Date of Award

Spring 2006

Document Type

Restricted Thesis

Terms of Use

© 2006 Jessica Gersh. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts

Department

Physics & Astronomy Department

First Advisor

Peter J. Collings

Abstract

Although the most recent studies of Sunset Yellow FCF, disodium chromoglycate, and several other chromonic liquid crystals suggest that chromonic liquid crystals form rod-shaped aggregates with a distribution of sizes that shifts towards larger aggregates as the concentration increases, limited studies of another chromonic liquid crystal, Benzopurpurin 4B (BPP 4B), suggest that the aggregation process is very different for BPP 4B. These studies found that unlike other chromonic liquid crystals, BPP 4B solutions scatter visible light and form a liquid crystal phase at significantly lower concentrations, which implies that their aggregates are much larger. To extend this research, both the phase diagram in water and the aggregate size of BPP 4B were investigated. To determine the phase diagram, the temperatures marking the beginning and end of the coexistence region between the liquid crystal and isotropic liquid phases were measured optically. The results suggest that BPP 4B forms aggregates with a distribution of sizes and has a liquid crystal phase at significantly lower concentrations and volume fractions than other chromonic liquid crystals. Additionally, measurements of the hydrodynamic and optical radii, the relative scattering intensity, and the absorption coefficient suggest that the size distribution does not change with concentration. One possible explanation is that BPP 4B forms micelles with a distribution of sizes. However, the presence of an impurity much larger than the aggregates might also explain these results. Although the exact aggregate structure of BPP 4B remains largely uncertain, the results of these experiments suggest that it is very different from the simple, rod-like structures of other chromonic liquid crystals. 2

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