Modifications of polymers by additives and irradiations and their characterizations

Abstract

Polymer properties are often engineered in desired directions by additives or by irradiations or by both. However, in space and certain other applications, energetic particles or γ -rays may damage the polymeric parts in undesired directions, needing prior radiation damage studies for necessary precautions. Case studies of three completely different polymeradditive composites follow: (1) shielding e lectro m agnetic i nterference (EMI) by different composites of a polymeric binder, (2) electrical, thermal, mechanical (Young ' s Modulus, Y) and positron lifetime (PL) characterizations of solid polymer electrolytes (SPEs), and (3) determination of total free volume and hole size by pressure-volume-temperature (P-V-T) and positron lifetime techniques, respectively, in two types of polymers. One type consists of complexes of poly-(ethylene oxide), PEO, with a suitable salt, PEO-salt SPEs. The other type consists of silica-fi lled and pure varieties of poly(dimethyl siloxane), PDMS. Melting point and glass transition temperature of these polymers have been determined from PL techniques as well as from differential scanning calorimetry (DSC). Electrical contact problem has been addressed by measuring impedance as a function of pressure, p, and then extracting p = 0 values of impedance and Young ' s Modulus. These illustrative measurements have been carried out for better characterization of the polymers. DSC thermogram showed that radiation induced changes of melting point of PEO-salt samples are in opposite directions for 160 MeV Ne 6 + ion and 1.25 MeV γ -ray irradiations. This interesting feature hints at different mechanisms of radiation damage in two cases.

Conductivity and dielectric studies of Li3+-irradiated PVP-based polymer electrolytes

“…Therefore, ions can migrate in the amorphous region. The dominance of darker portion which is amorphous was also confirmed by many other scientists 38,39…”

Conductivity Modulation in Polymer Electrolytes and their Composites due to Ion-Beam Irradiation

“…At higher dose, the conductivity drops down and the matrix retains its original backbone, therefore, the variation in conductivity can be attributed to the variation in the number of charge carriers due to possible cutting of the chains. It is reported that the low dose of the ions cut the long chain and create regions of local increased amorphicity, but at higher dose exposure may cause the release of hydrogen and hence carbonization of polymer films may also occur [124,125]. The fluence of the ion beam was gradually increased up to the limit where the backbone of the polymer film does not collapse and hydrogen is released from the chain.…”

Ion Irradiation Effects in some Electro-Active and Engineering Polymers Studies by Conventional and Novel Techniques

“…This energy is equally distributed into two oppositely emitted photons (each of energy 511 keV in the electron-positron centre of mass) to meet the criteria of momentum conservation. The start-stop coincidence γ-spectrometer detects the 1.27 MeV photon as the start and one of the two 511 keV photons as the stop for a time to pulse height (TPH) analyzer [181]. The time difference between the occurrences of these two events is measured as the lifetime of the positron and the lifetime spectrum N(t) vs. t is recorded by a multi channel analyzer or a computer.…”