Alison M. Voice

The detection of drugs of abuse in fingerprints using Raman spectroscopy I: latent fingerprints

This paper describes the application of Raman spectroscopy to the detection of exogenous substances in latent fingerprints. The scenario considered was that of an individual handling a substance and subsequently depositing a contaminated fingerprint. Five drugs of abuse (codeine phosphate, cocaine hydrochloride, amphetamine sulphate, barbital and nitrazepam) and five non-controlled substances of similar appearance, which may be used in the adulteration of drugs of abuse (caffeine, aspirin, paracetamol, starch and talc), were studied in both sweat-rich and sebum-rich latent fingerprints. The substances studied could be clearly distinguished using their Raman spectra and were all successfully detected in latent fingerprints. Photobleaching was necessary to reduce the fluorescence background in the spectra of some substances. Raman spectra obtained from the substances in sweat-rich latent fingerprints were of a similar quality to spectra that obtained from the substances under normal sampling conditions. Interfering Raman bands arising from latent fingerprint material were present in the spectra obtained from the substances in sebum-rich fingerprints. These bands did not prevent identification of the substances and could be successfully removed by spectral subtraction. The most difficult aspect of the detection of these substances in latent fingerprints was visually locating the substance in the fingerprint in order to obtain a Raman spectrum.

Electrostrictive response of an ideal polar rubber

This article considers the electrostrictive response of an ideal polar rubber in which each random link carries a dipole which is constrained to remain perpendicular to the link but is free to rotate about it. It thus mimics typical polar polymers with dipoles essentially perpendicular to the chain backbone and which rotate preferentially about the local chain axis (Stockmayer type B). In such materials, there is a genuine interplay between mechanical deformation and the electrical permittivity since an applied strain can produce preferential segmental orientation, align dipole rotation axes, and thus cause a change in permittivity. Though this is a plausible mechanism of electrostriction in polar rubbers, the quantitative analysis presented in this article suggests that the effect makes only a small contribution to the observed deformation of actuators based on typical polar rubber films with compliant electrodes.

Structure of poly(vinylidene fluoride) gel electrolytes

Abstract Polymer gel electrolytes have three constituents: polymer, salt and solvent. This paper gives structural information on polymer gel electrolytes made from poly(vinylidene fluoride), lithium triflate and tetraglyme. These electrolytes exhibit a room-temperature ionic conductivity in the region of 10 −3 S cm −1 while maintaining sufficient mechanical rigidity to form self-supporting films (having elastic moduli in the region of 100 kPa). Differential scanning calorimetry and dynamic mechanical analysis have been used to show that the majority of the network junctions of the gel are crystalline in nature. Wide angle X-ray diffraction has revealed that when no salt is included in the gel, these crystal junctions are almost an order of magnitude larger in their lateral dimensions than when salt is present. The salt is thought to nucleate crystallisation. The modulus is significantly reduced by inclusion of salt; however, DSC suggests that apparent crystallinity is only slightly reduced by the presence of salt. This discrepancy is attributed to either the uncertainty in the heat of fusion of PVDF, or to the formation of small crystalline particles that are not incorporated in the network junctions. Gels with polymer concentrations between 15 and 40% (by weight) maintain their mechanical rigidity up to temperatures around 100 °C. However, once melted, the gel structure only reforms at much lower temperatures. The variation of ionic conductivity of salted gels with temperature shows no such hysteresis, and it is concluded that the ionic conductivity is independent of the mechanical state of the gel.

An interferometric prediction of the intrinsic optical properties for cold-drawn iPP, PTFE and PVDF fibres

Interference polarizing (Pluta and Interphako) microscopes have been used to measure the birefringence and refractive indices during the cold-drawing of isotactic poly(propylene) (iPP), poly(tetrafluoroethylene) (PTFE) and poly(vinylidene fluoride) (PVDF) fibres. The intrinsic birefringence (Δn0) and refractive indices (niso, and ) of iPP, PTFE and PVDF fibres were interferometrically predicted using affine and pseudo-affine models. In terms of these intrinsic values, a new way of calculating the orientation parameter is discussed. A selection of microinterferograms is given for illustration.

Electrostrictive response of an ideal polar rubber: comparison with experiment

This presentation considers the electrostrictive response of an ideal polar rubber in which each random link carries a dipole constrained to remain perpendicular to the link but free to rotate about it In such materials, there is a possibility of a genuine interplay between mechanical deformation and the electrical permittivity since an applied strain can align the dipole rotation axes. This is a plausible mechanism of genuine electrostriction in polar rubbers but our quantitative analysis has shown that the effect should make only a small contribution to the observed deformation of actuators constructed from polar rubber films with compliant electrodes. This prediction has been confirmed by quantitative measurement of the thickness strain in polar films subjected to high electric fields, the deformation being measured by laser-Doppler vibrometry. Measurements made on Viton B, in particular, show the material to be viscoelastic with a significant phase lag between the applied electric field and the observed strain. This phase lag is shown to be due primarily to the mechanical phase lag at twice the frequency of the applied electric field.

Adsorption of DNA onto Charged Spheres

The complexation behaviour of linear DNA (negatively charged) with surface functionalised sub-micron latex spheres is studied by dynamic light scattering (DLS), small-angle neutron scattering (SANS), small-angle x-ray scattering (SAXS), and micro rheology. The complexes are measured in solution as a function of component concentration ( C DNA , C SPH ) and added salt concentration ( C s ). In the absence of salt, measured radius increases with C DNA ( C SPH held constant) up to a plateau value. The presence of salt causes a decrease in the measured complex radius, which may be due either to increased flexibility of the chains allowing them to form a more compact layer on the sphere surface, or dissociation of the two components due to screened electrostatics. More detailed experiments to determine this are underway.