Swift heavy ion induced modification in dielectric and microhardness properties of polymer composites

Polymer composites with different concentrations of organometallics (ferric oxalate) dispersed PMMA were prepared. PMMA was synthesized by solution polymerization technique. These films were irradiated with 120 MeV Ni¹⁰⁺ ions in the fluence range 10¹¹-5 × 10¹² ions/cm². The radiation induced modifications in dielectric properties, microhardness, structural changes and surface morphology of polymer composite films have been investigated at different concentrations of filler and ion-fluences. It was observed that electrical conductivity and hardness of the films increase with the concentration of the filler and also with the fluence. The dielectric constant (?) obeys the Universal law given by ?αfⁿ⁻¹. The dielectric constant/loss is observed to change significantly due to irradiation. This suggests that ion beam irradiation promotes the metal to polymer bonding and convert polymeric structure into hydrogen depleted carbon network. This makes the composites more conductive and harder. Surface morphology of the films has been studied using atomic force microscopy (AFM) and scanning electron microscopy (SEM). The average surface roughness is observed to increase after irradiation as revealed by AFM studies. The SEM images show the blisters type of phenomenon on the surface due to ion beam irradiation.     

Effect of gamma radiation on the structural and optical properties of Polyethyleneterephthalate (PET) polymer

Effect of 1.25 MeV gamma radiation on the structural and optical properties of virgin and gamma irradiated (0-2000 kGy) Polyethyleneterephthalate (PET) polymer samples are analyzed using powder X-ray diffractometer and UV-vis spectrophotometer. Diffraction pattern of PET polymer indicates the semi-crystalline in nature whereas the crystallinity increases with increasing dose of irradiation. The remarkable variation in crystallite size is also observed. The absorption and activation energy increase and the optical band gap (E_g) decreases with increasing dose in UV-vis studies. The existence of the maximum absorption, their shifting and broadening due to gamma irradiation in PET polymer are also discussed.     

Facile synthesis of PbTe nanoparticles and thin films in alkaline aqueous solution at room temperature

A novel, simple, and cost-effective route to PbTe nanoparticles and films is reported in this paper. The PbTe nanoparticles and films are fabricated by a chemical bath method, at room temperature and ambient pressure, using conventional chemicals as starting materials. The average grain size of the nanoparticles collected at the bottom of the bath is ∼25 nm. The film deposited on glass substrate is dense, smooth, and uniform with silver gray metallic luster. The film exhibits p-type conduction and has a moderate Seebeck coefficient value (∼147 μV K⁻¹) and low electrical conductivity (∼0.017 S cm⁻¹). The formation mechanism of the PbTe nanoparticles and films is proposed.     

Surface and bulk properties of severely fluorinated carbon fibres

The development of ultra-inert composites using fluorinated carbon fibres as the reinforcement requires fluorinated carbon fibres with a durable surface composition. Here we report the effect of direct fluorination using an F₂/N₂ mixture at 653 K on the surface and bulk properties of two types of high strength carbon fibres. These were treated up to a surface fluorine content of ∼64 at.% and a bulk fluorine content of ∼15 mass%. A colour change was observed after fluorination caused by the changes in the graphitic band structure of the carbon fibres by the introduction of carbon sp³ hybridisation. The tensile strength and Young's modulus decrease after fluorination by up to 33 and 22%, respectively. XRD shows marginal changes in the interlayer distance but the crystallite size increases. Changes in the electrical conductivity of the fluorinated carbon fibres indicate that the modification is confined to the near surface volume. Predominantly covalent C-F bonds are formed as shown by X-ray photoelectron spectroscopy (XPS) and measured zeta (ζ)-potentials. Hence the fluorinated fibres are hydrophobic and have low surface tensions. This and the large increase in fibre surface area, as determined by nitrogen adsorption, is expected to facilitate interfacial interaction between fluorinated carbon fibres and fluoropolymers.     

The effect of nitrogen on the cycling performance in thin-film Si1−xNx anode

The effects of nitrogen on the electrochemical properties of silicon-nitrogen (Si_1−xN_x) thin films were examined in terms of their initial capacities and cycling properties. In particular, Si_0.76N_0.24 thin films showed negligible initial capacity but an abrupt capacity increase to ∼2300 mA h/g after ∼650 cycles. The capacity of pure Si thin films was deteriorated to ∼20% of the initial level after 200 cycles between 0.02 and 1.2 V at 0.5 C (1 C=4200 mA/g), whereas the Si_0.76N_0.24 thin films exhibited excellent cycle-life performance after ∼650 cycles. In addition, the Si_0.76N_0.24 thin films at 50 °C showed an abrupt capacity increase at an earlier stage of only ∼30 cycles. The abnormal electrochemical behaviors in the Si_0.76N_0.24 thin films were demonstrated to be correlated with the formation of Li₃N and Si₃N₄.     

PET-SWNT nanocomposites through ultrasound assisted dissolution-evaporation

Poly(ethylene terephthalate) (PET) based nanocomposites have been prepared with single walled carbon nanotubes (SWNTs) through an ultrasound assisted dissolution-evaporation method. Differential scanning calorimetry studies showed that SWNTs nucleate crystallization in PET at weight fractions as low as 0.3%, as the nanocomposite melt crystallized during cooling at temperature 24 °C higher than neat PET of identical molecular weight. Isothermal crystallization studies also revealed that SWNTs significantly accelerate the crystallization process. Mechanical properties of the PET-SWNT nanocomposites improved as compared to neat PET indicating the effective reinforcement provided by nanotubes in the polymer matrix. Electrical conductivity measurements on the nanocomposite films showed that SWNTs at concentrations exceeding 1 wt% in the PET matrix result in electrical percolation. Comparison of crystallization, conductivity and transmission electron microscopy studies revealed that ultrasound assisted dissolution-evaporation method enables more effective dispersion of SWNTs in the PET matrix as compared to the melt compounding method.     

Optical and Electrical Characteristics of Polymer Films Modified with Nanostructured Silver Aggregates

To study the formation of a new dispersed phase in polymer layers, the absorption of radiation-generated silver aggregates in cellophane films was examined. Stable silver nanoparticles were prepared by the radiation-chemical reduction of silver ions in a solution of inverted micelles of the composition AgNO₃(AgClO₄)/H₂O/AOT/octane. On irradiation of cellophane films immersed in a micellar solution, the formed silver aggregates Ag^m+ _nbecame incorporated into the films. The modified films exhibited a stable yellow color. The intensity of an optical absorption band of the films with _max 420–440 nm increased proportionally to the radiation dose absorbed by an aqueous micellar solution. The light sensitivity of these films was examined. A 35-min exposure of the films at = 365 nm resulted in an increase in the intensity of the main absorption band by 17% and in a bathochromic shift of the maximum. The electrical characteristics of modified films were determined depending on the radiation dose. It was found that the incorporation of nanostructured silver clusters exhibiting the characteristic optical absorption band with _max 420–440 nm increased the conductivity of cellophane films by two to three orders of magnitude.     

Influence of High-energy electron-beam on photocatalytic activity of TiO2 films on carbon-fiber deposited by atomic layer deposition

High-energy electron-beam with energy of 1 MeV was used for modifying surface structure of TiO₂ thin films on carbon fiber prepared by using atomic layer deposition under atmospheric pressure. TiO₂ nanoparticles (∼20 nm) on carbon fiber underwent structural modification of the surface upon electron-beam treatment, resulting in enhanced photocatalytic activity. In contrast, a thicker film of TiO₂ did not show such changes in surface structure and photocatalytic activity by electron-beam treatment. We demonstrate that electron-beam can be used for modifying surface structure of photocatalysts consisting of nanoparticles for improvement of their activity.     

MeV Si ions bombardments effects on thermoelectric properties of SiO2/SiO2+Ge nanolayers

The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT=S²σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and K is the thermal conductivity. ZT can be increased by increasing S, increasing σ, or decreasing K. We have prepared the thermoelectric generator device of SiO₂/SiO₂+Ge multilayer superlattice films using the ion beam assisted deposition (IBAD). The 5 MeV Si ion bombardments have been performed using the AAMU Pelletron ion beam accelerator at five different fluences to make quantum structures (nanodots and/or nanoclusters) in the multilayer superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric generator devices before and after MeV Si ions bombardments at the different fluences we have measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity, Raman spectra to get some information about the sample structure and bond structures among the used elements in the superlattice thin film systems.     

New rod-coil block copolymers consisting of terfluorene segments and electron transporting units as the flexible blocks

A series of new rod-coil block copolymers having a well-defined terfluorene unit as the rigid segment with three different electron transporting moieties as the flexible part, such as side chain oxadiazole (TFPOXD), side chain quinoline (TFPQN) and a molecule containing two oxadiazole rings in the side chain (TFPDOXD), were synthesized using the atom transfer radical polymerization (ATRP) technique. All the synthesized copolymers were extensively examined with respect to their optical properties as pristine films, upon thermal annealing (200 °C for 30 min in air) and photo-oxidation treatment in air. Thermal annealing of the block copolymers resulted in stable blue light emission from TFPOXD and TFPDOXD while TFPQN showed the appearance of the undesired 520 nm emission band. In addition, TFPOXD does not exhibit the low-energy emission band at 520 nm after photo-oxidation under prolonged diffuse UV radiation at ambient atmosphere, despite the fluorenone formation on the terfluorene segment, in contrast to all the other copolymers.     

Thermogravimetric studies on Polyamide-6,6 modified by electron beam irradiation and by nanofillers

This paper reports the results of thermogravimetric studies on: (a) Polyamide-6,6 (abbreviated henceforth as PA66) specimens which were modified by electron beam radiation in air, (b) organic-inorganic hybrid nanocomposite films of PA66/silica prepared by the sol-gel technique and (c) unmodified multi-walled carbon nanotube (abbreviated henceforth as MWCNT) reinforced PA66 films. The activation energies were determined using the Kissinger and the Flynn-Wall-Ozawa methods, which do not require knowledge of the reaction mechanism. The results showed that PA66 specimens which received an irradiation dose of 200 kGy in air had a higher thermal stability than both the neat PA66 and PA66 specimens which received a radiation dose of 500 kGy in air. The PA66/silica hybrid nanocomposites up to a silica loading of 1.5 wt% also showed higher thermal stability over neat PA66 films. At MWCNT loadings of 0.5-1.0 wt% the composite films exhibited higher activation energies than the neat PA66 film but at higher MWCNT loading the activation energy was lower than that obtained for the neat PA66 film.     

Carbon ion beam induced modifications of optical,structural and chemical properties in PADC and PET polymers

We report a study on the carbon ion beam induced modifications on optical, structural and chemical properties of polyallyl diglycol carbonate (PADC) commercially named as CR-39 and Polyethyleneterepthalate (PET) polymer films. These films were then irradiated by 55 MeV C⁵⁺ ion beam at various fluences ranging from 1×10¹¹ to 1×10¹³ ions/cm². The pristine as well as irradiated samples were subjected to UV–Visible spectral study (UV–Vis), Photoluminescence (PL), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. It has been found that ion irradiation may induce a sort of defects in the polymers due to chain scission and cross linking as observed from PL spectral study. It is revealed from UV–Vis spectra absorption edge shifted towards longer wavelength region after irradiation with increasing ion fluence. This shift clearly reflects decrease in optical band gap. The XRD study indicates the gradual decrease in intensity in case of PADC with increasing ion fluence. However, the intensity pattern increased in case of PET at fluence of 10¹¹ ion/cm² then decreased with further increase in fluence. Crystalline size of PADC was found to be decreasing gradually with increase of ion fluence. Whereas, the crystalline size of PET films found to increase with lower fluence and decreases with higher ion fluence. FTIR spectrum also shows the change in intensity of the typical bands after irradiation in the both the polymers. The results so obtained can be used successfully in heavy ions dosimetry using well reported techniques.     

Degradation and stability of polyaniline on exposure to electron beam irradiation (structure-property relationship)

Polyaniline (PAni) was prepared by electrochemical polymerization and subjected to different doses of electron beam (EB) irradiation. The effect of EB irradiation causes both chain scission and cross-linking process in PAni, which depends on irradiation dose. The degree of chain scission and cross-linking in PAni by EB irradiation is characterized through XRD, TGA, DSC, solubility, EPR and electrical properties measurement. The results reveal that with increase in EB irradiation dose from 0 to 150 kGy DC and AC conductivity and dielectric constant are found to increase mainly due to the chain scission or further doping in PAni. Due to irradiation there is change in the structure of PAni, such as decrease in the d-spacing, inter-chain separation, thermal stability and T_g but increase in the percent crystallinity and solubility. With further increase in the EB irradiation dose from 150 kGy onwards the DC and AC conductivity and dielectric constant are decreased due to the cross-link formation or dedoping in PAni, which causes the decrease in percentage of crystallinity and solubility and increase in d-spacing, inter-chain separation, thermal stability and T_g of PAni.     

Effect of cobalt carboxylates on the photo-oxidative degradation of low-density polyethylene. Part-I

The effect of three cobalt carboxylates of increasing chain length, namely cobalt laurate, cobalt palmitate and cobalt stearate on the photo-oxidative degradation of low-density polyethylene (LDPE) films has been investigated. LDPE films containing cobalt carboxylates were irradiated with UV-B light at 30 °C for extended time periods. FTIR spectroscopy, mechanical testing, morphological studies, molecular weight, density and MFI measurements were performed to monitor the degradation behaviour. The results of these studies were analysed to explain the structural and chemical modifications taking place in the polyethylene matrix due to UV-B exposure. FTIR studies indicate that the degradation is dominated by formation of carbonyl and vinyl species. The studies on mechanical properties reveal that samples containing cobalt carboxylates, become mechanically fragile after UV exposure for 400 h, while neat LDPE exhibits insignificant changes during this period. The degradation was found to increase proportionally with increasing chain length and follows the order CoSt₃ > CoPal₃ > CoLau₃. Migration studies were performed on food simulant systems to investigate the applicability of these films for food packaging.     

Novel interpenetrating smart polymer networks grafted onto polypropylene by gamma radiation for loading and delivery of vancomycin

Gamma radiation was used in every step of the synthesis of a sequential interpenetrating polymer network made of two “smart” polymers: poly(acrylic acid) (PAAc) and poly (N-isopropylacrylamide) (PNIPAAm), the latter grafted onto polypropylene (PP) films (PP-g-PNIPAAm) with the aim of developing medicated coatings for medical devices. Three steps were followed for obtaining net-PP-g-PNIPAAm-inter-net-PAAc: graft copolymerization of PNIPAAm onto PP films by gamma pre-irradiation oxidative method, cross-linking of PP-g-PNIPAAm by gamma irradiation in water to form the first network, with or without N,N′-methylenebis(acrylamide) (MBAAm), and finally the formation of the second network through the polymerization and cross-linking of AAc inside cross-linked PP-g-PNIPAAm by a low gamma radiation dose of 2.5 kGy. The films were characterized regarding the amount of grafted polymers and their composition (FTIR-ATR), thermal behavior (DSC), temperature- and pH-responsive swelling and contact angle (critical pH 6 and lower critical solution temperature ∼33 °C), and loading and release rate of vancomycin. Drug loading was driven by specific interactions between vancomycin and PAAc. Drug-loaded films sustained the delivery for several hours at pH 7.4 and provided release rate values adequate for killing bacteria attempting to adhere the surface of the films.     

Characterization of oxygen and argon ion flux interaction with PET surfaces by in-situ XPS and ex-situ FTIR

The effects of low (2.5, 0.2 keV) energy reactive oxygen ion bombardment and argon ion bombardment on poly(ethylene terephthalate) thin film (PET) surface chemical composition were studied. PET films have a high potential as a material for biomedical and electrical industries. The source of ions was an ECR Ion Gun with settable acceleration voltages. PET films were sputtered by ion bombardment for variable process time and the modified films were investigated by in-situ X-ray Photoelectron Spectroscopy (XPS) and ex-situ Fourier transform infrared spectroscopy (FTIR). The significant changes in the chemical composition of surface layers were quantitatively studied by XPS. The ion bombardment scissions the chains in PET film surface layers. Selective sputtering of oxygen atoms from PET surface was observed when argon ion flux used. The 0.2 keV and 2.5 keV argon ion decreased O/C ratio from 0.37 to 0.25, 0.04 respectively. This phenomenon is responsible for the creation of carbon-rich up 96 at.% surface layer and the oxygen in ester bonds is detached first. The oxygen 2.5 keV ion bombardment had similar effect as argon ion bombardment; the ratio O/C was decreased. The ester bond was broken first. But oxygen 0.2 keV ion flux irradiation created an oxygen rich surface; the O/C ratio was in increased from 0.37 to 0.46. The changes in surface conductivity were investigated by shifts in C1s binding energy. Good agreement with atomic concentration of carbon in C-C bonds on the films surface was found. The FTIR analyses identified changes in chemical composition but with no obvious correlation to surface changes. Photons from the ion source irradiating the PET film during ion bombardment probably caused the observed changes in FTIR spectra.     

Unusual photo-induced behaviour in a side chain liquid crystalline azo-polyester

An unusual behaviour has been observed in the photo-induced response of an azobenzene side chain liquid crystalline polyester (P6d4). Room temperature irradiation with linearly polarised 488 nm light does not induce any birefringence (Δn) in films of this polymer that have been quenched from the isotropic state. However, using the same irradiation conditions Δn is induced in quenched films that have been kept in darkness for a few minutes. Besides, no photo-induced Δn is observed in films irradiated with 488 nm light that have been previously irradiated with UV light. In this case, Δn can be recorded if the UV irradiated films have been kept in darkness for several hours. In another set of experiments performed with the P6d4 polymer, irradiation with high intensity linearly polarised 488 nm light induces an initial increase of Δn and then it goes back to zero. Subsequent irradiation with linearly polarised 633 nm light induces an orientation of the azobenzene chromophores perpendicular to the polarisation of the 488 nm light and independent of the 633 nm light polarisation direction. These results are very different from those obtained in other side chain polyesters which only differ from P6d4 in the end substituent. The anomalous behaviour of P6d4 is discussed in terms of a supercooling effect of the isotropic phase, the trans to cis back isomerization, the trans aggregation kinetics and a memory effect associated with the main chain orientation.     

The lower surface free energy achievements from ladder polysilsesquioxanes with fluorinated side chains

The surface free energy of non-F and F-containing ladder polyepoxysilsesquioxanes was calculated by two- and three-liquid methods based on contact angle measurements. These ladder polyepoxysilsesquioxanes exhibited lower surface free energy (<17 mJ/m²) because of their main chain packing on the surface of the films where the side chain alignment was promoted by their ladder structure. And the surface free energy of the polyepoxysilsesquioxanes could be reduced further by the incorporation of perfluoroalkyl group into the side chains (∼13 mJ/m²). The X-ray diffraction results revealed that the F-containing side chain lead to the ladder main chain much more flattening on the surface of the films, explaining the contributions of side and main chain arrangements to the surface free energy.     

Enhanced electrical conductivity of Ag-mercaptosuccinic acid-redoped polyaniline nanoparticles during thermal cycling above 200 °C

Ag-doped polyaniline (PANI) nanoparticles are prepared via doping-dedoping-redoping with the thiol group in mercaptosuccinic acid (MSA) providing the linkage between PANI molecules and Ag atoms. Ag-MSA-doped PANI maintains the electrical conductivity well above the room-temperature value of 3.0 S/cm up to 220 °C, reaching its maximum (9.0 S/cm) at 180 °C. In addition, Ag-MSA-doped PANI nanoparticles show remarkable stability against repeated thermal aging at 120 °C. The room-temperature conductivity, in fact, increases by a factor of ∼3 after 3 cycles of thermal aging. The enhanced stability against repeated thermal aging is attributed to the formation of uniformly distributed Ag nanoparticles within the PANI particles upon heating.