Effects of the molecular weight of poly(ether imide) on the viscoelastic phase separation of poly(ether imide)/epoxy blends

The phase separation of diglycidyl ether of bisphenol A/methyl tetrahydrophthalic anhydride blends modified with three poly(ether imide)s (PEIs) of different molecular weights was investigated with scanning electron microscopy (SEM) and time‐resolved light scattering (TRLS). The morphologies observed by SEM for the three blends were all close to a cocontinuous structure with different periodic distances. The results of TRLS indicated that the phase separation for the PEI‐modified epoxy blends took place according to the spinodal decomposition mechanism and the onset time of phase separation, with the periodicity of the phase structure depending on the PEI molecular weight and cure temperature. The time‐dependent peak scattering vector was simulated with a Maxwell‐type viscoelastic relaxation equation, indicating that the coarsening process of epoxy droplets was mainly controlled by the viscoelastic flow. Relaxation times obtained at different temperatures for the three blends could be described by the Williams–Landel–Ferry equation. The effects of the PEI molecular weight on the processes of viscoelastic phase separation were investigated, and the observed trends could be explained qualitatively through thermodynamic analysis. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Phase separation of poly (methyl methacrylate) / poly (styrene-co-acrylonitrile) blends in the presence of silica nanoparticles

The effects of silica nanoparticles on the phase separation of poly (methyl methacrylate)/poly (styrene-co-acrylonitrile) (PMMA/SAN) blends are studied by the rheological method. The binodal temperatures of near-critical compositions were obtained by the gel-like behavior during spinodal decomposition, which is a character of polymer blends with co-continuous morphology. The shifted Cole–Cole plot method was introduced to determine the binodal temperatures of off-critical compositions based on the appearance of shoulder-like transition in the terminal regime of blends with droplet morphology. Such method is found also applicable in nanoparticle filled polymer blends. Moreover, a new method to determine the spinodal temperature from Fredrickson-Larson mean field theory was suggested, where the concentration fluctuation's contribution to the storage modulus is used instead of the whole dynamic moduli. This method was also successfully extended to nanoparticle filled polymer blend. The influences of the concentration and the average diameter of silica particles on the phase separation temperature were studied. It was found that the small amount of the silica nanoparticles in PMMA/SAN blends will significantly change the phase diagram, which is related to the selective location of silica in PMMA. The comparisons with thermodynamic theory of particle-filled polymer blends are also discussed.     

Effects of molecular weight of polysulfone on phase separation behavior for cyanate ester/polysulfone blends

The effects of molecular weight of polysulfone (PSF) on the morphology of bisphenol‐A dicyanate (BADCy)/PSF blends were studied. Because the viscosity of the blend increased and the miscibility between BADCy and PSF decreased with the increase of PSF molecular weight, these two competing effects on the phase‐separation were investigated. It was observed that the effect of viscosity was predominant: the viscosity of the blends at the onset point of phase separation increased with the increase of PSF molecular weight. The phase separation mechanism depends on the viscosity of the blends at the onset point of phase separation and determines the morphology of the blends. Because the increasing viscosity with increasing the molecular weight of PSF suppressed the nucleation and growth even with 10 phr of PSF content, phase separation occurred through spinodal decomposition to form the combined morphology having both PSF particle structure and BADCy particle structure. The combined morphology and the BADCy particle structure were obtained with a smaller amount of high molecular weight PSF content. This indicates that the viscosity of the blends at the onset point of phase separation is the critical parameter that determines the morphology of the blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 921–927, 2000     

Morphology development and characterization of the phase-separated structure resulting from the thermal-induced phase separation phenomenon in polymer solutions under a temperature gradient

This paper studied the morphological development during the fabrication of anisotropic polymeric materials using the thermal-induced phase separation phenomenon (spinodal decomposition) in a model binary polymer solution under a linear spatial temperature gradient using mathematical modeling and computer simulation. The model incorporated the non-linear Cahn-Hilliard theory for spinodal decomposition and the Flory-Huggins theory for polymer solution thermodynamics. Moreover, the slow mode theory and Rouse law were used to account for polymer diffusion. The two-dimensional numerical results showed that an anisotropic morphology was developed when a temperature gradient was imposed along the polymer solution sample. The droplet size and droplet density decrease as temperature increases during the intermediate stage of spinodal decomposition. The spatial temperature gradient, however, had insignificant effect on the droplet shape.     

Phase‐separation mechanism and corresponding final morphologies of thermoset blends based on unsaturated polyester and low‐molar‐weight saturated polyester

The final morphology of cured blends based on unsaturated polyester, styrene, and low‐molar‐weight saturated polyester as a low profile additive (LPA) was investigated with atomic force microscopy and scanning electron microscopy. The observed structure was compared to those obtained with widely used poly(vinyl acetate) (PVAc). On the surface and in the bulk, a network of particles, ranging in size from 50 to 60 nm, was observed with saturated polyester as an LPA. The influence of the molar weight and LPA content was investigated. To determine the mechanism of formation of such a morphology, in situ experiments were carried out to elucidate the phase‐separation mechanism. Small‐angle laser light scattering and small‐angle neutron scattering experiments were performed on ternary blends containing PVAc and saturated polyester, respectively. The first stage of spinodal decomposition was observed in both cases. Within our experimental conditions, gelation froze further evolution and led to a two‐phase cocontinuous structure that imposed the final morphology characteristics. In particular, the period and amplitude of the concentration fluctuations generated during the phase separation played essential roles. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1459–1472, 2005     

聚丙烯腈原丝的凝固成形与相分离研究进展

以热力学相图为工具,探讨了聚丙烯睛(PAN)原丝凝固成形过程。从相图中原丝凝固成形的不同途径和相应的织态结构可以知道,原液体系以旋节方式分相是最佳的热力学路径。原丝凝固成形可以看作是浓度致变相分离(CIPS)和热致变相分离(TIPS)两种相分离形式的组合,通过后者得到高性能原丝要容易实现得多。可以根据相图来优化纺丝工艺条件,通过调节凝固浴浓度、纺丝液浓度、初始纺丝温度以及淬火深度.削弱CIPS过程在凝固成形中的作用,使凝固成彤尽可能多的以TIPS方式通过旋节线和双节线的交界处进行,以得到具有理想结构的优质的PAN原丝。     

Reaction induced phase separation in semicrystalline thermoplastic/epoxy resin blends

The phase separation behaviour and phase morphology of blends of 4,4′-diaminodiphenyl sulphone cured diglycidyl ether of bisphenol-A with poly(ε-caprolactone) were investigated by means of scanning electron microscopy, small angle light scattering and optical microscopy. The components are miscible prior to curing. High-temperature isothermal curing induces phase separation. Blends with near to critical concentrations demix via spinodal decomposition. The associated co-continuous morphology is only preserved in the actual critical compositions whereas for off-critical compositions it rapidly breaks up into spherical particles. The proceeding reaction in the separated phases induces a secondary phase separation. Occasionally, tertiary phase separation is observed as well. Off-critical compositions that are further away on either side from the critical point, phase separate via the direct formation of spherical particles, most likely as a result of the dynamic asymmetry of these blends. The influence of the amount, the molar mass of PCL and the cure temperature is discussed.     

Comparison of the phase behaviour of the liquid-crystalline polymer/poly(methyl methacrylate) and poly(vinyl acetate)/poly(methyl methacrylate) blends

The phase behaviour of blends of a liquid-crystalline polymer (LCP) and poly(methyl methacrylate) (PMMA), as well as the phase state of blends of PMMA and poly(vinyl acetate) (PVA) has been investigated using light scattering and phase-contrast optical microscopy. The blends of LCP and PMMA have been obtained by coagulation from ternary solutions. The cloud point curves were determined. It was established that both pairs demix upon heating, ie have an LCST. In the region of intermediate composition, the phase separation proceeds according to a spinodal mechanism; however for LCP/PMMA blends, the decomposition proceeds according to a non-linear regime from the very onset. In the region of small amounts of LCP, the phase separation follows a mechanism of nucleation and growth. For PMMA/PVA blends, the spinodal decomposition proceeds according to a linear regime, in spite of the molecular mobility that PVA chains develop at lower temperatures. Only after prolonged heat treatment does the process transit to a non-linear regime. The data show a similarity between the phase behaviour of blends of liquid-crystalline and of flexible amorphous polymers. The distinction consists of the absence of a linear regime of decomposition for LCP-PMMA blends. © 1999 Society of Chemical Industry     

Thermodynamic Modeling of Phase Diagrams in Binary Alkali Silicate Systems

A thermodynamic modeling of phase diagrams in binary alkali silicate systems is described by using the Gibbs free energy of the phases. Simple models employing regular, quasi-regular, and subregular solution models were applied to describe the liquid phase. The interaction parameters of the liquid phases were obtained by using the liquidus curves of silica (and subliquidus data) through a multiple linear regression method. The present calculated liquidus curves agree very well with Cs₂O—SiO₂ and Rb₂O—SiO₂ systems. In the K₂O—, Na₂O—, and Li₂O—SiO₂ systems, the calculations permitted discrimination between sets of data and, based upon the calculation choices, could be correctly made to select the most appropriate phase diagram. Also, the spinodals were calculated where phase separation can occur by a spinodal decomposition process.     

Morphology control in symmetric polymer blends using spinodal decomposition

This paper studied, through modeling and computer simulation, the thermal-induced phase separation phenomenon in a symmetric polymer blend via spinodal decomposition. The one-dimensional model consisted of the Cahn–Hilliard theory for spinodal decomposition, and incorporated the Flory–Huggins–deGennes free energy equation, the slow mode mobility theory and reptation model for polymer diffusion. The numerical results replicated frequently reported experimental observations published in the literature for the early and intermediate stages of spinodal decomposition for symmetric polymer blends. Furthermore, the numerical results indicate that a dimensionless diffusion coefficient may be used as a parameter to control the formation and evolution of the phase-separated regions during spinodal decomposition as a means to customize functional polymeric materials with predefined material properties.     

Morphological evaluation and phase behavior of PVDF/PEO blends in the presence of graphene nanoplatelets through rheological measurements

In this study, graphene nanoplatelets (GNPs) were incorporated into poly(vinylidene fluoride) (PVDF), poly(ethylene oxide) (PEO), and PVDF/PEO blends using solution casting method in order to achieve binary and ternary polymer nanocomposites. The focus of the work is on the compatibilizing effects of the GNPs on partially miscible PVDF/PEO blends. X-ray diffraction method, rheological measurements, scanning electron microscopy (SEM), and atomic force microscopy observations enabled us to track the dispersion state and localization of the graphene nanosheets in the nanocomposites. The results exhibited that the nanoplatelets were preferentially distributed through the PVDF phase and/or at the interface of the PVDF/PEO phases. Evaluation of the wetting parameter for the PVDF/PEO/GNPs nanocomposite also verified better affinity of the selected nanofiller with the PVDF component. Extend of the miscibility in the nanocomposites was studied by a well-known rheological method. A tangible increment in binodal (T_b) and spinodal (T_s) decomposition temperatures by addition of a very low content of the GNPs (0.5 wt %) revealed well-defined compatibilization effects of the graphene on this binary polymer blend. SEM images at different temperatures confirmed the rheologically determined liquid–liquid phase diagram. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48017.     

Morphology–composition–processing relationships in poly(methyl methacrylate)–polytriethylene glycol dimethacrylate shrinkage‐controlled blends

An innovative method to control shrinkage in polymer blends, by using N,N‐dimethyl‐p‐toluidine to produce phase separation in an acrylic system, was applied to synthesize polymer blends from polymethyl methacrylate (PMMA) and polytriethylene glycol dimethacrylate (PTEGDMA). The morphology of several compositions, as analyzed by scanning electron microscopy, reveals microdomains as a function of the specific composition, in contrast to conventional MMA–TEGDMA copolymers synthesized by thermal decomposition of benzoyl peroxide, used here as reference materials. Micro‐Raman and DSC analyses were also carried out to support the electron microscopy results as well. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1254–1260, 2004     

Thermally induced phase separation in liquid crystalline polymer/polycarbonate blends

Thermally induced phase separation in liquid crystalline polymer (LCP)/polycarbonate (PC) blends was investigated in this study. The LCP used is a main‐chain type copolyester comprised of p‐hydroxybenoic acid and 6‐hydroxy‐2‐naphthoic acid. Specimens for microscopic observation were prepared by melt blending. The specimens were heated to a preselected temperature, at which they were held for isothermal phase separation. The preselected temperatures used in this study were 265, 290, and 300°C. The LCP contents used were 10, 20, and 50 wt %. These parameters corresponded to different positions on the phase diagram of the blends. The development of the phase‐separated morphology in the blends was monitored in real time and space. It was observed that an initial rapid phase separation was followed by the coarsening of the dispersed domains. The blends developed into various types of phase‐separated morphology, depending on the concentration and temperature at which phase separation occurred. The following coarsening mechanisms of the phase‐separated domains were observed in the late stages of the phase separation in these blends: (i) diffusion and coalescence of the LCP‐rich droplets; (ii) vanishing of the PC‐rich domains following the evaporation‐condensation mechanism; and (iii) breakage and shrinkage of the LCP‐rich domains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Phase separation behavior of cyanate ester resin/polysulfone blends

The composition of the blends and the curing temperature affect the morphology of the blends and the phase separation mechanism. The phase separation mechanism depends on the viscosity of medium at the initial stage of phase separation determined by the amount of thermoplastics and the curing temperature, and is closely related with the final morphology. When the homogeneous bisphenol A dicyanate (BADCy)/polysulfone (PSF) blends with low content of PSF (less than 10 wt %) were cured isothermally, the blends were phase separated by nucleation and growth (NG) mechanism to form the PSF particle structure. On the other hand, with more than 20 wt % of PSF content, the BADCy/PSF blends were phase separated by spinodal decomposition (SD) to form the BADCy particle structure. With about 15 wt % of PSF content, the blends were phase separated by SD and then NG to form a combined structure having both the PSF particle structure and the BADCy particle structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 33–45, 1999     

Microporous Membranes Based on Electro-Conducting Polymers

Microporous membranes were prepared from polyaniline-diluent systems by exploiting the thermally induced phase separation, using three polymer concentrations, two quenching temperatures, and different extraction conditions. Both binodal and spinodal curves of polyaniline-diluent systems were determined by differential scanning calorimetry. The membrane morphology was determined by scanning electron microscopy and optical microscopy. Phase separation may be carried out by nucleation and growth mechanism under the conditions used in this study. A closed cell structure was obtained for the PANI-concentrated samples. In contrast, an open structure composed of strings of small beads resulted for the PANI-dilute samples. It was also found that the membrane morphology varied with the extraction temperature and extractants. A great effect of coarsening, attributed to the extremely low molecular weight of PANI and mild quenching temperature, gave large pores in the final membrane structure.     

Computer vision methods for the study of spinodal decomposition in polymer blends

We demonstrate the use of computer vision techniques and optical microscopy to follow the kinetics and microstructure during spinodal decomposition of a polymer blend. Among other features, the mean of the population of the local maxima of the gradients in each image is computed; this global feature is shown to co-develop with the phase separation of the blend. An algorithm is presented which employs the gradient magnitude technique to analyze optical images of spinodally decomposing polymer blends. This algorithm has been used to extract the Cahn-Hilliard spinodal growth rates for a binary blend of polystyrene with poly(vinyl methyl ether). We show that the spinodal temperature can be found from the temperature dependence of this growth rate. We also show how additional shape features such as compactness might be used to study, the same binary blend.     

Nonlinear phase‐separation behavior of poly(methyl methacrylate)/poly(styrene‐co‐maleic anhydride) blends

The nonlinear phase‐separation behavior of poly(methyl methacrylate)/poly(styrene‐co‐maleic anhydride) (PMMA/SMA) blends over wide appropriate temperature and heating rate ranges was studied using time‐resolved small‐angle laser light scattering. During the non‐isothermal process, a quantitative logarithm function was established to describe the relationship between cloud point (T_c) and heating rate (k) as given by T_c = Alnk + T₀, in which the parameter A, reflecting the heating rate dependence, is much different for different compositions due to phase‐separation rate and activation energy difference. For the isothermal phase‐separation process, an Arrhenius‐like equation was successfully applied to describe the temperature dependence of the apparent diffusion coefficient (D_app) and the relaxation time (τ) of the early stage as well as the late stage of spinodal decomposition (SD) of PMMA/SMA blends. Based on the successful application of the Arrhenius‐like equation, the related activation energies could be obtained from D_app and τ of the early and late stages of SD, respectively. In addition, these results indicate that it is possible to predict the temperature dependence of the phase‐separation behavior of binary polymer mixtures during isothermal annealing over a range of 100 °C above the glass transition temperature using the Arrhenius‐like equation. © 2012 Society of Chemical Industry     

HYDRODYNAMIC EFFECTS IN THE PHASE SEPARATION OF BINARY POLYMER MIXTURES

The phenomenon of phase separation by spinodal decomposition was studied for polymer blends made by compositional quenching. The modified Cahn-Hilliard theory of phase separation was extended to include hydrodynamics, with a volumetric body force, due to concentration gradients, that induced convective flows. This force influenced the morphology and the growth rate of the average domain size. Unlike the conventional treatment of flows driven by surface tension, the velocity and pressure fields were treated as continuous functions of spatial position.

Numerical solutions for the phase separation in a binary mixture were obtained for a three-dimensional system with periodic boundary conditions. For near critical quenches with similar volume fractions for the two components, cocontinuity was destroyed by the hydrodynamics, giving discrete domains. The breakup in interconnectivity is believed to be a universal phenomenon. The domain growth rate followed a power law, r → τⁿ. The growth exponent depended on the dimensionless viscosity group, ξ = (R_g T/v_s) (Km/μD_AB) and ranged from n = 0.32 ± 0.006 for ξ J = 0 (no hydrodynamic effects) to n ∼ 1 for ξ = 1. For off-critical quenches in which a dispersed phase would be formed by diffusion alone, the scaling exponent showed little enhancement. The simulations accurately predicted the particle size formed in the early stages of spinodal decomposition.     

Viscoelastic effects on the phase separation in thermoplastics modified cyanate ester resin

A high temperature thermosetting bisphenol-A dicyanate, BADCy was blended with a thermoplastic poly(ether imide) (PEI). The phase separation behavior of the blend was investigated by scanning electron microscopy (SEM) and time resolved light scattering (TRLS). It was found by SEM that the blend with 20 and 25 wt% PEI had a phase inversion structure. The results of TRLS displayed clearly that the phase separation took place according to a spinodal decomposition (SD) mechanism and the evolution of both scattering vector q_m and the maximum scattering intensity I_m followed Maxwell-type relaxation equation. The temperature-dependent relaxation time τ for the blends can be described by the Williams-Landel-Ferry equation. It demonstrated experimentally that the phase separation behaviors in PEI/BADCy blends were affected by viscoelastic effect.     

Linear viscoelasticity of polymer blends with co-continuous morphology

The co-continuous morphology of polymer blends has received much attention not only because of its potential promotion of mechanical or electrical properties of polymer blends, but also due to its importance in phase separation by spinodal decomposition. Compared to the recent advances in the characterization of co-continuous structure, the rheology of co-continuous blends has not been understood clearly. In this work, a rheological model is suggested to correlate the linear viscoelasticity and the structural information of co-continuous blends. The dynamic modulus of co-continuous blends is composed of the contribution from components and the interface. The interfacial contribution, which is most important in the rheology of blends, is calculated from a simplified co-continuous structure. This model has been compared satisfactorily with available experimental results, which proves a reasonable connection between the co-continuous structure and linear viscoelasticity of blends.