D.Phil. Student, University of Oxford, 1999–2005
Postdoctoral Research Assistant, Durham University, 2005–2006
External Reflection FTIR Spectroscopy of Surfactants at the Dynamic Air–Water Interface
Dynamic surfactant adsorption at the air–water interface is an important phenomenon in nature and in industrial processes, e.g. pulmonary surfactants and inkjet printing. This thesis describes the application of external reflection Fourier transform infrared spectroscopy (ER-FTIRS) to the study of the adsorption of surfactants under steady-state conditions at the expanding liquid surface of an overflowing cylinder (OFC). I will show how ER-FTIRS can be employed to obtain quantitative information on the structure and composition of surfactant monolayers on an OFC for pure and mixed surfactant systems.
The implementation of the experiment, which involves the detection of small peaks from a single layer of molecules at the surface of a weakly reflective substrate, is non-trivial. The design, construction and optimisation of an optical bench are described. The interpretation of spectra requires a model for the interaction of infrared radiation with an air–monolayer–solution interface, which is developed in this thesis. Two very different methods of processing the spectra are employed. A traditional method removes the strongly varying baseline from the subphase by subtraction. A chemometric method, based on target factor analysis, allocates component weights to a refined spectrum of each species, and can deconvolute overlapping peaks, e.g. from two components in a surfactant mixture, or from the same surfactant adsorbed at the interface and dissolved in solution.
Structural information is derived from polarised monolayer spectra of pure solutions of a cationic hydrocarbon, a non-ionic hydrocarbon and an anionic fluorocarbon surfactant, and the amount of adsorption is quantified down to 10% surface coverage in each case. For each surfactant, the data are compared with values of the dynamic surface excess measured independently by neutron reflection and ellipsometry. ER-FTIR spectra of binary mixtures of the three surfactants are discussed in terms of the adsorption of both components, and the solution chemistry.
J. P. R. Day, R. A. Campbell, O. P. Russell, C. D. Bain "Adsorption Kinetics in Binary Surfactant Mixtures Studied with External Reflection FTIR Spectroscopy" Journal of Physical Chemistry C 2007, 111, 8757-8774 (DOI).
R. A. Campbell, P. A. Ash, C. D. Bain "Dynamics of Adsorption of an Oppositely Charged Polymer-Surfactant Mixture at the Air-Water Interface: Poly(dimethyldiallylammonium chloride) and Sodium Dodecyl Sulfate" Langmuir 2007, 23, 3242-3253 (DOI).
R. A. Campbell, J. P. R. Day and C. D. Bain "External Reflection Fourier Transform Infrared Spectroscopy of Surfactants at the Air–Water Interface: Separation of Bulk and Adsorbed Surfactant Signals" Applied Spectroscopy 2005, 59, 993–1001.
M. Sekine, R. A. Campbell, D. S. Valkovska, J. P. R. Day, T. D. Curwen, L. J. Martin, S. A. Holt, J. Eastoe and C. D. Bain "Adsorption Kinetics of Ammonium Perfluorononanoate at the Air–Water Interface" Physical Chemistry Chemical Physics 2004, 6, 5061–5065.
R. A. Campbell, S. R. W. Parker, J. P. R. Day and C. D. Bain "External Reflection FTIR Spectroscopy of the Cationic Surfactant Hexadecyltrimethylammonium Bromide (CTAB) on an Overflowing Cylinder" Langmuir 2004, 20, 8740–8753.
R. A. Campbell and C. D. Bain "External-Reflection FT-IR Spectroscopy of C10E8 at an Expanding Water Surface" Vibrational Spectroscopy 2004, 35, 205–211.
D. Valkovska, K. M. Wilkinson, R. A. Campbell, C. D. Bain, R. Wat and J. Eastoe "Measurement of the Dynamic Surface Excess of the Nonionic Surfactant C8E4OMe by Neutron Reflection and Ellipsometry" Langmuir 2003, 19, 5960–5962.
During my time in Oxford, I was a keen member of the University’s walking club. In addition to serving on committee as President and Trip & Safety Coordinator, I led many rewarding weekend trips to the mountains, hills and coastline of England & Wales. I also enjoy walking and travelling around the UK and further afield, usually listening to lots of music as I go. I have also designed and maintained some websites, including this one. I hope to live and work in mainland Europe in the future.