternary blends of polystyrene (PS), polyisoprene (PI), and poly(styrene-b-isoprene) (PS-PI). Three series of blends were prepared using the same PS and PI homopolymers; two of them contain nearly monodisperse components while the third includes a polydisperse PS-PI diblock. The PS and PI homopolymers and two of the PS-PI diblocks were prepared by anionic polymerization using sec-butyllithium and have narrow molecular weight distributions. The polydisperse PS-PI diblock was prepared by anionic polymerization using the functional organolithium 3-tert-butyldimethylsilyloxy-1-propyllithium; this diblock has a polydisperse PS block (Mw/Mn = 1.57) and a nearly monodisperse PI block (Mw/Mn < 1.1). The phase behavior of the three series of blends was probed using a combination of dynamic mechanical spectroscopy, small-angle X-ray scattering, and cloud point measurements, and a bicontinuous microemulsion channel was identified in each system. These results prove that monodisperse components are not required to form bicontinuous microemulsions and highlight the utility of polydispersity as a tool to tune polymer blend phase behavior. The random-phase approximation, originally advanced by de Gennes, and self-consistent field theory are used to provide a theoretical supplement to the experimental work. These theories are able to predict the directions of the polydispersity-driven shifts in domain spacing, order-disorder transition temperatures, and the location of the microemulsion channel. Self-consistent field theory is also used in conjunction with the experimental data from a series of nearly monodisperse blends to probe the variations of chi with temperature. A single linear relation of the form chi = alpha/T + beta does not describe chi at all blend compositions. Rather, two separate relations describe chi as a function of temperature; one is obtained from data on the diblock-rich side of the bicontinuous microemulsion channel while the other is obtained from data on the homopolymer-rich side of the channel. The blend morphology, rather than the composition (homopolymer fraction), apparently dictates whether the system is in the "diblock chi" or "homopolymer chi" regime. These results reinforce the notion that a true understanding of chi still eludes the polymer science community.

Miscibility Study of Stereoregular Poly(methyl methacrylate) Blends. Experimental Determination of Phase Diagrams and Predictions

Miscibility behavior of blends of isotactic and syndiotactic poly(methyl methacrylate) (iPMMA and sPMMA) was investigated as a function of annealing temperature and molecular weight of the iPMMA component. Annealing experiments clearly indicate that for the high molecular weight iPMMA sample formation of stereocomplexes between isotactic and syndiotactic PMMAs is hindered. Annealing experiments carried out in the temperature range 313−473 K, followed by DSC measurements, showed that iPMMA is completely miscible with sPMMA only in a narrow temperature range around 350 K. To explain these experimental data, a simple theoretical model for the prediction of phase behavior of polymer blends involving dispersive interactions, is presented. This model accounts for subtle structural differences (e.g., stereoisomerism) between the repeat units of the blend components, and by incorporating the surface to volume ratios into the original Flory−Huggins solubility parameter approach, which makes it possible to account ...

Shear induced phase coarsening in Polystyrene/Styrene-ethylene-butylene-styrene blends

The phase behavior of polymer blends under the effect of shear has been a subject of considerable interest from the viewpoint of both theoretical research and industrial application, because the shear stress is unavoidable during processing. In this work, we reported the change of phase behavior and mechanical properties of Polystyrene (PS)/Styrene-ethylene-butylene-styrene (SEBS) blends achieved via a shear-assistant injection molding, which was called dynamic packing injection molding (DPIM). The size of dispersed SEBS particles in PS matrix was found to be increased for the samples obtained by dynamic packing injection molding (DPIM), compared with those obtained by conventional molding, indicating a shear induced phase coarsening. The shear induced phase coarsening can be further demonstrated by the decrease of impact strength of dynamic packing injection molded samples. However, the shear-induced phase coarsening will be eliminated after annealing the samples at high temperature for certain time. The particle size, which related to the capability to deform under the effect of shear, was found to play an important role to determine the phase morphology. Our result suggested that shear stress induced phase coarsening was a process of not only molecular configuration change but also deformation change under shear.

Effect of Polydispersity on the Phase Behavior of Polymer Blends

AbstractSummary: The effect of polydispersity on polymer blend phase behavior is studied by in situ small‐angle X‐ray scattering. In a polydisperse polyethylene (PE)/isotactic poly(propylene) (iPP) blend, the enthalpic portion of the interaction parameter is greater than that of a corresponding blend with lower polydispersity. This is attributed to the presence of long chains, which provide a higher interaction energy and packing constraint, reducing the system miscibility. As expected, the radius of gyration is higher in the system with higher polydispersity.Comparison of phase diagrams of the iPP/PE system used in this study (thin lines) with that obtained from the literature (thick lines). The solid lines represent binodals and the dashed lines are spinodals.imageComparison of phase diagrams of the iPP/PE system used in this study (thin lines) with that obtained from the literature (thick lines). The solid lines represent binodals and the dashed lines are spinodals.

Thermodynamics of Poly(dimethylsiloxane)/Poly(ethylmethylsiloxane) (PDMS/PEMS) Blends in the Presence of High-Pressure CO2

Processing polymer blends in the presence of high-pressure carbon dioxide (CO2) affords numerous advantages over organic solvents and is becoming a commercially viable and environmentally responsible alternative in the development of new multicomponent materials. A prerequisite to such processing is a fundamental understanding of how high-pressure CO2 influences the phase behavior of polymer blends. In this work, we use high-pressure spectrophotometry to measure the cloud point (Tcp) of poly(dimethylsiloxane)/poly(ethylmethylsiloxane) (PDMS/PEMS) blends as a function of CO2 pressure (P) in the vapor phase. Results obtained here at different blend compositions indicate that values of Tcp for this upper critical solution temperature (UCST) blend (i) generally increase with increasing pressure and (ii) collapse onto a master curve of ΔTcp(P) for pressures up to about 35 MPa. These data are analyzed by the Sanchez−Lacombe equation of state to ascertain the temperature dependence of an effective interaction pa...

Universal behavior of polymers in blends, solutions, and supercritical mixtures and implications for the validity of the random phase approximation

Blending (or mixing) of macromolecules is widely used to tailor the properties of polymeric materials and small-angle neutron scattering (SANS) has provided detailed information at the molecular level on the ability of different polymer species to mix or segregate at various thermodynamic conditions. For two decades, SANS data have been analyzed via the de Gennes “random phase approximation” (RPA) [P.-G. de Gennes, Scaling Concepts in Polymer Physics, second ed., Cornell University Press, Ithaca, London, 1979], which is based on the assumption that the dimensions of polymer chains remain unchanged on mixing for all concentrations and temperatures. Here we investigate the effect of temperature and concentration on the dimensions of macromolecules in blends using SANS and high-concentration labeling methods and construct a generic phase diagram, which specifies the range of validity of the RPA. Using scaling arguments, we demonstrate a parallel between the structure–property relationships in blends and solutions of polymers in small molecule solvents and reveal the impact of the chain length of the polymeric solvent on the phase behavior of polymer blends. The results offer new insights into the universality of the thermodynamic properties and structure of macromolecules in polymeric, liquid and supercritical solvents.

The effects of end groups on thermodynamics of polymer blends III LCST phase diagrams

The effect of end group substitution on the phase behavior of blends of poly(styrene) (PS) and poly(vinyl methyl ether) (PVME) is characterized by determination of experimental cloud point curves. Incorporation of a fluorosilane end group on PS increases the lower critical solution temperature by 10 °C indicating enhanced miscibility. The end group effect is modeled by a modification of Sanchez–Lacombe–Balazs (SLB) theory that employs binary interaction theory to account for the end group effect. The increased miscibility is quantitatively predicted by the modified theory when binary interaction parameters are calculated by group contribution methods. SLB theory is also compared to phase diagrams of PS/PVME blends previously reported by Halary et al., and Yang et al., but fails to reproduce the observed behavior over the entire molecular weight range. Optimal fits of these data yield interaction energy parameters that are molecular weight dependent, suggesting that the SLB theory may require molecular weight dependent equation of state parameters in order to reproduce the phase behavior of polymer blends.

Combinatorial Methods for Investigations in Polymer Materials Science

AbstractWe review recent advances in the development of combinatorial methods for polymer characterization. Applied to materials research, combinatorial methodologies allow efficient testing of structure–property hypotheses (fundamental characterization) as well as accelerated development of new materials (materials discovery). Recent advances in library preparation and high-throughput screening have extended combinatorial methods to a wide variety of phenomena encountered in polymer processing. We first present techniques for preparing continuous-gradient polymer “libraries” with controlled variations in temperature, composition, thickness, and substrate surface energy. These libraries are then used to characterize fundamental properties such as polymer-blend phase behavior, thin-film dewetting, block-copolymer order–disorder transitions, and cell interactions with surfaces of biocompatible polymers.

Infrared studies of polymer blends containing a copolymer of tetrafluoroethylene and a hexafluoroisopropanol substituted vinyl ether

An essentially alternating 1:1 copolymer of tetrafluoroethylene and a hexafluoroisopropanol-modified vinyl ether has been recently synthesized. This is an interesting copolymer for both experimental and theoretical studies of the phase behavior of polymer blends because (1) it is amorphous and has a relatively low glass transition temperature (12°C); (2) it has a relatively low solubility parameter [≈7 (cal cm−3)−0.5]; (3) it is soluble in moderately polar solvents, and (4) it contains the hexafluoroisopropanol group that is a strong hydrogen bond donor. We report the results of experimental infrared and thermal analysis studies of polymer blends with (co)polymers containing acetoxy, methacrylate, and aliphatic ether groups and compare them to our theoretical predictions of miscibility maps.