Date of Award

Fall 2008

Document Type

Restricted Thesis

Terms of Use

© 2008 Chris McKitterick. 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


Physics & Astronomy Department

First Advisor

Peter J. Collings


Benzopurpurin 4B (BPP) is a textile dye that has been studied in the Liquid Crystal Laboratory at Swarthmore College over the last two years. Previous investigations have utilized the commercially available impure material. One of the goals of this study was to use a purified sample of BPP to establish a phase diagram. The impurity was previously determined to be salt, and so purification was achieved through dialysis. Once purified, the liquid crystal transition of different concentrations of BPP in water was examined by monitoring the optical retardation of the sample as the temperature was increased from below room temperature to up to 95°C. The other portion of the work involved determining the dependence of the absorption coefficient on concentration and imaging the aggregates in the system with a confocal microscope. Absorption coefficient measurements were taken on very dilute samples of BPP using a spectrophotometer.

The phase diagram produced showed that the liquid crystal phase forms at much lower concentrations than in other chromonic systems. This suggests that the aggregates of BPP may form differently than those of most other chromonic liquid crystals. The absorption spectrum showed a smooth development with concentration, indicative of a gradual and continuous aggregation process as is characteristic of chromonic liquid crystals. Images taken with the confocal microscope over several weeks suggest that the aggregation process occurs very slowly. Using these images, the length of BPP aggregates was estimated to be between 3 and 5 microns initially, but after a longer period of time the aggregates reached lengths over 10 microns. The diameter of the aggregates was estimated to be no greater than 140 nanometers. A more precise measurement could not be achieved since the aggregate diameter lies well below the resolution of the confocal microscope.