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D. Lightbody

Bio: D. Lightbody is an academic researcher from University of Strathclyde. The author has contributed to research in topics: Vacancy defect & Phase (matter). The author has an hindex of 5, co-authored 6 publications receiving 1644 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the temperature dependence of positron lifetimes in both the brittle and plastic phases of trimethylacetic (pivalic) acid was examined using the positron lifetime technique.

1,640 citations

Journal ArticleDOI
TL;DR: In this article, the temperature dependence of position lifetimes in both the brittle and plastic phases of cyclohaxane has been examined, and a correlation was established between the molecular packing coefficients for plastic and brittle crystals and the ortho-Ps lifetime in the crystals.

50 citations

Journal ArticleDOI
TL;DR: In this paper, the formation energy of the defects which trap ortho-positronium is estimated at E f v = 70 ± 10 kJ mol -1 (0.73 ± 0.1 eV).

30 citations

Journal ArticleDOI
TL;DR: In this article, an examination of the brittle/plastic phase transformation in the molecular crystals cyclohexane, DL-camphene and succinonitrile using the positron annihilation technique was made.
Abstract: An examination has been made of the brittle/plastic phase transformation in the molecular crystals cyclohexane, DL-camphene and succinonitrile using the positron annihilation technique. In each material, the transition is characterized by a distinct increase in ortho-positronium lifetime. The influence of impurities on the transition was examined for DL-camphene. Addition of the impurity tricylene in concentrations in the range 0.14-4.0 mol % resulted in a lowering of the transition temperature from 176 to 167 K and a broadening of the transition region.

23 citations

Journal ArticleDOI
TL;DR: In this article, the authors used the defect trapping model devised for metals, and evaluated activation energies for vacancy formation for adamantane, bicyclooctane, succinonitrile and dl-camphene.
Abstract: Ortho-positronium annihilation has been used to assess vacancy formation energies and vacancy concentrations in several plastic crystalline solids. In general, the ortho-positronium lifetimes showed a gradual increase with temperature at low temperatures consistent with normal lattice expansion, coupled with sudden larger increases at the brittle-plastic phase transformation. In most solids, at about O.7Tm, a larger sigmoid increase occurred indicative of the trapping of ortho-positronium in thermally generated defects in the lattice. The lifetimes in the defect state are consistent with the conclusion that the defects are of a size equivalent to vacant lattice sites. On this basis and using the defect trapping model devised for metals, activation energies for vacancy formation were evaluated for adamantane, bicyclooctane, succinonitrile and dl-camphene. The data are consistent with a vacancy concentration of 10−7 to 10−3 vacancy fraction over the range 0. 7Tm-Tm (melting temperature)

21 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the temperature dependence of positron lifetimes in both the brittle and plastic phases of trimethylacetic (pivalic) acid was examined using the positron lifetime technique.

1,640 citations

Journal ArticleDOI
TL;DR: In this paper, a review of microporous materials with a particular emphasis on amorphous polymers that possess intrinsic microporosity (IM), which is defined as microporeosity that arises directly from the shape and rigidity of component macromolecules.
Abstract: 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.

704 citations

Journal ArticleDOI
TL;DR: Positron annihilation spectroscopy for chemical analysis (PASCA) has been developed to analyze the microstructure of polymers as discussed by the authors, where the positronium atom is trapped in the atomic-scale holes which have a size ranging from 1 to 10 A. Theoretical aspects, experimental developments, and examples in analyzing the microstructures of epoxy, PEEK, and PMMA polymers are presented.

694 citations

Journal ArticleDOI
TL;DR: In this paper, the authors synthesized 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.
Abstract: 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.

614 citations