Dissertation Defenses

Doctoral students who have an upcoming dissertation oral defense are posted here. So why not take this opportunity to learn about the research that our graduate students are doing!

Dissertation Defense for Tyler Galpin

Program: CHEMISTRY: PHD

Department Contact Email: cindi.rohwer@unh.edu

Defense Title: OPTICAL PROPERTIES OF LABORATORY GENERATED AEROSOL: COMPLEX REFRACTIVE INDEX RETRIEVAL FOR VANILLIC ACID AND POLYSTYRENE LATEX SPHERES, AND EXTINCTION ENHANCEMENT OF MONTMORILLONITE BY WATER SWELLING

Defense Date and Time: 07/31/17 1:00 pm

Defense Location: Parsons Hall, Room W131

Defense Advisor: Professor Margaret E. Greenslade


Defense Abstract: Aerosol have the ability to alter climate through the interaction with solar radiation by absorbing and scattering solar radiation. Absorption and scattering are governed by the chemical composition dependent complex refractive index (CRI), the physical properties of the aerosol such as size, and other atmospheric parameters such as relative humidity (RH). CRI is commonly reported as the real portion at a single wavelength, or is unknown, which introduces uncertainty when these values are used as input for climate models. Two optical interrogation techniques, Aerosol Extinction Differential Absorption Spectroscopy (AE-DOAS) and Cavity Ring-Down Spectroscopy (CRD), allow for controlled measurements of laboratory generated aerosol.

The AE-DOAS has facilitated the retrieval of wavelength dependent CRI for polystyrene latex spheres (PSL) and vanillic acid. The instrument includes a white-type multi-pass gas cell coupled to a spectrometer designed to maximize sensitivity over the spectral range of 235-700 nm where particularly the UV region is not possible with most other aerosol instruments. For PSL, retrievals are achieved by iteratively minimizing the disagreement between Mie theory and measured extinction as a function of sphere size showing agreement to previously published literature results. Vanillic acid, an atmospherically relevant carbon containing molecule displaying wavelength dependent absorption characteristics, retrievals are achieved by coupling the AE-DOAS with complimentary measurements of absorption and scattering.

The CRD has allowed for precise measurement of extinction for montmorillonite aerosol. The instrument includes a laser source at 532 nm and two cavities allowing for a direct comparison of measured extinction at different RH. Montmorillonite is an alumina silicate clay composed of a layered structure allowing for generated aerosol particles to swell in the presence of increased RH. Studies were conducted comparing two different generation methods, wet and dry, for aerosol samples. Experimental results indicate that the ability to fully dry wet generated aerosol may significantly impact the amount of adsorbed water.


 

Dissertation Defense for Justin Cole

Program: CHEMISTRY: PHD

Department Contact Email: cindi.rohwer@unh.edu

Defense Title: Bio-Inspired Synthetic Systems

Defense Date and Time: 08/04/17 9:00 am

Defense Location: Parsons Hall, Room W131

Defense Advisor: Professor Erik Berda


Defense Abstract: The structure and activity of proteins are the gold standard for functional polymeric materials. From advances in sequence-controlled polymers (primary structure), to peptidomimetics, foldamers, single-chain nanoparticles (secondary and tertiary structure), accessing the various structural aspects of protein chemistry is a vibrant research area. Likewise, the properties and utility of proteins in applications such as catalysis and molecular recognition are being emulated in the laboratory with great promise.

Design and synthesis of these materials requires the application of chemistry that is uncommon in the field of protein-mimicry, which opens up entirely new architectures not accessible by biocompatible materials. Characterization of these materials requires that we approach them with the same precision as we would with a biological material, something that is unnecessary in traditional polymer chemistry. These are the two biggest challenges in the field of polymer chemistry: ab initio design of function based on polymer architecture and characterization techniques as precise as those being applied to biopolymers. This work tackles both of these challenges head on.

Here, we describe new materials that emulate various aspects of protein structure and fluorogenic imaging sensors that were inspired by electron transfer reactions that are ubiquitous in biological systems. We hope that these new polymer systems provide a glimpse into the future of synthetic materials.


 

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