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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 Sean Dinneen

Program: CHEMISTRY: PHD

Department Contact Email: cindi.rohwer@unh.edu

Defense Title: OPTICAL PROPERTIES OF THE PIGMENTS FROM CEPHALOPOD CHROMATOPHORES: SOLUTION AND PARTICLE DETERMINATION

Defense Date and Time: 05/25/18 9:00 am

Defense Location: Parsons Hall, Room W131

Defense Advisor: Professor Margaret E. Greenslade


Defense Abstract: Cephalopods are arguably one of the most photonically sophisticated marine animals, as they can rapidly adapt their dermal color and texture to their surroundings using both structural and pigmentary coloration. Their chromatophore organs facilitate this process, but the molecular mechanism potentiating color change is not well understood. The central hypothesis of this work is that the pigments, which are localized within nanostructured granules in the chromatophore, enhance the scattering of light within the dermal tissue. To test this, phenoxazone-based pigments were first extracted from the chromatophore and their complex refractive index (RI) from experimentally determined real and approximated imaginary portions of the RI were extrapolated. Mie theory was used to calculate the absorbance and scattering cross sections (cm2/particle) across a broad diameter range at λ = 589 nm, where both portions of RI were determined. The results indicated that the pigments were more likely to scatter attenuated light than absorb it and that these characteristics may contribute to the color richness of cephalopods.
Next, pigment-containing nanostructures were fabricated, and their optical extinction and refractive index were experimentally determined. The pigment solution extracted from native squid chromatophores was nebulized, forming aerosols. Their size-dependent optical extinction was measured using cavity ring-down spectroscopy at λ = 532 nm, where a relationship between extinction cross section and particle concentration and size was elucidated.
Finally, a detailed analysis of the optical features of the pigment aerosols was developed and optimized. This analysis incorporated corrections that accounted for particle charging and solvent effects that accumulated during the aerosolizing process using an innovative iterative approach tied to retrieved refractive index values. RI retrievals were obtained via the best fit between the corrected, experimentally observed extinction efficiencies compared to those calculated by Mie theory for a specific RI at selected sizes. In addition to these retrievals, the impact of solvent on the particles’ optical properties was also examined via the Maxwell–Garnett mixing rule. Ultimately, an aerosol RI was obtained with a real portion (n) of 1.66 (±0.05) representing a lower limit and an imaginary portion (k) of 0.13 (±0.08)i representing an upper limit for the generated aerosols. Together, the analytical approaches used to retrieve RI values of the squid pigments presented here are advancements to the field of bio-optics that could one day inform the design of new bio-inspired optical materials.


 

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