The Micelle Shuttle Timothy P. Lodge, University of Minnesota

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The Micelle Shuttle Timothy P. Lodge,
University of Minnesota Twin Cities, DMR 0804197
Ionic liquids have received much attention as
potential green solvents for industrial scale
chemical transformations. The appealing
environmental aspect of ionic liquids is that
they have no vapor pressure, thereby enabling
compete containment and recycling. However, as
many possible ingredients of chemical reactions,
or their products, are not readily soluble in a
chosen ionic liquid, it is desirable to develop
surfactant systems that can reliably and rapidly
transport such insoluble molecules into or out of
an ionic liquid medium. We have developed a
remarkable, thermoreversible shuttle system, in
which block copolymer surfactant micelles can be
made to pass intact from water into an ionic
liquid, and vice versa. The key feature is to
design the copolymer and the ionic liquid such
that at low temperature the micelles reside
exclusively in the aqueous phase, but at high
temperature they prefer the ionic liquid. This
discovery offers a means to use aqueous streams
to do the final separation and purification
steps, with little or no adverse environmental
consequence. We have recently quantified the
mechanism and thermodynamic parameters f this
process 1. Thermodynamics and Mechanism of the
Block Copolymer Micelle Shuttle between Water and
an Ionic Liquid, Z. Bai and T. P. Lodge, J.
Phys. Chem. B, submitted. 2. Block Copolymer
Micelle Shuttles with Tunable Transfer
Temperatures Between Ionic Liquids and Aqueous
Solutions, Z. Bai, Y. He and T. P. Lodge,
Langmuir, 24, 5284-5290 (2008). 3. A
Thermoreversible Micellization-Transfer-Demicelliz
ation Shuttle Between Water and an Ionic Liquid,
Z. Bai, Y. He, N. P. Young, and T. P. Lodge,
Macromolecules, 41, 6615-6617 (2008).
The micelle shuttle as it transfer from the
(upper) aqueous phase to the (lower) ionic
liquid. The micelles are formed from
poly(butadiene-block-ethylene oxide) (PB-PEO)
copolymers, and contain Rhodamine B labeled PB
homopolymers as cargo. During the first two
hours, ionic liquid slowly displaces water in the
PEO corona, leading to an increase in density and
sedimentation to the interface. Then the micelles
complete the solvent exchange, and diffuse into
the ionic liquid. In practical situations the
system would be stirred vigorously, greatly
accelerating the transfer.
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Broader Impact Undergraduates doing Polymer
Research Timothy P. Lodge, University of
Minnesota Twin Cities, DMR 0804197