Blend Thin Films Research Articles

Phase separation morphology of thin films of polystyrene/polyisoprene blends

We present the results of a study of the morphology of phase separation in a thin film blend of polystyrene (PS) and polyisoprene (PI) in a common solvent of toluene. The blend is quenched by rapid solvent evaporation using a spincoating technique rather than a temperature quench. The mass fraction of polystyrene is varied to determine the effect of the substrate on thin film phase separation morphology. We compare the phase separation morphology for very thin films of the PS/PI blend cast onto three different substrates: Si(001) with a native oxide layer (Si (SINGLEBOND) SiOx), Si(001) etched in hydrofluoric acid (Si-H), and a Au/Pd alloy sputtered onto Si(001). We observe large differences between the morphologies of 1000 A thick blend films on the Si(SINGLEBOND) SiOx and Si-H substrates as the mass fraction is varied due to the difference in the wetting properties of PS on the two substrates. Smaller differences are observed between the films on the Si(SINGLEBOND) SiOx and Au/Pd substrates only for film thicknesses h < 600 A. © 1996 John Wiley & Sons, Inc.

Analysis of the phase transition of polymer blends using quartz crystal analyser

In this communication we show that an AT-cut quartz crystal analyser (QCA) can be applied to the investigation of the phase transition of polymer blend thin films. The phase transition phenomena of blend films of poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) have been elucidated by simultaneous measurement of the resonant frequency and resonant admittance of the QCA. The PMMA/PVAc blend cast from ethyl acetate exhibited critical changes of resonant frequency and resonant admittance at the glass transition point.

Polymer Light-Emitting Electrochemical Cells: In Situ Formation of a Light-Emitting p−n Junction

Solid-state polymer light-emitting electrochemical cells have been fabricated using thin films of blends of poly(1,4-phenylenevinylene) and poly(ethylene oxide) complexed with lithium trifluoromethanesulfonate. The cells contain three layers: the polymer film (as the emissive layer) and indium-tin oxide and aluminum films as the two contact electrodes. When externally biased, the conjugated polymers are p-doped and n-doped on opposite sides of the polymer layer, and a light-emitting p-n junction is formed in between. The admixed polymer electrolyte provides the counterions and the ionic conductivity necessary for doping. The p-n junction is dynamic and reversible, with an internal built-in potential close to the band gap of the redox-active conjugated polymer (2.4 eV for PPV). Green light emitted from the p-n junction was observed with a turn-on voltage of about 2.4 V. The devices reached 8 cd/m(2) at 3 V and 100 cd/m(2) at 4 V, with an external quantum efficiency of 0.3-0.4% photons/electron. The response speed of these cells was around 1 s, depending on the diffusion of ions. Once the light-emitting junction had been formed, the subsequent operation had fast response (microsecond scale or faster) and was no longer diffusion-controlled.

Analysis of the Phase Change Phenomena of PMMA and PVAC Blends Using Quartz Crystal Analyzer(Q.C.A.)

Abstract This paper shows that an AT-cut quartz crystal analyzer can be applied to the phase change study of polymer blend thin films. The phase trasition and phase separation phenomena of blend films of poly (methyl methacrylate) (PMMA) and poly (vinyl acetate) (PVAc) cast from ethyl acetate have been investigated by quartz crystal analyzer(Q.C.A.). The resonant frequency and resonant admittance are measured simultaneously and the mass change and viscoelastic change of the polymer blend thin films are analyzed.

Surface Composition of Amorphous and Crystallizable Polyethylene Blends As Measured by Static SIMS

The surface composition of several thin-film semicrystalline polyolefin blends is quantified using secondary ion mass spectroscopy (SIMS). These experiments indicate that the component having the l...

Experimental study of surface segregation and wetting in films of a partially miscible polymer blend.

We have studied composition-depth profiles in thin films of blends of deuterated polystyrene and poly(\ensuremath{\alpha}-methyl styrene) using neutron reflectometry and $^{3}\mathrm{He}$ nuclear reaction analysis. Some of the neutron reflectometry data are analyzed using a maximum entropy technique with Bayesian probability. One blend is miscible for all compositions at the temperature studied (180 \ifmmode^\circ\else\textdegree\fi{}C), and we are able to obtain a bare surface energy difference between the two polymers from the equilibrium surface profile. The other blend that is studied is partially miscible, and here we have compared the approach to wetting in this blend with a simple model based on mean field theory. For quenches deeper into the metastable region of the phase diagram, the simple model fails due to, we believe, a competition between wetting and bulk nucleation and growth. \textcopyright{} 1996 The American Physical Society.

Surface Modification via Chain End Segregation in Polymer Blends

We have explored the use of chain end segregation as a means of controlling the properties of a polymer surface. Thin film blends of homopolystyrene (PS) and PS synthesized with low-energy oligotetrafluoroethylene chain ends (PS-TFE) were studied using neutron reflectivity. The fraction of PS-TFE that localizes near the surface was found to increase as a function of its concentration in the blend. Contact angle measurements indicate corresponding reductions in the surface tension due to the surface localization of the TFE chain ends. For a 10% blend of 6000 mol wt PS-TFE in 3 × 105 mol wt PS, the surface coverage of fluorocarbon ends was found to be >20%. A free energy model of the blends gives good qualitative agreement with the experimental results.

The morphology of blends of ethylcellulose with hydroxypropyl methylcellulose as used in film coating

Near-equilibrium morphologies of thin films (< 0.2 μm) of ethylcellulose-rich incompatible blends of ethylcellulose (EC) with hydroxypropyl methylcellulose (HPMC) consist of HPMC-rich macroscopic polydisperse domains (3-approx. 20 μm) dispersed in an EC-rich matrix implying complete leaching of the water soluble phase. However, for thick films (> 100 μm) complete leaching was observed only for systems with above 60% w/w HPMC, whereas all other systems showed some HPMC retention. The observed HPMC leaching behaviour is attributed to deviations of the phase decomposition from equilibrium during film formation arising from the rate of viscosity increase and changes in the solvent system composition.

The role of social protection of young mothers in prevention of perinatal pathology

The local glass transition temperature (Tg) of heterogeneous polymer surfaces has been successfully determined by lateral force microscopy (LFM) on the submicron–nanometer scale. This paper addresses interfacial confinement effects in thin films of blends and emulsions from polystyrene (PS), poly(butylmethacrylate) (PBMA) and poly(methylmethacrylate) (PMMA). The paper addresses the difficulty of thermal rheological experiments with a microscopic scanning technique, and introduces an in-situ calibration method.

Outcome of pregnancy in villagers exposed to production-ecologic factors

The local glass transition temperature (Tg) of heterogeneous polymer surfaces has been successfully determined by lateral force microscopy (LFM) on the submicron–nanometer scale. This paper addresses interfacial confinement effects in thin films of blends and emulsions from polystyrene (PS), poly(butylmethacrylate) (PBMA) and poly(methylmethacrylate) (PMMA). The paper addresses the difficulty of thermal rheological experiments with a microscopic scanning technique, and introduces an in-situ calibration method.

Mechanism of DNP-enhanced polarization transfer across the interface of polycarbonate/polystyrene heterogeneous blends

Abstract : The same integrated intensity is observed for the interface-PC signal in PC(13C)/PS(12C/*) and PC(13C)/PS(2D/*) thin film blends in a DNP-difference experiment. This result proves that the dominant mechanism of polarization transfer from the electrons in the PS phase to the protons in the PC phase is by direct polarization transfer. The interface-PC signal intensity arises from a 60-A region which is 2% of the PC film thickness. Minor polarization transfer from the DNP-enhanced protons of PS to the PC protons across the PC/PS interface via H-H spin diffusion in PC(13C)/PS(12C/*) may also occur. Even in BDPA-doped homopolymers, the enhancement mechanism is mainly via direct solid-effect polarization transfer, a conclusion based on the similarity of the time dependence of the electron-proton polarization transfers for PS(*) and PS(2D/*).

Spinodal decomposition in thin films of a polymer blend.

Spinodal decomposition in thin films of a blend of deuterated polystyrene and poly(styrene-co-4-bromostyrene) was studied with time-of-flight--elastic-recoil detection and light microscopy. We found different demixing behavior, depending on whether the films were prepared on the oxide layer of a silicon wafer or on a chromium-plated one. On the latter surface a bilayer of the two bulk phases is formed, whereas on the oxide layer a domain structure remains. The formation of the bilayer is ascribed to the complete wetting of each surface by the corresponding, preferentially adsorbed component.

Studies of surface and interface segregation in polymer blends by secondary ion mass spectrometry

Dynamic secondary ion mass spectrometry (SIMS) has recently been employed to obtain high resolution depth profiles in polymer blend thin films and is now regarded as a key probe of surface and interfacial segregation in these systems. Segregation phenomena strongly impact blend properties such as adhesion, friction and weatherability. The strengths and limitations of the SIMS polymer profiling technique are described and contrasted with the complementary techniques of forward recoil elastic scattering (FRES) and neutron reflectivity (NR). The procedures developed for sample preparation and data acquisition are discussed. Experimental results for the effect of incident O2 + energy and angle on depth resolution and sputtering rate in polystyrene (PS) are presented. Ongoing SIMS studies of model blend systems are described: Segregation from dPS (deuterated)/PS blends to vacuum and Si interfaces is examined as a function of the molecular weight of the blend components and preparation of the Si substrate, reve...

Degradation of polymer blends: Part V—Compatibility and photo-oxidation of LDPE-LLDPE blends in natural weathering conditions: A differential scanning calorimetry study

Thin films of extruded-blown LDPE-LLDPE blends have been photo-oxidized in natural weathering conditions in the absence and in the presence of a photo-initiator. DSC has been used to study the compatibility of the components of the blend and the changes of morphology induced by the degradation processes. Changes in the shape of the curves, increase in the heat of fusion and shift of T max have been observed and attributed to a reorganization of the oriented amorphous-crystalline structure due to physical ageing and to the decrease of molecular weight and branching.

A microstructural study of polystyrene—polyether sulphone polymer blends

AbstractPolystyrene (PS)‐polyether sulphone (PES) polymer blend thin films were prepared for investigation in a scanning transmission electron microscope. The microstructures of PS‐PES films (prepared by drawing from solutions at temperatures above ambient) of three different compositions were characterized: (1) 75 wt% PS‐25 wt% PES, (2) 50 wt% PS‐50 wt% PES, and (3) 25 wt% PS‐75 wt% PES. For films prepared at ∼ 40°C all three compositions exhibited microstructures consisting of spherical inclusions, ranging from ∼0.2μm to ∼ 1.2μm in diameter. The microscope used here was equipped with an energy‐dispersive X‐ray spectrometer, and this was employed to determine the chemical content of the inclusions and the matrix material. From X‐ray analysis, it was found that films (1) and (2) consisted entirely of PES‐rich inclusions, while film (3) contained both PS‐rich and PES‐rich inclusions. In addition, these analyses revealed that films (2) and (3) possessed a ‘mixed’ PS‐PES matrix phase. At the other temperatures for film preparation some significant differences in morphology were observed, reflecting the different rates of solvent evaporation.

Complexities in STEM analyses of polymer blend thin films

Polystyrene (PS)-polyether sulphone (PES) polymer blend thin films were prepared for examination in a scanning transmission electron microscope. The microstructures observed in 75 wt % PS-25 wt % PES films consisted of spherical inclusions, ranging from ≈0.2 to ≈1.2μm in diameter. X-ray spectrometric analysis in the microscope revealed that the inclusions were PES-rich, while the matrix contained only PS. Attention in this paper is paid to the contrast in the annular dark-field detector (ADF) images from these thin films. This image contrast has a complicated dependence on both the angular range subtended by the dark-field detector and “mass-thickness” variations within the films. On microscopes with appropriate lens controls which permit the acceptance angle of the ADF detector to be varied, it becomes possible actually to reverse the contrast between the two phases.

Stem Observations of the Microstructures Present in Polymer Blend Thin Films.

AbstractThis paper examines the effectiveness of scanning transmission electron microscopy (STEM) as an analytical tool for determining composition in multi-phase polymer blend microstructures. The polymer blend polystyrene (PS) - polyether sulphone (PES) thin film used in this study exhibited a two-phase microstructure consisting of PES-rich inclusions, ranging from 0.2μm to 1.2μm in diameter, in a PS-rich matrix. Emphasis in this presentation is placed on the use of annular dark-field (ADF) STEM image contrast to infer information concerning the local composition of adjacent microstructural features.

Morphology, crystallization and thermal behaviour of poly(ethylene oxide)/poly(vinyl acetate) blends

AbstractBlends of poly(ethylene oxide) (PEO) and poly(vinyl acetate) (PVAc) show a unique value of the glass transition temperature, intermediate between that of plain polymers. The addition of PVAc to PEO causes a depression in both the spherulite growth rate (G) and the overall kinetic rate constant (Kn). Such depression is larger at higher undercooling and, at a given crystallization temperature, it increases with the content of PVAc. The experimental G and Kn data were analyzed by means of latest kinetic theories in order to determine the influence of composition on the process of surface secondary nucleation. The melt behaviour of PEO/PVAc blends cannot be explained only in terms of diluent effects due to the compatibility of the components in the melt. Especially, at lower undercooling it is likely that annealing and morphological effects must also be taken into account. The morphology of thin films of blends, isothermally crystallized from melt, suggests that an amorphous mixed phase (PEO + PVAc) is formed in interlamellar regions. It was found that plain PEO crystals grow according to a regime I process of surface secondary nucleation while in the case of blends the crystals of PEO grow via regime II mechanism.

Tensile properties and morphology of blends of polyethylene and polypropylene

AbstractThe tensile behavior of blends of linear polyethylene (PE) and isotactic polypropylene (PP) was examined in relation to their morphology. Yield stress increases monotonically with increasing PP content, while true ultimate strength is much lower in all blends than in the pure polymers as a result of early fracture. The blends fail at low elongation because of their two‐phase structure, consisting of interpenetrating networks or of islands of PE in a PP matrix, as shown by scanning electron microscopy of fracture surfaces and transmission electron microscopy of thin films. While spherulites in PP are very large (∼100 μm in diameter), addition of 10% or more of PE drastically reduces their average size. This, together with the profusion of intercrystalline links introduced by PE, may be associated with maximization of tensile modulus in blends containing ∼80% PP. Introduction of special nucleating agents to PP reduces average spherulite size and is accompanied by slight improvements in modulus. Thin films of blends strained in the electron microscope neck and fibrillate in their PE regions, but fracture cleanly with little fibrillation in areas of PP.