pubs.acs.org/Langmuir © 2009 American Chemical Society
Reverse Water-in-Fluorocarbon Microemulsions Stabilized by New Polyhydroxylated Nonionic Fluorinated Surfactants Khaled Debbabi,† Frederic Guittard,† Julian Eastoe,‡ Sarah Rogers,§ and Serge Geribaldi*,† †
Institut de Chimie de Nice FR 3037 CNRS, Laboratoire de Chimie des Mat eriaux Organiques et M etalliques, CMOM, UFR Sciences, Universit e de Nice-Sophia Antipolis, Parc Valrose, 06108 Nice Cedex 02, France, ‡ School of Chemistry, University of Bristol, Bristol, BS8 1TS, United Kingdom, and §ISIS- STFC Neutron Scattering Facility, Harwell Science and Innovation Campus, Didcot, OXON, OX11 0QX, United Kingdom Received October 28, 2008. Revised Manuscript Received February 24, 2009
New polyhydroxylated nonionic perfluorosurfactants CnF2n+1-CH2-O-SO2-NHCONH-C(CH2OH)3 have been synthesized, and their capacity for stabilization of reverse water-in-fluorocarbon microemulsions has been extensively studied. These investigations showed that, regardless of the composition used, transparent one-phase systems could not be obtained if the fluorinated surfactants were used without a sufficient amount of a semifluorinated alcohol. The mixed oil phase used to prepare microemulsions consisted of a 9:1 mixture of perfluorohexane and 1H,1H,2H, 2H-perfluorohexan-1-ol. Various scattering techniques, dynamic light scattering (DLS), small-angle X-ray (SAXS), and neutron scattering (SANS) have been used for structural characterization of these fluorinated microemulsions. Valuable information on the size, shape, and internal colloidal structure in these novel fluorinated microemulsions is described and discussed.
Introduction Reverse water-in-fluorocarbon (FC) microemulsions (W/FC) have been investigated in many fields for their peculiar applications such as liquid-assisted ventilation,1 drug or gene delivery,2-4 and supercritical fluids for extraction processes.5-11 In addition, highly fluorinated reverse microemulsions are known to be biologically inert with low toxicity and a capacity to dissolve significant levels of gases (e.g., O2 and CO2) as compared to water or organic hydrocarbons.12,13 W/FC microemulsions are generally composed of water, fluorocarbon liquids as oil phase, and fully or partially fluorinated surfactants to ensure dispersion of water droplets in oil. The use of highly fluorinated alcohols in these ternary systems is often necessary to effectively stabilize the microemulsions,14-16 because the amount of microemulsified *Corresponding author. Professor Serge Geribaldi, Serge.GERIBALDI@ unice.fr, tel: (33) 4 92 07 61 12, Fax: (33) 4 92 07 61 56. (1) Wolfson, M. R.; Greenspan, J. S.; Shaffer, T. H. Pediatr. Pulmonol. 1998, 26, 42–63. (2) Krafft, M. P. Adv. Drug Delivery Rev. 2001, 47, 209–228. (3) Butz, N.; Porte, C.; Courrier, H.; Krafft, M. P.; Vandamme, T. F. Int. J. Pharm. 2002, 238, 257–269. (4) Weiss, D. J.; Banneau, L.; Liggitt, D. Mol. Ther. 2001, 3, 734–745. (5) Heitz, M. P.; Carlier, C.; deGrazia, J.; Harrisson, K. L.; Johnston, K. P.; Randolph, T. W.; Bright, F. V. J. Phys. Chem. B 1997, 101, 6707–6714. (6) Eastoe, J.; Dupont, A.; Steytler, D. C. Curr. Opin. Colloid Interface Sci. 2003, 8, 267–273. (7) Baglioni, P.; Gambi, C. M. C.; Giordano, R.; Senatra, D. J. Mol. Struct. 1996, 383, 165–169. (8) Dupont, A.; Eastoe, J.; Murray, M.; Martin, L.; Guittard, F.; Taffin de Givenchy, E.; Heenan, R. K. Langmuir 2004, 20, 9953–9959. (9) Dupont, A.; Eastoe, J.; Martin, L.; Steytler, D. C.; Heenan, R. K.; Guittard, F.; Taffin de Givenchy, E. Langmuir 2004, 20, 9960–9967. (10) Eastoe, J.; Gold, S.; Steytler, D. C. Langmuir 2006, 22, 9832–9842. (11) Keeper, J. S.; Simhan, R.; Desimone, J. M.; Wignall, G. D.; Melnichenko, Y. B.; Frielinghaus, H. J. Am. Chem. Soc. 2002, 124, 1834– 1835. (12) Riess, J. G. Tetrahedron 2002, 58, 4113–4131. (13) Riess, J. G. J. Fluorine Chem. 2002, 114, 119–126. (14) Alany, R. G.; Rades, T.; Kustrin, S. A.; Davies, N. M.; Tucker, I. G. Int. J. Pharm. 2000, 196, 141–145. (15) Glatter, O.; Orthaber, D.; Stradner, A.; Scherf, G.; Fanun, M.; Garti, N.; Clement, V.; Leser, M. E. J. Colloid Interface Sci. 2001, 241, 215–225. (16) Patel, N.; Marlow, M.; Lawrence, M. J. J. Colloid Interface Sci. 2003, 258, 345–353.
Langmuir 2009, 25(16), 8919–8926
water is generally large compared to the surfactant concentration (w = [water]/[surfactant] from 10 to 60). The molecular structure of nonionic fluorinated surfactants used for the formulation of water-in-fluorocarbon microemulsions is very important. Indeed, only a few fluorinated nonionic amphiphiles capable of stabilizing W/FC microemulsions have been cited in the literature. These are as follows: (i) The perfluoroalkylated dimorpholinophosphate C8F17(CH2)11OP(O)[N(CH2CH2)2O]2 (F8H11DMPs) is found to stabilize reverse water-in-perfluorooctyl bromide (PFOB) microemulsions as drug delivery systems.17 (ii) Polyoxyethylene perfluoroalkyls CmF2m+1-(CH2)n-(OCH2CH2)pOH (where m = 4, 6, or 7; n = 1 or 2; and p = 4, 5, or 6) were used to solubilize water in perfluorodecaline (C10F18) or perfluoromethyldecaline (C11F20).16-21 (iii) Polyoxyethylene thioperfluoroalkyls CmF2m+1-C2H4-SC2H4(OCH2CH2)pOH (with m = 6; and p = 2, 3, 5, or 7) allow the formation of water in perfluorodecaline microemulsions.22,23 (iv) Perfluorooctanoic acid and its ethylene oxide ester C7F15CO-(OCH2CH2)mOCH3 (with m = 7.2) provide reverse microemulsions perfluorohexane (PFH) and perfluorooctane (PFO).24,25 With the aim of developing new fluorinated surfactants that are effective at stabilizing W/FC microemulsions, we have investigated the synthetic potential of oxosulfonylisocyanates as starting materials in the preparation of a new series of non-ionic (17) Courrier, H. M.; Vandamme, T. F.; Krafft, M. P. Colloids Surf. A 2004, 244, 141–148. (18) Robert, A.; Tondre, C. J. Colloid Interface Sci. 1984, 98, 515–522. (19) Burger-Guerrisi, C.; Tondre, C.; Canet, D. J. Phys. Chem. 1988, 92 4974–4979. (20) Ravey, J. C.; Stebe, M. J. Prog. Colloid Polym. Sci. 1987, 73, 127–133. (21) Mathis, G.; Leempoel, P.; Ravey, J. C.; Selve, C.; Delpuech, J. J. J. Am. Chem. Soc. 1984, 106, 6162–6171. (22) Serratrice, G.; Matos, L.; Delpuech, J. J.; Cambon, A. J. Chim. Phys. 1990, 87, 1969–1980. (23) Krafft, M. P.; Chittofrati, A.; Riess, J. G. Curr. Opin. Colloid Interface Sci. 2003, 8, 251–258. (24) LoNostro, P.; Choi, S. M.; Ku, C. Y.; Chen, S. H. J. Phys. Chem. B 1999, 103, 5347–5352. (25) Peng, C. A.; Huang, F. J. Dispers. Sci. Technol. 2008, 29, 46–51.
Published on Web 04/03/2009
DOI: 10.1021/la803579b
8919
Article
Debbabi et al.
Chart 1. Fluorinated surfactants (FPHS) synthesized from oxosulfonylisocyanates
fluorinated surfactants bearing a sulfamate connector between the fluorinated tail and the final polar head.26,27 Of the different series synthesized (Chart 1) and tested with various fluorocarbon oils, only the fluorinated polyhydroxylated surfactants (FPHS) were able to stabilize reverse water-in-FC microemulsions, and only with perfluorohexane as oil. In this paper, we report the synthesis of these novel polyhydroxylated amphiphiles (FPHS), as well as the structural characterization and temperature stability of reverse water-in-FC microemulsions obtained with a mixture of perfluorohexane (PFH) and 1H,1H,2H,2H-perfluorohexan-1-ol (PFHOL).The structural characterization of these new reverse W/FC microemulsions has been performed using various scattering techniques, dynamic light scattering (DLS), small-angle X-ray, and neutron scattering (SAXS and SANS).
Experimental Section Materials. Chlorosulfonylisocyanate (Aldrich 1189-71-S, 98%), 2-amino-2-(hydroxymethyl)-1,3-propanediol [tris(hydroxymethyl)aminomethane, (Aldrich, 77-86-1, >99.8%)], 1H,1H, 2H,2H-perfluorohexan-1-ol (Aldrich, 2043-47-2, 97%), perfluorodecaline (Fluka, 77264, >95%), and 1-F-alkylmethylalcohols perfluoroalkyl alcohols graciously given by DuPont de Nemours were used as received. Polydimethysiloxane trimethylsiloxy terminated, M.W. 237, (Aldrich, 9016-00-6) was vacuum distilled before use. Milli-Q ultrapure water with resistivity no less than 18.4 MΩ cm was used. IR spectra of FPHS were recorded at room temperature on a Perkin-Elmer paragon 1000 FT-IR spectrometer (KBr pellets). 1 H NMR (chemical shifts measured in deuterated methanol) are given in ppm from TMS as internal standard, 19F NMR (CFCl3 as internal reference), and 13C (TMS internal standard) spectra were recorded on a Bruker AC 200 MHz spectrometer, using (CD3)2CO as solvent (5-10% w/w). Mass spectra were run on MS-MS apparatus Finnigan MAT INCOS 500E by direct introduction using electronic ionization at 70 eV. Synthesis of Fluorinated Surfactants. Typically, a total of 15 mmol of chlorosulfonylisocyanate (CSI) dissolved in 30 cm3 of dried chlorobenzene was added dropwise at 20 °C to a solution of 15 mmol of perfluoroalkylalcohol in 40 mL of chlorobenzene. The mixture was stirred at 100-130 °C for 24 h and then concentrated to a light brown viscous residue by vacuum distillation. The residue was distilled from a Kugelrohr apparatus to give the desired pure colorless oxosulfonylisocyanate (first step). In the last step, 2 mmol of tris(hydroxymethyl) aminomethane was added dropwise to 20 cm3 of diethyl ether solution containing 2 mmol of freshly prepared oxosulfonylisocyanate. The reaction solution was stirred at room temperature for 2 h and then concentrated under vacuum to give a white solid residue. The residue was washed with petroleum ether to remove traces of impurities. (26) Debbabi, K.; Guittard, F.; Geribaldi, S. J. Colloid Interface Sci. 2008, 326, 235–239. (27) Debbabi, K.; Guittard, F.; Geribaldi, S. Prog. Colloid Polym. Sci. 2004, 126, 79–82.
8920 DOI: 10.1021/la803579b
FPHS6. Yields: first step, 70%; second step, 82%; white solid; mp, 152-154 °C. MS (EI, 70 eV) 576.0 (M+,
