Polymer electrolytes based on poly(vinylidene fluoride-co-hexafluoropropylene) with crosslinked poly(ethylene glycol) for lithium batteries

The combination of a poly(ethylene glycol) (PEG) network and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) copolymer chains is one of the most efficient means for modifying PVDF-HFP gel electrolytes. Previous preparations tend to introduce contamination into the polymer gel electrolyte because of irradiation, high temperature or the initiator needed for crosslinking which might result in the electrochemical degradation. In order to overcome the above disadvantages, a new method has been developed to successfully prepare the semi-interpenetrating polymer networks of PVDF-HFP based electrolytes with crosslinked diepoxy polyethylene glycol (DIEPEG). In this process, impurities are avoided because of a moderate reaction temperature at 50 °C and poly(ethylenimine) (PEI) as the crosslinking agent. Microporous films with various compositions are prepared and characterized. Thermal, mechanical, swelling and electrochemical properties, as well as microstructures of the prepared polymer electrolytes have been investigated using thermogravimetric analysis, electrochemical impedance spectroscopy, linear sweep voltammetry, and scanning electron microscopy. The results show that the blend polymer electrolyte with PVDF-HFP/PEI + DIEPEG (60:40 w/w) has an ionic conductivity of 2.3 mS cm^? 1 at room temperature in the presence of 1 M LiPF₆ in EC and DMC (1:1 w/w). All the blend electrolytes are electrochemically stable up to 4.8 V versus Li/Li⁺. The results reveal that this new method may be very promising for improving PVDF-HFP based electrolytes.     

Synthesis of modified multi-walled carbon nanotube poly(benzimidazole-imide) composites: assessment of morphological and thermo-mechanical properties

A fully aromatic poly(benzimidazole-imide) (PBI) containing triazole side units and amine-modified multi-wall carbon nanotube (MWCNT)/PBI composites were fabricated via a polymerization process of monomer reactants and solution mixing with ultrasonication excitation. The polymer and composites were characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. According to the microscopic characterizations, the MWCNTs homogeneously dispersed in the composites. The mechanical properties of the composite films were also measured by tensile test. The test results evidently indicated that the Young’s modulus increased by about 60.0% at 1 wt% CNT loading, and further modulus growth was observed at higher filler loading. The composite films hold preferable thermal stability the same as the pure PBI. The improvement of the mechanical and thermal properties was attributed to the incorporation of the surface modified CNTs. For CNT-reinforced polymer composites, strong interfacial adhesion and uniform dispersion of CNTs are more crucial factors for improving such properties.     

Preparation and properties of crosslinked hybrid proton exchange membrane based on sulfonated poly (arylene ether nitrile) with improved selectivity for fuel cell application

Novel sulfonated poly (arylene ether nitrile) with pendant carboxylic group copolymers have been prepared as proton exchange membranes which were applied in direct methanol fuel cells (DMFCs). Compared with others, this work shows two main advantages: the crosslinked method is uncomplicated and the membranes were prepared via the hydroquinonesulfonic acid potassium salt (SHQ) as crosslinker mingled in sulfonated poly (arylene ether nitrile) (SPEN) to avoid the decrease of proton conductivity. The obtained crosslinked membranes exhibited improved dimensional stability; larger tensile strength than that of pure SPEN; and good thermal, mechanical properties. Furthermore, after crosslinking, the membranes had low methanol permeability values (0.78–3.4 × 10^?7 cm² s^?1) and displayed good proton conductivities in the range of 0.0328–0.0385 S·cm^?1 at room temperature. The sample of SPEN-SHQ-5 % showed highest selectivity value of 4.205 × 10⁵ S·s cm^?3, which was 11.9 times higher than that of Nafion 117. All of these results indicated that these membranes would be the potential candidates as proton exchange membranes (PEMs) in DMFCs.     

Phase Structure of Polyamide 6/Poly(styrene-co-acrylonitrile) and Poly(styrene-b-(ethylene-co-butylene)-b-styrene) or Poly(maleated Styrene/Ethylene-co-Butylene/Styrene) Ternary Blends

Two sets of ternary blends; polyamide 6/poly(styrene-co-acrylonitrile)/poly(styrene-b-(ethylene-co-butylene)-b-styrene) (PA6/SAN/SEBS) and polyamide 6/poly(styrene-co-acrylonitrile)/poly(maleated styrene/ethylene-co-butylene/styrene) (PA6/SAN/SEBS-g-MA), based on 70 wt% of matrix and 30 wt% of the dispersed phases at various concentrations of the minor components, were prepared via melt blending. Morphologies of the ternary systems were studied using scanning electron microscopy (SEM) and compared with the predictions of the spreading coefficient (SC), minimum relative interfacial energy (RIE), and dynamic interfacial energy (DIE) phenomenological models. The effects of different reported surface tensions of the used polymers and different protocols of the core-shell ratio calculation on the prediction of the models were investigated. The core-shell structure for PA6/SAN/SEBS system and two separate minor phases for PA6/SAN/SEBS-g-MA were observed at all of the compositions. The results indicated that the most important parameter for the accurate prediction of the models is the accurate calculation of the interfacial tension of the used polymers, in both the static and dynamic conditions.     

Synthesis of photosensitive poly(methyl methacrylate-co-glycidyl methacrylate) for optical waveguide devices

Photosensitive poly(MMA-co-GMA) for optical waveguide was synthesized, and the refractive index of the polymer film was tuned in the range of 1.481–1.588 at 1550 nm by mixing with bis-phenol-A epoxy resin. The film, which was made by spinning coated the poly(MMA-co-GMA) with photo initiator, had good UV light lithograph sensitivity, high glass transition temperature (T _g : 153°C, after crosslinking) and good thermal stabilities (T _d : up to 324°C, after crosslinking). The optical waveguides with very smooth top surface were fabricated from the resulting polymer by direct UV exposure and chemical development. For waveguides with cladding, the propagation losses of the channel waveguides were measured to be below 3 dB/cm at 1550 nm.     

PEG crosslinked poly(vinylbenzene boronic acid) polymer electrolytes for Li-ion batteries

Poly(4-vinylbenzeneboronic acid), PVBBA was synthesized via free-radical polymerization of 4-vinylbenzeneboronic acid (4-VBBA) and followed by crosslinking with polyethylene glycol (PEG) with different molecular weights to produce boron containing crosslinked polymers. Prior to crosslinking, the materials were doped with CF₃SO₃Li at several stoichiometric ratios to get PVBBAPEGX-Y where X is the molecular weight of PEG and Y is the EO/Li ratio. The materials were characterized by using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and differential scanning calorimeter (DSC). The ionic conductivity of these novel crosslinked electrolytes was studied by dielectric-impedance spectroscopy. Li-ion conductivity of these polymer electrolytes depends on the length of the side units as well as the doping ratio. PVBBAPEG200-10 illustrated a satisfactory ionic conductivity of 3.1 × 10^?5 S/cm at 20 °C and 1.8 × 10^?3 S/cm at 100 °C.     

Platinum particles dispersed poly(diphenylamine) modified electrode for methanol oxidation

A modified potentiostatic method, termed the ‘pulse pontentiostatic method’ (PPSM) was used to get nano fibrillar poly(diphenylamine) (PDPA) film on Indium tin oxide (ITO) coated glass electrode and also for making modified electrode with platinum particles dispersed in PDPA. Platinum clusters were electrodispersed under constant potential on PDPA films to obtain catalytic electrodes for methanol oxidation. Energy dispersive analysis of X-rays (EDAX) results showed that the Pt microparticles are deposited into PDPA film. Scanning electron micrograph, SEM images show that the deposition results spherical catalytic particles. X-ray photoelectron spectroscopy (XPS) results inform that the net electronic charge on carbon atom and also the imine/amine ratio was not affected by Pt loadings. The modification of electrode surface by nano fibular PDPA improves the electrocatalytic activity for methanol oxidation.     

NMR studies of interfaces,strain and anisotropy in Co/Cu multilayers

⁵⁹Co NMR studies of multilayers are able to give three direct pieces of information: (i) the crystal phase of Co, fcc (217.4 MHz), hcp (220–228 MHz) and in exotic cases bcc (198 MHz) for films measured at T= 4.2 K, (ii) the nature of the interfaces from low frequency satellite lines, and (iii) the strain state deduced from small changes in the line positions. Extensive studies of Co/Cu multilayer interfacial structures as a function of deposition technique, layer thickness, substrate/buffer layer structure and annealing temperature have been undertaken. This work has shed new light on the relationship between interfacial structure and magnetoresistance and in particular has demonstrated that flat, atomic scale, interfaces lead to greater magnetoresistance. The difference between the Co and Cu lattice constant results in an extensive, tensile in-plane strain developing in Co layers provided that some epitaxial registry is present. Information on strain effects can be obtained from the position and width of the NMR lines. The magnetic anisotropy field can be determined by measuring the field dependence of the enhancement effect due to electronic magnetisation. This provides unique insight into the distribution of magnetic anisotropy within the Co layers, as the enhancement can be investigated independently for each NMR line and, hence, provides environment specific information on magnetic anisotropy at the interfaces and in the interior of the layers. This revised version was published online in August 2006 with corrections to the Cover Date.     

Preparation and characterization of zirconium sulfophenyl phosphate-doped sulfonated poly(phthalazinone ether sulfone) composite proton exchange membrane

Polymer composite membranes based on sulfonated poly(phthalazinone ether sulfone) (SPPES) and zirconium sulfophenyl phosphate (ZrSPP) were prepared. Three ZrSPP concentrations were used: 10, 20, and 30 wt%. The membranes were characterized by infrared spectroscopy (IR), X-ray diffraction spectroscopy, thermal gravimetric analysis, and scanning electron microscopy (SEM). The IR results indicated the formation of intense hydrogen bonds between ZrSPP and SPPES molecules. The SEM micrographs showed that ZrSPP well dispersed with SPPES and form a lattice structure. The proton conductivity of the SPPES (degree of sulfonation (DS) 64 %)/ZrSPP (10 wt%) composite membrane reached 0.39 S/cm at 120 °C 100 % relative humidity and that of the 30 wt% of SPPES (DS 16.1 %)/ZrSPP composite membrane reached 0.18 S/cm at 150 °C. The methanol permeabilities of the SPPES/ZrSPP composite membranes were in the range of 2.1?×?10^?8 to 0.13?×?10^?8?cm²/s, much lower than that of Nafion®117 (10^?6?cm²/s). The composite membranes exhibited good thermal stabilities, proton conductivities, and good methanol resistance properties.     

Direct laser interference patterning of poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT-PSS) thin films

We have developed a patterning procedure based on selective ablation using interference patterns with ns-laser pulses to fabricate periodic arrays on large areas of poly(3,4-ethylene dioxythiophene)-poly(4-styrene sulfonic acid) (PEDOT-PSS) thin films over a metallic gold–palladium layer. Single pulse laser-ablation experiments were performed to study the ablation characteristics of the thin films as a function of the film thickness. The ablation threshold fluence of the PEDOT-PSS films was found to be dependent on thickness with values ranging from 43 mJ/cm² to 252 mJ/cm². Additionally, fluences at which the PEDOT-PSS films could be ablated without inducing damage in the underlying metallic films were observed (128 mJ/cm² and 402 mJ/cm² for film thicknesses of 70 nm and 825 nm, respectively). Linear periodic arrays with line spacings of 7.82 μm and 13.50 μm were also fabricated. The surface topography of these arrays was analyzed using scanning electron and atomic force microscopy. For thicker polymeric layers, several peeled sub-layers of the conjugated polymer with average thicknesses of about 165–185 nm were observed in the ablation experiments. The size and scale of structures produced by this technique could be suitable for several biomedical applications and devices in which controlling cell adhesion, promoting cell alignment, or improving biocompatibility are important.     

Surface-modified antibacterial TiO2/Ag nanoparticles: Preparation and properties

Studies were performed on surface modification of antibacterial TiO₂/Ag⁺ nanoparticles by grafting γ-aminopropyltriethoxysilane (APS). The interfacial structure of the modified particles was characterized by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and thermogravimetric analysis. The thickness of the surface layer was determined by using Auger electron spectroscopy (AES). The results show that APS is chemically bonded to the surface of antibacterial TiO₂/Ag⁺ nanoparticles. Furthermore, the modified particles were mixed in PVC to prepare composites whose antibacterial property was investigated. The results suggest that surface modification has no negative effect on antibacterial activity of TiO₂/Ag⁺ nanoparticles and PVC-TiO₂/Ag⁺ composites exhibits good antibacterial property.     

Chemical relaxation of cis-1,4-polybutadiene radiation-crosslinked at high pressure

Chemical relaxation for cis-l,4-polybutadiene crosslinked at 7000 kg/cm² by γ-irradiation was compared with that for one crosslinked at atmospheric pressure. The degree of thermal degradation was similar in both specimens, but the specimen crosslinked at 7000 kg/cm² formed fewer new networks in the initial stage than the specimen crosslinked at atmospheric pressure. The G value for the formation of crosslinking points was proportional to the-0.5 power of the dose rate at high pressure. This indicates that the radiation-induced crosslinking at high pressure proceeds in a chain reaction as proposed from the high G value in a preceding paper. The lower formation of new network chains for the specimens crosslinked at 7000 kg/cm² is concluded to be due to lower mobility of polymer radicals that crosslink by recombination near the clusters of crosslinking points produced by the chain reaction.     

Characterization of the Plasmonic Fluorescence Enhancement of Poly (3-hexylthiophene) for Organic Solar Cell Applications

The dependence of surface-enhanced fluorescence of the semiconducting polymer poly (3-hexylthiophene) on the diameter of silver nanoparticles was studied. Particle suspensions with a high degree of monodispersity, ranging in diameter from 15 to 153 nm, were synthesized. Polymer films were spin-cast onto substrates containing immobilized silver particles. Fluorescence enhancement factors ranged from 0.9 to 4.9 and generally improved with increasing particle size. Normalization of the fluorescence enhancement to the number of interrogated particles showed an 800-fold increase in enhancement between the smallest and largest particles.     

Microstructures and Mechanical Properties of Poly(Trimethylene Terephthalate)/Maleic Anhydride Grafted Poly(Ethylene-octene)/Polypropylene Blends

A range of blends based on 70 wt% of poly(trimethylene terephthalate) PTT with 30 wt% dispersed phase were produced via melt blending. The dispersed phase composition was varied from pure maleic anhydride grafted poly(ethylene-octene) (POE-g-MA) over a range of POE-g-MA:polypropylene (PP) ratios. The micromorphology and mechanical properties of the ternary blends were investigated. The results indicated that the domains of the POE-g-MA are dispersed in the PTT matrix, and at the same time the POE-g-MA encapsulate the PP domains. The interfacial reaction between the hydroxyl-end group of PTT and maleic anhydride (MA) during melt blending changes the formation from “isolated formation” to “capsule formation,” where the PP domains are encapsulated by POE-g-MA. Compared to the PTT/POE-g-MA blends, mechanical properties of ternary blends, such as tensile strength and Young's modulus, were improved significantly.     

Aromatic poly(ester carbonate)/poly-(ethylene terephthalate) alloys

When mixtures of poly(ester carbonate) (PEC) and poly(ethylene terephthalate) (PET) containing up to two-thirds of the latter are melt extruded, they produce a single-phase amorphous “alloy.” This alloy is characterized by a sharp, single, composition-dependent glass transition temperature, T_g. When annealed below T_g, the alloy remains unaltered, but when annealed above its T_g, the alloy separates into minute pure-PET crystallites and an amorphous PEC/PET phase. The thermal and dynamic mechanical behavior, crystallization kinetics, and SAXS patterns all strongly suggest the PEC-rich alloys to be solid solutions in which the PET molecules are dispersed individually or in small aggregates containing only a few PET molecules each. Calculations of the interaction parameter and assumed interfacial layer thickness tend to support this suggestion. Use of appropriate solvents allows one to selectively dissolve the PEC and recover from the alloys both PET and PEC in the original purity and molecular weights. Diffusion constants of PET molecules through the amorphous alloys were obtained from studies of PET crystallization above T_g of the alloys. The magnitude of the constants are in the range of expectation. The mechanical properties of the amorphous alloys in the glassy state do not deviate greatly from simple additivity of the respective properties of the parent polymers. However, the melt viscosity of the PEC-rich alloys and their plateau modulus above T show drastic decreases from straight additivity. A qualitative, but not quantitative, explanation of these observations is offered.     

Fractal and structural aspects of adhesion in particulate-filled polymer composites

Two types of composites based on poly(hydroxy ether) and graphite with various amounts of a filler have been investigated by various methods. The methods have been used to estimate the characteristics of adhesion and interfacial layer, including its thickness and tensile strength and interdependence between these values and adhesion. The results are treated on the basis of the theory of irreversible aggregation, cluster theory of the polymer structure and fractal analysis. It is established that all important characteristics of adhesion, interfacial layer and mechanical properties are interconnected with the difference between fractal dimensions of the surface of the aggregates of filler particles and of a polymer matrix, whose structure is distorted under the influence of the filler surface.     

Solid electrolyte membranes from semi-interpenetrating polymer networks of PEG-grafted polymethacrylates and poly(methyl methacrylate)

Solid polymer electrolyte membranes were prepared as semi-interpenetrating networks by photo-induced polymerization of mixtures of poly(ethylene glycol) (PEG) methacrylate macromonomers in the presence of poly(methyl methacrylate) (PMMA) and lithium bis(trifluoromethanesulfonyl)imide salt. The composition of the membranes was varied with respect to the PMMA content, the degree of cross-linking, and the salt concentration. Infrared analysis of the membranes indicated that the lithium ions were coordinated by the PEG side chains. Calorimetry results showed a single glass transition for the blend membranes. However, dynamic mechanical measurements, as well as a closer analysis of the calorimetry data, revealed that the blends were heterogeneous systems. The ionic conductivity of the membranes increased with the content of PEG-grafted polymethacrylate, and was found to exceed 10^− 5 S cm^− 1 at 30 °C for membranes containing more than 85 wt.% of this component in the polymer blend.     

Toughening poly(lactic acid) (PLA) through in situ reactive blending with liquid polybutadiene rubber (LPB)

Abstract

Liquid polybutadiene rubber (LPB) was blended with poly(lactic acid) (PLA) through reactive and non-reactive routes to enhance the toughness of the PLA. The reactively blended PLA (PBR10) was prepared by melt blending the PLA with the LPB in the presence of dicumyl peroxide (DCP), a radical initiator, while the PB10 was just melt blended without the DCP. Fourier transform infrared (FTIR) spectra and wide-angle X-ray diffraction (WAXD) patterns were used to study the molecular structure of the blends. Properties were investigated through universal testing machine (UTM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron microscope (SEM) analysis, and rheological measurements. The results indicated that the radical crosslinking by the DCP could increase the compatibility between the PLA and LPB and disperse the rubber particles at the nanoscale in the PLA matrix. As a result, the toughness and melt viscosity of the PLA was significantly enhanced through the reactive blending, which is promising for the practical application of the modified PLA in the area of packaging.     

Temperature-controlled depth profiling in polymeric materials using cluster secondary ion mass spectrometry (SIMS)

Secondary ion mass spectrometry (SIMS) employing an SF₅⁺ polyatomic primary ion source was used to depth profile through poly(methylmethacrylate) (PMMA), poly(lactic acid) (PLA) and polystyrene (PS) thin films at a series of temperatures from −125 °C to 150 °C. It was found that for PMMA, reduced temperature analysis produced depth profiles with increased secondary ion stability and reduced interfacial widths as compared to analysis at ambient temperature. Atomic force microscopy (AFM) images indicated that this improvement in interfacial width may be related to a decrease in sputter-induced topography. Depth profiling at higher temperatures was typically correlated with increased sputter rates. However, the improvements in interfacial widths and overall secondary ion stability were not as prevalent as was observed at low temperature. For PLA, improvements in signal intensities were observed at low temperatures, yet there was no significant change in secondary ion stability, interface widths or sputter rates. High temperatures yielded a significant decrease in secondary ion stability of the resulting profiles. PS films showed rapid degradation of characteristic secondary ion signals under all temperatures examined.     

Graphene oxide doped poly(vinylidene fluoride-co-hexafluoropropylene) gel electrolyte for lithium ion battery

Gel poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer electrolytes doped with graphene oxide (GO) (GO/PVDF-HFP) were designed and fabricated through a phrase inversion method and followed by LiPF₆ solution uptake. It was demonstrated that the as-prepared GO/PVDF-HFP polymer electrolytes have uniform porous morphologies, and their crystalline state, thermal stability, interfacial resistance, and electrolyte uptake and retention capabilities can be tuned by varying the GO contents. Further, it was found that the GO can prominently enhance the ionic conductivity of the GO/PVDF-HFP polymer electrolyte. The electrochemical property measurements show that the lithium ion batteries using as-prepared GO/PVDF-HFP polymer electrolytes afford admirable charge/discharge rate and cycle stability.