Senior Research Fellow
0113 343 3799
Clothworkers' Building South, Room 1.12
- Senior Research Fellow – University of Leeds, UK
- Visiting Scientist – The Getty Conservation Institute, USA
- AHRC/EPSRC Science and Heritage Programme Postdoctoral Research Fellow
- Senior Experimental Officer – University of Liverpool, UK
- PhD – University of Manchester, UK
- Msc Chemistry – Free University Berlin, Germany
- Congress Bundestag Youth Exchange Program participant
- UG year abroad – University of Sussex, UK
- BA Chemistry – Northwestern University, USA
My current focus is in understanding chemical changes at the uppermost surface (sub-micron) of paint films through detailed characterisation of pigments, surfactants, binder and other additives in the piant films with X-ray spectroscopies (NEXAFS/XPS) suitable for detailed characterisation of primarily organic materials.
- Heritage/Conservation Science of coatings, plastics, textiles
- artists’ acrylic paints
- colloid and interface science – microemulsions, surfactants
- X-ray spectroscopy – XPS, XAS (NEXAFS, XANES, EXAFS)
- synchrotron analytical methods
- chemistry of synthetic organic pigments
- quantum chemical calculations
Prior fields of work include: heterogeneous catalysis, operando spectroscopy, small molecule crystallisation, high throughput analytical methods, design of instruments for studying gas/solid and liquid/solid reactions and scientific data management (LIMS,ELN).
(2014) “Conservation of artists' acrylic emulsion paints: XPS, NEXAFS and ATR-FTIR studies of wet cleaning methods”, Surface and Interface Analysis. 46.10-11: 776-780.
DOI: 10.1002/sia.5376, Repository URL: http://eprints.whiterose.ac.uk/82532/
© 2014 The Authors. Surface and Interface Analysis published by John Wiley & Sons, Ltd. Works of art prepared with acrylic emulsion paints became commercially available in the 1960s. It is increasingly necessary to undertake and optimise cleaning and preventative conservation treatments to ensure their longevity. Model artists' acrylic paint films covered with artificial soiling were thus prepared on a canvas support and exposed to a variety of wet cleaning treatments based on aqueous or hydrocarbon solvent systems. This included somewith additives such as chelating agents and/or surfactants, and microemulsion systems made specifically for conservation practice. The impact of cleaning (soiling removal) on the paint film surface was examined visually and correlated with results of attenuated total reflection Fourier transform infrared, XPS and near-edge X-ray absorption fine structure analyses - three spectroscopic techniques with increasing surface sensitivity ranging from approximately - 1000, 10 and 5 nm, respectively. Visual analysis established the relative cleaning efficacy of the wet cleaning treatments in line with previous results. X-ray spectroscopy analysis provided significant additional findings, including evidence for (i) surfactant extraction following aqueous swabbing, (ii) modifications to pigment following cleaning and (iii) cleaning system residues.
© 2014 Willneffet al. Introduction: Artists' acrylic emulsion paints are used in many contexts such as paintings, murals, sculptures, works on paper and mixed media; and are forming increasing proportions of modern and contemporary art collections. Although acrylic emulsion paints have been the focus of museum-led research over the past decade, the impact of artists' technique and conservation treatment on the upper-most surface of these paints remains essentially unexplored. Results: This paper summarises previous studies using vibrational (FTIR) spectroscopy and presents initial assessments of paint surfaces using X-ray spectroscopies (XPS and NEXAFS) aimed at characterising artists' acrylic paint film surfaces after natural ageing and wet surface cleaning treatment. Both techniques were found to be well suited for surface-sensitive investigations of the organic materials associated with artists' acrylic paints, including explorations into: (A) cleaning system residues, (B) surfactant extraction from paint surfaces, (C) the identification of migrated surfactant, and (D) monitoring pigment changes at the paint/air interface of paint films. Conclusions: It has been shown is that these X-ray spectroscopic techniques can be used for the analysis of almost purely organic materials in a way that complements mass spectroscopic techniques, FTIR and XRF. This investigation forms part of broader, currently ongoing, multi-technique investigation into the properties of artists' acrylic paints and development of conservation treatments for works-of-art made with these materials.
(2010) “Synthesis of Uniform Porous Silica Microspheres with Hydrophilic Polymer as Stabilizing Agent”, INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH. 49.2: 602-608.
(2009) “A novel route to polymeric sub-micron fibers and their use as templates for inorganic structures”, CHEMICAL COMMUNICATIONS. 26: 3946-3948.
(2006) “Dynamic electronic structure of a Au/TiO<inf>2</inf>catalyst under reaction conditions”, Journal of the American Chemical Society. 128.37: 12052-12053.
The electronic structure of a highly active Au/TiO 2 powder catalyst was probed in situ by synchrotron X-ray photoelectron spectroscopy (XPS) in the 10 -1 mbar range. The electronic structure of the Au component was found to respond sensitively to changes in temperature and indicated the absence of bulklike metallic Au under the conditions of highest catalytic activity. Concurrent modification of interfacial sites adjacent to Au on the TiO 2 support was not evident from the Ti photoemission, but may have been below the detection limit of XPS. Copyright © 2006 American Chemical Society.
(2004) “Evidence and use of metal-chromophore interactions: Luminescence dichroism of terthiophene-coated gold nanoparticles in polyethylene oriented films”, Journal of Materials Chemistry. 14.24: 3495-3502.
Nanocomposites with unusual and anisotropic optical properties have been obtained through the dispersion of gold nanoparticles and gold-binding chromophores in a stretched polymer matrix (Ultra High Molecular Weight PolyEthylene, UHMWPE). Strongly dichroic terthiophene-based chromophores, previously used in anisotropic UHMWPE dispersions, were modified with a thiol group and used for the preparation of gold nanoparticles. We demonstrate that the electronic systems of the chromophores are coupled with the gold nanoparticles. For the first time, evidence is reported that the polarization of the absorbed radiation can be preserved during energy transfer between a chromophore and a metal particle.
(2003) “Gas phase transport of gold with gold(III) oxide and carbon monoxide”, Chemical Communications. 9.2: 258-259.
A transport reaction of gold occurs during the reaction of Au 2 O 3 with CO at temperatures around 400 °C. The reaction proceeds through a short-lived gas phase species of Au; analysis of quartz powder substrates placed downstream of the Au 2 O 3 indicates volatilisation yields of a few wt% Au 2 O 3 .
(2003) “Extended X-ray absorption fine-structure (EXAFS) of a complex oxide structure: A full multiple scattering analysis of the Au L<inf>3</inf>-edge EXAFS of Au<inf>2</inf>O<inf>3</inf>”, Solid State Communications. 125.6: 317-322.
Crystalline Au 2 O 3 was obtained by hydrothermal synthesis at 3000 atm and its extended X-ray absorption fine-structure (EXAFS) at the Au L 3 -edge was measured at room temperature. A detailed full multiple scattering (MS) analysis using FEFF8 theory shows that only a small number of scattering paths contribute significantly to the EXAFS of Au 2 O 3 . Because of the complex unit cell (low local symmetry) of the Au 2 O 3 structure, contributions of MS paths are almost negligible. The results indicate that FEFF8 theory provides a good reference for the analysis of Au-O phases. © 2003 Elsevier Science Ltd. All rights reserved.
(2016) Cleaning acrylic paints: mineral spirits-based microemulsions and the question of residues. 7th International Conference Color and Conservation 2015 Proceedings: CESMAR7 – Colore y Conservazione 2015 Il Prato.
Repository URL: http://eprints.whiterose.ac.uk/99659/
This paper presents a summary of some research into the evaluation of mineral spirits-based microemulsions as wet surface cleaning systems for artists’ acrylic emulsion paint films. Examples from four different mineral spirits-based microemulsion systems were evaluated, each having a different primary surfactant component. Particular attention is given here to determination, using surface-sensitive analytical techniques (ATR-FTIR, XPS and ToF-SIMS), of possible microemulsion surfactant residues remaining on paint films after wet cleaning treatment. Three different test paint films were subjected to simulated cleaning treatments: Golden Heavy Body Acrylic PY3 (azo yellow); Liquitex Heavy Body Artist Acrylic PY3 (azo yellow); and Liquitex Heavy Body Artist Acrylic PW6 (titanium white). In comparison with untreated controls, samples were analysed by the above methods at two stages: after treatment with cleaning liquid but without any clearance step, and again after clearance of any residue with hydrocarbon solvent. These investigations have shown that only trace amounts of surfactant residues may remain on paint surfaces. Indications of the presence of residual surfactant naturally depends on the respective sensitivities of the different analytical techniques: the detection limit for ATR-FTIR is lower than XPS and ToF-SIMS. As has been shown to be the case for aqueous treatments, levels of intrinsic surfactant in acrylic paint films and migrated surfactant located at paint surfaces can also be affected by these cleaning treatments.
(2010) Porous silica spheres in macroporous structures and on nanofibres. Proceedings: PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES 368.1927: 4351-4370.
(2006) Development and applications of an inexpensive and modular medium-throughput microcrystalliser for the preparation and characterisation of solid phases. Proceedings: Journal of Crystal Growth 294.1: 29-34.
Identification, isolation, and control of solid form are important for process and product control of specialty chemicals and pharmaceutical compounds. Solid forms are commonly isolated by crystallisation from solution and as a consequence acquisition of both phase equilibrium and kinetic information is vital. In these cases, control of solid form requires a complete assessment of the relationship between crystallisation conditions and both structural and physical aspects of solid form through a number of experiments which may run into many hundreds for complex systems. Traditionally such experiments have been completed sequentially. To fully characterise complex systems in this manner often takes years and so to accelerate this process and characterise a wider phase space, tools for studying multiple samples have been developed to increase throughput. These high-throughput synthetic and analytical techniques are often prohibitively expensive for smaller-scale research laboratories. As a solution to this problem, we have developed a low cost ( < 4000 GBP) and modular medium-throughput microcrystalliser and optical tomography system for acquisition of phase equilibria, crystallisation kinetic, and solid-form data on organic materials. The design and typical applications of this equipment are presented here. © 2006 Elsevier B.V. All rights reserved.
Research Projects & Grants
- AHRC/EPSRC Science and Heritage Programme Postdoctoral Research Fellow
- NSLS beamtime 2014 “NEXAFS-Characterisation of the Impact of Wet Cleaning Treatments on Modern and Contemporary Works-of-Art Made with Artists’ Acrylic Paints” (PI)
PhD & Postdoctoral Supervision
PhD students (co-supervisor)
- L. Al-Madhagi (2015-): in situ X-ray absorption spectroscopy