The temperature dependence of positron lifetimes in solid pivalic acid

Program system for analysing positron lifetime spectra and angular correlation curves

The past decade has seen the development of microporous materials (i.e., materials containing pores of dimensions <2 nm) derived wholly from organic components. Here we review this nascent area with a particular emphasis on amorphous polymers that possess intrinsic microporosity (IM), which is defined as microporosity that arises directly from the shape and rigidity of component macromolecules. Although IM can be readily identified within soluble non-network polymers and oligomers, for network polymers it is harder to differentiate IM from template effects that are responsible for the microporosity within hyper-cross-linked networks. The numerous examples of microporous polymers assembled from rigid monomers by the formation of rigid linking groups are surveyed and their IM assessed. The potential applications of these materials are highlighted.

Exploitation of Intrinsic Microporosity in Polymer-Based Materials

Positron annihilation spectroscopy for chemical analysis: A novel probe for microstructural analysis of polymers☆

As synthesised ZIF-8 nanoparticles (size ∼ 60 nm and specific surface area ∼ 1300–1600 m2 g−1) were directly incorporated into a model polymer matrix (Matrimid® 5218) by solution mixing. This produces flexible transparent membranes with excellent dispersion of nanoparticles (up to loadings of 30 wt%) with good adhesion within the polymer matrix, as confirmed by scanning electron microscopy, dynamic mechanical thermal analysis and gas sorption studies. Pure gas (H2, CO2, O2, N2 and CH4) permeation tests showed enhanced permeability of the mixed matrix membrane with negligible losses in selectivity. Positron annihilation lifetime spectroscopy (PALS) indicated that an increase in the free volume of the polymer with ZIF-8 loading together with the free diffusion of gas through the cages of ZIF-8 contributed to an increase in gas permeability of the composite membrane. The gas transport properties of the composite membranes were well predicted by a Maxwell model whilst the processing strategy reported can be extended to fabricate other polymer nanocomposite membranes intended for a wide range of emerging energy applications.

/pdf/zeolitic-imidazolate-framework-zif-8-based-polymer-dnstq6swrl.pdf

Zeolitic imidazolate framework (ZIF-8) based polymer nanocomposite membranes for gas separation

The vacancy formation energy in crystalline adamantane determined by position annihilation techiniques

The use of the positron annihilation technique (PAT) in the investigation of vacancies and phase transformations in molecular crystals is discussed.

M. Eldrup

Papers

The temperature dependence of positron lifetimes in solid pivalic acid

The vacancy formation energy in crystalline adamantane determined by position annihilation techiniques

Positron Annihilation Studies of Vacancies and Polyvacancies in Molecular Crystals