Determination of Equation-of-State Parameters by Molecular Simulations and Calculation of the Spinodal Curve for Polystyrene/Poly(vinyl methyl ether) Blends (original) (raw)
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Molecular Simulation, 2008
We have performed Molecular Dynamics simulations for atomistic representations of polyvinylmethylether/polystyrene blends using the "Discover" module of the Materials Studio software platform with the "compass" forcefield. The simulation boxes are constructed with the "Amorphous Cell" module, introducing polymer chains designed with the "Visualizer" building tools. The simulations yield trajectories files, whose coordinates have been employed to calculate the collective scattering structure factor. Comparison of the numerical data obtained for this property with the predictions of random phase approximation theory, depending on the Flory-Huggins parameter, has allowed us to obtain numerical results for this parameter, commonly accepted as a good indicator of compatibility. The results depend on the method used to assign partial charges though they are always reasonably close to existing data obtained through neutron scattering experiments. The charge equilibration method gives a correct prediction of compatibility in the studied temperature range. Moreover, it shows a positive variation of the Flory-Huggins parameter with temperature, in agreement with the phase behavior of these blends that show a lower critical temperature. However, the parameter absolute values are too high. When forcefield assigned charges are introduced, the Flory-Huggins parameter are slightly positive and a non-monotonous variation with temperature is found. However, the values for the highest temperatures are remarkably close to the experimental data.
Polymer, 1988
The binary interaction parameter Z=fr has been obtained for deuterated polystyrene/poly(vinyl methyl ether) blends as a function of temperature, composition and molecular weight from small-angle neutron scattering experiments. The consistency of the correlation length 4, the zero-wavenumber scattering intensity S(0) and the Xar parameter with the mean-field prediction has been demonstrated by the q dependence of the static structure factor S(q) and the 1/T dependence of ~-2, S(0)-1 and X=~. The effective interaction parameter Xe~ can be related to the Flory-Huggins interaction parameter ZF. The free-energy function as well as the spinodal curve and cloud-point curve have been constructed.
Rheology and phase separation in polystyrene/poly(vinyl methyl ether) blends
Journal of Polymer Science Part B: Polymer Physics, 1988
Blends of monodisperse polystyrene and poly(viny1-methyl-ether) of various compositions were prepared from solution in benzene. Dynamic rheological properties of these blends were studied at different temperatures below, near, and above T,, the temperature of phase separation, and in a frequency range from 0.05 to 100 rad/s. A flattening in the storage modulus and an initial plateau for the complex Viecoeity were observed near and above T, in the low-frequmcy region; in contrast, below T, the behavior of the blends was similar to that of the homopolymers. The WLF superposition principle appliee only at temperatures below T,, i.e., in the miscible and homogeneous region. G" versus G' repmantations for the blends were found to be independent of temperature and to vary with composition in the miscible region but are temperature and composition-dependent in the immiscible region. It is also shown that the q" versus q' representation is a useful tool for charactmizing phase separation of blends and is more sensitive than the classical frequency dependence of the material functions.
Phase Behavior and Segmental Mobility in Binary Blends of Polystyrene and Poly(vinyl methyl ether)
Macromolecules, 2000
The phase behavior and segmental mobility in binary blends of polystyrene (PS) and poly-(vinyl methyl ether) (PVME) were investigated. Two nearly monodisperse PSs having weight-average molecular weights (M w) of 57 000 and 95 000 with polydispersity indexes (PDI) of 1.06 and 1.09, respectively, and PVME having Mw) 99 000 with a PDI of 2.13 were used for this study. Two sets of PS/PVME binary blends with varying compositions were prepared by solvent casting from toluene. Thermograms from differential scanning calorimetry showed that each blend has a single, yet very broad glass transition temperature. Cloud point measurements via He-Ne laser light scattering were taken to determine phase equilibria in each blend, which exhibited lower critical solution temperature (LCST) behavior. Solid-state nuclear magnetic resonance (NMR) spectroscopy was used to examine segmental mobility and component domain sizes. 1 H T1F experiments were run at temperatures ranging from-40 to 140°C. We observed only small differences in 1 H T1F values of PS and PVME at temperatures below 45-80°C (depending on blend composition) and a large divergence of 1 H T1F values at higher temperatures. 13 C T1F and wide-line separation (WISE) experiments were run at room temperature on untreated and heat-treated samples. WISE experiments revealed that heterogeneities from 3.5 nm to greater than 30 nm existed within the blends, depending on the temperature of heat treatment. Since it has been found that 1 H T1F measurements can give ambiguous domain information, 1 H-NOESY NMR was used to examine several blend compositions at 100°C. We conclude from this study that nanoheterogeneities exist in these PS/PVME blends at temperatures below the binodal curve determined by cloud point measurements and that a broad, single glass transition should not be construed as evidence of miscibility at the molecular level. It has been shown that nanoheterogeneities exist on a segmental level and that there are large changes in mobility at temperatures above 45-80°C. However, the blend does not phase separate until the critical temperature (LCST), determined by cloud point measurements, is reached.
Thermodynamic analysis on the phase behavior of copolymer blends: an equation of state approach
Macromolecules, 1992
A model of copolymer blends based on the PrigogineFlory-Patterson equation of state theory is presented to understand quantitatively the effect of comonomer on the LCST behavior of copolymer blends. According to Patterson's treatment, the free volume effect was introduced to the Flory-Huggins interaction parameter xm of copolymer blends. The model explains that the intramolecular interaction within copolymers contributes not only to the interactional term but also to the free volume term. Unlike its contribution to the interactional term, the repulsion is not always favorable to the free volume term which depends on the difference in the characteristic temperatures between blend components. Since the characteristic parameters P and P of the copolymers are a function of those of the copolymer components, the difference depends on the magnitudes of the characteristic parameters of selected comonomer as compared with those of base polymer. The applicability of the proposed model was examined for poly(viny1 methyl ether) (PVME)/styrene copolymer blends. The calculated variation of xwith the copolymer composition at a given temperature was in agreement with the variation of the LCST with the copolymer composition and the type of comonomer.
Polymer, 2003
Molecular simulations of poly(vinyl phenol)/poly(vinyl methyl ether) (PVPh/PVME) blends were performed and their degree of miscibility evaluated as a preliminary step before orientation simulations. A minimum of three periodic boundary condition amorphous models was constructed and analysed in terms of solubility parameter, X-ray pattern, pair correlation function, hydrogen bond fraction and backbone conformation. The values obtained are consistent with miscibility of the systems, although it is suggested that the degree of mixing is not uniform for the different models.
Journal of Applied Polymer Science, 2008
Molecular simulations are the most important tools to predict the properties of polymers and their blends. In this work, we have predicted the blend incompatibility of poly(n-vinyl pyrrolidone) (PVP) and poly(bisphenol-A-ether sulfone) (PES). Atomistic simulations were performed to compute the Flory-Higgins interaction parameter over all the compositions ranging from 90 to 10% of the individual polymers, which confirmed that the blends are incompatible (Bhattacharya et al., J Membr Sci 2003, 227, 23). Kinetics of phase separation was examined via density profiles calculated using MesoDyn approach. For incompatible blends, the critical value of 0.32 computed from the Flory-Huggins theory agreed with the value of 0.29, suggesting the validity of our approach. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008