Douglas H. Adamson
Associate Professor of Chemistry
Ph.D. University of Southern California
Phone: (860) 486-4716
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.
We are investigating several systems with the goal of using synthetic, non-peptide polymers to mimic the functions and characteristics of naturally occurring materials. One example is the protein Silicatein α. Silicatein α is a protein found in the marine sponge Tethya aurantia. It has been shown to catalyze the condensation of silica precursors such as tetraethoxysilane (TEOS) at neutral pH and ambient temperatures. The strategy for mimicking this protein begins with the synthesis of functional block copolymers, namely poly(2-vinylpyridine-b-1,2 butadiene). This polymer is made by sequential high vacuum anionic polymerization and hydroxylated using hydroboration chemistry to give a block copolymer with functional groups that mimic the histidine and serine residues that have been shown to be active in the catalytic function of the protein. This strategy has proven successful, and we are currently funded by NSF to explore the applications of this system.
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 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.
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.
Polymer Program: 860.486.3582: email@example.com