Effect of shear history on the morphology and coarsening behaviour of polycarbonate/poly(styrene-co-acrylonitrile) blend

The morphology and coarsening behaviour of polycarbonate (PC) blend with styrene-co-acrylonitrile (SAN) random copolymer of 25 wt% AN have been investigated as a function of shear history using transmission electron microscope (TEM) and time resolved light scattering techniques. Simple shear apparatus of two parallel plates geometry was used to generate different shear rate values depending on the different distances from the centre of the sample disk. The morphology of PC/SAN-25=70/30 blend showed that the dispersed phase of SAN was elongated and broken-up in the direction of flow with weaker contrast at high shear rate values. The shear rate was found to suppress the concentration fluctuations and enhance the miscibility of SAN (dispersed phase) in the PC matrix to a great extent. The average of the dispersed particle diameter was evaluated as a function of different shear memories at 240 °C for different time intervals based on the Debye-Bueche theory. The obtained data were found to be shear memory dependent i.e. the average particle diameter decreases with increasing shear memory. This result indicated that the coarsening process is greatly suppressed by shear memory and the shear could produce a permanent morphological change (irreversible change) over the time scale of the measurement. This behaviour was attributed to the very high melt viscosities of the blend components, which in turn led to a very long relaxation time and consequently a high difficulty to erase the effect of shear at the experimental temperature. Furthermore, the coarsening process for all the measured samples followed the general power law, , regardless of the shear memory of the blend. This behaviour implied that the shear could only retard the rate of domain growth without any effect on the coarsening mechanism.     

Effect of hydrodynamics on dynamics of phase separation in polystyrene/poly(vinyl methyl ether) blend

Polystyrene/poly(vinyl methyl ether) (PS/PVME) phase diagram was assessed by rheological tools and by on-line microscopy observations both under quiescent and shear flow conditions. Shear flow was found to induce both mixing and demixing of the mixture depending on the amplitude of the imposed shear rate. Viscoelastic properties of PS/PVME blends were also measured under steady shear flow near the phase separation temperature. At lower shear rate, flow enhances concentration fluctuation and induces phase segregation. At high shear rate, flow suppresses fluctuations and the polymer mixture keeps its miscible state. Several rheological signatures of phase transition were found. In steady shear flow, a secondary plateau in viscosity was observed when the temperature was close to T_s whereas, at the start-up shear flow, transient shear stress showed a second overshoot after a few minutes of shearing.     

Composition fluctuations before dewetting in polystyrene/poly(vinyl methyl ether) blend thin films

We report structural development in blend thin films of deuterated polystyrene (dPS) and poly(vinyl methyl ether) (PVME) below 200 nm in two phase region during the incubation period before dewetting using neutron reflectivity (NR) and atomic force microscopy (AFM). As was predicted by the former optical microscope (OM) and small-angle light scattering (LS) measurements on blend thin films of protonated PS and PVME [Ogawa H, Kanaya T, Nishida K, Matsuba G. Polymer 2008;40:254–62.], the NR results clearly showed that the tri-layer structure consisting of the surface PVME layer, the middle blend layer and the bottom PVME layer was formed in the one phase region. After the temperature jump into the two phase region, it was found that the phase separation of the middle blend layer proceeded in the depth direction during the incubation period before dewetting, suggesting that the dewetting was induced by the composition fluctuations during the incubation period.     

The effects of flow on miscibility in a blend of polystyrene and poly(vinyl methyl ether)

Shear and extensional flows can have a significant effect on the miscibility for a blend of polystyrene with poly(vinyl methyl ether). The cloud point temperature in a planar stagnation flow is elevated by as much as 12 K; the magnitude depends on the extension rate, the strain, and the blend composition. Flow-induced miscibility is also observed in the shear flow between parallel plates which has been used to test smaller samples and to prepare solid samples for further characterization. At lower temperatures, as much as 30 K below the coexistence temperature, flow-induced phase separation occurs in both shear flow and extensional flows. The stress, rather than deformation rate, appears to be the most important parameter in flow-induced phase separation.     

Effect of thermal history on the molecular orientation in polystyrene/poly(vinyl methyl ether) blends

The effect of thermal history on the orientation and relaxation behavior of blends of polystyrene with poly(vinyl methyl ether) (PS/PVME) has been studied using polarization modulation infrared linear dichroism (PM-IRLD) and differential scanning calorimetry (DSC). DSC shows that miscible PS/PVME blends containing 70% of PS can be physically aged at temperatures above their mean glass transition temperature (T_g). PM-IRLD measurements reveal that both components become more oriented upon stretching at 51 °C (8 °C above T_g) if the sample is aged at the deformation temperature prior to stretching. Room-temperature aging can also lead to an increased orientation if the heating time at 51 °C is kept short. Moreover, PS and PVME develop a larger orientation in phase-separated blends than in miscible ones, and their relaxation is hindered. The results have been interpreted considering the morphology of the samples, including the presence of concentration fluctuations in miscible blends, and the effect of the local environment on the rigidity of the chains.     

Cloud point curves for poly(vinyl methyl ether) and monodisperse polystyrene mixtures

The compatibility behaviour of poly(vinyl methyl ether) (PVME) and monodisperse polystyrene (PS) is studied for solution cast films. The molecular weight of monodisperse PS ranges from 2100 to 2 000 000 whereas the PVME used is polydisperse and has weight-average molecular weight of 51 500. When cast from toluene solution, the mixtures undergo phase separation at elevated temperatures. The cloud point curves move to markedly lower temperatures with increasing molecular weight which is similar to the lower critical solution temperature (LCST) behaviour for polymer solutions. They move to lower temperatures until the molecular weight of PS reaches about 51 500.The effect of molecular weight distribution on the cloud point of equal amounts of PS and PVME mixtures simulated by mixing two monodisperse polystyrenes of different molecular weight for PS part is accurately predicted by using weight-average molecular weight for PS in this range. However, if the molecular weight of PS exceeds about 110 000 the molecular weight dependence of cloud point temperature is reversed and the prediction for polydisperse polymer by using weight-average molecular weight fails. This phenomenon is discussed from several viewpoints including the possibility of the effect of chain entanglement.Mixtures of PVME and PS of M_w = 20 400 were also cast from an ‘incompatible’ solvent, trichloroethylene. Compatibility is found to be dependent on composition and even phase-separated samples show at least one cloud point, indicating at least partial mixing of the two polymers. Finally, it is demonstrated that crosslinking of compatible films can be achieved by electron irradiation to form true interpenetrating networks. The cloud point temperatures are increased drastically after crosslinking.     

Noble gas transport in poly(methyl vinyl ketone) and poly(methyl vinyl ether)

A systematic study and interpretation of the transport parameters characterizing the permeation of the noble gases, He, Ne, Ar and Kr through poly(methyl vinyl ketone) and poly(methyl vinyl ether) are presented. The results and correlations are compared with related measurements on poly(methyl acrylate) and poly(vinyl acetate). In general the measurements were conducted above the glass transition temperatures of the respective polymers. The results are interpreted in terms of the systematic variations in the physicochemical parameters of these closely related polymers. Free volume and dipoledipole interactions appear to dominate the observed behaviour and the composite results may be explained in these terms. The size distribution of the fluctuating free volume elements and chain stiffness are also to be considered.     

Phase separation and dewetting in polystyrene/poly(vinyl methyl ether) blend thin films in a wide thickness range

Phase separation and dewetting processes of blend thin films of polystyrene (PS) and poly(vinyl methyl ether) (PVME) in two phase region have been studied in a wide film thickness range from 65 μm to 42 nm (∼2.5R_g, R_g being radius of gyration of a polymer) using optical microscope (OM), atomic force microscope (AFM) and small-angle light scattering (LS). It was found that both phase separation and dewetting processes depend on the film thickness and were classified into four thickness regions. In the first region above ∼15 μm the spinodal decomposition (SD) type phase separation occurs in a similar manner to bulk and no dewetting is observed. This region can be regarded as bulk. In the second region between ∼15 and ∼1 μm, the SD type phase separation proceeds in the early stage while the characteristic wavelength of the SD decreases with the film thickness. In the late stage dewetting is induced by the phase separation. In the third region between ∼1 μm and ∼200 nm the dewetting is observed even in the early stage. The dewetting morphology is very irregular and no definite characteristic wavelength is observed. It is expected that the irregular morphology is induced by mixing up the characteristic wavelengths of the phase separation and the dewetting. In the fourth region below ∼200 nm the dewetting occurs after a long incubation time with a characteristic wavelength, which decreases with the film thickness. It is considered that the layered structure is formed in the thin film during the incubation period and triggers the dewetting through the capillary fluctuation mechanism or the composition fluctuation one.     

Orientation and relaxation in uniaxially stretched poly(vinyl methyl ether)-atactic polystyrene blends

Infrared measurements of the dichroic ratio of polystyrene and poly(vinyl methyl ether) absorption bands allow us to determine chain orientation for each component in their compatible blends. Influence of strain rate and temperature of stretching on orientation of both polymer chains in blends containing up to 25% PVME has been studied. Mechanical relaxation master curves at a reference temperature T=T_g+40°C have also been determined. Results are compared to previous results obtained in PS-PPO compatible blends. Although PPO and PVME chains behave differently PS chains behaviour is similar in the two types of blends and interpreted in terms of a hindrance of relaxation of PS chains induced by a modification of friction coefficients due to the molecular interactions which are at the origin of compatibility.     

Temperature dependence of sorption parameters near Tg for propane in a miscible blend of polystyrene and poly(vinyl methyl ether)

The sorption of propane by 75:25% (w/w) miscible blends of polystyrene and poly(vinyl methyl ether) with different thermal histories was investigated near T_g. The dual-mode sorption model was used to analyze the results. The evidence indicates that the Henry's law constant for states below T_g cannot be smoothly extrapolated from the rubbery state.     

Deformation studies of polystyrene/poly(vinyl methyl ether) blends by mechanical-vibrational spectroscopy

We have analyzed the deformation behavior of compatible and incompatible polystyrene (PS) and poly(vinyl methyl ether) (PVME) blends by a combination of mechanical and vibrational spectroscopy. Macroscopic properties and segmental orientation were found to be sensitive to molecular weight, strain rate, and temperature of measurement above the glass-transition temperature. Considerably different orientation functions were found for the PS and PVME components. For the experiments carried out above the T_g of the blends, the deformation behavior measured was consistent with expectations of a rubbery network.     

Incoherent neutron scattering study on the local dynamics in polystyrene and poly(vinyl methyl ether) blends

Neutron scattering study using the fixed elastic window technique is performed to investigate the effect of blending on the local dynamics of each component for polystyrene and poly(vinyl methyl ether) blends. The non-Gaussian scattering behavior observed above a certain temperature for the PVME component can be well explained by considering the rotational motions of methyl groups around O-CH₃ axis. The mean-square displacements of the vibrational motions were approximately proportional to absolute temperature below the glass transition temperature, which is a signature of harmonic oscillations, and were hardly affected by blending PS. On the other hand, the mean-square displacement of the PS component in the blend was almost the same as that of pure PS, while the non-Gaussian parameter for the former was much larger in comparison with that of the latter. Blending with PVME leads to a large increase in the dynamical heterogeneity for the PS component.     

Effects of phase separation on the mechanical properties of polystyrene/poly(vinyl methyl ether) blends

The effects of phase separation temperature and time on the tensile, dynamic mechanical, and tear properties of blends of polystyrene and poly(vinyl methyl ether) were investigated after phase separation above their respective cloud points with specified temperature-annealing time protocols. The results are analyzed in terms of the phase connectivity, interfacial adhesion, and changes in the glass transition temperature.     

Effect of tacticity on the transition behaviour of poly(methyl methacrylate)/poly(vinyl chloride) blends. Thermally stimulated depolarization study

The transition behaviour of blends of poly(vinyl chloride) (PVC) and poly(methyl methacrylate) isotactic (i-PMMA) and syndiotactic (s-PMMA) was determined in the temperature range ?150°C to +130°C by the thermally stimulated depolarization currents method (TSDC). The evolution of the current spectra was analysed as a function of blend composition. From the variation of properties of the peaks (presence or not of two T_g peaks, shifting or not of their positions, existence or not of interfacial components, regular or complex variation of the peak amplitudes ...), it was concluded that i-PMMA and PVC form an incompatible system over the entire concentration range while in s-PMMA/PVC blends, some compatibility probably exists but only for concentrations in s-PMMA not higher than 10 wt%. By referring to literature data, this value is much smaller than the compatibility range found from d.s.c. and mechanical measurements but is close to that determined from optical and electronic spectroscopy methods. These results emphasize the important role played by the type of method used to find out compatibility of a given polymer pair and show that the TSDC technique may be particularly useful for studying the interfacial phenomena associated with phase separation owing to its exceptional ability for easily detecting Maxwell-Wagner-Sillars polarization generated by the trapping of charge carriers at phase boundaries.     

Janus combs with polystyrene and poly(methyl vinyl ether) branches: Design,characterization and properties

The synthesis of Janus like comb copolymers constituted of polystyrene and poly(methyl vinyl ether) branches attached to a diblock backbone has been achieved using living/controlled cationic and anionic building steps associated to grafting from and grafting onto coupling processes. These comb-b-comb structures behave as isolated objects in good solvents as well as when deposited on an appropriate substrate from a good solvent. In contrast, thanks to their amphiphilic Janus-like structure, they behave like linear diblock copolymers when placed in a selective solvent of one of the comb moieties, forming stable large spherical super-micelles that could be observed on mica support.     

13C NMR characterization of intermolecular interactions for polymers. Part 3. Solvent effect on the blend compatibility of poly(vinyl methyl ether) and polystyrene

The solvent has an influence on the homogeneity of the poly(vinyl methyl ether)-polystyrene, PVME-PS blends Prepared by drying cosolutions. This influence has been analyzed in terms of the competition among polymer-polymer and polymer-solvent interactions. Model solutions have been prepared in which intermoleeular interactions correspond to the interactions in this blend and in some of the cosolutions. These interactions in the model solutions have been detected and identified by applying Rummens' method. The 13C NMR spectra have been determined for PVME and for styrene oligomer dissolved in n-alkanes, cyclohexane, diethyl ether, isopropyl methyl ether, diisopropyl ether, and chloroform, and for PVME dissolved in benzene, toluene, and cumene. The chemical shifts have been plotted against the parameter g² = [(n₂² ? 1)/(n₂² + 1)]², where n₂ is the refractive index of the solvent. If the structural segment represented by certain carbon and some solvent has an interaction that is stronger than dispersive, the chemical shift for this carbon will deviate from the line formed by its shifts in n-alkane solutions, these deviations indicate characters and intensities of the intermoleeular interactions. Results indicate that cyclohexane exhibits weak interactions with both of the polymers and does not interfere with their mutual interaction, leading to a compatible blend. Results also suggest that benzene and toluene interact in the PVME in the same manner as PS. This leads to a gradual increase of the number of polymer-polymer interactions as the concentration of the polymers is increased by solvent removal, resulting in a compatible blend. Chloroform apparently interacts more strongly with PVME than with PS but interacts strongly enough with both to restrict interaction among the two polymers. As the concentration of polymers in the cosolution is increased, PS forms a separate phase. This leads to an inhomogeneous blend when the solvent is evaporated.     

Controlling morphology of polystyrene/poly(vinyl methyl ether) blends undergoing spinodal decomposition process by photo-crosslinks

The morphology developing during the spinodal decomposition process of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blends was successfully controlled by photo-crosslink reactions between PS chains. The crosslink reaction was carried out by taking advantage of the photodimerization of anthracene moieties that are labeled on PS chains. Effects of photo-crosslinks on the morphology induced by temperature jumps (T-jump) from the one-phase region into the spinodal region were examined under several experimental conditions such as T-jump depths and irradiation times. It was found that the concentration fluctuations developing during the spinodal decomposition process were efficiently frozen upon irradiation using a XeF excimer laser as well as a mercury (Hg) lamp. Furthermore, these ordered structures are quite stable upon annealing. These results demonstrate that the morphology developing during the spinodal decomposition process can be well controlled by easily accessible light sources such as high pressure mercury lamps. Thus the photo-crosslink reaction described in this work can provide the basis for a potential technique to design multiphase polymer materials with controllable ordered structures.     

Comparison of interdiffusion at polystyrene–poly(vinyl methyl ether) and polystyrene–poly(isobutyl vinyl ether) interfaces

The effect of polymer–polymer compatibility on interdiffusion at polymer interfaces with dissimilar mobilities was investigated by attenuated total internal reflectance infrared spectroscopy. The polymer pair consisting of polystyrene and poly(vinyl methyl ether) was used to study interdiffusion at the interface of compatible polymers. The polymer pair consisting of polystyrene and poly(isobutyl vinyl ether) was used to study interdiffusion at the interface of incompatible polymers. Results indicate that the extent of interdiffusion is controlled by the polymer–polymer compatibility parameter, irrespectively of the differences in the mobility of the polymers.     

Miscibility and interactions in polystyrene and sodium sulfonated polystyrene with poly(vinyl methyl ether) PVME blends. Part II. FTIR

The miscibility and specific interactions of polystyrene (PS) and sodium sulfonated polystyrene (Na-SPS) with poly(vinyl methyl ether) (PVME) blends (ranging from 10 to 90% PS by weight) were examined experimentally by FTIR spectroscopy. The FTIR studies at different temperatures have shown that changes in spectra of polymer blends, as reported in the literature can be explained by temperature changes in pure homopolymers. This indicates that molecular interactions, which are responsible for miscibility, are not detectable by infrared absorptions and are therefore of unspecific strength and location. The FTIR of SPS/PVME blends show that sulfonate groups of PS affect polymer miscibility through changes in configuration of molecules, rather than through direct interaction with the PVME.     

Study of the nonlinear phase‐separation behavior of a polystyrene/poly(vinyl methyl ether) blend using small‐angle light scattering

The thermally induced phase‐separation behavior of a polystyrene/poly(vinyl methyl ether) (PS/PVME) blend was studied mainly using time‐resolved small‐angle light scattering, as a function of temperature and heating rate. Under a non‐isothermal field, the dependence of the critical temperature on heating rate deviated obviously from linearity, even at very low heating rates. Such a nonlinear dependence was consistent with the deviation from linearity of the temperature dependence of the isothermal phase‐separation behavior in a wider temperature range from 100 to 140 °C. It was also found that a Williams–Landel–Ferry (WLF)‐like equation could be employed to describe the temperature dependence of the apparent diffusion coefficient (D_app) and the relaxation time (τ) of normalized scattering intensity at the early stage of spinodal decomposition (SD), as well as τ of phase behavior at the late stage of SD for the PS/PVME blend. The equilibrium phase‐separation temperature could hardly be established through the conventional linear extrapolation of heating rate or D_app to zero at the early stage of SD. The successful use of the WLF‐like function for PS/PVME blends extends the applicability of the time–temperature superposition principle for describing the phase‐separation behavior of binary polymer mixtures over a relatively large temperature range. Copyright © 2010 Society of Chemical Industry