Positron annihilation and 129Xe NMR studies of free volume in polymers

Linking the structures, free volumes, and properties of ionic liquid mixtures

“…Previous correlations have been seen between PALS and 129 Xe NMR free volume analysis for a wide range of amorphous, semi-crystalline and crystalline polymers in the solid state. 57 , 84 , 85 It is worth highlighting that the direct linear correlations between v h and δ in liquid systems are unprecedented and remarkable given the vastly different timescales involved. This is important for a number of reasons.…”

“… 61 , 62 The chemical shift of solvated Xe is sensitive to its environment and, in condensed phases, has been related to the sum of three terms (eqn (1)): δ = δ 0 + δ wall + δ Xe–Xe ρ + δ E where δ represents the chemical shift (in ppm); δ 0 is the reference chemical shift of an isolated Xe atom; δ wall is the chemical shift effect arising from the interaction of Xe with the wall of the cavity it is solvated in; δ Xe–Xe represents the chemical shift arising from Xe–Xe interactions; ρ is the density of the gas phase; and δ E accounts for the polarisation of Xe in response to an external field, in this case the IL or IL mixture. 57 , 63 DFT calculation and MD simulations have revealed that wall effects contribute more to the deshielding of Xe than the other factors when Xe is solvated in a liquid and hence changes in Xe chemical shift give insight into the average size of voids, i.e. the free volume, of the liquid.…”

Structure and Dynamics of Drawn Gel‐Spun Ultrahigh‐Molecular‐Weight Polyethylene Fibers by 1H, 13C and 129Xe NMR

“…[26,27] Following the success of the positron annihilation [28] and 129 Xe NMR [29] as sensitive probes for the cavity space in microporous solids such as zeolites and clathrates, these techniques have recently been applied to elucidate the properties of free volume in polymers. [30] The aim for this study was to reveal the structure and developments therein as well as chain dynamics, and the characteristic of voids as a function of Young modulus for a series of drawn sol/gel UHMWPE fibers. Multinuclear and multidimensional 1 H, 13 C and 129 Xe NMR that include advanced methods like 1 H spectra at ultrafast magic-angle spinning (MAS), WISE NMR and the newly developed quantitative 13 C/ 1 H cross-polarization magic-angle spinning (QUCPMAS) were used for the measurements of phase composition, chain dynamics and voids concentration for a series of drawn sol/gel UHMWPE fibers.…”

Characterization of 6FDA‐based hyperbranched and linear polyimide–silica hybrid membranes by gas permeation and 129Xe NMR measurements

“…Observed δ for polymers, therefore, can be explained as a sum of δ(S) and δ(Xe). Essentially the contribution of δ(S) to observed δ is larger than δ(Xe), and the δ value is strongly correlated with the shape and dimensions of free volume holes in polymers30–32; observed δ values of sorbed 129 Xe in polymers with larger free volume holes appear in higher magnetic fields, close to the resonance of free Xe gas.…”