Impact of Heating on the Structure of Perfluorinated Polymer Electrolyte Membranes: A Positron Annihilation Study

Abstract

The ortho‐positronium (o‐Ps) lifetime was measured as a function of temperature for the perfluorinated PEMs Nafion NR212 and Aquivion E8705. The o‐Ps lifetime in Aquivion E8705 was found to be shorter than Nafion NR212 in the entire temperature range studied. Abrupt changes in the temperature coefficient of the o‐Ps lifetime were noticed and the α‐relaxation, β‐relaxation, and stress relief temperatures were identified. It turned out that Aquivion E8705 has higher α‐relaxation and stress relief temperatures than Nafion NR212. Dissociation of the ionic clusters and large change in the nanostructure after heating to 160 °C were observed for Nafion NR212 but not for Aquivion E8705. It is demonstrated that Aquivion E8705 has a higher thermal stability than Nafion NR212. magnified image

Electrical conductivity and mechanical properties, free volume, and γ‐ray transmission of ethylene propylene diene monomer/butadiene rubber composites

“…The general definition of the free volume is the open space that is freely moving in a medium . In a series of experiments in polymers, the free volume size (open hole size), its fraction, and its distribution as a function of sorption gas, permeability, electric field, time, temperature, and doped concentration, have been investigated using the positron annihilation lifetime (PAL) technique.…”

Microstructure Characterization of Nafion®g HP JP as a Proton Exchange Membrane for Fuel Cell: Positron Annihilation Study

“…This inflection point can be also called T g which happens to amorphous polymers. This can be connected to the α-relaxation of Nafion ® which is associated with the onset of long-range mobility of both the main-and side-chains [16]. In the first region, below T g , σ decreases with increase of temperature up to T g due to the loss of surface and bound water gradually, leading to a decrease in the ionomer cluster order responsible for the proton transport.…”

“…• C which could be associated with α-relaxation of the polymer segments [16]. This temperature is known as glass transition temperature T g at which the polymer exhibits phase transition from the glassy state to the rubbery state.…”

“…The stress relief normally is caused by the rearrangement of the chains in a polymer with stress accumulated during its preparation [19]. In Nafion ® HP JP, it is observed that the chain motions are more restricted (due to the small free volume holes) and more energy is required to activate the long range motions of the ionomer molecular chains, which is responsible for its higher α-relaxation temperature [16].…”

Study of the nanostructure of γ‐irradiated high‐density polyethylene/carbon black composite and its durability as geomembrane

“…Positron annihilation spectroscopy (PAS) has been generally connected to polymeric solids, especially to polyethylene. The impact of various physical parameters, for example, crystallinity, thickness, temperature, weight, electric or attractive field, light portion, and so forth, have been analyzed inside this setting to think about structural changes and fundamentally to recognize the starting point of the different lifetime parts . A small number of lively positrons, embedded into a polymer, by and large, structure the bound state with an electron, positronium (Ps).…”