Combination of atomic force microscopy and chemical hydrolysis to characterize degradable regions in polymer blends

In this study, we demonstrate the usefulness of chemical‐based method in combination with atomic force microscopy (AFM) to characterize the degradable regions in a wide range of polymer blends. This approach is based on selective hydrolysis of one of the components in a multiple‐phase system, and the ability of AFM to provide nanoscale lateral information about the different phases in the polymer system. Composite films containing different percentage of hydrolyzable polymer were either melt processed or solution casted and then exposed to a hydrolytic acidic environment. Tapping mode AFM was used to analyze the samples before and after hydrolysis. Dramatic topographic changes such as pits were observed on the acid exposed samples, indicating that the degradation was localized and the more susceptible component in the blend was hydrolyzed. Additionally, the progressive hydrolysis of the composites was studied by attenuated total reflection FTIR (ATR‐FTIR) analyses to confirm the AFM results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 726–733, 2006     

Surface phase separations of PMMA/SAN blends investigated by atomic force microscopy

The thin films of poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile) (SAN) and their blends were prepared by means of spin-coating their corresponding solutions onto silicon wafers, followed by being annealed at different temperatures. The surface phase separations of PMMA/SAN blends were characterized by virtue of atomic force microscopy (AFM). By comparing the tapping mode AFM (TM-AFM) phase images of the pure components and their blends, surface phase separation mechanisms of the blends could be identified as the nucleation and growth mechanism or the spinodal decomposition mechanism. Therefore, the phase diagram of the PMMA/SAN system could be obtained by means of TM-AFM. Contact mode AFM was also used to study the surface morphologies of all the samples and the phase separations of the blends occurred by the spinodal decomposition mechanism could be ascertained. Moreover, X-ray photoelectron spectroscopy was used to characterize the chemical compositions on the surfaces of the samples and the miscibility principle of the PMMA/SAN system was discussed.     

Electroactive polymer blends

The rapid development of two new classes of electrically active polymer materials, electronically conducting and electroactive polymers and ion-conducting polymers respectively, offers new possibilities for application of both classes of material, especially in combination with each other. While some of these combinations have been attempted before, they all met serious problems due to poor interpenetration of the two polymers. The recent availability of solubilized and soluble electroactive and conductive polymers has greatly advanced the possibilities of reducing the interpenetration problem. Some experimental studies using the combination of solubilized electroactive polypyrrole with poly(ethylene oxide) in an electroactive polymer blend electrode for solid-state polymer batteries are discussed. The opportunities for using polymer blends for solid-state electrochemical polymeric devices, and avenues for the development of materials for such devices, are also reviewed.     

Structure of polymer within the coating: an atomic force microscopy and small angle neutrons scattering study

Synthetic latex is widely used as a binder in waterbased paints. Upon dehydration of the dispersion, latex particles are brought into contact with mineral pigments: this process results in coating structuration and consolidation. This composite layer is described as a porous mineral structure, whose pores are covered by latex particles. Therefore, it is of fundamental interest to study the ordering of binder particles in the coating, and the wetting of pigments by polymer particles, toward understanding properties of coating such as: optical properties, adhesion, cohesion, sensitivity to water, etc. In this regard, we have used small angle neutron scattering and atomic force microscopy to study the ordering, the spreading, and the adhesion of latex particles on calcium carbonate within the coating. We discuss the structure of the coating.     

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.     

Compatibilization and morphology development of immiscible ternary polymer blends

We report a novel and effective strategy that compatibilizes three immiscible polymers, polyolefins, styrene polymers, and engineering plastics, achieved by using a polyolefin-based multi-phase compatibilizer. Compatibilizing effect and morphology development are investigated in a model ternary immiscible polymer blends consisting of polypropylene (PP)/polystyrene(PS)/polyamide(PA6) and a multi-phase compatibilizer (PP-g-(MAH-co-St) as prepared by maleic anhydride (MAH) and styrene (St) dual monomers melt grafting PP. Scanning electron microscopy (SEM) results indicate that, as a multi-phase compatibilizer, PP-g-(MAH-co-St) shows effective compatibilization in the PP/PS/PA6 blends. The particle size of both PS and PA6 is greatly decreased due to the addition of multi-phase compatibilizer, while the interfacial adhesion in immiscible pairs is increased. This good compatibilizing effect is promising for developing a new, technologically attractive method for achieving compatibilization of immiscible multi-component polymer blends as well as for recycling and reusing of such blends. For phase morphology development, the morphology of PP/PS/PA6 (70/15/15) uncompatibilized blend reveals that the blend is constituted from PP matrix in which are dispersed composite droplets of PA6 core encapsulated by PS phase. Whereas, the compatibilized blend shows the three components strongly interact with each other, i.e. multi-phase compatibilizer has good compatibilization between the various immiscible pairs. For the 40/30/30 blend, the morphology changed from a three-phase co-continuous morphology (uncompatibilized) to the dispersed droplets of PA6 and PS in the PP matrix (compatibilized).     

Dielectric spectroscopy using dielectric probes: a new approach to study glass transition dynamics in immiscible apolar polymer blends

Dielectric relaxation spectroscopy using dielectric probes was applied to study the (glass transition) dynamics in binary blends of isotactic PP, PS and LDPE. The blends were prepared by melt-mixing and doped with 0.5% of the dielectric probe 4,4′-(N,N-dibutylamino)-(E)-nitrostilbene (DBANS) (van den Berg O, Sengers WGF, Jager WF, Picken SJ, Wübbenhorst M. Macromolecules 2004;37:2460. [17]). Due to the selective amplification of the dielectric relaxation processes related to the dynamic glass transition of the polymers, accurate relaxation data were obtained, even for the minor phases. No substantial influence of the blend composition and the blend morphology on the glass transition dynamics was found, indicating that both blend constituents behave like homogeneous bulk materials. The normalised relaxation strength of glass transition processes remained constant, regardless of the blend type and blend composition. This indicates that the probe molecule, DBANS, was equally distributed over the two blend components in all three polymer combinations PE-PP, PE-PS and PP-PS.     

Interface morphology snapshots of vertically segregated thin films of semiconducting polymer/polystyrene blends

We present atomic force microscopic images of the interphase morphology of vertically segregated thin films spin coated from two-component mixtures of poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) and polystyrene (PS). We investigate the mechanism leading to the formation of wetting layers and lateral structures during spin coating using different PS molecular weights, solvents and blend compositions. Spinodal decomposition competes with the formation of surface enrichment layers. The spinodal wavelength as a function of PS molecular weight follows a power-law similar to bulk-like spinodal decomposition. Our experimental results indicate that length scales of interface topographical features can be adjusted from the nanometer to micrometer range. The importance of controlled arrangement of semiconducting polymers in thin film geometries for organic optoelectronic device applications is discussed.     

Carbon black self-networking induced co-continuity of immiscible polymer blends

This work aims to clarify the mechanism of nanoparticle-induced co-continuity in immiscible polymer blends. An industrially relevant system, carbon black (CB)-filled acrylonitrile-butadiene-styrene (ABS)/polyamide 6 (PA6) blends, is investigated via scanning electron microscopy, selective extraction tests, dynamic mechanical analysis, and electrical conductivity measurements. The CB particles are found to be preferentially localized in the PA6 phase, and with an increase in CB loading (Φ_CB), the critical volume fraction of PA6 (Φ_PA6) that is essential for building the co-continuous structure decreases. The product of Φ_PA6 and Φ_CB, n, remains constant for the given system, suggesting that there exists an intrinsic cooperative effect between the CB and the CB-localized polymer phase. A further decrease in Φ_PA6 is achieved either by loading CB with a higher self-networking capability or by isothermal post-treatments for sufficient self-agglomeration of the CB clusters. It is demonstrated that, under the direction of CB self-networking, the CB-localized polymer domains tend to fuse together into co-continuous organization with little phase coarsening. Therefore, CB self-assembly not only plays a key role in extending phase co-continuity over a much larger composition range but also acts on stabilizing the co-continuous polymer domains during the melt processing.     

Single polymer chain rubber elasticity investigated by atomic force microscopy

A method, which is called as ‘nanofishing’, enabled us to stretch a single polymer chain adsorbed on an Au(111) substrate with picking it at its two thiol-modified termini using atomic force microscope equipped with a gold-coated probe. A force-extension curve obtained for a single polystyrene chain in a Θ solvent (cyclohexane) showed a good agreement with a so-called worm-like chain model, and thus gave microscopic information about entropic elasticity. Solvent effects on the statistical properties of single polymer chains were also investigated. For example, the second virial coefficient in cyclohexane was determined at a single polymer basis, which was almost comparable with a simple Flory's lattice model.     

Light emission in phase separated conjugated and non-conjugated polymer blends

Phase separations in conjugated polymer (MEH-PPV) and non-conjugated polymer (PMMA) blended films are studied by photoluminescent (PL) near-field scanning optical microscope and spectrometer. The morphologies of blended films changed from stripe patterns to isolated islands as PMMA concentrations increased. The PL spectra in isolated micron dots are the same as MEH-PPV. Nevertheless, we found new PL spectra, peaked at 500 nm wavelength, in the PMMA matrix. Since, PMMA does not emit light, the new spectra indicate some MEH-PPV diluted in the PMMA rich regions. The excitons of MEH-PPV in the PMMA matrix are localized and emit light as PPV oligomers.     

Phase morphology control of immiscible polymer blends under vibration force field

The formulas of polymer melt velocity, shearing rate, and shearing stress under vibration force field are established through simplifying coaxial cylinder circular flow into plane motional flow. On the basis of the concept of energy ratio model, the rate of energy dissipation and the energy ratio about blending systems are expressed, and the affected factors on phase morphology are studied theoretically. The calculated and analytical results of dynamic flow field and energy ratio show that with the increasing of vibration strength, the fluctuating shearing force field exerted on polymer melt and the negative pressure diffusion behavior of instantaneous impulse strengthen. The energy consumption for phase inversion of immiscible polymer blends under vibration force field is less than that of steady state. The parameter controllability of vibration force field provides a more effective method for realizing phase inversion of immiscible polymer blends. The analysis of transmission electron microcopy micrographs of ethylene–propylene–diene terpolymer/polypropylene blends verifies that the energy ratio model and its phase morphology controlling theory have a good coincidence in comparison with experimental results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2299–2307, 2006     

Miscibility and surface crystal morphology of blends containing poly(vinylidene fluoride) by atomic force microscopy

The miscibility and surface crystalline structure of blends containing poly(vinylidene fluoride) (PVDF) composed of and γ phases were investigated by atomic force microscopy (AFM) and differential scanning calorimeter (d.s.c.) measurements. It was found that the surface crystalline phase of PVDF and the degree of surface enrichment of a lower surface free energy component in a blend might strongly be affected by the magnitude of the intermolecular interaction, even though the blend is miscible. Also, the segmental interaction parameters was determined by combining the T_m depression of PVDF in a blend and the binary interaction model. According to the binary interaction model, the introduction of a carboxyl group for miscible [poly(methyl methacrylate)/PVDF] and [poly(vinyl acetate)/PVDF] blends decreased their miscibility.     

Efficiency of graft copolymers as compatibilizers for immiscible polymer blends

This work was aimed at studying the emulsification efficiency of graft copolymers and the effect of feeding mode on the emulsification efficiency using the emulsification curve approach. The blends were composed of polystyrene (PS) and polyamide 6 (PA6). PS was always the matrix and PA6 the dispersed phase. A series of graft copolymers of PS and PA6, denoted as PS-g-PA6, with different molecular structures were used as emulsifiers. Feeding mode had a very significant effect on the size of the dispersed phase domains at short mixing time and its effect decreased or became negligible at long mixing time. This indicates that feeding mode affected mostly the time necessary for the PS-g-PA6 emulsifier to reach and emulsify the PS/PA6 interfaces. The molecular structure of the PS-g-PA6 graft copolymer also had a profound effect on its emulsification efficiency. The longer the PA6 grafts (from 1.7 to 5.1 kg/mol), the higher the emulsification efficiency. On the other hand, the number of PA6 grafts had little effect on the emulsification efficiency when the PA6 grafts were short (1.6-1.7 kg/mol). The effect of the blend composition was also investigated.     

Highly efficient polymer blends from a polyfluorene derivative and PVK for LEDs

The photophysical and electroluminescent properties of blends of a polyfluorene derivative of the PPV type, poly[(9,9-dihexyl-9H-fluorene-2,7-diyl)-1,2-ethenediyl-1,4-phenylene-1,2-ethenediyl] (labeled as LaPPS16) and poly(vinylcarbazole) - PVK are presented and discussed in terms of the operating light emission mechanisms. Static and dynamic fluorescence measurements and morphology data showed a powerful exciton migration from the host (PVK) to the guest (LaPPS16) resulting in emission coming from solely LaPPS16, even when in concentrations small as 1%. Electroluminescence was greatly enhanced with the blending; increases of 18 times in efficiency and 20 times in luminance were achieved in the blend containing 20% LaPPS16, with 3 V applied voltage.     

Probing polymer interdiffusion in carboxylated latices with force modulation atomic force microscopy

Interdiffusion of polymer chains between latex particles is a prerequisite for the development of good mechanical strength and homogeneity in a latex film. This process may be retarded in carboxylated latices if the particles are surrounded by a hard cell wall consisting of ionic groups on the particle surface. The presence of an ionic cell wall can be indirectly detected by atomic force microscopy (AFM) because surfactant migration to the film/air interface is retarded compared with a non-ionic case. In this paper we have used force modulation atomic force microscopy to directly probe the relative polymer density across the film surface during annealing thereby qualitatively monitoring the interdiffusion process. The applicability of this method to study polymer interdiffusion will be discussed.     

Hydrogen-bonding in polymer blends

Hydrogen bonding in polymer blends is a topic of great interest to polymer scientists because such systems have many potential applications. Introducing functional groups to one component to make it capable of forming hydrogen bonds to another, thereby enhancing the miscibility of otherwise immiscible blends, is one of the major achievements during the past 20 years of polymer science. The Painter–Coleman association model generally describes these interactions accurately. This Review discusses in detail the effects of hydrogen bonding on the miscibility and thermal properties of polymer blend systems.     

Growth process of homogeneously and heterogeneously nucleated spherulites as observed by atomic force microscopy

A poly(bisphenol A octane ether) (BA-C8) was synthesized. The isothermal spherulitic growth process was studied in situ using atomic force microscopy (AFM) at room temperature. For spherulites formed by homogeneous nucleation, the growth process includes the birth of a primary nucleus, the development of a founding lamella and the growth of the founding lamella into a spherulite. An embryo below a critical size is unstable. A stable embryo grows into a founding lamella. There is only one founding lamella in each spherulite. All other lamellae originate from this founding lamella. Two eyes can be seen at the center of a spherulite. For spherulites formed through heterogeneous nucleation, many lamellae grow at the nucleus surface and propagate outward radially. The spherulites acquire spherical symmetry at the early stage of crystallization. No eyes are found for this kind of spherulites.     

A rheological model for polymer blends based on the concentric multilayer approach. I. Homogeneous polymer blends

The melt rheological behavior of polymer blends was investigated by means of a capillary rheometer. The systems chosen for study were blends of polystyrene (PS) with different molecular weights and blends of polymethylmethacrylate (PMMA) with different molecular weights. A modified concentric multilayer model was proposed to correlate the rheological properties of the polymer blends with the composition and shear rate. The agreement between the calculated values and the measured ones is satisfactory.     

Relaxation behavior of polymer blends with complex morphologies: Palierne emulsion model for uncompatibilized and compatibilized PP/PA6 blends

This paper deals with the dynamic rheological behavior of polypropylene/polyamide6 (PP/PA6) uncompatibilized blends and those compatibilized with a maleic anhydride grafted PP (PP/PP-g-MAH/PA6). The terminal relaxation times of the blends predicted by the Palierne emulsion model were compared with those obtained from experimental relaxation time spectra. The Palierne model succeeded well in describing PP/PA6 uncompatibilized blends with relatively low dispersed phase contents (10 wt%) and failed doing so for those of which the dispersed contents were high (30 wt%). It also failed for the compatibilized ones, irrespective of the dispersed phase content (10 or 30 wt%) and whether or not interface relaxation was taken into consideration. In the case of the uncompatibilized blend with high dispersed-phase content, interconnections among inclusions of the dispersed phase were responsible for the failure of the Palierne model. As for the compatiblized blends, in addition to particle interconnections, the existence of emulsion-in-emulsion (EE) structures was another factor responsible for the failure of Palierne model. A methodology was developed to use Palierne emulsion model upon taking into account the effects of the EE structure on the viscosity of the continuous phase and the effective volume fraction of the dispersed phase.