Research
We are a materials synthesis group.
Typically these materials are model polymers: well-defined
polymers normally synthesized by high vacuum anionic
polymerization and well characterized with respect to
molecular weight, composition, microstructure and chain
architecture. In addition, our studies include the self-assembly
of these materials as well as polymer composites with
nanofillers.
The advantage of anionic polymerization
is the lack of significant termination or chain transfer
reactions. They are thus referred to as living systems,
or living polymers. Living anionic polymers react with
monomer and stay reactive, even as the monomer is used
up. If more monomer is added, the living polymer reacts
with the additional monomer until it is also gone, still
maintaining the reactive anion. In this way, block copolymers
or more exotic architectures can be built. Block copolymers
consist of two or more segments of different polymers
covalently bound. This living character also allows
for other architectures such as stars, where linking
agents can be added to living polymers. These linking
agents react with the anions at the chain ends, and
in effect tie together separate polymer chains.
Well-defined polymers have applications
in a large number of research areas. Our research is
commonly done in collaboration with physicists, engineers,
and biologists. I am currently involved in a wide range
of research areas. Several of these are described in
the following paragraphs.
Polymersomes
Polymersomes are vesicles formed by
amphiphilic block copolymers. This project also could
be considered bio-inspired, as these vesicles are analogous
to ones formed in biological systems from lipids. In
that case the vesicles are termed liposomes, in our
case they are called polymersomes. In both cases, vesicles
are made of amphiphilic molecules which self-assemble
to form a bilayer membrane. This membrane assembles
itself in such a way as to have the hydrophilic ends
facing the water and burying the hydrophilic ends in
the center. This is the same basic configuration as
a cell membrane (although the cell membrane is much
more complex with different lipids and transmembrane
proteins). An attractive characteristic of this system
is that a very small amount of material will encapsulate
a large volume of water.
We have developed a solvent injection method for forming
polymersomes. This involves injecting a chloroform solution
of the polymer into excess water. This solution is then
dialyzed against pure water to remove all of the chloroform.
We use fluorescence microscopy and dynamic light scattering
to visualize the polymersomes and to measure their size
and size distributions. We have also concentrated the
vesicles by removing water and find a sharp viscosity
increase measured by parallel plate rheology. We have
recently published a manuscript describing the solvent
injection technique and its mechanism of formation.
Nanofillers
We are also investigating the use of
nanofillers in polymer composites. Carbon nanotubes
as well as exfoliated graphite are the fillers we are
interested in. With carbon nanotubes we are making fiber
using a suspension of nanotubes and surfactants in water.
This suspension is then injected into an aqueous polymer
solution to form fibers. These fibers are then studied
for use as long term implants for sensing and actuation
in the body.
We are also investigating the use of exfoliated graphite,
or graphene, in composites. We produce this material
in our labs by oxidizing graphite. This then forms graphite
oxide, or GO. This material can then be thermally exfoliated
and reduced, or exfoliated in solution by sonication.
The thermally exfoliated material has a crumpled morphology
with much of the original graphite lattice in place.
This can be important in applications were conductivity
is required. The sonically exfoliated GO retains its
functional groups and has a flat morphology. This can
be useful for compatiblization with various matrixes.
Both graphene materials represent a new class of fillers
with very high aspect ratios and relatively low costs.
Recent Publications
1. Adamson, D. H.; Dabbs, D. M.; Pacheco,
C. R.; Giotto, M. V.; Morse, D. E.; Aksay, I. A., “Non-Peptide
Polymeric Silicatein a Mimic for Neutral pH Catalysis
in the formation of Silica” Macromolecules, 2007,
40, 5710-5717.
2. Angelescu, D. E.; Waller, J. H.;
Adamson, D. H.; Register, R. A.; Chaikin, P. M., “Enhanced
Order of Block Copolymer Cylinders in Single-Layer Films
Using a Sweeping Solidification Front”, Adv. Mater.,
2007, 19, 2687-2690.
3. Tinsley, J. F.; Prud’homme,
R. K.; Guo, X. H.; Adamson, D. H.; Callahan, S.; Amin,
D.; Shao, S.; Kriegel, R. M; Saini, R., “Novel
laboratory cell for fundamental studies of the effect
of polymer additives on wax deposition from model crude
oils” Energy and Fuels, 2007, 21(3), 1301-1308.
4. Hong, Y.-R.; Asakawa, K.; Adamson,
D. H.; Chaikin, P. M.; Register, R. A., “Silicon
Nanowire Grid Polarizer Fabricated from a Shear-Aligned
Diblock Copolymer Template” Opt. Lett., 2007,
32, 3125-3127.
5. McAllister, M. J.; Li, J.-L.; Adamson,
D. H.; Schniepp, H. C.; Abdala, A. A.; Liu, J.; Herrera-Alonso,
M.; Milius, D. L.; Car, R.; Prud’homme, R. K.;
Aksay, I. A., “Single Sheet Functionalized Graphene
by Oxidation and Thermal Expansion of Graphite”
Chemistry of Materials, 2007, 19, 4396-4404.
6. Register, R. A.; Angelescu, D. E.;
Pelletier, V.; Asakawa, K.; Wu, M. W.; Adamson, D. H.;
Chaikin, P. M., “Shear-Aligned Block Copolymer
Thin Films as Nanofabrication Templates” J. Photopolymer
Science, 2007, 4, 493-498.
7. Yildiz, M. E.; Prud’homme,
R. K.; Robb, I.; Adamson, D. H., “Formation and
characterization of polymersomes made by a solvent injection
method” Polymers for Advanced Technologies, 2007,
18, 427-432.
8. Vedrine, J.; Hong, Y.-R.; Marencic,
A. P.; Register, R. A.; Adamson, D. H.; Chaikin, R.
M., “Large-Area, Ordered Hxagonal Arrays of Nanoscale
Holes or Dots from Block Copolymer Templates”
Appl. Phys. Lett., 2007, 91, 143110.
9. Pelletier, V.; Adamson, D. H.; Register,
R. A.; Chaikin, P. M., “Writing mesoscale patterns
in block copolymer thin films through channel flow of
a nonsolvent fluid” Applied Physics Letters, 2007,
90, 163105-3.
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