Micellization of economically viable surfactants in CO(2).
Stability and aggregation structures of various economically viable surfactants for CO(2) are reported. The compounds are either commercially available octylphenol nonionics (Triton X-100, X-100 reduced, and X-45) or custom-made analogues of aerosol-OT (J. Am. Chem. Soc. 123 (2001) 988). These were selected to reveal the influence of chain terminal group structure, namely highly methylated t-butyl units, on solubility and aggregation in CO(2). In addition the mean ethylene oxide block length is varied for the Triton surfactants (X-100 approximately EO(10), X-45 approximately EO(8)). High-pressure small-angle neutron scattering (SANS) experiments revealed the presence of aggregates, consistent with spheroidal reverse micelles. The nonionics show a temperature and pressure dependence on solubility. These results confirm the special affinity of highly methyl-branched tails for CO(2). However, none of these systems were able to disperse significant amounts of water or brine; therefore hydrated reversed micelles or microemulsion droplets were not stabilized. Hence the utility of these cheap methyl-branched surfactants in CO(2) is limited, and so groups of greater CO(2)-philicity are needed to achieve the goal of water-hydrocarbon surfactant-CO(2) dispersions.
Eastoe
Julian
J
School of Chemistry, University of Bristol, BS8 1TS, Bristol, UK. julian.eastoe@bristol.ac.uk
Dupont
Audrey
A
Steytler
David C
DC
Thorpe
Matthew
M
Gurgel
Alexandre
A
Heenan
Richard K
RK