Gamma irradiation effects on polymethyl methacrylate

Al-Qaradawi, I.Y.; Abdulmalik, D. A.; Madi, N.K.; AlMaadeed, Mariam Al-Ali

doi:10.1002/pssc.200675846

Cited by 15 publications

(11 citation statements)

References 12 publications

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“…It is clearly seen that aging lead to the development of macroscopic cracks on the surface of LLDPE, resulting in the loss of mechanical integrity of the sample. This is expected to be due to the oxidation of the samples due to the UV irradiation, as the creation of defects is a common phenomenon in polymers after irradiation [27,28] and after weathering for gamma irradiated samples, in which oxygen enters the amorphous parts in the samples and reacts with free radicals creating cracks [29]. Fig.…”

Section: Optical Microscopymentioning

confidence: 99%

The stabilizing effect of expanded graphite on the artificial aging of shape stabilized phase change materials

et al. 2015

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Section: Optical Microscopymentioning

confidence: 99%

The stabilizing effect of expanded graphite on the artificial aging of shape stabilized phase change materials

et al. 2015

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“…In some blends, however, stronger changes have been observed and attributed to a phase separation during the early aging period (89). Further fields studied by using PALS are the γ-irradiation of polymers (124,125) and cross-linking of rubbers (126,127). Of particular interest are studies of the free volume in permeable membranes (82,102,109,128) and among them in those with high internal microporosity (129).…”

Section: The Influence Of Other Structural Properties On Palsmentioning

confidence: 99%

Positron Annihilation Spectroscopy

Dlubek

2008

Encyclopedia of Polymer Science and Technology

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FundamentalsThe positron is the antiparticle of the electron, ie, it has the opposite charge but otherwise the same properties. In matter, a positron may be created either by the β + decay of an unstable nucleus or from a high-energy γ-photon via e + -e − pair production. If the positron encounters an electron, both particles annihilate, ie, they are transformed into photons of an energy, which is given by the famous Einstein equation, E = 2mc 2 . Here, m is the mass of the electron, c the speed of light in vacuum, and for particles at rest E = 2 × 0.511 MeV. The selection rules for the γ-photon emission are derived from the conservation laws of energy and momentum and parity considerations. Free positrons annihilate mainly into two γ-photons of energy 0.511 MeV emitted in almost collinear directions, or with much less probability into three photons of an overall energy of 1.022 MeV (16,24,25).In nonconducting materials, such as polymers, positrons can exist as free particles (e + ) or as positronium (Ps, e + e − ), which is a positron-electron bound state. Ps was experimentally discovered by DeBenedetti and Richings in 1952 (26). The "chemical" symbol Ps for positronium appears to have been introduced by McGervey and DeBenedetti in 1959 (27). Its properties and interaction with matter were reviewed in several articles (25-30). Ps is a particle of the size of a hydrogen atom, r Ps = 0.53Å, but only the mass of two electrons, and a binding energy of 6.8 eV, that is half of the ionization energy of hydrogen. The lifetime of a Ps atom depends on the relative spin orientation of positron and electron. The para-Ps (p-Ps, singlet state, spins antiparallel) decays into two photons with a mean intrinsic lifetime (self-annihilation in a vacuum) of τ pPs 0 = 0.125 ns. The ortho-Ps (o-Ps, triplet state, spins parallel) can decay only into three photons, a much slower process than two-photon emission. Therefore, o-Ps has an intrinsic lifetime of τ oPs 0 = 142 ns. The formation probabilities of the p-Ps and o-Ps states are 0.25 and 0.75 of the total Ps yield (16,25).In condensed matter studies, 22 Na is usually used as the positron source. This isotope has a half-life of 2.6 years and emits positrons with an energy distribution that has its maximum at 0.20 MeV and ranges up to 0.54 MeV (10,16). The stopping profile of positrons is a decreasing exponential function. In materials with a density of 1 g/cm 3 50%, 90%, and 99% of positrons are stopped within a thickness of 0.170, 0.60, and 1.20 mm, respectively. The energetic positrons lose their energy rapidly via ionization and excitation of electrons and finally phonons. After a few picoseconds, the positrons are in thermal equilibrium with the ambient material. In defect-free molecular crystals, positrons migrate over a mean distance of typically 100 nm before annihilating. In defected crystals and in amorphous matter, positrons may annihilate from local free volumes. The mean positron lifetimes are typically τ e+ = 200-400 ps.

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“…It is obviously caused by photodegradation, in which monomers and other low molecular weight degradation products are formed. The decrease of glass transition temperature due to the intensive chain scission has been also reported for PMMA exposed to highly energetic gamma irradiation 38…”

Section: Resultsmentioning

confidence: 99%

Atomic force microscopy studies of poly(methyl methacrylate) doped with photoinitiator

Kaczmarek

Gałka

Szalla

2011

J of Applied Polymer Sci

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Atomic force microscopy has been applied for measuring the nanomechanical characteristics of poly (methyl methacrylate) thin films containing 5% photoinitiator (Irgacure 651). The nanohardness, Young's modulus, and adhesion to AFM tip have been evaluated for the unexposed samples and after UV-irradiation. Additionally, FTIR spectroscopy and differential scanning calorimetry (DSC) have been applied to explain the observed changes in nanomechanical properties. It was found that the exposure to ultraviolet changed the nanomechanical properties of polymer because of photo-oxidative degradation and relaxation processes. These studies lead to the conclusion that the applied photoinitiator has no noticeable effect on nanohardness and Young modulus during PMMA irradiation, but efficiently participates in polymer photo-oxidation increasing the surface hydrophilicity and adhesion to Si 3 N 4 . Moreover, the initiator hampers the relaxation of PMMA macromolecules, what was proved by DSC.

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Gamma irradiation effects on polymethyl methacrylate

Cited by 15 publications

References 12 publications

The stabilizing effect of expanded graphite on the artificial aging of shape stabilized phase change materials

The stabilizing effect of expanded graphite on the artificial aging of shape stabilized phase change materials

Positron Annihilation Spectroscopy

Atomic force microscopy studies of poly(methyl methacrylate) doped with photoinitiator

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