M.A. de Araújo

Modifications in the chemical bonding and optical absorption of PPS by ion bombardment

Abstract Commercial-grade thin poly(p-phenylene sulphide) (PPS) foils, 2 μm thick, have been bombarded with 1H+ (380 keV), and with 0.61 MeV/amu 4He+, 12C2+, 16O3+, 32S3+, 79Br9+ and 127I14+ ions. The completely modified foils have been analyzed by Fourier transform infrared absorption spectroscopy (FTIR) and by ultraviolet-visible absorption spectroscopy (UV-VIS). The bond breaking and rearrangement processes were followed by using the FTIR results. The absorbance of bands related to CS, SS, CH and most of the ring carbon bonds show an exponential decrease as a function of fluence. The absorption bands most sensitive to the ion bombardment are those assigned to CS and SS bonds. The CC and CH bonds are less sensitive and certain absorption band changes indicate carbon-carbon aliphatic and or aromatic conjugation, due to their increasing intensity as a function of the ion fluence. Damage cross sections have been extracted from the plots of IR absorbance versus fluence. The values of the damage cross sections obtained scale roughly with the square of d E d x (independent of the nature of the chemical bond). The optical absorption coefficient has also been followed as a function of the ion fluence.

Study of the thermal stability of PPS films bombarded with B+ and Ar2+ ions

Abstract The thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and solubility tests, can be advantageously used on the study of chemical effects on ion-bombarded polymeric materials. Ionic implantation affects both chemical and physical structures of these materials and at low fluences these changes are hard to detect. TGA allows a qualitative assessment of the degradation process through the analysis of residual mass thermograms and a quantitative evaluation of the bombarded samples activation parameters by means of dynamic kinetic measurements. For PPS (paraphenylene sulfide) samples irradiated with 10 12 B + /cm 2 fluence the activation energy ( E A ), calculated for low conversions (10–30%), is 290 kJ/mol, which is similar to the value of the pristine polymer. Higher fluences B + led to lower E A showed a drop of 30% in relation to the pristine. Effects on PPS, poly(paraphenylene sulfide), bombarded with B + and Ar 2+ led to a gradually increasing loss of thermal stability and higher residual mass. Multimodal thermograms revealed increasing complexity of the resulting polymeric materials as fluences become higher. Ion stopping power played a key role on the thermal behavior of the modified polymer chains. The TGA results correlated well with the FTIR results, in which C-S and S-S bonds showed to be more susceptible to the ionic bombardment and thermal degradation process than the other bonds. Progressive crosslinking in the bombarded samples is followed by solubility tests and residual mass.

Morphological changes induced in PPS by ion bombardment: amorphisation and recrystallization ability

Abstract Thin poly(paraphenylene sulfide) (PPS) films (Torelina, from Toray Co., Japan, 2 μm thick) were bombarded with energetic 1 H + (300 keV), 4 He + (380 keV), 10 B + (350 keV) and 40 Ar 2+ (700 keV) ions at fluences ranging from 10 12 to 8 × 10 14 ions/cm 2 . The beam current density was kept at 20 nA/cm 2 in order to avoid excessive heating and outgassing damage. The modified samples were analysed by differential scanning calorimetry (DSC). Both the melting onset temperature and the enthalpy of fusion, that are related to the crystalline structure, decrease with increasing ion fluence. This systematic study, made with successive heating and cooling cycles in the DSC measurements, shows that the ion bombarded polymer gradually lost its crystallinity and its ability for recrystallization, as the ion fluence increases. Over a critical fluence, which depends on the bombarding ion and energy, the amorphisation process accelerates and above a certain fluence the polymer becomes completely amorphous. The above discussed modification in the PPS morphology occurs in a fluence range where the chemical degradation was not significantly noticed by Fourier transform infrared spectroscopy (FTIR) measurements. The modification radii for the amorphisation process were extracted and the results discussed considering the energy deposition density.

Chemical damage and aging of ion bombarded PPS

Abstract Thin foils of commercial grade polyphenylene sulfide (PPS), 2 μm thick, were bombarded with energetic H+ (300 keV), He+ (350 keV), B+ (350 keV) and Ar++ (700 keV) ions at fluences ranging from 1012 to 10 15 ions/cm 2 . Fourier transform infrared spectroscopy (FTIR), Rutherford backscattering analysis (RBS) and chemical elemental analysis (CHN) were performed to evaluate the chemical changes induced by ion bombardment in the polymeric samples. It was verified that the S–S and C–S acyclic bonds were more susceptible to ion bombardment, and the aromatic ring bonds are the most resistant ones. The effective modification radii for the bond breaking and recombination processes were extracted. The aging of bombarded PPS was monitored and oxygen and nitrogen uptake increased linearly with time.

Damage and ageing effects on proton beam irradiated C60 films

Abstract In this paper, we report results on the interaction of 400 keV H + ions with thin C 60 films focusing on post-irradiation ageing effects. Infrared spectroscopy and resonant α-scattering have been used for characterization of the targets. The analysis were made at different times after bombardment during a period of several months. It has been observed that the signal from the characteristic C 60 IR bands decrease up to 50–70% after the first post-irradiation analysis of the targets. Such ageing is correlated to the appearance and evolution of the oxygen signal in the resonant α-scattering spectra, as well as to the presence of carbonyl bands in the IR spectra of aged targets. For a fixed ageing time the intensity of C 60 IR bands decrease exponentially as a function of fluence.

Synthesis and characterization of EPDM films

A series of ethylene-propylene-2-ethylidenebicyclo[2.2,1]hept-5-ene terpolymers have been prepared using the VOCl 3 /Al 2 Et 3 Cl 3 catalyst under various initial Al/V ratios and diene concentrations. The V/C and Al/V ratios in EPDM films were determined by Rutherford backscattering spectrometry. The concentration of incorporated vanadium increases with the increase of the iodine number, i.e., with the number of double bonds in the polymer. However, the concentration of incorporated V in the terpolymers remains relatively low, which is attributed to the small percentage of V(III) active species due to the presence of the diene. On the other hand, the Al/V molar ratio in the terpolymers was seen to be roughly constant (between 6 and 8), independent of the iodine number and of the initial Al/V molar ratio in the reaction mixture. The polymerization yield was seen to increase with the augmentation of the initial Al/V ratio and of the diene concentration, until reaching a maximum of about 500 g polymer/g V.

Bulk and surface modifications of insulating poly (paraphenylene sulphide) films by ion bombardment

Abstract Thin poly(paraphenylene sulphide) (PPS) films (2 μm thick), bombarded with He + (380 keV), B + (350 keV) and Ar 2+ (700 keV) at fluences ranging from 10 12 to 2 × 10 16 ions cm −2 , were analysed by X-ray diffractometry, UV-visible absorption spectroscopy, electrical resistance measurements and solubility tests. The polymer gradually underwent an amorphization process indicated by the decrease in the main X-ray diffraction peak area and also lost its solubility with increasing ion fluence. This behaviour revealed the formation of cross-linking and amorphous structures. A red shift of the optical absorption threshold with increasing fluence was also observed by UV-visible spectroscopy. This trend is usually attributed to the conjugation of unsaturated carbon bonds which gives rise to non-localized π electrons. From these spectral data the gap between valence band and conduction band (optical gap E g ) using a model for amorphous semiconductors can be obtained. The conjugation process increased with fluence resulting in a decrease in the optical gap. For Ar 2+ -bombarded samples the optical gap saturated at 0.9 eV for fluences around 10 15 cm −2 . The decrease in E g with increasing fluence is a direct indication that a new group of conducting structures is being formed in the polymeric material. Electrical measurements made immediately after 2 × 10 16 Ar 2+ cm −2 bombardment revealed that the electrical resistivity decreased by 18 orders of magnitude in relation to the original PPS. When the bombarded samples were exposed to air the electrical conductivity decreased. This electrical instability was assigned to the free radicals present in the polymer chain after ion bombardment. This work shows that different hydrogenated amorphous carbon films can be obtained from one common polymeric matrix by judicious choice of the projectile ion stopping mechanism.