Preparation of a new micro-porous poly(methyl methacrylate)-grafted polyethylene separator for high performance Li secondary battery

In this study, micro-porous poly(methyl methacrylate)-grafted polyethylene separators (PE-g-PMMA) were prepared by a radiation-induced graft polymerization of methyl methacrylate onto a conventional PE separator followed by a phase inversion. After the phase inversion, the micro-pores were generated in the grafted PMMA layer. The prepared micro-porous PE-g-PMMA separators showed an improved electrolyte uptake and ionic conductivity due to their improved affinity with a liquid electrolyte and the presence of pores in the grafted PMMA layer. The PE-g-PMMA separators exhibited a lower thermal shrinkage compared to the original PE separator. The PE-g-PMMA separators showed a better oxidation stability up to 5.0 V when compared to the original PE separator (4.5 V).     

New separator prepared by electron beam irradiation for high voltage lithium secondary batteries

Grafted separators, for which poly(ethylene glycol) borate acrylate (PEGBA) was grafted onto polyethylene (PE) separator, were newly prepared by electron beam irradiation. The grafted separators were characterized by FT-IR, energy dispersive X-ray spectrometer (EDS). The morphological changes of the grafted separators were investigated by scanning electron microscopy (SEM). The degree of grafting was increased with irradiation doses. The ionic conductivity of the grafted separator showed the highest value of 6.24 × 10⁻⁴ S cm⁻¹ at 10 kGy. In addition, its lithium ion transference number and electrochemical stability were enhanced to 0.53 and 4.8 V, respectively owing to anion trapping effect of the grafted unit. The Li ion cells using the grafted separator showed better cycle performances than that using conventional PE separator at various C-rates and high voltage operation conditions. It is suggested that this grafted separator can be a promising candidate for high voltage operation of lithium secondary batteries.     

Preparation of polymer-coated separators using an electron beam irradiation

A polymer-coated polyethylene (PE) separator was prepared by a dip-coating of PVDF-HFP/PEGDMA on both sides of a PE separator followed by an electron beam irradiation. The thermal and electrochemical properties of the polymer-coated PE separator were investigated by using FT-IR, SEM, DSC and an impedance analyzer. The results showed that the coated PVDF-HFP/PEGDMA layer was covalently bound to the PE separator and also crosslinked by an electron beam irradiation. Thermal shrinkage dramatically decreased with an increase in the absorption dose and the PEGDMA content due to the crosslinking of the coated PVDF-HFP/PEGDMA by an irradiation. The PE separator coated with the composition of PVDF-HFP/PEGDMA (9.5/0.5) and irradiated to 150 kGy showed the highest electrolyte uptake of 125% and ionic conductivity of 3.82 × 10⁻⁴ S/cm at room temperature.     

Influence of a surfactant on single ion track etching: Preparing and manipulating cylindrical micro wires

The influence of the alkali resistant surfactant Dowfax 2A1 on single ion track etching in 30 μm polycarbonate foils is studied at low etch rate (5 M NaOH at 41.5 ± 2 °C) using electro conductivity measurements. At surfactant concentrations above 10⁻⁴ vol.% break-through times are predictable (Δt/t < 0.25). At high surfactant concentrations (?0.1 vol.%) the formation of cylindrical channels is favoured. The shape of these channels (length ? 26 μm, diameter ? 1.8 μm) is verified by electro-replication and SEM observation of the resulting wires. Agreement of radii is better than 0.1 μm. Depending on the current limit set during electro replication compact or hollow cylinders can be obtained. A technique for localizing and manipulating individual micro wires by their head buds is described.     

Radiation-chemical synthesis of poly(vinyl alcohol) hydrogel containing dicyclohexano-18-crown-6

Radiation-chemical synthesis of poly(vinyl alcohol) hydrogels containing physically immobilized dicyclohexano-18-crown-6 was carried out. Remarkable gel fraction of 40-70% was observed at absorbed dose of about 5 kGy. Increasing degree of poly(vinyl alcohol) crosslinking led to growth of the efficiency of crown ether immobilization. Post-irradiation thermal annealing of the hydrogel samples at 120 °C for 0.5-5 h resulted in an increase of crown ether retention as compared with non-annealed samples by approximately 20% at the same absorbed dose. Preliminary results on a sorption behavior of the crown-containing hydrogels with respect to Sr²⁺ cations in 2.4 M HNO₃ solution are presented.     

Radiation-induced grafting of inorganic particles onto polymer backbone: A new method to design polymer-based nanocomposite

Polypropylene/polyhedral oligomeric silsesquioxane (PP/POSS) nanocomposites were prepared by in situ radiation-induced grafting of POSS onto PP. Radiation-induced grafting of POSS was confirmed by FT-IR spectroscopy. The mechanical property of PP/POSS nanocomposites increased with the increase in POSS content and with the increase in absorption dose up to 5 kGy, above which it started to decrease. The reduction of mechanical property at high doses can be attributed to the chain scission of PP by radiation. The degree of reduction in decomposition temperature of irradiated PP/POSS nanocomposites was found to be much less than that of neat PP due to the covalent grafting of POSS onto PP by radiation.     

Modification of poly(ether ether ketone) by ion irradiation

Poly(ether ether ketone) was irradiated with 3.0 MeV Si²⁺, 3.25 MeV Cu²⁺ and 4.8 MeV Ag²⁺ ions to the fluences from 10¹² to 10¹⁴ cm⁻² and the effects of irradiation were studied using ERDA, RBS and FTIR methods. The irradiation leads to release of hydrogen from the PEEK surface layer modified by the ion beam. The release is mild for low ion fluences but it becomes more pronounced at the ion fluences above 10¹³ cm⁻². At highest ion fluences the hydrogen concentration falls to 20-35% of its initial value. In contrast to hydrogen no significant oxygen release was observed. The kinetic of the hydrogen release is similar for the three ion species. FTIR measurement shows deep structural changes of the polymer structure resulting from the ion irradiation.     

Effect of swift heavy ion irradiation on structure, optical, and gas sensing properties of SnO2 thin films

Swift heavy ion irradiation has been successfully used to modify the structural, optical, and gas sensing properties of SnO₂ thin films. The SnO₂ thin films prepared by sol-gel process were irradiated with 75 MeV Ni⁺ beam at fluences ranging from 1 × 10¹¹ ion/cm² to 3 × 10¹³ ion/cm². Structural characterization with glancing angle X-ray diffraction shows an enhancement of crystallinity and systematic change of stress in the SnO₂ lattice up to a threshold value of 1 × 10¹³ ions/cm², but decrease in crystallinity at highest fluence of 3 × 10¹³ ions/cm². Microstructure investigation of the irradiated films by transmission electron microscopy supports the XRD observations. Optical properties studied by absorption and PL spectroscopies reveal a red shift of the band gap from 3.75 eV to 3.1 eV, and a broad yellow luminescence, respectively, with increase in ion fluence. Gas response of the irradiated SnO₂ films shows increase of resistance on exposure to ammonia (NH₃), indicating p-type conductivity resulting from ion irradiation.     

Structural changes in chlorine implanted poly(vinyl alcohol) films

Poly(vinyl alcohol) (PVA) films were implanted with chlorine ions in the fluence range of 10¹³-10¹⁶ ions/cm² on to PVA films of thickness 40 μm. FTIR spectroscopic study was carried out to see the structural changes. It was found that oxidation and carbonization progressively occurs in the film as a function of total fluence. The structural change occurs in the form of scission of C-C, C-OH and C-H bonds. SEM studies were carried out which revealed the surface defects in the form of cracks and etching. ESCA studies established that Cl⁺ ions get deposited on the surface. Changes in the crystallinity were observed from the X-ray diffraction studies. The implanted chlorine ions enhanced the electrical conductivity by the order of 10⁺² S/cm.     

Tailoring optical and electrical properties of MgO thin films by 1.5 MeV H implantation to fluences

Thin films of magnesia (MgO) with (1 0 0) dominant orientations were implanted with 1.5 MeV H⁺ ions at room temperature to various fluences of 10¹³, 10¹⁴ and 10¹⁵ ions/cm². X-ray analysis unambiguously showed crystallinity even after a peak damage fluence of 10¹⁵ ions/cm². Rutherford backscattering spectrometry combined with ion channeling (RBS/C) was used to analyze radiation damages and defect distributions. Optical absorption band observed at 5.7 eV in implanted films was assigned to the anion vacancies and the defect was completely disappeared on annealing at 450 °C. Number of F-type defects estimated was 9.42 × 10¹⁵ cm⁻² for the film implanted with 10¹⁵ ions/cm². DC electrical conductivity of 4.02 × 10⁻⁴ S cm⁻¹ was observed in the implanted region which was three orders higher than the as-deposited films. In unison, film surface was modified as a result of the formation of aggregates caused by the atomic mixing of native matrix atoms (Mg and O) and precipitated hydrogen.     

Hydrocarbon proton-conductive membranes prepared by radiation-grafting of styrenesulfonate onto aromatic polyamide films

Novel method for preparing aromatic hydrocarbon proton-conductive membranes without sulfonation and membrane casting process is achieved by radiation-grafting of sodium styrenesulfonate to an aromatic polyamide, poly(m-xylylene adipamide) (Nylon-MXD6) films and subsequent ion-exchange. The styrenesulfonate was easily grafted into the Nylon-MXD6 films from an oxygen-free dimethyl sulfoxide (DMSO) solution at 60 °C. As a result, the resulted styrenesulfonic acid-grafted Nylon-MXD6 films, namely proton-conductive membrane, with high ion-exchange capacity up to 1.63 mmol/g, can be obtained. The membrane was transparent and highly hydrophilic. The proton conductivity, water uptake and methanol permeability of the proton-conductive membranes were investigated with respect to their use in fuel cells. The high proton conductivity reached 0.083 S/cm, comparable to Nafion. Furthermore, the methanol permeability was significantly lower than that of the Nafion membrane. Therefore, the Nylon-MXD6-based proton-conductive membrane is a more promising material for the direct methanol fuel cells (DMFCs).     

Studies on the high electronic energy deposition in polyaniline thin films

We report here the physico-chemical changes brought about by high electronic energy deposition of gold ions in HCl doped polyaniline (PANI) thin films. PANI thin films were synthesized by in situ polymerization technique. The as-synthesized PANI thin films of thickness 160 nm were irradiated using Au⁷⁺ ion of 100 MeV energy at different fluences, namely, 5 × 10¹¹ ions/cm² and 5 × 10¹² ions/cm², respectively. A significant change was seen after irradiation in electrical and photo conductivity, which may be related to increased carrier concentration, and structural modifications in the polymer film. In addition, the high electronic energy deposition showed other effects like cross-linking of polymer chains, bond breaking and creation of defect sites. AFM observations revealed mountainous type features in all (before and after irradiation) PANI samples. The average size (diameter) and density of such mountainous clusters were found to be related with the ion fluence. The AFM profiles also showed change in the surface roughness of the films with respect to irradiation, which is one of the peculiarity of the high electronic energy deposition technique.     

Anisotropic proton-conducting membranes prepared from swift heavy ion-beam irradiated ETFE films

Poly(ethylene-co-tetrafluoroethylene) (ETFE) films were irradiated by swift heavy ion-beams of ¹²⁹Xe²³⁺ with fluences of 0, 3 × 10⁶, 3 × 10⁷, 3 × 10⁸ and 3 × 10⁹ ions/cm², followed by γ-ray pre-irradiation for radiation grafting of styrene onto the ETFE films and sulfonation of the grafted ETFE films to prepare highly anisotropic proton-conducting membranes. The fluence of Xe ions and the addition of water in the grafting solvent were examined to determine their effect on the proton conductivity of the resultant membranes. It was found that the polymer electrolyte membrane prepared by grafting the styrene monomer in a mixture of 67% isopropanol and 33% water to the ETFE film with an ion-beam irradiation fluence of 3.0 × 10⁶ ions/cm² was a highly anisotropic proton-conducting material, as the proton conductivity was three or more times higher in the thickness direction than in the surface direction of the membrane.     

Cytocompatibility of Ar plasma treated and Au nanoparticle-grafted PE

Polyethylene (PE) was irradiated with inert Ar plasma, and the chemically active PE surface was grafted with Au nanoparticles. The composition and the structure of the modified PE surface were studied using X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS). Changes in the surface wettability were determined from the contact angle measured in a reflection goniometer. The changes in the surface roughness and morphology were followed by atomic force microscopy (AFM). The modified PE samples were seeded with rat vascular smooth muscle cells (VSMC) or mouse NIH 3T3 fibroblasts, and their adhesion and proliferation were studied. We found that plasma discharge and Au grafting lead to dramatic changes in the surface morphology and roughness of PE. The Au nanoparticles were found not only on the sample surface, but also in the sample interior up to the depth of about 100 nm. In addition, plasma modification of the PE surface, followed with grafting Au-nanoparticles, significantly increased the attractiveness of the PE surface for the adhesion and growth of VSMC, and particularly for mouse embryonic 3T3 fibroblasts.     

Deposition of gold nano-particles and nano-layers on polyethylene modified by plasma discharge and chemical treatment

Polyethylene (PE) was treated in Ar plasma discharge and then grafted from methanol solution of 1,2-ethanedithiol to enhance adhesion of gold nano-particles or sputtered gold layers. The modified PE samples were either immersed into freshly prepared colloid solution of Au nano-particles or covered by sputtered, 50 nm thick gold nano-layer. Properties of the plasma modified, dithiol grafted and gold coated PE were studied using XPS, UV-VIS, AFM, EPR, RBS methods and nanoindentation. It was shown that the plasma treatment results in degradation of polymer chain, creation of excessive free radicals and conjugated double bonds. After grafting with 1,2-ethanedithiol the concentration of free radicals declined but the concentration of double bonds remained unchanged. Plasma treatment changes PE surface morphology and increases surface roughness too. Another significant change in the surface morphology and roughness was observed after deposition of Au nano-particles. The presence of Au on the sample surface after the coating with Au nano-particles was proved by XPS and RBS methods. Nanoindentation measurements shown that the grafting of plasma activated PE surface with dithiol increases significantly adhesion of sputtered Au nano-layer.     

Improvement on thermoelectric properties of multilayered Si1−xGex/Si by ion beam bombardment

We made n-type nano-scale thin film thermoelectric (TE) devices that consist of multiple periodic layers of Si_1−xGe_x/Si. The period is about 10 nm. The structure was modified by 5 MeV Si ion bombardment that formed a nano-scale cluster structure. In addition to the effect of confinement of the phonon transmission, formation of nanoclusters by the ionization energy of incident MeV Si ions further increases the scattering of phonons, increasing the chance of inelastic interaction of phonons, resulting in more annihilation of phonons. This limits phonon mean free path. Phonons are absorbed and dissipated along the layers rather than in the direction perpendicular to the layer interfaces, therefore cross plane thermal conductivity is reduced. The increase of the density of electronic states due to the formation of nanocluster minibands increases the cross plane Seebeck coefficient and increases the cross plane electric conductivity of the film. Eventually, the thermoelectric figure of merit of the TE film increases.     

Vitamin C hinders radiation cross-linking in aqueous poly(vinyl alcohol) solutions

Poly(vinyl alcohol) (PVA) is a promising semi-crystalline material for biomedical applications. It is soluble in water and can be formed into hydrogels by freezing and thawing or crystallizing from an aqueous theta solution such as that of polyethylene glycol (PEG). Radiation cross-linking caused by sterilization or high dose irradiation of concentrated PVA solutions could compromise some properties of these hydrogels. Therefore, we hypothesized that radiation cross-linking of PVA solutions and PVA-PEG theta gels could be prevented by using the antioxidant vitamin C as an anticross-linking agent. Our hypothesis tested positive. Vitamin C concentrations of 0.75 and 4.5 mol/mol of PVA repeating unit could prevent cross-linking in 17.5 wt/v% PVA solutions made with PVA molecular weight of 115,000 g/mol irradiated to 25 and 100 kGy, respectively. Vitamin C also prevented cross-linking in 25 kGy irradiated PVA-PEG theta gels containing up to 5 wt% PEG and decreased the viscosity of those up to 39 wt%.     

Synthesis and characterization of PEFC membranes based on fluorinated-polymer-alloy using pre-soft-EB grafting method

Polymer electrolyte fuel cell (PEFC) membranes based on thin film of crosslinked perfluorinated polymer-alloys (RX-FA) have been fabricated by soft electron beam (soft-EB) grafting with styrene monomers using soft-EB irradiation under nitrogen atmosphere at room temperature (RT). The characteristic properties of styrene-grafted materials (GRX-FA) and sulfonated materials (SRX-FA) have been measured by differential scanning calorimetry (DSC) and FT-IR spectroscopy, ionic conductivity and so on. The glass transition temperatures (dry state) of all obtained SRX-FA were about 105 ± 1 °C, which are higher than Nafion^®. The ion exchange capacities of SRX-FA have been achieved about 3.3 meq/g (dry). The ionic conductivity of obtained SRX-FA has showed about 0.17 S/cm at 60 °C with relative humidity (RH) of ∼95%. The ionic conductivities of the obtained SRX-FA were higher than that of conventional perfluoro-sulfonic acid membranes (PFSA). Fabricated membrane electrode assemblies (MEAs) based on the obtained SRX-FA have shown encouraging performance in the PEFC, compared with the conventional PFSA. The power density of obtained MEAs based on the SRX-FA was about 330-340 mW/cm² under 500 mA/cm² at 60 °C operation. Moreover, the maximum power densities of obtained MEAs based on the SRX-FA shows about 630 mW/cm² at 60 °C. On the other hand, the power density at 500 mA/cm² and maximum power density of MEA based on Nafion^®112 were about 320 and 590 mW/cm² at 60 °C. Thus, the power density of the obtained SRX-FA was higher than that of conventional PFSA.     

Surface structure of an ionic liquid with high-resolution Rutherford backscattering spectroscopy

The surface of an ionic liquid, trimethylpropylammonium bis(trifluoromethanesulfonyl)imide ([TMPA] [TFSI]), is observed by high-resolution Rutherford backscattering spectroscopy (HRBS). The composition depth profiles are derived from the observed HRBS spectra through spectrum simulation. The observed composition is in good agreement with the stoichiometric composition at depths larger than ∼1 nm. The observed composition profiles, however, show pronounced structures at the surface. Fluorine profile has a sharp peak at ∼0.1 nm and a broad peak at ∼1.0 nm. The sulfur profile also has a peak at ∼0.35 nm. These results indicate that the molecules show preferred orientations at the surface. From the observed profiles, it was concluded that the C₁ conformer of the [TFSI] anion is dominant over the C₂ conformer at the surface in contrast to bulk, where the C₂ conformer is known to be dominant. It was also found that C₁ conformers are oriented with their CF₃ groups pointing toward the vacuum in the outermost molecular layer.