Chemical modification of polystyrene by low‐energy (<100 eV) electron irradiation studied by mass spectrometry

Abstract

Dip-coated thin films of polystyrene were chemically modified (degraded) by low-energy electron irradiation (0-100 eV). The resulting degradation was studied by mass spectrometry with variable electron energy. In the negative-ion mode, H 2 was observed and was associated with two phenomena. The resonant structure at 9.1 6 0.4 eV was associated with dissociative electron attachment. The energy of the resonance peak agreed with the results obtained for organic molecules. At a higher energy, a monotonic rise of the emission yield was observed and was associated with nonresonant dipolar dissociation. More mass fragments were observed in the positive-ion mode. The predominant ion was H 1 at 100 eV of electron irradiation, and alkyl ions were detected at higher masses. Emission thresholds were measured for the most predominant positive ions. The shape of the emission curve showed that there was no resonant process in the formation of these ions. The energy threshold was measured at about 20 eV, and this meant that the carbon structure of the polymer broke with a recombination of the degradation products with hydrogen atoms before the emission occurred. Below 19 eV, there was only hydrogen loss; this implied that the possible degradation mechanisms did not break the general carbon structure of the material, leading to crosslinking.

Effect of Electron Beam Irradiation on Polymers

“…Their study suggested a significant increase in characteristic dose leading to a radiation damage as the electron beam diameter is reduced from 1 µm to below 1 nm. [24][25][26][27][28][29][30][31][32][33]2018 electron beam radiation damage of other polymers through TEM-EELS technique is also reported in literature [25,27,28]. The kinetic mechanism of polystyrene thermal degradation is being studied by Faravelli et al [29] through kinetic models and predicts the radical formation as the route cause of degradation.…”

“…Molecular weight dependent degradation of polystyrene was studied by Madaras et al [32] and observed that random chain scission coefficient depends on the Mw of PS. The effect of low energy (<100 eV) electron beam exposure to polystyrene was studied by mass spectrometer and a chemical modification was reported by Massey et al [33] The irradiation with electron beam leads to the radical formation and bond breakage and cleavage of the phenyl group from the chain. Svorcik et al [34] have irradiated the polystyrene surface with high energy electron beam and observed scission of aromatic ring followed by cross linking in the polymer.…”

“…[24][25][26][27][28][29][30][31][32][33]2018 There are two peaks observed in this region, which are common for polymers: peak around 5 eV from π to π* transition and peak around 23 eV from (π+σ) to (π+σ)* transition. It has been observed that the peak positions started to shift within fraction of seconds of exposure to the electron beam.…”

“…The order of stability can be translated as PC<PMMA<PET<PS<SMA as deduced from the dose required for degradation. [24][25][26][27][28][29][30][31][32][33]2018 degradation in polymers is unavoidable and the extent of degradation depends on the structure of the polymers.…”

Note: Transient negative ions as initiators of oxygen fixation in &lt;20 eV electron-irradiated DNA

“…The possibility of RCH x−1 • + H + contribution can be neglected since H + production does not involve a TNI, and the energy threshold to H + desorption is ~25 eV. 14,15 The maximum in Fig. 1(c) can thus be due to a TNI enhanced increase at this energy, in the population of states leading to dissociation, or perhaps reflects a competition between RCH x−1 • formation and another RCH x excitation/dissociation channel less efficient in producing sites for "oxygen fixation."…”