Effect of Electron Beam Irradiation on Polymers

Abstract

A B S T R A C TElectron energy loss spectroscopy (EELS) in combination with transmission electron microscopy (TEM) is widely used for chemical state analysis of variety of chemical compounds. High beam sensitivity of substances like polymers hinders the possibility of exploring in-depth analysis provided through the high spatially resolved EELS spectroscopy. In this study, the electron beam irradiation damage on polymers were analyzed with varying dose of electron beams. The stability of the polymers under electron beam exposure depends on the chemical structure on the polymers. In this study the polymers with and without phenyl groups namely Polycarbonate, Polyethylene terephthalate, Polystyrene, Styrene Maleic Anhydride and Polymethylmethacrylate are selected for the comparative degradation study. Effect of varying the electron dose on the stability of polymers were monitored by recording the low-loss EELS spectrum in π to π* transition and (π+σ) to (π+σ)* transition region.

The Effect of High-Energy Ionizing Radiation on the Mechanical Properties of a Melamine Resin, Phenol-Formaldehyde Resin, and Nitrile Rubber Blend

“…At present, a number of research papers are dedicated to the modification of polymers by EB radiation. The fundamental principles of all applications of radiation treatment of polymers are evaluated, for example, in [10]. In general, it is well known that some polymers can be cross-linked with EB radiation, while others tend to degrade.…”

Modelling the Stiffness-Temperature Dependence of Resin-Rubber Blends Cured by High-Energy Electron Beam Radiation Using Global Search Genetic Algorithm

“…Mostly very indistinctly double, asymmetric damping peaks with faint interphase between them in the rubbery state of the blend at temperatures approximately between 317 K and 455 K can be associated with the glass transition of melamine resin at temperature T g(MFR) [32] and phenol-formaldehyde resin at temperature T g(PF) [33], respectively. However, these temperatures are, depending on the size of the radiation dose, shifted closer to each other compared to the glass transition temperatures of the individual resins of the blend due to the relatively high degree of miscibility of their molecules and the chemical interactions between their macromolecular segments affected by ionising radiation [8]. At the same time, all three glass transition temperatures identified from the top of peaks on loss tangent curves are significantly shifted towards higher values compared to temperatures identified from peaks on loss modulus curves or from inflexion points on storage modulus curves.…”

“…The free chain radicals finally react with each other leading to the formation of a chemical cross-link accompanied by an increase in molecular weight. At lower radiation doses, cross-linking has a lateral character, while irradiation with higher radiation doses leads to the formation of a three-dimensional polymeric network [8]. On the other hand, radiation-induced degradation of irradiated polymers occurs by breakage of the main chains of the polymeric material, leading mainly to a decrease in its molecular weight [9].…”

100th Anniversary of Macromolecular Science Viewpoint: Polymeric Materials by In Situ Liquid-Phase Transmission Electron Microscopy

“…Therefore, post mortem verification of structure and chemistry is critical (see next section). Though many TEMs used for LPTEM videography are equipped with both X-ray and electron energy loss spectrometers (EELS), the background noise that is generated from the thick liquid layer and windows washes out any features related to the solvated polymers of interest, and in situ LCTEM spectroscopy of polymers is of most utility for measuring the approximate liquid thickness in the LC-vessel or for qualitative mapping of high-Z species. ,,, However, prior to running an in situ LCTEM experiment, we can run EELS analysis of a dried film (thin section) ,,− of our polymer sample to probe the various ionizations and excitations that comprise the total energy absorbed by that polymer during TEM beam irradiation at specific flux, fluence, and keV conditions. Such an analysis would yield information into direct beam damage to the polymer relevant to LPTEM.…”

“…For organic molecules or polymers under TEM beam irradiation, scattering events with Δ E ≤ 10 eV correspond to excitations in the UV absorption spectrum, those related to valence-π excitations (π → π*) and valence-π ionizations (π → π •+ + e SE – ) (Figure ). ,,,,,, These low-energy excitations are described by the material’s dielectric function, ,, and DFT methods can be used to model valence level excitations . Due to the very low Δ E involved and the delocalized nature of π-bonding electrons in carbon molecules, the energy transferred in (π → π*) excitation events is also delocalized and generally does not lead to complete bond breakage in the polymer; the excited state is distributed over several C atoms and relaxes via non-damaging deexcitation , PH * → PH ). , The ionization of π-bonded electrons, π → π •+ + e SE – , results in the instantaneous alteration to the polymer’s bonding structure (CC → C–C •+ ); the double bond converts to a radical-ion single bond (Figure ), and complete C–C bond scission is generally avoided by a slight molecular rearrangement or by intrapolymer electron transport in conductive polymers. ,, Aromatic compounds and polymers containing phenyl groups have especially large peaks in the π → π* excitation region, reflective of the high density of CC π-bonds, ,,, and are generally more resistant to direct radiation damage in bulk polymer samples …”