NSF REU at K-State: Interactions of Matter, Light and Learning
The K-State REU program offers summer fellowships to do world-class research in our friendly physics department in the scenic Flinthills. We are funded by the National Science Foundation.
Soft Condensed Matter and Biophysics
Nanofiber-based Refrigeration (Experiment)
Bret Flanders and Amy Betz, Mechancial & Nuclear Engineering
Email: bret.flanders@phys.ksu.edu or arbetz@k-state.edu
Conducting polymers, which are essentially plastics that conduct electricity, are also interesting conductors of heat. This project will investigate the thermal properties of poly 3, 4 ethylene dioxythiophene (PEDOT)-based polymers with the overall goal of producing a bed of PEDOT nanofibers that efficiently conducts heat between two contacting surfaces. The Seebeck coefficient of a material is a central parameter in thermoelectric refrigeration that describes the electric potential difference that arises across the sample when it is exposed to a temperature- gradient. An aim of this project will be to optimize the electrical and thermal properties of PEDOT nanofibers for thermoelectric applications. One strategy for doing is by varying the secondary polymer component (e.g. polystyrene sulfonate and heparin) of the polymer. Another direction of interest will be to optimize the design of the electrochemically grown PEDOT fiber beds, perhaps by refining the size, shape and material of the electrodes. This project is a collaboration between Bret Flanders and Amy Betz that combines conducting polymer nanofiber growth (Flanders) with thermoelectric device design (Betz). It is a good project for someone who enjoys both engineering and condensed matter physics.
Understanding Protein Self-assembly through Simplified Models (Theory)
Email: schmit@phys.ksu.edu
Alzheimer's, Huntington's, and prion diseases are examples of maladies caused by protein aggregates. When studied in the laboratory, the proteins responsible for these diseases show a prolonged lag phase before the appearance of fibril aggregates. Lag phases occur often in phase transitions and are understood to be the result of surface tension opposing the transition. However, this explanation does not apply to one-dimensional phases, like protein fibrils, because the surface term is just an additive constant to the free energy. In previous work, we showed that the conformational entropy of protein molecules contributes an entropic barrier to nucleation, very similar to the surface tension in higher dimensional aggregates. Interestingly, the rate equations in this model suggest that the dominant nucleation trajectories AVOID the pathway with the lowest free energy. The goal of this project is the develop simple computer models to observe nucleation trajectories in these systems and characterize how the dominant trajectories depend on parameters like the molecular size and binding affinity.
Suspensions as Solutions: Solubility of Nanoparticles (Experiment)
Email: sor@phys.ksu.edu
We have discovered that nanoparticle suspensions can act like solutions with thermally reversible, temperature dependent solubility. We have published one study [1] for 5 nm gold nanoparticles to determine their solubility as a function of their ligand shell and the solvent. We have extended these studies to the temperature dependence and data obtained by previous REU students has led to another paper published [2]. We are now collaborating with a group in Germany who make 2 nm ZnS nanoparticles that interact strongly with water and might show a negative solubility temperature dependence. i.e., they are less soluble at higher temperatures perhaps due to hydrogen bonding. The REU student would be involved in measuring the solubility of these nanoparticles in aqueous mixtures and investigating the effects of hydrogen bonding. This is a good project for someone who has interests in both physics and physical chemistry.
References (Bold type indicates REU student):
1. "Solubility of Gold Nanoparticles as a Function of Ligand Shell and Alkane Solvent", B. C. Lohman, J. A. Powell, S. Cingarapu, C. B. Aakeroy, A. Chakrabarti, K. J. Klabunde, B. M. Law, and C. M. Sorensen, Phys. Chem. Chem. Phys., 14, 6502- 6506 (2012).
2. "Temperature Dependent Solubility of Gold Nanoparticle Suspension/Solutions", J. A. Powell, R. M. Schweiters, K. W. Bayliff, E. N. Herman, N. J. Hotvedt, J. R. Changstrom, A. Chakrabarti and C. M. Sorensen*, RSC Advances 6, 70638–70643 (2016) DOI: 10.1039/C6RA15822F.
Catalytic Activity in a Vesicle (Experiment)
Email: bret.flanders@phys.ksu.edu
A vesicle is a non-living, membrane-enclosed compartment that is suspended in a salt-solution and whose interior may contain a solution of a second kind. This project will initiate an investigation into the onset of complex processes in vesicles, examples of which include membrane-based catalytic activity and intra-vesicular polymerization. Of particular interest are the mechanisms by which a vesicle may consume energy from its local environment to power such processes. As the first stage of a long term effort, this REU project will focus on the construction of the experimental tools necessary to observe proto-metabolic signatures in amphiphilic (and perhaps metal-sulphide) vesicles. These tools will include an optical microscope that supports dynamic light scattering on the single vesicle-level, and sub-micron electrodes for the localized application of electrical noise (and other signals) to individual vesicles. Additional tasks may include electrochemical data acquisition and automation; vesicle synthesis; and protocols for enzyme-insertion into the membrane. Possible outcomes for the summer research period are, for example, demonstration of dynamic light scattering on the single cell and single vesicle levels, or detection of a catalytic intra-vesicular chemical reaction. This is a good project for someone who has fun assembling equipment and optimizing its performance.
Towards the Simulation of Bulk Properties via Molecular Dynamics (Theory)
Email: schmit@phys.ksu.edu
Much of our understanding of biomolecule function comes from observing the molecules under the "computational microscope" of molecular dynamics (MD) simulations. However, these simulations are limited by the accuracy with which the computer code can mimic interactions in the real system. We have been interested in the representation of electrostatic interactions in MD. Electrostatic interactions are strongly influenced by mobile salt ions in the solution. Sodium or Chloride ions cluster around charged molecules, partially neutralizing them in a phenomenon known as screening. This means that the solvent/ion atmosphere around a biomolecule can be significantly different than the bulk solution. This has profound consequences for MD simulations because the simulation volumes are usually too small to achieve bulk-like characteristics. This can create artifacts if the simulation does not capture the effects of the solvent reservoir that surrounds molecules. We have recently shown how to predict the solvent content that should be used in a molecular simulation. The goal of this project is to take the next step and understand the effect of fluctuations in the ionic environment. This investigation will be done using analytic theory, not computer simulation.