Predictions of Some Internal Microstructural Models for Polymer Melts and Solutions in Shear and Elongational Flows

Summary: In this work, the behavior of some internal microstructural models with different mobility tensors has been studied for polymer melts and solutions under steady and transient simple shear and elongational flows. The time evolution equations for conformation and stress tensors in the models reviewed have their root in the Generalized Poisson bracket formalism. Two different families of conformational models have been selected for this study. The first family is based on the Modified Finitely Extensible Nonlinear Elastic (FENE‐P) energy while the second uses a Volume Preserving Conformational Rheological (VPCR) model based on the Hookean Helmholtz free energy function. Several expressions for the mobility tensor based on the previously mentioned energy functions are used to obtain the models. The sensitivity of both families of models to the choice of the mobility tensors on the prediction of material functions in the transient and steady flows is discussed. Also, effects of shear rate on the material functions in start‐up and relaxation shear flows for both models are studied. The predictions of both models are compared with experimental data taken from the literature for some polymer melts. These results show that the family of VPCR models is able to predict the steady shear and elongational flow material functions in an extended range of deformation rates whereas the family of FENE‐P models can predict the behavior of only some specified polymer melts.

Experimental data and VPCR model predictions for steady and elongational viscosity for PS [data of H. Munstedt, 1980].     

Rheology of a miscible polymer blend

Difference spectra of blends of cis-1,4-polyisoprene and atactic poly(vinylethylene), obtained from the measured FTIR spectra of the pure components and the blends, indicate that mixing of these polymers is not accompanied by any specific chemical interactions. Miscibility in this system arises solely due to the small combinatorial entropy of mixing. The conformation and configuration of the polymer chains in the blends are, therefore, identical to those in the pure melts. As a consequence it was found that the entanglement density of the blends varied monotonically with composition. This variation, however, was not in accordance with predictions based simply on the mechanical interaction density. The principle rheological effect of miscible blending was a large change in the monomeric friction coefficient, which arises from the strong dependence of free volume on composition. The zero shear viscosity and the terminal relaxation time of the blends reflected this change in local chain mobility. Empirical relations, which have previously been proposed for the properties of miscible polymer mixtures, were found to be without merit in describing the obtained experimental results.     

In‐line monitoring of immiscible polymer blends in a rheometer with a fiber‐optics‐assisted fluorescence detection system

In‐line studies of the initial stages of shear‐induced coalescence in two‐phase polymer blends were carried out with a home‐built device combining a cone and plate rheometer and a fiber‐optic‐assisted fluorescence detection system. A blend of 90 wt % poly(2‐ethylhexyl methacrylate) (PEHMA) and 10 wt % poly(butyl methacrylate) (PBMA) was prepared by the casting of films onto a solid substrate from mixed aqueous latex dispersions of the two polymers. The dispersions were prepared via emulsion polymerization under conditions in which both components were formed as spherical particles with a very narrow size distribution. By using a 14:1 particle ratio of PEHMA to PBMA, we obtained films in which 120‐nm PBMA particles were surrounded by a PEHMA matrix. The blend contained phenanthrene‐labeled PBMA particles and anthracene‐labeled PBMA particles in a ratio of 4:1, whereas the PEHMA matrix polymer was unlabeled. We monitored the anthracene‐to‐phenanthrene fluorescence intensity ratio (I₄₇₀/I₃₆₀) as a measure of direct nonradiative energy transfer from phenanthrene to anthracene, whereas the blend was sheared at different shear rates and temperatures. Under no‐shear conditions, the results of in‐line experiments were in good agreement with the results of off‐line measurements of energy transfer by conventional techniques. In blends under shear, the two sets of experiments, in‐line and off‐line, did not agree with each other. The cause of this disagreement was associated with normal forces in the blend under shear that affected the optical path length and the relative intensities of the fluorescence signals of the phenanthrene and anthracene groups in the blend. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2302–2316, 2001     

Influence of long‐chain branching on the miscibility of poly(ethylene‐r‐ethylethylene) blends with different microstructures

The melt miscibility of two series of poly(ethylene‐r‐ethylethylene) (PE_Exx) polymers with different percentages (xx) of ethylethylene (EE) repeat units was examined with small‐angle neutron scattering (SANS). The first series consisted of comb/linear blends in which the first component is a heavily branched comb polymer (B90) containing 90% EE and an average of 62 long branches with a weight‐average molecular weight (M_W) of 5.5 kg/mol attached to a backbone with M_W = 10.0 kg/mol. The comb polymer was blended with six linear PE_Exx copolymers, all of which had M_W ≈ 60 kg/mol and EE percentages ranging from 55 to 90%; they were denoted L55 to L90, with the number referring to the percentage of EE repeat units. The second series consisted of linear/linear blends; the first component, with M_W = 220 kg/mol and 90% EE, was denoted L90A, and the second components were the same series of linear polymers, with M_W ≈ 60 kg/mol and various EE compositions. The concentrations investigated were 50/50 w/w, except for the blend of branched B90 and linear L90 (both components were 90% EE), for which 25/75 and 75/25 concentrations were also examined. The SANS results indicated that for the comb/linear blends, only the dB90/L90 blends were miscible, whereas the other five blends phase‐separated; for the linear/linear blends, dL90A/L83 and dL90A/L78 were miscible, whereas the other three blends were immiscible. These results indicate that long‐chain branching significantly narrowed the miscibility window of these polyolefin blends. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 466–477, 2002; DOI 10.1002/polb.10102     

Structure of reactively extruded rigid PVC/PMMA blends

A novel route for producing polymer blends by reactive extrusion is described, starting from poly (vinyl chloride)/methyl methacrylate (PVC/MMA) dry blend and successive polymerization of MMA in an extruder. Small angle X‐ray scattering (SAXS) measurements were applied to study the monomer's mode of penetration into the PVC particles and to characterize the supermolecular structure of the reactive poly(vinyl chloride)/poly(methyl methacrylate) (PVC/PMMA) blends obtained, as compared to the corresponding physical blends of similar composition. These measurements indicate that the monomer molecules can easily penetrate into the PVC sub‐primary particles, separating the PVC chains. Moreover, the increased mobility of the PVC chains enables formation of an ordered lamellar structure, with an average d‐spacing of 4.1 nm. The same characteristic lamellar structure is further detected upon compression molding or extrusion of PVC and PVC/PMMA blends. In this case the mobility of the PVC chains is enabled through thermal energy. Dynamic mechanical thermal analysis (DMTA) and SAXS measurements of reactive and physical PVC/PMMA blends indicate that miscibility occurs between the PVC and PMMA chains. The studied reactive PVC/PMMA blends are found to be miscible, while the physical PVC/PMMA blends are only partially miscible. It can be suggested that the miscible PMMA chains weaken dipole–dipole interactions between the PVC chains, leading to high mobility and resulting in an increased PVC crystallinity degree and decreased PVC glass transition temperature (T_g). These phenomena are shown in the physical PVC/PMMA blends and further emphasized in the reactive PVC/PMMA blends. Copyright © 2005 John Wiley & Sons, Ltd.     

Blends of polycarbonate and acrylic polymers: Crystallization of polycarbonate

The microstructure of amorphous polymer blends has been extensively studied in the past, but now there is a growing interest for polymer blends where one or more of the components can crystallize. In this study we investigate such blends, namely miscible polycarbonate (PC)/acrylic blends. Using small angle X-ray scattering (SAXS) measurements, combined with atomic force microscopy (AFM), electron microscopy (SEM), and optical microscopy, we demonstrate that the amorphous acrylic component mostly segregates inside the spherulites between the lamellar bundles (interfibrillar segregation). Varying the PC molecular weight or the mobility of the amorphous component (by changing its molecular weight and T_g) does not change the mode of segregation. So far qualitative predictions of the mode of segregation in semicrystalline polymer blends have been proposed using the δ parameter (the ratio between the diffusion coefficient D of the amorphous component in the blend and the linear crystallization rate G), introduced by Keith and Padden. Our results suggest that other parameters have to be considered to fully understand the segregation process. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2197–2210, 1998     

Structure formation of PVDF/PMMA blends studied

Conformational formation and crystallization dynamics of miscible PVDF/at-PMMA and PVDF/iso-PMMA polymer blends from the molten state were studied by the simultaneous DSC/FT-IR measurement. Formation of TGTG' conformation occurred before starting crystallization exothermic peak in the PMMA content (_PMMA) range from 0 to 0.4 for both blends. The formation rate of TGTG' conformation, crystal growth rate and surface free energy of PVDF crystal in blends depended linearly on _PMMA for PVDF/at-PMMA, however, those rates for PVDF/iso-PMMA slightly influenced by _PMMA. These results suggested that the former was miscible blend in molecular level, however, the latter was a miscible blend with large concentration fluctuation or a partially segregated system.     

Characterisation of Hyaluronic Acid Blends Modified by Poly(N-Vinylpyrrolidone)

The viscosity behaviour and physical properties of blends containing hyaluronic acid (HA) and poly(N-vinylpyrrolidone) (PVP) were studied by the viscometric technique, steady shear tests, tensile tests and infrared spectroscopy. Viscometric and rheological measurements were carried out using blends of HA/PVP with different HA weight fractions (0, 0.2, 0.5, 0.8 and 1). The polymer films and HA/PVP blend films were prepared using the solution casting method. The study of HA blends by viscometry showed that HA/PVP was miscible with the exception of the blend with high HA content. HA and its blends showed a shear-thinning flow behaviour. The non-Newtonian indices (n) of HA/PVP blends were calculated by the Ostwald–de Waele equation, indicating a shear-thinning effect in which pseudoplasticity increased with increasing HA contents. Mechanical properties, such as tensile strength and elongation at the break, were higher for HA/PVP films with w_HA = 0.5 compared to those with higher HA contents. The elongation at the break of HA/PVP blend films displayed a pronounced increase compared to HA films. Moreover, infrared analysis confirmed the existence of interactions between HA and PVP. The blending of HA with PVP generated films with elasticity and better properties than homopolymer films.     

Interactions and prediction of phase diagrams in ternary blends comprising poly(vinyl acetate), poly(vinyl p‐phenol), and poly(methyl methacrylate)

This study investigated and discovered a new miscible ternary blend system comprising three amorphous polymers: poly(vinyl acetate) (PVAc), poly(vinyl p‐phenol) (PVPh), and poly(methyl methacrylate) (PMMA) using thermal analysis and optical and scanning electron microscopies. The ternary compositions are largely miscible except for a small region of borderline ternary miscibility near the side, where the binary blends of PVAc/PMMA are originally of a borderline miscibility with broad T_g. In addition to the discovering miscibility in a new ternary blend, another objective of this study was to investigate whether the introduction of a third polymer component (PVPh) with hydrogen bonding capacity might disrupt or enhance the metastable miscibility between PVAc and PMMA. The PVPh component does not seem to exert any “bridging effect” to bring the mixture of PVAc and PMMA to a better state of miscibility; neither does the Δχ effect seem to disrupt the borderline miscible PVAc/PMMA blend into a phase‐separated system by introducing PVPh. Apparently, the ternary is able to remain in as a miscible state as the binary systems owing to the fact that PVPh is capable of maintaining roughly equal H‐bonding interactions with either PVAc or PMMA in the ternary mixtures to maintain balanced interactions among the ternary mixtures. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1147–1160, 2006     

Effects of compatibility of poly(l‐lactic‐acid) and thermoplastic polyurethane on mechanical property of blend fiber

Blending poly(l ‐lactic‐acid) (PLLA) and thermoplastic polyurethane (TPU) has been performed in an effort to toughen PLLA without compromising its biodegradability and biocompatibility. The mixing enthalpy calculation of PLLA and TPU predicted that the blend was a thermodynamic miscible system. The viscoelastic properties and phase morphologies of PLLA/TPU blends were investigated further by dynamic mechanical analysis and scanning electron microscopy. It was found that the blend was a partially miscible system. The dynamic mechanical analysis showed that T_g of PLLA and TPU shifted toward with TPU content increasing. Scanning electron microscopy photos showed that the morphologies of the blends changed from a sea island structure to a bicontinuous structure as an increment in TPU content, which suggested that the miscibility of PLLA and TPU was enhanced when the TPU increased. PLLA/TPU blend fibers were fabricated. With the TPU content increasing from 0 wt% to 30 wt%, the tensile strength and initial modulus of blend fibers decreased first then increased, while elongation at break and fracture work gradually increased. The change of tensile properties indicated the toughening effects of TPU on PLLA fibers, also suggested that the formation of blend fibers was influenced by the blend rheological behavior other than the compatibility. Copyright © 2014 John Wiley & Sons, Ltd.     

Phase separation of polymer blends under shear field

The effect of shear flow on phase separation in critical polymer blends has been studied. For a low-molecular-weight blend, the response is in good agreement with the theoretical predictions of Onuki and Kawasaki. The breakup of large-scale critical fluctuations by the flow leads to a drop in the temperature T_c at which phase separation begins. For a high-molecular-weight blend, the data suggest that the mode-coupling contribution to the decay rate of composition fluctuations is significant in both the miscible and immiscible phases. However, the lack of change of structure factor in the vorticity direction implies that there is no apparent shear induced shift in T_c.     

Thermal,crystallization, mechanical,and rheological characteristics of poly(trimethylene terephthalate)/poly(ethylene terephthalate) blends

Blends of poly(trimethylene terephthalate) (PTT) and poly(ethylene terephthalate) in the amorphous state were miscible in all of the blend compositions studied, as evidenced by a single, composition‐dependent glass‐transition temperature observed for each blend composition. The variation in the glass‐transition temperature with the blend composition was well predicted by the Gordon–Taylor equation, with the fitting parameter being 0.91. The cold‐crystallization (peak) temperature decreased with an increasing PTT content, whereas the melt‐crystallization (peak) temperature decreased with an increasing amount of the minor component. The subsequent melting behavior after both cold and melt crystallizations exhibited melting point depression behavior in which the observed melting temperatures decreased with an increasing amount of the minor component of the blends. During crystallization, the pure components crystallized simultaneously just to form their own crystals. The blend having 50 wt % of PTT showed the lowest apparent degree of crystallinity and the lowest tensile‐strength values. The steady shear viscosity values for the pure components and the blends decreased slightly with an increasing shear rate (within the shear rate range of 0.25–25 s^?1); those of the blends were lower than those of the pure components. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 676–686, 2004     

FT‐IR Investigation into the miscible interactions in new materials for optical devices

In this article we determine the miscibility of azobenzene derivative (poly(4‐(N‐(2‐methacryloyloxyethyl)‐N‐ethylamino)‐4′‐nitroazobenzene)₉₀‐co‐(methyl methacrylate)₁₀)/poly(vinyl acetate) (PVAc) and azobenzene derivative/poly(vinyl chloride) (PVC) blends using Fourier Transform infrared (FT‐IR) spectroscopy. With this method we can clearly identify the exact interactions responsible for miscibility. In the azobenzene derivative 50:50PVAc blend new peaks were evident at 2960, 2890, 1237 and 959 cm^?1, these peaks depict miscible interactions. These wavenumbers indicate that the miscible interactions occurring are from the C? H stretching band, the vinyl acetate C?O, conjugated to the ester carbonyl, the cis‐transformation N?N stretch frequency and the acetate ester weak doublet. The azobenzene derivative 80:20PVC blend display peaks identical in profile to the blend homopolymers, indicating no miscible interactions. However, this could be due to overlapping of peaks within the same wavenumber region, making resolution difficult. This research demonstrates FT‐IR can deduce favorable interactions for miscibility and therefore numerous miscible blends can successfully be calculated if possessing the same groups responsible for miscibility. This paves the way for a new generation of designer optical materials with the desired properties. Copyright © 2003 John Wiley & Sons, Ltd.     

Complex phase behavior and state of miscibility in Poly(ethylene glycol)/Poly(l‐lactide‐co‐ε‐caprolactone) Blends

A miscibility and phase behavior study was conducted on poly(ethylene glycol) (PEG)/poly(l ‐lactide‐ε‐caprolactone) (PLA‐co‐CL) blends. A single glass transition evolution was determined by differential scanning calorimetry initially suggesting a miscible system; however, the unusual T_g bias and subsequent morphological study conducted by polarized light optical microscopy (PLOM) and atomic force microscopy (AFM) evidenced a phase separated system for the whole range of blend compositions. PEG spherulites were found in all blends except for the PEG/PLA‐co‐CL 20/80 composition, with no interference of the comonomer in the melting point of PEG (T_m = 64 °C) and only a small one in crystallinity fraction (X_c = 80% vs. 70%). However, a clear continuous decrease in PEG spherulites growth rate (G) with increasing PLA‐co‐CL content was determined in the blends isothermally crystallized at 37 °C, G being 37 µm/min for the neat PEG and 12 µm/min for the 20 wt % PLA‐co‐CL blend. The kinetics interference in crystal growth rate of PEG suggests a diluting effect of the PLA‐co‐CL in the blends; further, PLOM and AFM provided unequivocal evidence of the interfering effect of PLA‐co‐CL on PEG crystal morphology, demonstrating imperfect crystallization in blends with interfibrillar location of the diluting amorphous component. Significantly, AFM images provided also evidence of amorphous phase separation between PEG and PLA‐co‐CL. A true T_g vs. composition diagram is proposed on the basis of the AFM analysis for phase separated PEG/PLA‐co‐CL blends revealing the existence of a second PLA‐co‐CL rich phase. According to the partial miscibility established by AFM analysis, PEG and PLA‐co‐CL rich phases, depending on blend composition, contain respectively an amount of the minority component leading to a system presenting, for every composition, two T_g's that are different of those of pure components. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 111–121     

Shear‐induced Apparent Shift of Phase Boundary of Binary Polymer Blends

Summary: The combined influence of the thermodynamical and hydrodynamic effects of shear was tentatively considered for the first time, in the modeling of the shear‐induced phase behavior of binary polymer blends in this paper. In this model, the original “two‐fluid” model proposed by Onuki 1 , 2 was modified by replacing the quiescent thermodynamical term with the one defined in the frame of extended irreversible thermodynamics (EIT). 3 - 5 The stress term of the polymer blend was determined by using the mixing rule of “Double Reptation” 6 , 7 along with the Graessley's 8 functions to make the model applicable in both linear and weak non‐linear regions. Then the apparent shift of phase boundary of a model blend system was computed by using this theory. It's found that this modified theory can predict both the “miscibility gap” and anisotropical phase separation of the polymer blend, while the two different previous theories, that is the pure thermodynamical one and hydrodynamic one, could only predict one but not both of them. For example, this modified “two‐fluid” model predicts that the miscibility gap can be observable not only in vorticity direction but also in the velocity gradient direction.

The calculated reduced stored energy F_s/RT as a function of Φ_A and the temperature T (shear rate: 0.5 s⁻¹).     

Miscibility and phase structure of binary blends of polylactide and poly(methyl methacrylate)

Blends of amorphous poly(DL‐lactide) (DL‐PLA) and crystalline poly(L‐lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were prepared by both solution/precipitation and solution‐casting film methods. The miscibility, crystallization behavior, and component interaction of these blends were examined by differential scanning calorimetry. Only one glass‐transition temperature (T_g) was found in the DL‐PLA/PMMA solution/precipitation blends, indicating miscibility in this system. Two isolated T_g's appeared in the DL‐PLA/PMMA solution‐casting film blends, suggesting two segregated phases in the blend system, but evidence showed that two components were partially miscible. In the PLLA/PMMA blend, the crystallization of PLLA was greatly restricted by amorphous PMMA. Once the thermal history of the blend was destroyed, PLLA and PMMA were miscible. The T_g composition relationship for both DL‐PLA/PMMA and PLLA/PMMA miscible systems obeyed the Gordon–Taylor equation. Experiment results indicated that there is no more favorable trend of DL‐PLA to form miscible blends with PMMA than PLLA when PLLA is in the amorphous state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 23–30, 2003     

Improvement of thermoplasticity for s‐BPDA/PDA by copolymerization and blend with novel asymmetric BPDA‐based polyimides

Asymmetric biphenyl type polyimides (PI) derived from 2,3,3′,4′‐biphenyltetracarboxylic dianhydride (a‐BPDA) and p‐phenylenediamine (PDA) or 4,4′‐oxydianiline (ODA) show higher T_gs, and much better thermoplasticity than the corresponding isomeric PIs from symmetric 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (s‐BPDA). In addition, a‐BPDA‐derived PIs are completely amorphous owing to their bent chain structures and highly distorted conformations, whereas the PIs from s‐BPDA are semicrystalline. a‐BPDA‐derived PIs possessing these properties or the a‐BPDA monomer were used as a flexible blend component or a comonomer to improve the insufficient thermoplasticity of semirigid s‐BPDA/PDA homo polymer. The blends composed of s‐BPDA/PDA (80%) with a‐BPDA‐derived PIs (20%), as well as the s‐BPDA/PDA‐based copolymer containing 20% a‐BPDA, showed a certain extent of thermoplasticity above the T_gs without causing a decrease in T_g. In addition, these blends and copolymer provided comparatively low thermal expansion coefficient (ca. 18 ppm). The improved film properties for the blends are related to good blend miscibility. On the other hand, when s‐BPDA/ODA was used as a flexible matrix polymer instead of a‐BPDA‐derived PIs, the 80/20 blend film annealed at 400°C exhibited no prominent softening at the T_g. This result arises from annealing‐induced crystallization of the flexible s‐BPDA/ODA component. Thus, these results revealed that a‐BPDA‐derived PIs are promising candidates as matrix polymers for semirigid s‐BPDA/PDA for the present purpose. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2499–2511, 1999     

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     

X‐ray photoelectron spectroscopy of miscible poly(methyl methacrylate)/poly(styrene‐co‐acrylonitrile) and immiscible poly(methyl methacrylate)/polyacrylonitrile polymer surfaces metallized by nickel

A miscible blend of poly(methyl methacrylate) and poly(styrene‐co‐acrylonitrile) and an immiscible blend of poly(methyl methacrylate) and polyacrylonitrile were metallized by nickel, and their surfaces were analyzed by X‐ray photoelectron spectroscopy. Before metallization, the heteroatom distribution at the polymer surface was very different in the miscible and immiscible blends. However, this distribution was modified during metallization, which was only possible via polymer‐bond breaking, leading to similar compositions at the two interfaces. Oxygen exhibited a better affinity with nickel than nitrogen, but nickel oxide and nickel nitride were both formed at the interface. Nickel nitride prevented the metal from diffusing into the substrate, playing the role of a barrier, thus driving the oxygen to the metal layer. Amorphous carbon was also detected at the interface as a new carbon species, but it did not have any significant influence on the changes induced in the distribution of heteroatoms at the polymer surfaces. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1408–1416, 2004     

Phase separation of polyphosphazene/poly(lactide‐co‐glycolide) blends prepared under different conditions

Using a mutual solvent technique, blend films of poly[(alaine ethyl ester)_0.62(glycine ethyl ester)_0.38]phosphazene/poly(lactide‐co‐glycolide) (PAGP/PLGA blend) were prepared at different conditions including weight ratios, solvents, environmental humidity, film thickness, and substrates. The morphology and properties of blend films were characterized by scanning electron microscope (SEM), energy dispersive spectrometer (EDX), X‐ray photoelectron spectrometry (XPS), and solvent selective etching. Compared with dichloromethane and tetrahydrofuran (THF), chloroform was the better solvent to form miscible PAGP/PLGA blend films at relatively anhydrous atmosphere. However, in the humid atmosphere, the hexagonal arrangement of holes appeared on the surface of PAGP/PLGA blend films due to the ordered array of water droplets. A sandwich‐liked structure was formed with the hydrophilic PAGP component at the top and bottom, while the PLGA component in the middle. In addition, the surface morphology of PAGP/PLGA blend films was also influenced by the film thickness and the property of the substrate. Copyright © 2010 John Wiley & Sons, Ltd.