Polymer Blend Films Research Articles

Microporous phase-separated films of polymer blends for enhanced outcoupling of light from OLEDs

Thin microporous films were formed by dropcasting a toluene solution containing various ratios of polystyrene:polyethylene glycol blends on a glass substrate, with OLEDs on the ITO that coated the opposite side of that substrate. We demonstrate for the first time that such easily-fabricated films with surface and bulk micropores in the index-matching polystyrene can serve as random microlens-like arrays to improve forward OLED light extraction by up to ~60%. A theoretical interpretation of the angular emission profile of the device, considering the geometrical change at the substrate/air interface and the scattering by the pores within the films, was established in excellent agreement with the experiments. The use of such blended thin films provides an economical method, independent of the OLED fabrication technique, for improving the outcoupling efficiency.

Strength and deformation characteristics of polymer blend films obtained from water systems

The relationship between the tensile strength and deformation characteristics, composition, and structural organization of films obtained by casting of two-component water-based system blends — a solution of the rigid partly crystalline polymer polyvinyl alcohol (PVA) and an emulsion of the compliant amorphous polymer polyvinyl acetate (PVAc) — has been investigated. The aim of this investigation was to ascertain the possibility of obtaining film materials with increased deformability based on the biodegradable PVA. The composition dependences of the initial modulus of elasticity, the maximum stress, yield stress, the ultimate strength, the ultimate strain, and of the unit work of fracture and other characteristics of films have been analyzed. An analysis of the tensile true stress–strain curves of systems with volume fractions of PVA less than 0.5 points to their considerable orientation strengthening upon tension.

Surface Morphology and Properties of Poly(γ-benzyl L-glutamate)/Poly(butyl acrylate-co-methyl Methacrylate) Blend Film

Poly(γ-benzyl L-glutamate)/poly(butyl acrylate-co-methyl methacrylate) (PBLG/Poly(BA-co-MMA)) blend films were prepared by casting the polymer blend solution in dichloroethane. Surface morphology of the polymer blend film was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Thermal and mechanical properties of the polymer blend film were studied using differential scanning calorimeter (DSC) and tensile tests. It was revealed that the introduction of Poly(BA-co-MMA) into PBLG could exert marked effects on the surface morphology and the properties of the PBLG film.

Mechanical behavior and wrinkling patterns of phase-separated binary polymer blend film

The wrinkling of phase-separated binary polymer blend film was studied through combining the Monte Carlo (MC) simulation for morphologies with the lattice spring model (LSM) for mechanical properties. The information of morphology and structure obtained by use of MC simulation is input to the LSM composed of a three-dimensional network of springs, which allows us to determine the wrinkling and the mechanical properties of polymer blend film, such as strain, stress, and Young’s modulus. The simulated results show that the wrinkling of phase-separated binary polymer blend film is related not only to the structure of morphology, but also to the disparity in elastic moduli between polymers of blend. Our simulation results provide fundamental insight into the relationship between morphology, wrinkling, and mechanical properties for phase-separated polymer blend films and can yield guidelines for formulating blends with the desired mechanical behavior. The wrinkling results also reveal that the stretching of the phase-separated film can form the micro-template, which has a wide application prospect.

Simulation of Morphologies and Mechanical Properties of A/B Polymer Blend Film

The effects of blend composition and micro-phase structure on the mechanical behavior of A/B polymer blend film are studied by coupling the Monte Carlo (MC) simulation of morphology with the lattice spring model (LSM) of micro mechanics of materials. The MC method with bond length fluctuation and cavity diffusion algorithm on cubic lattice is adopted to simulate the micro-phase structure of A/B polymer blend. The information of morphology and structure is then inputted to the LSM composed of a three-dimensional network of springs to obtain the mechanical properties of polymer blend film. Simulated results show that the mechanical response is mainly affected by the density and the composition of polymer blend film through the morphology transition. When a force is applied on the outer boundary of polymer blend film, the vicinity of the inner cavities experiences higher stresses and strains responsible for the onset of crack propagation and the premature failure of the entire system.

Green light-emitting diodes based on a hybrid TiO2 nanoparticle-conducting polymer blend

The energy transfer in a blend of conducting polymers, poly[9-vinylcarbarzole] (PVK) and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), was investigated. Energy transfer from PVK to MEH-PPV leads to enhanced emission of MEH-PPV. Photoluminescence (PL) of the nanocomposite of TiO 2 and the blended polymer films was enhanced as the relative content of TiO 2 was increased, and, in particular, the most improved PL was observed for the optimal ratio of TiO 2 and these films emitted green light. These results provide further insight into the photophysics of conjugated polymers and the improvement of the current–voltage (I–V) characteristics of the devices based on blended conducting polymer systems.

Continuous Production of Functionalized Polymer Particles Employing the Phase Separation in Polymer Blend Films

This study reports a continuous prepartion of spherical or hemispherical polymer particles simply utilizing the phase separation in polymer blend films during the coating process. We took an advantage of the strong phase separation between a water-soluble crystalline polymer as a matrix and hydrophobic polymers as minor components. We demonstrated the prepartion of water-soluble polystyrene (PS) particles, nitrilotriacetic acid (NTA)-functionalized PS particles for protein separation, and semiconducting poly(3-hexylthiophene) (P3HT) particles. The sizes of the particles could be controlled by adjusting the film thickness and weight fraction of the minor component polymers in the blend film. It provides a simple facile way to prepare polymer particles in a continous process.

Photovoltaic properties of benzimidazole-derived perylene imides as an n-type material

Perylene imide derivatives were considered as an n-type material for a bulk-heterojunction solar cell. A perylene was modified to imide–imidazole derivatives comprised of a benzimidazole moiety with several polar substituents and a long alkyl chain for favorable electronic energy levels and solubility. The electron mobility of methoxy-derived imide–imidazole was measured to be 4.0 × 10 − 3 cm/V s under an electric field of 320 V/cm, being nearly comparable to the hole mobility of poly(3-hexylthiophene) (P3HT). The hole and electron mobilities of a blend film made of P3HT and the methoxy derivative were closely balanced at ca. 3 × 10 − 4 cm/V s. The power conversion efficiency of a photovoltaic cell using the blend film was improved with the increase in perylene content and reached 0.20%. The methoxy substitution at the imid–imidazole resulted in better power conversion efficiency than unsubstitution. On the contrary, an alkyl ester substitution provided a low conversion efficiency of less than 0.01% due to a small current from severe crystallization in a polymer blend film.

Electrochemical and TOF-SIMS investigations of PPy/PEG-modified LiFePO 4 composite electrodes for Li-ion batteries

The role of polyethylene glycol (PEG) in mixed polypyrrole (PPy) polymer blend for new cathode material used in Li-ion battery has been studied. The films of PPy containing PEG were prepared by chemical oxidative polymerization of pyrrole (Py) monomer. PEG has been applied as an additive during polymerization process to improve mechanical and structural properties of PPy in final PPy/PEG–LiFePO 4 cathode material aiming also better electronic conductivity. The electrochemical behavior of the samples was examined by galvanostatic charge/discharge technique and cyclic voltammetry (CV). It was found that PPy/PEG blend polymer decreases the contact resistance and improves the Li + intercalation/deintercalation during cycling. Charge/discharge measurements confirmed the increase in capacity when applying PEG in PPy. Time of flight secondary ion mass spectrometry (TOF-SIMS) analysis confirmed supporting effect of PEG in PPy predominantly for mixed polymer mechanical stability (important at charging cycles). Distribution of PPy, PEG and Li + fragments within blended polymer films were monitored by measuring the intensities of different secondary ions, applying SIMS.

White-light-emitting diodes using miscible polymer blend doped with phosphorescent dye

We demonstrate that voltage-independent and highly efficient white light-emitting diodes (WLED) can be obtained based on phosphorescent dye-doped conjugated polymer blend films. Conjugated polymers are used as the blue and green emitters, as well as the energy host, and a phosphorescent dye is used as the red emitter and guest material. The phase-separation between the conjugated polymers is suppressed by blending miscible polymer and copolymer having the same moiety. Therefore, we expect that efficient Förster-type energy transfer occurs through this homogeneous morphology. By introducing the copolymer into the emissive layer to enhance its miscibility, we obtained a voltage-invariant white emission from the polymeric LEDs. The luminous efficiency of the WLED with the single active layer is increased dramatically by introducing the phosphorescent dopant as a red emitter.

Influence of Film Thickness on the Phase Separation Mechanism in Ultrathin Conducting Polymer Blend Films

The film morphology of thin polymer blend films based on poly[(1-methoxy)-4-(2-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) and poly(N-vinylcarbazole) (PVK) is probed as a function of film thickness. Blend films are prepared with spin-coating of polymer solutions with different concentrations on top of solid supports. The blending ratio of both conducting polymers is kept constant. The film and surface morphology is probed with grazing incidence ultrasmall-angle X-ray scattering (GIUSAXS) and atomic force microscopy (AFM). A linear dependence between the film thickness and the averaged phase separation is found. In addition, X-ray reflectivity measurements show an enrichment of PVK at the substrate interface. UV/vis spectroscopy measurements indicate a linearly increasing amount of both homopolymers in the blend films for increasing film thicknesses. The generalized knowledge about the influence of the film thickness on the phase separation behavior in conducting polymer blend films is finally used to describe the phase separation formation during the spin-coating process, and the results are discussed in the framework of an adapted Flory-Huggins theory for rodlike polymers.

Domain Coalescence-Induced Nucleation and Anomalous Growth of Holes in Thin Polymer Blend Film

The phase evolution of a thin polymer blend film of polystyrene (PS) and poly(2-vinyl pyridine) (P2VP) triggered by solvent annealing is examined at both the bulk and single-(macro)molecule levels using wide-field microscopy (WFM). The transitions between different evolutionary stages in the nucleation and growth process are clearly visualized in real time and without intermittent breaks. The nucleation of PS holes arises from the coalescence and growth of P2VP domains and the holes expand in a complex manner involving the dewetting of PS and the absorption of P2VP domains into the holes.

Evaluation of two polymeric blends (EVA/PLA and EVA/PEG) as coating film materials for paclitaxel-eluting stent application

The ethylene vinyl acetate copolymer (EVA)/Poly (lactic acid) (PLA) blend and EVA/Poly (ethylene glycol) (PEG) blend were applied as the drug carrier materials for a bi-layer drug-loaded stent coating film, which consisted of a paclitaxel (PTX)-loaded layer and a drug-free EVA layer. The changes of weight and appearance of the drug-free polymeric blend films with increasing time were examined by X-ray diffraction analysis (XRD), gel permeation chromatography (GPC) tests and scanning electronic microscopy (SEM), and the results showed the degradation of PLA and the leaching of PEG from the films. The effects of PLA, PEG and drug contents on in vitro drug release were investigated, and the results demonstrated that the addition of PLA promoted the drug release while the addition of PEG almost did not. Franz cells diffusion test results indicated that the bi-layer structure successfully endowed the stent coating with the release of drug in a unidirectional fashion. The release profiles of films incorporated PTX and the mechanical performance of the film could be customized by readily adjusting the contents of the blend components. Therefore, the polymeric blends could be useful drug carrier materials for drug-loaded stent coating capable of releasing drug in a highly tunable manner.

Preparation, characterization and antibacterial properties of cyanoethylchitosan/cellulose acetate polymer blended films

Modification of chitosan (CS) by means of blending with other polymers is a convenient method to improve its physical properties for practical utilization. The similarity of cellulose and chitosan in primary structures might facilitate the formation of homogeneous films. Mixing cyanoethylchitosan (CECS) with cellulose acetate (CA) overcomes mechanical weakness of CS films. CECS is prepared by reaction of chitosan with acrylonitrile in the vapour phase under a different reaction conditions, namely, sodium hydroxide concentration and reaction period. Blended films of CECS and CA are made by casting from dimethylformamide (DMF) followed by impregnation in water. CECS/CA films obtained are characterized by nitrogen content, tensile strength, elongation at break, FTIR and thermogravimetric analysis (TGA). Antibacterial activity of films prepared against Gram (−ve) and Gram (+ve) bacteria is measured via both disk diffusion method and bacterial count method. Blended films show good antibacterial effects toward Gram (+ve) bacteria than Gram (−ve) ones. Antibacterial activities of blended films increased by increasing the CECS percent in the blended films while the tenacity of these films gradually decreased. Minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) show that CECS possesses higher effect on Gram (+ve) bacteria Staphylococcus aureus than Gram (−ve) bacteria Escherichia coli. In the meantime, CECS is much more powerful in inhibition of bacteria than CS itself.

Thin films of polymer blends deposited by matrix-assisted pulsed laser evaporation: Effects of blending ratios

In this work, we show successful use of matrix-assisted pulsed laser evaporation (MAPLE) for obtaining thin films of PEG:PLGA blends, in the view of their use for controlled drug delivery. In particular, we investigate the influence of the blending ratios on the characteristics of the films. We show that the roughness of the polymeric films is affected by the ratio of each polymer within the blend. In addition, we perform Fourier transformed infrared spectroscopy (FTIR) measurements and we find that the intensities ratios of the infrared absorption bands of the two polymers are consistent with the blending ratios. Finally, we assess the optical constants of the polymeric films by spectroscopic ellipsometry (SE). We point out that the blending ratios exert an influence on the optical characteristics of the films and we validate the SE results by atomic force microscopy and UV–vis spectrophotometry. In all, we stress that the ratios in which the two polymers are blended have significant impact on the morphology, chemical structure and optical characteristics of the polymeric films deposited by MAPLE.

Quantitative evaluation of evaporation rate during spin-coating of polymer blend films: Control of film structure through defined-atmosphere solvent-casting

Thin films of polymer mixtures made by spin-coating can phase separate in two ways: by forming lateral domains, or by separating into distinct layers. The latter situation (self-stratification or vertical phase separation) could be advantageous in a number of practical applications, such as polymer optoelectronics. We demonstrate that, by controlling the evaporation rate during the spin-coating process, we can obtain either self-stratification or lateral phase separation in the same system, and we relate this to a previously hypothesised mechanism for phase separation during spin-coating in thin films, according to which a transient wetting layer breaks up due to a Marangoni-type instability driven by a concentration gradient of solvent within the drying film. Our results show that rapid evaporation leads to a laterally phase-separated structure, while reducing the evaporation rate suppresses the interfacial instability and leads to a self-stratified final film.

Self-Assembled Stratified Structure in Polyalkylthiophene-6 and Polyvinylcarbazole Blend Film

Layered films of polyalkylthiophene-6 (PAT-6) and polyvinylcarbazole (PVK) which are expected to be a photo-electronic device were fabricated from blend solution by self-assembly at only one casting process. Cross-section structure of the blend polymer films were observed by digital microscope and analyzed by using Energy Dispersive Spectroscopy (EDS) and FT-IR spectrometer. Stratified structure with component distribution along thickness direction was found to be self-assembly at the suitable casting condition. It was considered that the structure was controlled by the evaporation speed of solvent and properties of the solubility parameter and density of the polymer.

Probing nanotribological and electrical properties of organic molecular films with atomic force microscopy

Structural aspects of organic molecular films, such as disordering, packing density, molecular bending or tilts, and phase separation, influence electrical properties as well as friction and adhesion. This indicates a correlation between nanomechanical and charge transport properties of molecular films at the molecular scale. In this review, we highlight the recent studies on correlations between charge transport and nanomechanical properties probed with atomic force microscopy. We discuss the key issues that determine charge transport and nanomechanical properties on several organic molecular films, including self-assembled monolayers formed by saturated hydrocarbon molecules conjugated molecules, and hybrid molecules as well as polymer and polymer blend films. We address the role of molecular deformation and bending in friction and conductance measurements.

Time-resolved opto-electronic properties of poly(3-hexylthiophene-2,5-diyl): Fullerene heterostructures detected by Kelvin force microscopy

Thin blend polymer films made of poly(3-hexylthiophene-2,5-diyl) (electron donor) and fullerene derivatives as electron acceptors ([6,6]-thienylC61 butyric acid methyl ester and [6,6]-thienylC71 butyric acid methyl ester) are prepared by the spin-coating technique on indium tin oxide covered glass substrates. Time-resolved photo-induced changes of surface potentials are detected by Kelvin force microscopy (KFM). Changes of surface potentials by 10–150 mV reveal different quality and kinetics of charge generation in the two blends in short (minutes) and long (hours) time periods. This is attributed to a combination of electron accumulation, trapping, and organic material degradation under ambient conditions. As KFM characterizes the blend films directly without metal contact layer, it reveals differences in the opto-electronic behavior of the blends, which are not detected by common photovoltaic cell characterization.

Topographically Uniform but Chemically Heterogeneous Nanostructures by Nanoimprinting Demixed Polymer Blends

Nanoimprint lithography is applied to fabricate topographically uniform patterns onto demixed polymer blend films. The high fidelity of pattern replications is achieved for 150 nm polystyrene (PS)/polymethylmethacrylate (PMMA) blend films with varying compositions. When imprinted at 150 °C, the morphology of the blend across the patterned structures is similar to that in the as-casted films. Significant morphological evolutions occur for patterns imprinted at 180 and 210 °C. For all the patterns, PMMA is found to segregate into the residual layer, driven by the preferential wetting of PMMA onto the SiO(x) surfaces. The combined domain coarsening and preferential wetting of PMMA leads to the formations of unique encapsulated structures within the topographically uniform features, ranging from blocks to threads.