Phase separation dynamics of a poly(vinyl methyl ether)/polystyrene (PVME/PS) blend studied by ultrafast differential scanning calorimetry

In this work, ultrafast differential scanning calorimetry (UFDSC) is used to study the dynamics of phase separation. Taking poly(vinyl methyl ether)/polystyrene (PVME/PS) blend as the example, we firstly obtained the phase diagram that has lower critical solution temperature (LCST), together with the glass transition temperature (T_g) of the homogeneous blend with different composition. Then, the dynamics of the phase separation of the PVME/PS blend with a mass ratio of 7:3 was studied in the time range from milliseconds to hours, by the virtue of small time and spatial resolution that UFDSC offers. The time dependence of the glass transition temperature (T_g) of PVME‐rich phase, shows a distinct change when the annealing temperature (T_a) changes from below to above 385 K. This corresponds to the transition from the nucleation and growth (NG) mechanism to the spinodal decomposition (SD) mechanism, as was verified by morphological and rheometric investigations. For the SD mechanism, the temperature‐dependent composition evolution in PVME‐rich domain was found to follow the Williams–Landel–Ferry (WLF) laws. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1357–1364     

Evolution of concentration fluctuation during phase separation of polystyrene/poly(vinyl methyl ether) blend in the presence of nanosilica

The influence of nanosilica on the concentration fluctuation of polystyrene/poly (vinyl methyl ether) (PS/PVME) mixtures was investigated during phase separation. The amplitude of concentration fluctuation was quantified by dielectric spectrums based on the idea of Lodge–Mcleish model and the linearized Cahn–Hilliard theory could describe the amplitude evolution of concentration fluctuation at the early stage of phase separation. Hydrophilic nanosilica A200 dispersed in PVME‐rich phase behaved an obvious inhibition effect on the concentration fluctuation of blend matrix, while hydrophobic nanosilica R974 dispersed in PS‐rich phase had little effect on the concentration fluctuation. The kinetics and amplitude evolution of concentration fluctuation during phase separation for PS/PVME/A200 nanocomposites were remarkably restrained due to the surface adsorption of PVME on A200. As the segmental dynamics of PVME and PS in homogeneous matrix was hardly influenced by A200 and R974, the enhanced miscibility and the significantly constrained flow relaxation of PVME chains might contribute to the retarded concentration fluctuation of PS/PVME/A200 nanocomposites. While the weak interaction between R974 and components of blend matrix and little effect of R974 on the molecular dynamics of PS chains may result in the weak retardation of concentration fluctuation for blend matrix. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1337–1349     

Morphological development and rheological changes of phenoxy/SAN blends during in‐situ polymerization

This article reports the results of an investigation into the time‐dependent morphological and rheological changes that accompany the in‐situ polymerization of blends composed of poly(hydroxyether of bisphenol A) (phenoxy) and poly(styrene‐co‐acrylonitrile) (SAN). The rheological behavior was monitored continuously during the in‐situ polymerization, whereas the miscibility and phase structure of blends formed in situ were examined at discrete stages of polymerization by differential scanning calorimetry and transmission electron microscopy. In the blend with 30 wt % SAN, a co‐continuous blend morphology was associated with gradual changes in the dynamic moduli, suggesting that phase separation proceeded by spinodal decomposition (SD). In contrast, phenoxy‐rich dispersions were uniformly dispersed in a continuous SAN‐rich matrix in the blend with 50 wt % SAN, and the corresponding rheological signature revealed a sharp initial increase in the dynamic moduli, followed by slower growth after long times, indicative of phase separation via nucleation and growth (NG). The rheological property changes are closely related to morphology development and mechanisms of phase separation induced duringin‐situ polymerization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2614–2619, 2007     

Effect of shear flow on the phase‐separation behavior in a blend of polystyrene and polyvinyl methyl ether

The phase behavior and phase‐separation dynamics of polystyrene/polyvinyl methyl ether (PS/PVME) blend with a critical composition of 70 vol % PVME were examined with a light scattering technique under a shear‐rate range of 0.1–40 s^?1. If the shear rates were less than 8 s^?1 and the starting temperatures of the measurement were 343 and 383 K, respectively, two cloud points were observed, whereas after the shear rate was higher than 8 s^?1, only one cloud point existed, 20 K higher than that of the static state of the blend. Investigation of the phase‐separation dynamics at 443 K suggested that in the vorticity direction the phase‐separation behavior at the early stage and the later stage can be explained by Cahn–Hilliard linearized theory and the exponent growth law, respectively. Phase separation occurs after a shearing time, which was called a delay time τ_d. The delayed time τ_d, the apparent diffusion coefficient, and the exponent term of the blend show strong dependence on shear rates. A theoretical prediction of the phase behavior of PS/PVME under a shear flow field by introducing an elastic energy term into Flory's equation‐of‐state theory was made, and the prediction was consistent with the experimental results. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 661–669, 2003     

Molecular dynamics and phase behavior of polystyrene/poly(vinyl methyl ether) blend in the presence of nanosilica

The variation of phase morphology, critical temperature of demixing, and molecular dynamics for polystyrene/poly(vinyl methyl ether)(PS/PVME) blends induced by hydrophilic nanosilica(A200) or hydrophobic nanosilica(R974) was investigated. With the phase separation of blend matrix, A200 migrated into PVME-rich phase due to strong interaction between A200 and PVME, while R974 moved into PS-rich phase. The thermodynamic miscibility and concentration fluctuation during phase separation of blend matrix were remarkably retarded by A200 nanoparticles due to the surface adsorption of PVME on A200, verified by the correlation length ξ near the critical region from rheological measurement and the weakened increment of reversing heat capacity(ΔC_p) during glass transition via modulated differential scanning calorimetry(MDSC). The restricted chain diffusion induced by nanosilica still occurred despite no influence of A200 and R974 on the segmental dynamics of homogenous blend matrix. The interactions between nanosilica and polymer components could restrict the terminal relaxation of blend matrix and further manipulate their phase behavior.     

Characterization of phase separation of polystyrene/poly(vinyl methyl ether) blends using fluorescence

We have investigated the fluorescence emission spectra of pyrene and anthracene dyes covalently bonded to polystyrene (PS) upon phase separation from poly(vinyl methyl ether) (PVME). The specific chemical structure of the fluorescent labels is found to affect the measured phase separation temperature T_S, with fluorophores covalently attached in closer proximity to the PS backbone identifying phase separation a few degrees earlier. The sharp increase in fluorescence intensity upon phase separation that occurs for all fluorophores with little change in spectral shape is consistent with a mechanism of static fluorescence quenching resulting from the specific interaction with a nearby quenching molecular unit. Based on recent work that has identified a weak hydrogen bond occurring between the aromatic hydrogens of PS and the ether oxygen of PVME, we believe a similar weak hydrogen bond is likely occurring between the PVME oxygen and the aromatic dyes providing a local (few nanometer) sensitivity to phase separation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Poly(ether ether ketone)/poly(aryl ether sulfone) blends: Melt rheological behavior

Dynamic rheological measurements were carried out on blends of poly(ether ether ketone) (PEEK)/poly(aryl ether sulfone) (PES) in the melt state in the oscillatory shear mode. The data were analyzed for the fundamental rheological behavior to yield insight into the microstructure of PEEK/PES blends. A variation of complex viscosity with composition exhibited positive–negative deviations from the log‐additivity rule and was typical for a continuous‐discrete type of morphology with weak interaction among droplets. The point of transition showed that phase inversion takes place at composition with a 0.6 weight fraction of PEEK, which agreed with the actual morphology of these blends observed by scanning electron microscopy. Activation energy for flow, for blend compositions followed additive behavior, which indicated that PEEK/PES blends may have had some compatibility in the melt. Variation of the elastic modulus (G′) with composition showed a trend similar to that observed for complex viscosity. A three‐zone model used for understanding the dynamic moduli behavior of polymers demonstrated that PEEK follows plateau‐zone behavior, whereas PES exhibits only terminal‐zone behavior in the frequency range studied. The blends of these two polymers showed an intermediate behavior, and the crossover frequency shifted to the low‐frequency region as the PEEK content in PES increased. This revealed the shift of terminal‐zone behavior to low frequency with an increased PEEK percentage in the blend. Variation of relaxation time with composition suggested that slow relaxation of PEEK retards the relaxation process of PES as the PEEK concentration in the blend is increased because of the partial miscibility of the blend, which affects the constraint release process of pure components in the blend. A temperature‐independent correlation observed in the log–log plots of G′ versus loss modulus (G″) for different blend systems fulfilled the necessary condition for their rheological simplicity. Further, the composition‐dependent correlations of PEEK/PES blends observed in a log–log plot of G′ versus G″ showed that the blends are either partially miscible or immiscible and form a discrete‐continuous phase morphology. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1548–1563, 2004     

Shear flow effect on phase behavior and morphology in polymer blends

The effect of simple shear flow on the phase behavior and morphology was investigated for both polystyrene/poly(vinyl methyl ether) (PS/PVME) and poly(methyl methacrylate)/poly(styrene‐co‐acrylonitrile) (PMMA /SAN‐29.5) blends, which have LCST (lower critical solution temperature)‐type phase diagram. The measurements were carried out using a special shear apparatus of two parallel glass plates type. The PS/PVME blends showed shear‐induced demixing and shear‐induced mixing at low and high shear rate values, respectively. In addition, the rotation speed and the sample thickness were found to have a pronounced effect on the phase behavior under shear flow. On the‐other hand, PMMA/SAN blend showed only shear‐induced mixing and the magnitudes of the elevation of the cloud points were found to be composition and molecular weight dependent. The morphology of the PMMA/SAN=75/25 blend indicated that shear‐induced mixing occurred at a critical shear rate value, below which the two phases were highly oriented and elongated in the flow direction.     

Molecular weight dependence of polystyrene segmental dynamics in dilute blends with poly(vinyl methyl ether)

The segmental dynamics of backbone‐deuterated polystyrenes (d₃PS) with varying molecular weights (1.7–67 kg/mol) have been measured in blends with poly(vinyl methyl ether) (PVME). ²H NMR T₁ values at 15 and 77 MHz are reported for the pure d₃PS and for the dilute d₃PS component in PVME matrices. The temperature shift that is needed to superpose the NMR T₁ data for the pure d₃PS and the d₃PS as a dilute component in the blend ranges from 45 to 70 K. In the framework of Lodge/McLeish model, the self‐concentration value for d₃PS in these dilute blends with PVME is found to be independent of molecular weight. We thus establish for this system that the substantial influence of molecular weight on the blend segmental dynamics can be explained by homopolymer T_g differences. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2252–2262, 2007     

Thermal diffusivity study of polystyrene/poly(vinyl methyl ether) blends by flash radiometry

This article presents thermal diffusivity (D) measurements by flash radiometry for the polymer blend of polystyrene (PS) and poly(vinyl methyl ether) (PVME) with lower critical solution temperature (LCST) phase diagram. Dependence of D on PS content measured at 100°C coincides a phase diagram determined by a cloud point measurement. D value for the blend decreases with increasing PS content and has minimum value at the PS content around 20 wt % from which D increases again with increasing PS content. If the concentration fluctuation between two components in the miscible states at the temperature close to LCST causes the remarkable phonon scattering, the composition dependence of D would resemble the phase diagram. D for the sample in the phase-separated state is larger than that for the miscible state. The larger D in the phase-separated sample would be due to the decrease of the total surface area microscopically contacted to the counter component in the phase-separated state. Dependence of D on temperature for the phase-separated sample is quite different from that of the miscible one. On an isothermal measurement of D for PS/PVME (10 : 90) at 110°C just below the cloud point, D started to increase at time above 100 min and leveled out above 250 min. Isothermal observation of sample film by a differential interference contrast microscopy showed the creation of some structure due to the nucleation and growth of interface at 225 min and it became obvious above 250 min. Thus, the increase in D at 110°C implies that D can sensitively reflect the change in microscopic structures which follows the nucleation and growth of interface. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1869–1876, 1997     

Photooxidation of blends of polystyrene and poly (vinyl methyl ether)

Photooxidation of blends of polystyrene and poly (vinyl methyl ether) was studied at 30°C. The oxygen uptake by PS was negligible but PVME oxidized readily. The induction period of oxidation of PVME was prolonged by the presence of PS. The steady state rate of oxidation of the blend was strongly influenced by the segmental mobility of the blend which also governed the kinetics and morphology of phase separation. The molecular weight of PVME decreased more slowly in the blend as PS content increased. It was believed that the reaction between PVME radicals and PS resulted in less reactive PS radicals which retarded oxidation. The PS radicals eventually underwent chain scission reactions.     

Rheology and morphology change with temperature of SEBS/hydrocarbon oil blends

The effect of hydrocarbon oil incorporation on the rheological and phase behaviors of poly(styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene) (SEBS) has been investigated. SEBS‐A1 (neat SEBS) shows a presence of very long relaxation time mode even at the highest temperature carried out here. On the other hand, G′ of SEBS‐A3 (oil concentration = 50 wt %) drastically decreases with increase of temperature at a critical temperature, which can be assigned to be order–disorder transition (ODT). The critical temperature was determined by two rheological criteria. Incorporation of hydrocarbon oil affects the ODT temperature. The rheological response is very sensitive to a few temperature increases around the ODT temperature. Above the critical temperature, G′ finally yields the terminal flow in the low frequency range. The morphological observation at various temperatures was determined using atomic force microscopy (AFM) equipped with environmental controller. This enabled in situ observation of structural change of SEBS induced by temperature and phase transition. We found that the layered texture, mostly aligned along the surface can be seen for SEBS‐A1 ranging from room temperature to 230 °C, though the image contrast reduced by an increase of temperature. SEBS‐A3 showed sphere domains at room temperature and also remains the structure at a critical temperature. The phase separated structure disappeared almost completely above ODT temperature, which was confirmed by the rheologial criteria. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 955–965, 2009     

Viscoelastic properties and interfacial tension of polystyrene–polyethylene blends

The linear viscoelastic properties of polystyrene polyethylene (PS/PE) blends have been investigated in the molten state. For concentrations of the dispersed phase equal to 30 vol %, the blends exhibited a droplet‐matrix morphology with a volume‐average diameter of 5.5 μm for a 70/30 PS/PE blend at 200 °C and 14.7 μm for a 30/70 PS/PE blend at 230 °C. Enhanced elasticity (G′) for both blends, in the terminal zone, compared to the modulus of the matrix (PS and PE, respectively) was observed. This is related to the deformation of the droplets in the matrix phase and hence to the interfacial forces between the blend components. The results for these uncompatibilized blends are shown to be in agreement with the predictions of the emulsion model of Palierne. These predictions were used to obtain the interfacial tension between PS and PE, which was found to be between 2 and 5 mN/m at 200 °C and 4 ± 1 mN/m at 230 °C. Independent interfacial tension measurements using the breaking‐thread method resulted in a value of 4.7 mN/m and 4.1 mN/m at 200 °C and 230 °C for the respective blends. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1359–1368, 2000     

The effect of compatibilization and rheological properties of polystyrene and poly(dimethylsiloxane) on phase structure of polystyrene/poly(dimethylsiloxane) blends

The compatibilization effect of polystyrene (PS)‐poly(dimethylsiloxane) (PDMS) diblock copolymer (PS‐b‐PDMS) and the effect of rheological properties of PS and PDMS on phase structure of PS/PDMS blends were investigated using a selective extraction technique and scanning electron microscopy (SEM). The dual‐phase continuity of PS/PDMS blends takes place in a wide composition range. The formation and the onset of a cocontinuous phase structure largely depend on blend composition, viscosity ratio of the constituent components, and addition of diblock copolymers. The width of the concentration region of the cocontinuous structure is narrowed with increasing the viscosity ratio of the blends and in the presence of the small amount diblock copolymers. Quiescent annealing shifts the onset values of continuity. The experimental results are compared with the volume fraction of phase inversion calculated with various theoretical models, but none of the models can account quantitatively for the observed data. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 898–913, 2004     

Thin films of PS/PS‐b‐pnipam and ps/pnipam polymer blends with tunable wettability

We developed thin films of blends of polystyrene (PS) with the thermoresponsive polymer poly(N‐isopropylacrylamide) (PNIPAM) (PS/PNIPAM) and its diblock copolymer polystyrene‐b‐poly(N‐isopropylacrylamide) (PS/PS‐b‐PNIPAM) in different blend ratios, and we study their surface morphology and thermoresponsive wetting behavior. The blends of PS/PNIPAM and PS/PS‐b‐PNIPAM are spin‐casted on flat silicon surfaces with various drying conditions. The surface morphology of the films depends on the blend ratio and the drying conditions. The PS/PS‐b‐PNIPAM films do not show an increase in their water contact angles with temperature, as it is expected by the presence of the PNIPAM block. All PS/PNIPAM films show an increase in the water contact angle above the lower critical solution temperature of PNIPAM, which depends on the ratio of PNIPAM in the blend and is insensitive to the drying conditions of the films. The difference between the wetting behavior of PS/PS‐b‐PNIPAM and PS/PNIPAM films is due to the arrangement of the PNIPAM chains in the film. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 670–679     

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 CO₂. 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 CO₂) 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.     

Study on nonlinear phase‐separation for PMMA/α‐MSAN blends by dynamic rheological and small angle light scattering measurements

The phase‐separation behavior of poly(methyl methacrylate)/poly(α‐methyl styrene‐co‐acrylonitrile) (PMMA/α‐MSAN) blends upon heating was studied through dynamic rheological measurements and time‐resolved small angle light scattering, as a function of temperatures and heating rates. The spinodal temperatures could be obtained by an examination of the anomalous critical viscoelastic properties in the vicinity of phase‐separation induced by the enhanced concentration fluctuation on the basis of the mean field theory. It is found that the dependence of the critical temperatures determined by dynamic rheological measurements and small angle light scattering on heating rates both deviates obviously from the linearity, even at the very low heating rates. Furthermore, the cloud‐point curves decrease gradually with the decrease of heating rates and present the trend of approaching T_gs of the blends. The nonlinear dependence is in consistence with that extracted from the isothermal phase‐separation behavior as reported in our previous paper. It is suggested that the equilibrium phase‐separation temperature could be hardly established by the linear extrapolating to zero in the plotting of cloud points versus heating rates. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1547–1555, 2006     

Investigation on LCST behavior of a new amorphous/crystalline polymer blend: Poly(n‐methyl methacrylimide)/poly(vinylidene fluoride)

The liquid–liquid phase‐separation (LLPS) behavior of poly(n‐methyl methacrylimide)/poly(vinylidene fluoride) (PMMI/PVDF) blend was studied by using small‐angle laser light scattering (SALLS) and phase contrast microscopy (PCM). The cloud point (T_c) of PMMI/PVDF blend was obtained using SALLS at the heating rate of 1 °C min^?1 and it was found that PMMI/PVDF exhibited a low critical solution temperature (LCST) behavior similar to that of PMMA/PVDF. Moreover, T_c of PMMI/PVDF is higher than its melting temperature (T_m) and a large temperature gap between T_c and T_m exists. At the early phase‐separation stage, the apparent diffusion coefficient (D_app) and the product (2Mk) of the molecules mobility coefficient (M) and the energy gradient coefficient (k) arising from contributions of composition gradient to the energy for PMMI/PVDF (50/50 wt) blend were calculated on the basis of linearized Cahn‐Hilliard‐Cook theory. The kinetic results showed that LLPS of PMMI/PVDF blends followed the spinodal decomposition (SD) mechanism. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1923–1931, 2008     

Thermoplastic blend demixing by a high‐pressure,high‐temperature process

The analysis of a thermoplastic polymer blend requires a precise separation of the blend components, which is usually performed by selective solvent extraction. However, when the components are high‐molecular‐weight polymers, a complete separation is very difficult. The use of fluids in near critical and supercritical conditions becomes a promising alternative to reach a much more precise separation. In this work, a method to separate reactive and physical blends from high‐molecular‐weight commercial polymers is proposed. Polyethylene (PE)/polystyrene (PS) blends were separated into their components with n‐propane, n‐pentane, and n‐heptane at near critical and supercritical conditions. The selectivity of each solvent was experimentally studied over a wide range of temperatures for assessing the processing windows for the separation of pure components. The entire PE phase was solubilized by n‐pentane and n‐heptane at similar temperatures, whereas propane at supercritical conditions could not dissolve the fraction of high‐molecular‐weight PE. The influence of the blend morphology and composition on the efficiency of the polymer separation was studied. In reactive blends, the in situ copolymer formed was solubilized with the PE phase by chemical affinity. The method proposed for blend separation is easy, rapid, and selective and seems to be a promising tool for blend separation, particularly for reactive blends, for which the isolation of the copolymer is essential for characterization © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2361–2369, 2005     

Effect of the liquid–liquid phase separation on the crystallization behavior of a poly(ethylene‐ran‐vinyl acetate) and paraffin wax blend

The effect of liquid–liquid phase separation (LLPS) on the crystallization behavior of poly(ethylene‐ran‐vinyl acetate) with a vinyl acetate content of 9.5 wt % (EVA‐H) in the critical composition of a 35/65 (wt/wt) EVA‐H/paraffin wax blend was investigated by small‐angle light and X‐ray scattering methods and rheometry. This blend exhibited an upper critical solution temperature (UCST) of 98°C, and an LLPS was observed between the UCST and the melting point of 88°C for the EVA‐H in the blend. As the duration time in the LLPS region increased before crystallization at 65°C, both the spherulite size and the crystallization rate of the EVA‐H increased, but the degree of the lamellar ordering in the spherulite and the degree of crystallinity of the EVA‐H in the blend decreased. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 707–715, 2000