Method to measure composition modifications in polyethylene terephthalate during ion beam irradiation

Matter losses of polyethylene terephthalate (PET, Mylar) films induced by 1600 keV deuteron beams have been investigated in situ simultaneously by nuclear reaction analysis (NRA), deuteron forward elastic scattering (DFES) and hydrogen elastic recoil detection (HERD) in the fluence range from 1 × 10¹⁴ to 9 × 10¹⁶ cm⁻². Volatile degradation products escape from the polymeric film, mostly as hydrogen-, oxygen- and carbon-containing molecules. Appropriate experimental conditions for observing the composition and thickness changes during irradiation are determined. ¹⁶O(d,p₀)¹⁷O, ¹⁶O(d,p₁)¹⁷O and ¹²C(d,p₀)¹³C nuclear reactions were used to monitor the oxygen and carbon content as a function of deuteron fluence. Hydrogen release was determined simultaneously by H(d,d)H DFES and H(d,H)d HERD. Comparisons between NRA, DFES and HERD measurements show that the polymer carbonizes at high fluences because most of the oxygen and hydrogen depletion has already occured below a fluence of 3 × 10¹⁶ cm⁻². Release curves for each element are determined. Experimental results are consistent with the bulk molecular recombination (BMR) model.     

Effects of electron beam irradiation on binary polyamide-6 blends with metallocene copolymers

The effect of electron beam irradiation on thermal and mechanical properties, and SEM morphology of polyamide-6 (PA-6) blends with grafted copolymers was investigated. High toughness materials were obtained with ethylene-polypropylene-diene grafted copolymers without significant variations in their thermal properties and Izod impact strength at room temperature and −30 °C with the irradiation doses used.     

Investigation of nanopore evolution in ion track-etched polycarbonate membranes

Single heavy ion tracks in polycarbonate foils were chemically etched in an electrolytical cell under various conditions (different temperatures, etchant concentrations, and applied potentials), and the pore evolution was monitored by measuring the current through the membrane. Different zones of the latent tracks could be identified via changes in the radial etching rate with time. Further it was found that the shape of the radial etching rate versus time curves depends on temperature, etchant concentration, and applied voltage. The functionalities are attributed to etching products (double-charged diphenylol-propane anions), which are adsorbed on the pore walls and, thus, affect the further etching process.     

Study on chemical structures of poly (tetrafluoroethylene-co-perfluoroalkylvinylether) by soft-EB irradiation in solid and molten state

Poly (tetrafluoroethylene-co-perfluoroalkylvinylether) (PFA) was irradiated by soft electron beam (soft-EB) under nitrogen gas atmosphere in solid-state and its molten state, respectively. The changes of thermal property and chemical structures of irradiated PFA in solid-state and molten state were studied by differential scanning calorimetric analysis (DSC) and solid-state ¹⁹F magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. By DSC analysis, the melting temperature shifted to lower temperatures, and crystallinity decreased with increasing soft-EB dose. By solid-state ¹⁹F MAS NMR spectroscopy, the new signals was observed and the detected new signals in irradiated PFA at 315 °C and at 30 °C were due to the tertiary carbon group with branching site (Y-type crosslinking site), perfluoro-propylene site and chain end methylene groups, respectively.Moreover, the molar ratio of perfluoroalkylvinylether (FAVE) structure to -CF₂- units decreased with increasing dose.     

Insights into oxidation mechanisms in gamma-irradiated polypropylene, utilizing selective isotopic labeling with analysis by GC/MS, NMR and FTIR

In an effort to shed additional light on the chemical mechanisms underlying the radiation-oxidation of polypropylene (PP), we are using samples having selective ¹³C isotopic labeling at the three unique sites within the macromolecular structure. After radiation exposure, we applied GC/MS, solid-state ¹³C NMR, and FTIR to evaluate the applicability of each technique in identifying the molecular labeling of the oxidation products, with the goal of determining the site of origin of the products with respect to the macromolecule. Using GC/MS, we have identified the position of origin of CO₂ and CO from the polymer. Most of the CO₂ (60%) and CO (>90%) come from the C(1) (methylene) position of PP, with (30%) of the CO₂ originating from the C(3) (methyl) position, and 10% coming from the C(2) (tertiary) position. By GC/MS we have also identified the labeling patterns in four volatile oxidation products (acetone, methylisobutylketone, isobutane, and methyl acetate), and have used this information to map each compound onto the macromolecular framework. Using NMR we have quantified the time-dependent formation of solid-phase degradation products occurring from post-irradiation aging of PP samples held for 28 months at room temperature in air. Most of the solid oxidation products occur at the C(2) (tertiary) site; the predominant species, C(2) peroxides, increase linearly during the first 2 years, after which they plateau at a relatively high concentration.     

Syntheses of amine-type adsorbents with emulsion graft polymerization of glycidyl methacrylate

Glycidyl methacrylate (GMA) which was precursor monomer for the synthesis of metal ion adsorbent was emulsified by surfactant of Tween 20 (Tw-20). The emulsion of 5% GMA in the water was stable for 48 h at Tw-20 concentration of 0.5%. Graft polymerization of GMA on polyethylene fiber was carried out in the emulsion state at various pre-irradiation doses. Degree of grafting (Dg) reached 103%, 301% and 348% for 1 h grafting at 40 °C with pre-irradiation of 10, 30 and 40 kGy, respectively. But the Dg was depressed when the pre-irradiation dose was over 50 kGy since cross-linking occurred simultaneously in the trunk polymer. Dg decreased with increment of Tw-20 concentration in emulsion of 5% GMA at pre-irradiation of 40 kGy. The three kinds of amine-type adsorbents were synthesized by reacting diethylenetriamine (DETA), triethylenetetramine (TETA) and ethylenediamine (EDA) with GMA-grafted polyethylene fiber. The synthesized EDA-type adsorbent had the highest selectivity against U ion and the distribution coefficient was 2.0 × 10⁶.     

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.     

Heavy ion beam micromachining on LiNbO3

In this work 3D micromachining of x-cut lithium niobate crystals was performed using the high energy heavy ion microbeam (HIM) at the Tandar Laboratory, Buenos Aires. The samples were machined using ³⁵Cl beams at 70 MeV bombarding energy combined with wet etching with hydrofluoric acid solutions at room temperature. As the ion beam penetrates the sample, it induces lattice damage increasing dramatically the local etching rate of the material. This technique was applied to the fabrication of 3D waveguides with long control electrodes. The resulting structures indicate that well defined contours with nearly vertical sidewalls can be made. The results also show that with fluences of only 5 × 10¹² ions/cm², this technique is suitable for the fabrication of different shapes of LiNbO₃ control-waveguides that can be used in different optical devices and matched with the existing optical fibers.     

Radiation-induced grafting of dimethylaminoethylmethacrylate onto PE/PP nonwoven fabric

A new adsorbent was prepared by radiation-induced graft polymerization of dimethylaminoethylmethacrylate (DMAEMA) onto polyethylene/polypropylene (PE/PP) nonwoven fabric. The trunk polymer was irradiated by electron beam at a voltage of 2 MeV and a current of 3 mA in nitrogen atmosphere at dry-ice temperature to different doses. The degree of grafting was determined as a function of irradiation dose, monomer concentration, temperature and reaction time. Grafting conditions were optimized and about 150% grafted samples were used for further experiments. DMAEMA grafted polymer was later protonated in acid solution to prepare specialty adsorbent for the removal of phosphate. Adsorption experiments were performed in column mode for removal of phosphate. It was shown that 2000 bed volumes of phosphate-free water can be produced from 100 ppb phosphate (as P) solution at high space velocity.     

Development of sulfonated FEP-Nafion hybrid proton exchange membranes for PEFC

The performance of polymer electrolyte fuel cell (PEFC) is affected by an interfacial property between a proton exchange membrane (PEM) and electrodes. Thus, to develop a well-laminated membrane electrode assembly (MEA), a hybrid PEM (FN) was fabricated by mixing a radiation grafted membrane (sulfonated FEP) with ionomer (Nafion^® dispersion) which is applied to coat the interface of the PEM and electrodes.The obtained FN, sulfonated FEP and Nafion^®112 were characterized in terms of water uptake, ion exchange capacity (IEC), polarization performance and electrochemical impedance. FN showed high IEC and water uptake, which would induce the highest ionic conductivity (IC) among tested PEMs. In terms of FN, the interface between the PEM and electrodes should have been improved because FN showed the lowest charge transfer resistance than other tested PEMs. The high IC and improved interface between the PEM and electrodes resulted in the best cell performance of FN in tested PEMs.     

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.     

The investigation of energy loss and damage in polycarbonate induced by MeV carbon clusters

Carbon cluster ions (n = 1-5) and Cl⁺, Ti⁺, Ni⁺ ions were used to bombard polycarbonate (PC) films. By comparing the electronic energy loss and the number of chromophores at a fixed wavelength, we obtained the electronic energy loss S_e of carbon cluster ions in PC.     

Cell patterning on a glass surface by a mask-assisted ion implantation

A simple patterning method of cells on a glass has been developed by using ion implantation. The glass was implanted through a pattern mask with 150 keV Ar ions in the absence or presence of oxygen. Surface properties of the ion-implanted glass were investigated by means of X-ray photoelectron spectroscopy, contact angle measurement and cell culture test. The results showed that more hydrophilic groups were formed on the glass surface implanted in the presence of oxygen. Thus, the glass surface implanted in the presence of oxygen showed lower contact angle compared with the glass surface implanted in the absence of oxygen. The cells were strongly adhered to and proliferated on the ion-implanted regions of the glass. The cell population was found to be the highest on the glass implanted at a fluence of 1 × 10¹⁶ ions/cm² in the presence of oxygen.     

Radiation effects on hydroxypropyl methylcellulose phthalate in aqueous system

A water-insoluble cellulose derivative, hydroxypropyl methylcellulose phthalate (HPMCP) hydrogels, was converted to Na type to form hydrogel in paste-like status by radiation crosslinking. Mechanism for radiation crosslinking of cellulose-derivatives in paste-like status was discussed. Crosslinkers, i.e. methyl N,N-bis-acrylamide (MBA) or ethyleneglycol dimethacrylate (EGDMA) has been used to decrease gelation dose (Dg) of synthesis HPMCP hydrogels and improve its mechanical properties. HPMCP-MBA hydrogels were found to be more rigid and HPMCP-EGDMA hydrogels were more flexible. Swelling degree of HPMCP hydrogel in many kinds of salt solutions followed Hofmeister series, which is ubiquitous in polyelectrolyte hydrogel. Specific reswelling was observed in concentrated KF solution, implying a very strong F⁻ binding ability of benzyl group. The comprehensive results obtained in this study will be utilized on the design of HPMCP-based controlled release system.     

Track-etched nanopores in spin-coated polycarbonate films applied as sputtering mask

Thin polycarbonate films were spin-coated on silicon substrates and subsequently irradiated with 1-GeV U ions. The ion tracks in the polymer layer were chemically etched yielding nanopores of about 40 nm diameter. In a second process, the nanoporous polymer film acted as mask for structuring the Si substrate underneath. Sputtering with 5-keV Xe ions produced surface craters of depth ∼150 nm and diameter ∼80 nm. This arrangement can be used for the fabrication of track-based nanostructures with self-aligned apertures.     

Ti-PS nanocomposites by plasma immersion ion implantation and deposition

We synthesize Ti-PS nanocomposites by plasma immersion ion implantation and deposition (PIII&D) technique. Ti nanoparticles at size of 5-15 nm are found in PS matrix. We propose the formation of Ti nanoparticles as a result of the combined effect of ion implantation and ion condensation in PIII&D process. X-ray photoelectron spectroscopy measurements reveal that Ti atoms have three different chemical states, metal, oxide and carbide. While surface Ti atoms are oxidized, embedded Ti atoms keep their metallic states by surrounding PS matrix. We characterize optical absorbance of Ti-PS nanocomposites by UV-VIS measurements. An adsorption peak due to the excitation of localized surface plasmon is found at wavelength 337.5 nm and the fractal nature of Ti-PS nanocomposites broaden absorption wavelength from UV to infrared. In addition, we use a protein assay to measure protein immobilization. It is found that the amount of protein immobilized on Ti-PS nanocomposites is almost twice than that on pristine PS. The enhancement mechanisms are attributed to the increased surface roughness as well as covalent linkages between protein molecules and functional groups on the surface of Ti-PS nanocomposites.     

Electronic stopping power for proton in amino acids and protein in 0.05-10 MeV range

The stopping powers for 0.05-10 MeV protons in a group of 15 amino acids and a protein have been systematically calculated. The calculations are based on Ashley’s dielectric model. An approach of evaluating the optical energy loss function is incorporated into the Ashley’s model because no experimental optical data are available for these bioorganic compounds. The Barkas-effect correction and Bloch correction are included and an empirical minimum impact parameter a is used for the Barkas-effect correction. The proton stopping powers for the 15 amino acids and the protein in the energy range from 0.05 to 10 MeV are presented here for the first time and might be useful for studies of various radiation effects in these materials.     

Thermo-mechanical characteristics of UV-irradiated polyurethane elastomers extended with α, ω-alkane diols

A series of polyurethane elastomers were prepared by the reaction of poly ε-caprolactone and 4,4′-diphenylmethane diisocyanate. The prepolymer was extended using α, ω-alkane diols as chain extenders having 2-10 methylene units in their structure. The synthesized samples were irradiated for 50, 100 and 200 h in an ultra violet (UV) exposure unit. Modifications in the chemical structure before and after irradiation were characterized using Fourier Transform Infrared spectroscopy. The thermal and mechanical properties were affected by the ultra violet irradiation time and the number of methylene units in the chain extenders. The experimental results indicated that the morphological structure changed during irradiation as a consequence of hard segment and soft segment degradation.     

Initial stage of etching through pores in PET films irradiated by Ar ions

Changes in the diameters and depths of pores were studied in the process of etching polyethyleneterephthalate (PET) films irradiated by Ar ions having an energy of 1 MeV/n. Information about the pore diameters and lengths was obtained with JSM-840 and TEM-125 electron microscopes. The solutions of NaOH (0.5 mol/dm³ and 2 mol/dm³) were used as etchants. Etching was performed at 55 °C and 70 °C. Two methods of sensitization were used: the first one by UV illumination and treatment in dimethylformamide (DMF), the second method just by UV illumination. It was found that the diameters and the depths of pores are larger in films treated according to the first sensitization method. Etching duration (breakthrough time), which leads to through-going pores of the minimal radius, was established. After sensitization according to the first method the track etch rate grows quicker than the transverse etch rate. This gives a possibility to obtain through pores with diameters ranging from 50 nm to several micrometers.     

Production and characterization of thin Li targets fabricated by ion implantation

Very high fluence implantation of ⁷Li⁺ ions was used to promote the formation of a thin and high density ⁷Li target in the surface region of Al samples. The implanted volume was characterized by particle induced gamma-ray emission, Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy and nuclear reaction analysis, revealing that the implanted surface is a combination of Li₂CO₃, metallic lithium, LiOH and C, with almost no Al present. Radiation damage effects by proton beams were studied by observing the evolution of the ⁷Li(p, α)⁴He nuclear reaction yield with the accumulated charge, at different proton energies, revealing high stability of the produced Li target.