Date of Award

Spring 2014

Document Type

Restricted Thesis

Terms of Use

© 2014 Margaret H. Regan. 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

IR-806 is a near infrared dye that self-assembles in aqueous solution and forms a chromonic liquid crystal at concentrations of 0.5 wt% and higher. In the liquid crystal phase, the assemblies tend to orient in the same direction as they diffuse throughout the volume. Usually, chromonic liquid crystals have one type of assembly structure. However, IR-806 shows a two-step assembly process: a non-threshold process at lower concentrations followed by a threshold process at higher concentrations. By numerically solving for the equilibrium conditions when the many reactions that form intermediate-size assemblies occur together with reactions in which intermediate-size assemblies form large assemblies, a model that agrees with the experimental data on IR-806 is possible.

Pinacyanol acetate is another dye that may have a two-step assembly process. For example, pinacyanol acetate forms assemblies in solutions with water that in turn form a chromonic liquid crystal phase at concentrations as low as 0. 75 wt%. Many absorption spectra of pinacyanol acetate were analyzed and decomposed into six Gaussian peaks. The behavior of the amplitude of the peaks as the concentration increases gives evidence for a two-step process, but there is no clear indication of a threshold concentration to mark the formation of the large assemblies as is true for IR-806. Measurements of the phase diagram and absorption (at varying temperature) reveal different concentration-temperature dependences, indicating that the assemblies that form the liquid crystal phase do not form in any numbers until a concentration higher than 0.1 %. Finally, the kinetics of assembly formation in pinacyanol acetate is much faster than for IR-806.

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