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Welcome to the Pulham Group!
Welcome to the website for the research group of Professor Colin Pulham. Our interests cover a diverse range of fields, from heat storage and energetic materials, to biofuels and computational chemistry.
Our group specialises in studying the crystal structures of these various materials under a variety of conditions, typically extremes of pressure and temperature. The overall aim of doing so is to determine how changes in these crystal structures influence the resulting properties of the materials - be that their thermochemical balance, energetic sensitivity and performance, or suitability for use in car engines - so as to influence the design of better heat storage materials, safer explosives and propellants, or more efficient biofuels.
A Michalchuk et al (2018) PCCP, 2018, 20, 29061-29069
Vibrationally induced metallisation of the energetic azide α-NaN3
As initiation of an energetic material requires rupture of a covalent bond, and therefore population of antibonding electronic states, consideration of the electronic band gap has dominated initiation mechanisms for solid state materials. Most prominent are models based on metallisation, where static mechanical perturbation leads to closing of the electronic band gap. This work explores an alternative mechanism for the dynamic metallisation of a model energetic material, where vibrational excitation resulting from mechanical impact is found to induce transient metallisation of α-NaN3. The normal coordinates associated with bending the azido anion close the electronic band gap, facilitating the formation of highly reactive species important for initiation of energetic materials. The DFT simulated vibrational spectrum of α-NaN3 exhibits excellent reproduction of the experimental low-temperature inelastic neutron scattering spectrum (INS).
X. Liu et al. (2018) CrystEngComm. DOI: 10.1039/C8CE01055B
Temperature-induced polymorphism in methyl stearate
The crystallisation of methyl stearate under a range of crystallisation conditions has been studied and three new polymorphs have been identified and structurally characterised. Form III (monoclinic, space group Cc, Z = 8) was obtained at room temperature by slow evaporation of a saturated solution in CS2. Form IV (monoclinic, space group C2/c, Z = 4) was obtained by slow cooling of the melt. Both structures were characterised by single crystal X-ray diffraction. Form V (monoclinic, space group Cc, Z = 4) was obtained from the melt by rapid cooling. X-ray and neutron powder diffraction methods were employed in the determination of this structure. Form V shows highly anisotropic thermal expansion, with expansion along the crystallographic b-axis being substantially greater than along the other two axes.
The Pulham Group
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