Phase Behavior Of Polymer Blends Research Articles

Description of Phase Behavior of Polymer Blends by Different Equation-of-State Theories. 1. Phase Diagrams and Thermodynamic Reasons for Mixing and Demixing

A comparison has been made between the Sanchez-Lacombe equation-of-state theory and the theory of Patterson for describing the phase behavior of various polymer blends. Phase diagrams have been determined as well as PVT data, in order to determine the reduction parameters of the polymers used. With these data the phase diagrams were simulated applying these two theories. Furthermore, the cause of compatibility or incompatibility, i.e., the influence of free volume and enthalpic effects were investigated. Both theories show surprisingly similar behavior with respect to the mentioned properties.

A rheo-light-scattering instrument for the study of the phase behavior of polymer blends under simple-shear flow

A rheo-light-scattering instrument for investigating the influence of shear on the phase behavior of polymer blends was constructed from a commercial parallel-plate rheometer. Laser light scattering from the sample plane formed by the flow and vorticity directions was projected on a screen, and a combination of a camera lens and a charge-coupled device detector was used to record the scattering pattern. The rheometer, which can generate angular velocities of up to 100 rad/s and measure torque and normal forces up to 9.8×103 N m and 9.8×105 N, respectively, is suitable for studying polymer melts at stresses up to 9.1 kPa. The maximum accessible q range was from 5.72×10−4 to 7.11×10−3 nm−1 (3°–42° scattering angle and a laser wavelength of λ=632.8 nm). The performance of the light-scattering instrumentation and the accuracy of the correction algorithms were tested with a Ronchi ruling diffraction grating and a colloid of monodisperse polystyrene spheres. Example rheo-light-scattering measurements were made with a 50/50 blend of polystyrene and polyisobutylene oligomers and a 40/60 blend of polybutadiene and polyisoprene. All components had narrow molecular weight distributions. The first blend exhibits an upper critical solution temperature while the second blend shows a lower critical solution temperature.

Rheo‐Optical behavior of binary polymer blends: The effect of simple shear flow on phase behavior

AbstractThe phase behavior of polymer blends under simple shear flow has been studied using a custom‐designed rheo‐optical system consisting of a two‐dimensional small‐angle light scattering (SALS) device incorporated into a conventional rheometer. Two‐dimensional SALS images were gathered for model polymer blend systems with different quiescent phase behavior: polystyrene/polyisobutylene (PS/PIB) that exhibits upper critical solution temperature phase behavior and polystyrene/poly(vinyl methyl ether) (PS/PVME) that shows lower critical solution temperature phase behavior. For the PS/PIB blend, shear‐induced phase mixing occurred at a critical shear rate. Below that critical shear rate, the dispersed phase was highly elongated parallel to the flow direction. For PS/PVME blends, a streak scattering pattern was observed even though the sample became optically clear after shearing. We observed, apparently for the first time, the development of a bright‐streak pattern from a transient dark‐streak pattern for a polymer blend system under shear. Rheo‐microscopy studies revealed an intriguing wave pattern that developed coincident with the observation of a streak pattern by SALS. The relationship between the two phenomena has not yet been established.

Phase behavior of polymer blends under equilibrium and nonequilibrium conditions

AbstractThis contribution embraces two topics related to phase behavior of polymer blends under equilibrium and nonequilibrium. 1. Polymer blends can undergo different phase changes as liquid‐liquid phase transition and crystallization. Coupling of demixing and crystallization may occur at the kinetic stage. This is illustrated by blends of poly(ϵ‐caprolactone)(PCL) and poly(styrene‐co‐acrylonitrile)(SAN). 2. Extension of studies to blend systems under flow is necessary for the better understanding of structure formation in polymer blends outside equilibrium. Polymer molecules will be oriented and stretched when subjected to flow. This may result in flow‐induced phenomena. Effects of flow on the phase behavior have been studied only for a few blends, as yet. The primary observation was flow‐induced miscibility. Apparent shifts of the phase transition temperatures will be discussed qualitatively in terms of a decoupled mode theory.

Random copolymer blends of styrene, para-fluoro styrene and ortho-fluoro styrene

This study completes the investigation of the phase behaviour of polymer blends involving styrene (S), ortho-fluoro styrene (oFS) and para-fluoro styrene (pFS). As before, due to the proximity of the glass transition temperatures of most blends investigated, the miscibility or immiscibility is established using the alternative thermal analysis method based on enthalpy recovery of samples annealed in the glassy state. In most respects the phase behaviour is similar to that of the corresponding chlorinated systems. The value of the Flory-Huggins parameter χ S,oFS is much smaller than χ S,pFS. However, the latter is approximately the same as χ oFS,pFS and, as a consequence, a miscibility window as found in the system PS/P(ClS- co-pClS) is only present in PS/P(oFS- co-pFS) blends for rather low molecular weights.

Mean-field lattice equations of state: 5. Influence of pressure on liquid-liquid phase behaviour of polymer blends

The semi-phenomenological (SP) treatment and a modified form of the mean-field lattice-gas (MFLG) model were used to investigate the influence of pressure on the phase behaviour of polymer blends. It was shown that the peculiar phase relations of the system poly(ethyl acrylate)/poly(vinylidene fluoride) could be reproduced in a qualitative way. Positive and negative signs for the excess volume could be predicted in accordance with the observed pressure-temperature-weight fraction relations. Furthermore the effect of pressure on the location of binodals for oligomeric mixtures of polybutadiene and polystyrene was represented quantitatively with the MFLG model and the SP treatment. It was shown that end group contributions cannot be neglected if polymers of low molar mass are involved. It was further demonstrated that the SP approach only requires one interaction function to represent all critical data whereas in the MFLG model different interaction terms, one for each system, are necessary in order to obtain good descriptions. Both descriptions are found to be superior to a modified version of the Flory equation of state theory.

Phase Behavior of Polymer Blends under Conditions of Equilibrium and Flow

Phase Behavior of Polymer Blends under Conditions of Equilibrium and Flow

The phase behavior of polymer blends – Effects of thermodynamics and rheology

AbstractPart one of the paper is devoted to the thermodynamics of the phase behaviour of polymer blends. According to an equation‐of‐sate theory the phase behaviour is directed by the interplay of three effects: the interaction between the segments, the free‐volume effect, and the size‐effect. When the size‐effect is negligible only lower critical solution temperature (LCST) behaviour occurs. Phase separation at elevated temperatures is an entropy driven process whereas at an upper critical solution temperature (UCST) an unfavourable enthalpic effect associated with the size‐effect acts as driving force for phase separation. Also positive volumes of mixing can be related to the size‐effect. In the second part the phase behaviour of blends exposed to shear is discussed. For blends it has been found experimentally that shear flow elevates phase‐separation temperatures. Obviously, shear‐induced phase changes depend on the stored elastic excess energy. A negative stored excess energy corresponds to an additional attraction between the different segments, hence, the miscibility region of the system is enlarged theoretical and experimental reuslts agree qualitatively.

Shear-induced phase changes in polymer blends

The phase behaviour of polymer blends exposed to shear is analysed in terms of a mean-field theory. One result of the theory is that shear-induced phase changes depend on the stored elastic excess energy. For a negative stored excess energy the miscibility region of the system is enlarged. The shift of the binodal for blends for poly(methyl methacrylate) and poly(styrene- co-acrylonitrile) undergoing shearing flow is determined by light-scattering experiments. It has been found for these blends that shear flow elevates phase-separation temperatures.

Phase Behavior of Polymer Blends

Abstract Major emphasis is placed on the phase behavior of miscible polymer blends. To understand the complex phase behavior of blends, a refined version of an equation-of-state theory is discussed. This theory makes the simultaneous occurrence of upper critical solution temperature and lower critical solution temperature in blends of high molar mass polymers conceivable. The kinetics of isothermal phase dissolution as it emanates from different experimental routes is discussed in terms of CahN′s linearized theory of phase separation. The rate of phase dissolution varies as a function of quench depth, which indicates the rate is directed by both the thermodynamic driving force and the mobility.

Phase Behavior of Polymer Blends

Abstract We have demonstrated in two separate cases that SANS experiments can be used to obtain binary interaction parameters effectively and accurately. With measured χ as a function of composition and temperature, the free energy of mixing can be obtained at least numerically. The phase diagram including spinodal curves and cloud-point curves can be predicted. The second derivative of free energy of mixing w.r.t. composition, ∂2ƒ/∂ϕ2, can be used directly in the kinetics studies of spinodal decomposition. In the polybutadiene/polybutadiene case, individual pair interaction parameters can be separated out. Microstructure effect is the main contribution to the incompatibility of the blends. Nevertheless, with the use of the random copolymer theory, phase behavior can be predicted.

Apparatus for Simultaneous Small Angle Neutron Scattering and Steady Shear Viscosity Studies of Polymer Melts and Solutions.

The design and construction of an apparatus for studying the simultaneous small angle neutron scattering (SANS) and steady shear viscosity behavior of polymer melts and concentrated solutions is discussed. Successful operation of the device is demonstrated on a blend of 20 weight percent deuterated polystyrene and 80 weight percent poly(vinylmethylether). The effects of shear on the critical behavior of the blend are observed in the SANS behavior as a function of temperature and shear rate and indicate shear induced mixing behavior for the range of shear rates examined. The steady shear viscosity results alone are insufficient for detecting the transition from one to two phases. The examination of shear effects in polymer blends is important for understanding the critical behavior of binary systems. Technologically, knowledge of the phase behavior of polymer blends under shear are important for the design and improvement of commercial blend processing.

Phase Behavior of Polymer Blends

Phase Behavior of Polymer Blends

Shear Induced Phase Behavior of Polymer Blends by Small Angle Neutron Scattering

ABSTRACTThe phase behavior of polymer blends and solutions can be changed dramatically by a flow field using a variety of flow geometries. Unlike simple binary fluids which require extremely high shear rates to produce only small shifts in the phase boundary, polymer phase behavior may be influenced by as much as 10 degrees with the application of much lower shear rates. However, there is a large body of conflicting data concerning the nature of these shear effects in polymers.Here we report on the effects of shear on the phase behavior of polymer blends by small angle neutron scattering (SANS). Experiments were conducted using a specially constructed, concentric cylinder apparatus for in situ studies of concentrated polymer solutions and melts. Two separate systems will be discussed: 1) a blend of polystyrene and polybutadiene. 2) a blend of polystyrene and poly(vinylmethylether). Both systems exhibit shifts in the phase behavior which indicate shear induced mixing in agreement with previous results obtained by other techniques. These results will be interpreted within the context of existing theories of shear induced phase behavior.

Characterization of Phase Behavior in Polymer Blends by Light Scattering

Abstract It is well known that most pairs of high molecular weight polymers are immiscible. This is so because the combinatorial entropy of mixing of two polymers is dramatically less than that of two low molecular weight compounds [1–3]. The enthalpy of mixing, on the other hand, is often a positive quantity. Therefore, dissimilar polymers are only miscible if there are favorable specific interactions between them leading to a negative contribution to the Gibbs free energy of mixing. Miscible polymers tend to phase separate at elevated temperatures. This lower critical solution temperature (LCST) behavior is interpreted in terms of the equation of state or the freevolume contribution [1–3]. About 30 pairs of dissimilar polymers have been found to exhibit the LCST behavior.

Effect of pressure on phase behavior in polymer blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide) and poly(styrene‐co‐p‐fluorostyrene) copolymers

AbstractThe effect of pressure on the miscibility of blends of poly(2,6‐dimethyl‐l,4‐phenylene oxide) (PPO) with a random copolymer of styrene and para‐fluorostyrene, P(S‐co‐p‐FS), has been studied by high pressure differential thermal analysis (HPDTA). P(S‐co‐p‐FS) copolymers less than 36 mole % p‐FS are miscible with PPO in all proportions irrespective of pressure up to 200 MPa, using the customary criterion of a single calorimetric glass relaxation. P(S‐co‐p‐FS) copolymers containing 40 to 50 mole % p‐FS undergo phase separation upon annealing at elevated temperatures, indicating the existence of a lower critical solution temperature (LCST). In these blends, pressure displaces the phase boundary associated with the LCST to higher temperatures causing an apparent increase in polymer miscibility. The phase diagram for the blend of PPO and P(S‐co‐p‐FS) containing 46 mole % p‐FS, shows that the critical composition at about 50 wt % PPO does not change with pressure, but the consolute temperature Tc increases with increasing pressure. The pressure dependence of the LCST (dTc/dP) of this system is about 0.35°C/MPa.

Effect of pressure on phase behavior in polymer blends of poly(2,6-dimethyl-1,4-phenylene oxide) and poly(o-fluorostyrene-co-p-fluorostyrene) copolymers

The effect of pressure on miscibility and phase separation in blends of random copolymers of ortho- and para-fluorostyrene, P(o-FS-co-p-FS) and poly(2,6-dimethyl-1,4-phenylene oxide), PPO, has been studied by differential thermal analysis (DTA) at pressures up to 300 MPa. At 200 MPa the copolymers containing from 10 to 38 mol% p-FS are miscible with PPO below 230°C using the customary criterion of a single calorimetric glass transition temperature (Tg). Each blend undergoes phase separation upon annealing at higher temperatures at both atmospheric and elevated pressures indicating the presence of a lower critical solution temperature (LCST). When the phase behaviors of the 50/50 wt% blends are examined as a function of temperature and copolymer composition, a symmetric miscibility “window” can be observed in the resulting temperature-composition diagram with a maximum at about 22 mol% p-FS. In a complementary set of experiments, the pressure dependence of the phase boundary for the blend of PPO and P(o-FS-co-p-FS) in which the copolymer contained 29 mol% p-FS was studied. The temperature minimum of the phase boundary is at about 50 wt% PPO and is independent of pressure. The consolute temperature, Tc, increases at about 0.10°C/MPa up to 200 MPa and then becomes independent of pressure to reach an asymptotic value at around 270°C. Similar behavior is also observed for blends in which the copolymer composition contains either 16 or 23 mol% p-FS. In these blends the decrease of dTc/dP at higher pressures may indicate that the negative volume of mixing approaches zero above 200 MPa. This study shows therefore, that pressure no longer plays a role in increasing the miscibility above 200 MPa.

Compatibility of polymers in polymer blends investigated by gas chromatography

AbstractPolymer‐polymer and polymer‐solvent Flory‐Huggins interaction parameters are given for the systems polystyrene/poly(methyl vinyl ether), polystyrene/solvent, and poly(methyl vinyl ether)/solvent. In principle polymer‐polymer interaction should be independent of the solvent probes used. In this study it was found that polymer‐polymer interaction is influenced by the solvent probe. These influences are discussed as a function of the chemical nature of the interacting vapour phase. However, these effects are not decisive for the phase behaviour of polymer blends. Phase separation was observed at high temperature. Gas chromatography measurements facilitated a quantitative thermodynamic description of the system polystyrene/poly(methyl vinyl ether) over a wide range of temperature and composition.

Thermodynamics of polymer miscibility

AbstractThe phase behaviour of polymer blends containing random copolymers is discussed in terms of the PRIGOGINE‐FLORY theory. For a miscible high molecular mass system the interaction parameter XAB has to be negative in polymer/copolymer systems, however, miscibility does not require any specific interactions. Repulsion between the segments comprisiing the copolymer can lead to XAB < 0 and favour miscibility. At elevated temperatures immiscibility occurs due to the unfavourable free volume term depending on the difference in thermal expansion coefficients of the components. The phase diagrams of polymer/copolymer systems calculated by the presented theory agree satisfactorily with the experimental data.

A Fourier transform infra-red study of the phase behaviour of polymer blends. Ethylene-vinyl acetate copolymer blends with poly(vinyl chloride) and chlorinated polyethylene

Fourier transform infra-red studies of ethylene-vinyl acetate (EVA) blends with poly(vinyl chloride) (PVC) and chlorinated polyethylene (CPE) are presented. Previous studies have demonstrated that these blends are compatible at ambient temperature and exhibit lower critical solution temperatures ( LCST) in a range that is readily accessible and below the onset of significant polymer degradation. Infra-red spectra of EVA-PVC and EVA-CPE films cast from solution and recorded at room temperature exhibit the familiar frequency shifts and band broadenings of the carbonyl stretching vibration that are consistent with compatible blend systems. Significantly, at temperatures above the LCST, these spectral features are not observed, which implies phase separation. By monitoring the frequency of the EVA carbonyl stretching vibration in samples of the blends, an estimation of the relative strength of the intermolecular interactions has been obtained as a function of temperature. A non-linear relationship is observed and the temperature at which the relative strength of the intermolecular interaction appears very weak correlates with the LCST. The implications of these results are discussed.