FTIR analysis of water in supercritical carbon dioxide microemulsions using monofunctional perfluoropolyether surfactants Frank Loeker, Patricia C. Marr, Steven M. Howdle * School of Chemistry, The University of Nottingham, University Park, Nottingham NG7 2RD, UK Received 10 June 2002; accepted 18 July 2002 Abstract We describe perfluoropolyether (PFPE) surfactants which are capable of stabilising the water/CO 2 interface and present FTIR spectroscopic evidence for the formation of water in supercritical carbon dioxide microemulsions. A wide variety of single chain surfactants of differing chain lengths but similar structure has been screened and the effect of the surfactant chain length on the water uptake was studied. The ammonium carboxylate of the PFPE surfactant Krytox FSL TM with an average molecular weight of 2500 g mol 1 was demonstrated to be the surfactant capable of dissolving the most water out of all the tested surfactants and hence to have the optimum chain length. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Supercritical carbon dioxide; Microemulsion; Perfluoropolyether surfactant; Reverse micelles; FTIR spectroscopy 1. Introduction Due to their special solvent properties super- critical fluids have become very attractive replace- ments for organic solvents in many applications. Supercritical fluids are not only cheap, environ- mentally friendly and easy to separate from reaction products, they can also be easily recycled and their solvent properties are tuneable by variation of their density. The higher the pressure of a supercritical fluid at a given temperature the higher its density and consequently its dissolution power. Moreover, like gases they have a high diffusivity and low viscosity, but their densities are similar to those of liquids. These properties make supercritical fluids commercially interesting sol- vents e.g. for the synthesis of cosmetics, drugs, food additives and for large scale extractions [1 / 5]. Carbon dioxide is by far the most commonly used supercritical fluid. Its critical parameters are moderate (T c /31.0 8C, p c /73.8 bar) [6], and supercritical carbon dioxide (scCO 2 ) is non-flam- mable, non-toxic, cheap and possesses mixed solvent properties of non-polar organic solvents like n -pentane or cyclohexane and of perfluori- * Corresponding author. Tel.: /44-115-951-3486; fax: /44- 115-951-3058 E-mail address: steve.howdle@nottingham.ac.uk (S.M. Howdle). Colloids and Surfaces A: Physicochem. Eng. Aspects 214 (2003) 143 /150 www.elsevier.com/locate/colsurfa 0927-7757/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII:S0927-7757(02)00407-7