David A. Hoagland
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Degree Information: Mailing Address: Phone:
413-577-1125 413-577-1513 Email:
Fax:
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Research Interests:
Current Research: Polymers underlie a diverse spectrum of “soft materials”, from solutions and gels to suspensions, emulsions, and pastes. In addition to their central role in living systems (DNA and proteins are polymers!), soluble or swollen polymers are present in products such as foods, coatings, and sensors as well as technologies such as water-treatment, DNA sequencing, and ink-jet printing. Projects in the Hoagland group examine molecular structure and dynamics in these environments using a host of experimental methods, some rather complex (dynamic light scattering, electrophoresis) and others rather simple (viscometry, thermal analysis). The goal is nearly always to understand the behaviors of individual polymer molecules, i.e., their average conformation, where and how they move, or how rapidly they deform/recover when challenged with an external force. Current projects focus on problems in (i) polyelectrolytes (highly charged polymers), (ii) polymers in ionic liquids (salts that melt near or below room temperature), (iii) imaging of the dynamics of confined polymers, and (iv) polymer aspects of carbon nanotube membranes. The figure at right shows a time sequence (left-to-right) of conformations for a flexible polymer (DNA moving through a porous chromatography column (pore structure not visible). The time-evolving location and conformation of this single, labeled molecule are revealed via fluorescence microscope imaging. In the imposed solvent flow (toward upper left), the molecule initially “entangles” around a contact point between chromatography beads, and through subsequent ‘pulley-like” motion about this spatial constraint, extends in the flow direction and eventually releases. Dynamic light scattering examination of the protein lysozyme in the room temperature ionic liquid [EMIM][EtSO4] generated the correlation function shown at left. The position and sharpness of the decay not only reveal that the protein dissolves in the liquid but also that it retains a molecular size comparable to that adopted in buffer. Circular dichroism and infrared spectroscopy show that proteins in the ionic liquid are generally not in native states, but absent hydrophobic effects to drive aggregation, these states can be recovered upon transfer to buffer. We are currently determining the phase behavior and activity of proteins in ionic liquid-aqueous buffer mixtures.
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Honors and Distinctions:
- Sigma Chi Distinguished National Lecturer, 2004-2005
- Fellow, American Physical Society, 2003
- Director- Light Scattering Facility
- The OMNOVA Solutions Foundation Signature University Award for Outstanding Research, 2000
- Organizing Committee, International Symposium on Polyelectrolytes, 2004
- IBM Faculty Development Award, 1986
- Co-coordinator of the MRSEC’s IRG III, Aqueous Polymer Assembly
- Invited Speaker: Gordon Conferences on Polymers (2x), Polymer Physics, Membranes, Scattering and Macromolecular Solutions, and Ion-Containing Polymers (2x); APS March Meeting (2x); International Symposium on Polymer Analysis and Characterization (2x); Heraeus Conference on Nano-Physics of DNA; John Ferry Symposium; ACS Division of Analytical Chemistry; Telluride Workshop on Polymer Theory vs. Polymer Experiment (2x); Electrophoresis Society Annual Meeting; AIChE Annual Meeting; First Conference on Polymers and Ionic Liquids
