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.     

Effect of a Drying Pretreatment on Morphology of Porous Poly(Ether-Imide) Membrane Prepared Using Vapor-Induced Phase Separation

Symmetric porous membranes were prepared from concentrated poly(ether-imide) (PEI) solutions using vapor-induced phase separation (VIPS) coupled with a drying pretreatment. Moderately concentrated solutions of PEI in N-methylpyrrolidinone (NMP) (14–16 wt%) were first cast on glass plates and the solvent was then allowed to evaporate under a dry air flow up to the desired concentration (16–38 wt%) before forming the membrane structure by VIPS. The polymer concentration profiles (confocal Raman microscopy) and model predictions were in good agreement to show that the evaporation stage did not induce a polymer gradient concentration with PEI/NMP systems. These results were confirmed by examination of the final membrane morphology (SEM).     

Effect of a Drying Pretreatment on Morphology of Porous Poly(Ether-Imide) Membrane Prepared Using Vapor-Induced Phase Separation

Symmetric porous membranes were prepared from concentrated poly(ether-imide) (PEI) solutions using vapor-induced phase separation (VIPS) coupled with a drying pretreatment. Moderately concentrated solutions of PEI in N-methylpyrrolidinone (NMP) (14-16 wt%) were first cast on glass plates and the solvent was then allowed to evaporate under a dry air flow up to the desired concentration (16-38 wt%) before forming the membrane structure by VIPS. The polymer concentration profiles (confocal Raman microscopy) and model predictions were in good agreement to show that the evaporation stage did not induce a polymer gradient concentration with PEI/NMP systems. These results were confirmed by examination of the final membrane morphology (SEM).     

Asymmetric porous membranes formed by coagulation-induced phase separation in poly(ether sulfone)/poly(vinyl pyrrolidone)/genistein blends

Development of asymmetric channel morphology driven by coagulation-induced phase separation of genistein (G) modified poly(ether sulfone)/poly(vinyl pyrrolidone) (PES/PVP) blends has been examined in relation to their miscibility phase diagram. PES/G pairs turned out to be miscible in the amorphous state, whereas solid–liquid phase separation occurred at high genistein compositions. The solid–liquid phase diagram involving the liquidus and solidus lines were computed self-consistently in the framework of the combined free energy of Flory-Huggins for liquid–liquid phase separation and phase field free energy for crystal solidification. The ternary phase diagram of PES/PVP/G blends was subsequently established that consisted of various coexistence regions. The actual amounts of genistein incorporated in the PES/PVP membranes were determined as a function of weight percent of genistein in feed. On the basis of UV-vis spectroscopy, the extent of genistein leaching during incubation in human blood was evaluated in conjunction with the PVP leaching from the blend membrane.     

Toughening of immiscible PPE/SAN blends by triblock terpolymers

The mechanical performance of immiscible blends of poly(2,6-dimethyl-1,4-phenylene ether) (PPE) and poly(styrene-co-acrylonitrile) (SAN) and the subsequent influence of compatibilisation by tailored polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock terpolymers (SBM) on the mechanical performance under static and dynamic loads is analysed in detail. A PPE/SAN 60/40 blend was selected as a base system for the compatibilisation experiments. The observed static tensile behaviour is described by micromechanical models and correlated to the blend microstructures as observed by transmission electron microscopy. In most cases, the addition of the SBM triblock terpolymers further enhances the ductility of the blend while only leading to a minor reduction of modulus and strength. Triblock terpolymers with symmetric end blocks, mainly located at the interface between PPE and SAN, led to nearly isotropic specimens. In contrast, SBM materials with a longer polystyrene block predominantly formed micelles in the PPE phase and the blends revealed a highly anisotropic morphology. Comparative investigations of the fatigue crack growth behaviour parallel to the direction of injection also reflected this variation in mechanical anisotropy of the compatibilised blends. A poor toughness and a predominant interfacial failure were observed in the case of the SBM with a long polystyrene block. In contrast, a considerable improvement in properties as a result of pronounced plastic deformations was observed for blends compatibilised by triblock terpolymers with symmetric end blocks. The systematic correlation between morphology and mechanical performance of compatibilised PPE/SAN blends established in this study provides an efficient way for the desired selection of suitable and effective compatibilising agents, ensuring both a superior multiaxial toughness as well as a high strength and modulus of the overall system.     

Co-continuous morphology development in partially miscible PMMA/PC blends

Poly(methyl methacrylate) (PMMA)/polycarbonate (PC) partially miscible blends were produced via melt blending in an internal mixer over the entire range of composition at two different viscosity ratios. The morphology of this low interfacial tension system was investigated by scanning electron microscopy, solvent extraction/gravimetry and surface area measurement (BET) after selective extraction. The partial miscibility of these blends was evaluated by T_g measurements from dynamic mechanical thermal analysis. The co-continuous morphology development curve obtained from gravimetry is commonly reported in the literature as the %continuity vs. the vol% fraction of the dispersed phase for fully phase separated systems. Such systems possess pure phases of A and B. Partially miscible blends on the other hand demonstrate immiscibility between an A-rich phase and a B-rich phase. Quantitative estimation of the partial composition of the minor components in each respective rich phase was calculated using the Fox equation. Using this data, an approach to correcting the gravimetry results to take into account the partial miscibility of the PMMA/PC system is proposed. The co-continuous morphology development curve is then presented as the %continuity vs. the vol% fraction of the PMMA-rich phase. This corrected curve demonstrates the features of a highly interacting polymer blend: a low percolation threshold and a broad co-continuity region. The BET technique shows that the pore size of the extracted co-continuous blends is dependent on composition, the pore diameter increases with total PMMA content. Use of a low molecular weight PC shifts the co-continuous morphology development curve to higher volume fraction values of PMMA-rich phase. It is suggested that this is the result of a lower dispersed phase thread stability due to the lower matrix viscosity.     

Phase diagram prediction for a blend of Poly(2,6-dimethyl-1,4-phenylene ether) (PPE)/epoxy resin during reaction induced phase separation

The phase behavior of a Poly(2,6-dimethyl-1,4-phenylene ether) (PPE)/diglycidyl ether of bisphenol A type epoxy (DGEBA)/diethyltoluenediamine (DETDA) blend during reaction induced phase separation is predicted using Flory-Huggins theory. DGEBA and DETDA are treated as a single pseudo-component in order to reflect the crosslinking polymerisation that occurs between them, and both the PPE and the DGEBA/DETDA pseudo-component are treated as polydisperse. The Flory-Huggins χ parameter was determined by measuring the extent of reaction at the on-set of phase separation for different compositions and temperatures and comparing the results with theory. The χ parameter is then used to determine the coexistence curves as a function of conversion of the DGEBA/DETDA pseudo-component, from which the extent of reaction at which vitrification occurs is predicted. The model is shown to be in good agreement with experimental results.     

On the structure and morphology of polyvinylidene fluoride-nanoclay nanocomposites

Polyvinylidene fluoride (PVDF)-nanoclay nanocomposites were prepared by both solution casting and co-precipitation methods with the nanoclay loading of 1-6 wt%. The structure and morphology of the nanocomposite were investigated by wide angle X-ray diffraction (WAXD), polarized light microscopy and transmission electron microscopy (TEM) techniques. PVDF phase transformation behavior was investigated using differential scanning calorimetry and in situ thermal WAXD. All the three typical nanoclay morphologies, namely, exfoliated, partially intercalated and phase separated morphologies, were observed in the PVDF-nanoclay nanocomposites prepared by different methods. In solution-cast samples, phase separation and intercalation occurred depending upon the organic modifiers while complete exfoliation of the nanoclays was observed in the co-precipitated nanocomposites. Furthermore, unique parallel orientation of the nanoclay layers and polymer film surface was achieved in solution-cast samples. β-form PVDF was observed in all the nanocomposites regardless of the nanoclay morphology and contents. Both crystallization and melting temperatures of PVDF were increased with the addition of nanoclay, possibly due to the formation of the β-form PVDF.     

Lithium orthosilicate ceramics with preceramic polymer as silica source

Lithium orthosilicate ceramics powders were synthesized using a preceramic polymer as the source of silica. Stoichiometric, as well as batches lean and rich in lithium, were prepared by the said approach to understand the thermal stability of the orthosilicate phase at 1000 °C. All of the batches produced phase pure orthosilicate ceramics with sintered density up to 82%. However, different batches showed markedly different microstructural evolution with the lithium lean and stoichiometric compositions exhibiting formation of flower-like lithium metasilicate phase. The lithium rich composition showed no phase separation of the orthosilicate ceramic phase as confirmed by electron microscopy and x-ray diffraction. The high volatilization of the lithium species at high temperature was ascribed to the phase separation of the orthosilicate phase in the lithium lean compositions. The current report provides an alternative and novel method to fabricate lithium orthosilicate, and shows promise for application as tritium breeding blankets in fusion technologies.     

Dynamic viscoelastic behavior of polypropylene/polybutene-1 blends and its correlation with morphology

In this study the rheology, morphology, and interfacial interaction of polypropylene (PP)/polybutene-1 (PB-1) blends in different percentages of PB-1 are investigated. The morphology of cryo-fractured surfaces of samples was studied by scanning electron microscopy (SEM). The SEM images showed a droplet-matrix structure in all range of compositions and the size of dispersed phase increased proportionally with PB-1 content. The miscibility of blends at various compositions is evaluated by viscoelastic parameters determined by dynamic oscillation rheometry in the linear viscoelastic region. A distinct Newtonian plateau at low frequencies is observed and the variations of complex viscosity (η*) against angular frequency (ω) for all blends are in agreement with Cross model. The complex viscosity of samples at various percentages of PB-1 showed the log-additivity mixing rule behavior in low frequencies and positive-negative deviation behavior (PNDB) at high shear rates. The phenomena such as decrease in the sensitivity of storage modulus to shear rate in the terminal region, the deviation of Cole–Cole plots from the semi-circular shape, and the tail in relaxation spectrums at high relaxation times are the evidences of two phase heterogenous morphology. The effect of time–temperature on the phase behavior is studied and the interfacial tension between matrix and dispersed phase was evaluated by using emulsion theoretical models. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Dissipative particle dynamics study on the phase morphologies of the ultrahigh molecular weight polyethylene/polypropylene/poly(ethylene glycol) blends

The dissipative particle dynamics (DPD) simulation method has been used to study mesophase formation of the binary UHMWPE/PP and ternary UHMWPE/PP/PEG blends. The effects of shear rates and volume fractions of each of the blend components on end-to-end distances of UHMWPE, diffusivities and mesoscale morphologies of the blends have been investigated in detail. As compositions of the UHMWPE/PP and UHMWPE/PP/PEG blends vary, the mesoscale simulations have predicted the ordered structures with defined morphologies of lamellas, perforated lamellas, hexagonal spheres, and body-centered-cubic spheres. Micelle-like melted structures between totally disordered and the ordered phases have also been found in the UHMWPE/PP (10/90) blends. Immiscibility property of UHMWPE, PP and PEG induces the phase separation and exhibits different mesoscpic morphologies at different shear rates and volume fractions. Taking the shear rates dependence of mesophase into account, the change in morphology of the UHMWPE/PP/PEG blends with shear rate is also well studied in this work. As a function of PP concentration, the end-to-end distances of UHMWPE are found to decrease with the increase of PP concentration. This effect is more prominent for a high amount of PP.     

Preparation of a polymeric membrane with a fine porous structure by dry casting

We prepared a polymeric membrane with a fine porous structure from polystyrene (PS), poly(ethylene glycol) (PEG), and solvent solutions by exploiting the phase separation induced in the course of dry casting. To determine the effect of the drying rate and phase separation on the developed porous structure, six different solvents, including toluene, chlorobenzene, tetrahydrofuran, methyl ethyl ketone, 1,4‐dioxane, and chloroform, were used. The pore size and density drastically changed with the different solvents and drying conditions. The polymer concentration at the onset of the phase separation into PEG‐rich and PS‐rich phases also strongly affected the cellular structure. The solubility of PEG into PS and the solvent solutions changed the concentration, which corresponded to the viscosity of the PS‐rich solution at the onset of the phase separation. The higher solubility of PEG in the solutions delayed the onset of phase separation during drying and increased the viscosity. The higher viscosity and the higher drying rate prevented the phase‐separated PEG domains from coalescing and made the resulting pore size smaller and the pore density larger. The finest porous structure, with a pore size of approximately 1 μm and a pore density of 0.08 1/μm², was prepared from PS/PEG and a 90 wt % chloroform solution. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structure, dynamics and interactions of complex sol-gel hybrid materials through SSNMR and DSC: Part II, ternary systems based on PE-PEG block copolymer, PHS and silica

This work is the second part of a study aimed at understanding in more depth structure, dynamics, interactions and correlations between morphology and barrier properties against oxygen diffusion of complex PE-PEG/PHS/SiO₂ hybrids prepared through a sol-gel process. Using a combined DSC and solid-state NMR approach, including ¹³C and ²⁹Si experiments and ¹H ultra-fast MAS spectra, the structural, phase and interaction properties of three PE-PEG/PHS/SiO₂ samples with different compositions, exhibiting different barrier performances, have been investigated, also taking into account the results obtained for the simpler one- and two-component systems (Part I). While the structure of the silica domains has been found to be not affected by composition, many differences have been observed concerning the phase and dynamic properties of the organic components (PE and PEG crystallinity and mobility of their amorphous domains) and the inter-component interactions (strength of the hydrogen bonds between PHS and both silica and PEG and PHS/PEG miscibility). In particular peculiar phase and interaction properties of the sample exhibiting the best barrier properties have been identified and characterized.     

Simple route to prepare stable liquid marbles using poly(ionic liquid)s

Individual “liquid marbles” were prepared by encapsulation of water droplets using flocculated polymer latexes stabilized with poly(ionic liquid)s. At first, the emulsion polymerization of poly(styrene) and poly(methyl methacrylate) using different poly(ionic liquid)s as stabilizers was investigated. Stable latexes composed of spherical polymer particles with sizes ranging between 300 and 700 nm as characterized by dynamic light scattering and scanning electron microscopy were obtained. Subsequently, the polymer particles were flocculated by anion exchange precipitation of the poly(ionic liquid)s provoked by the addition of lithium bis(trifluoromethanesulfonyl)imide salt. After simple filtration and drying processes, the flocculated latexes led to hydrophobic powders with similar micrograin size compared to the original latexes. Very stable “liquid marbles” were prepared by gently shaking water droplets of different volumes onto the hydrophobic powders. The morphology and stability of the liquid marbles were characterized by optical and confocal microscopy.     

Laser scanning confocal microscopy versus scanning electron microscopy for characterization of polymer morphology: Sample preparation drastically distorts morphologies of poly(2‐hydroxyethyl methacrylate)‐based hydrogels

The internal morphologies for a series of heterogeneous PHEMA and P[HEMA‐co‐MeO‐PEGMA] [PHEMA = poly(2‐hydroxyethyl methacrylate), MeO‐PEGMA = poly(ethylene glycol) methyl ether methacrylate] hydrogels were characterized by scanning electron microscopy (SEM) in conjunction with a sample drying procedure, and by laser scanning confocal microscopy (LSCM) without prior drying. Compared to SEM, LSCM was far simpler and more rapid technique for imaging hydrogels. LSCM also allowed the native hydrated morphology of the hydrogels to be characterized, whereas SEM could only characterize the morphology of samples in their dehydrated state. No dehydration method used in this study preserved the true native morphology, but plunge freezing/freeze drying was the most suitable method that best preserved the native morphology for all hydrogel compositions. Refrigerated freezing/freeze‐drying and critical point drying introduced significant morphological artifacts, the severity of the artifacts being dependant on the sample's composition and Tg. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermodynamic analysis of phase separation in an epoxy/polystyrene mixture

The phase separation process of an epoxy prepolymer based on diglycidyl ether of bisphenol A (DGEBA) with a thermoplastic polystyrene (PS) was thermodynamically studied in the frame of the Flory-Huggins theory. The thermodynamic treatment was carried out in two steps: first analysing the phase separation in cloud point conditions, and second analysing the advance of the phase separation for two compositions of 2 and 10% in volume of PS. The effect of the polydispersity of thermoplastic on phase separation was also studied. The polydispersity of PS produces a displacement of the threshold temperature to lower thermoplastic volume fraction (between 2 and 3%) and higher temperature value and the fact that the shadow curve and coexistence curves do not superimpose with the cloud point curve. Theoretical calculations of molecular weight distributions of PS at different degrees of phase separation were realized and different average molecular properties were obtained in each separated phase.     

Crystallization,morphology, and mechanical behavior of polylactide/poly(ε‐caprolactone) blends

Optically pure polylactides, poly(L ‐lactide) (PLLA) and poly(D ‐lactide) (PDLA), were blended across the range of compositions with poly(ε‐caprolactone) (PCL) to study their crystallization, morphology, and mechanical behavior. Differential scanning calorimetry and dynamic mechanical analysis (DMA) of the PLA/PCL blends showed two T_gs at positions close to the pure components revealing phase separation. However, a shift in the tan δ peak position by DMA from 64 to 57°C suggests a partial solubility of PCL in the PLA‐rich phase. Scanning electron microscopy reveals phase separation and a transition in the phase morphology from spherical to interconnected domains as the equimolar blend approaches from the outermost compositions. The spherulitic growth of both PLA and PCL in the blends was followed by polarized optical microscopy at 140 and 37°C. From tensile tests at speed of 50 mm/min Young's modulus values between 5.2 and 0.4 GPa, strength values between 56 and 12 MPa, and strain at break values between 1 and 400% were obtained varying the blend composition. The viscoelastic properties (E′ and tan δ) obtained at frequency of 1 Hz by DMA are discussed and are found consistent with composition, phase separation, and crystallization behavior of the blends. POLYM. ENG. SCI., 46:1299–1308, 2006. © 2006 Society of Plastics Engineers     

用拟二元方法研究iPP-DBP-DOP三元体系的热致相分离热力学

采用拟二元方法研究等规聚丙烯（iPP）‐邻苯二甲酸二丁酯（DBP）‐邻苯二甲酸二辛酯（DOP）三元聚合物溶液的热致相分离热力学,得出了拟二元相图的数学关联方法.采用光学显微镜法测定浊点温度, 采用差式扫描量热法（DSC）测定熔点、动态结晶温度.利用浊点测定数据回归聚合物-共溶剂的交互作用参数 χ的表达式,χ是共溶剂配比和温度的函数,以此为基础计算的拟二元相图与实验数据吻合较好.发现共溶剂中DBP份数增加,相分离类型由单纯固液分相形式转变为液液分相、固液分相依次发生形式,共溶剂配比能调控拟二元相图结构.研究表明,只需测定一个较低冷却速率下几种共溶剂配比的拟二元溶液的浊点温度、分别测定几个冷却速率下iPP–DOP二元溶液的动态结晶温度即可掌握该三元溶液热致相分离热力学的全部信息.其可用来指导制膜过程,并能准确预测形成的膜结构形貌.     

Identification of the morphology of a thin film by fluorescence laser-scanning confocal microscopy

This study is an extension of our previous paper (Hayashi, M. et al. Polymer, 1998, 39, 299) dealing with the phase separation and structure formation of a polysulfone (PSU)/polyamide (PA) blend as observed by laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). Here we use fluorene-labelled PSU in order to apply fluorescence LSCM for more detailed morphological investigations of the internal structure of a thin film as-cast from solution.     

Continuity development in polymer blends of very low interfacial tension

Phase continuity development and co-continuous morphologies are highly influenced by the nature of the interface in immiscible polymer blends. Blends of ethylene-propylene-diene terpolymer (EPDM) and polypropylene (PP) possess an interfacial tension of about 0.3 mN/m and provide an interesting model system to study the detailed morphology development in a very low interfacial tension binary system. A variety of blends with viscosity ratios of 0.2-5.0 and shear stresses of 11.7-231.4 kPa were considered. Using a variety of sophisticated morphology protocols it is shown that at low blend compositions, the dispersed phase actually exists as stable fibers of extremely small diameter of 50-200 nm and the continuity develops by fiber-fiber coalescence. An analysis using break-up times from Tomotika theory also supports the notion of highly stable dispersed fiber formation. These results challenge the current view of the dispersed phase as small spherical droplets. It is shown, under these conditions, that a seven-fold variation in the viscosity ratio has virtually no influence on % continuity or morphology, while a large change in the matrix shear stress from 11.7 to 90.9 kPa has an important effect on pore diameter. Both sides of the continuity diagram are studied and highly symmetrical continuity behavior is observed with composition. In fact a single master continuity curve is observed for these blends varying in viscosity ratio from 0.7-5.0 and with shear stresses from 11.7-90.9 kPa. Although the glass transition temperatures indicate that these materials are completely immiscible after melt mixing and cooling, it is shown that the blends demonstrate the morphological features of a partially miscible system. These results support a concept that the blend was partially miscible during melt blending, at which time the gross morphological features of the blend were developed, but becomes fully phase separated upon cooling. It appears that the quenching of the EPDM/PP blend from the melt is rapid enough to preserve the imprint of that partial miscibility on the gross blend morphology.