Date of Award

Spring 2003

Document Type

Restricted Thesis

Terms of Use

© 2003 Michael Loeb. 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


This study examined the phase behavior of four different Langmuir monolayers. The four different monolayers were 1,2-Dipalimitoyl, sn-Glycero-3-Phophocholine (DPPC), cetyltrimethylammonium bromide (CTAB), Isocarb-24 (1-24), and stearic acid (STA). The monolayers were individually deposited on an aqueous surface and then subjected to compression in a Langmuir trough. Surface pressure measurements were made throughout the compressions using a Wilhelmy plate. Plots of surface pressure (SP) vs. Mean molecular area (Mma), known as isotherms, were obtained for all of the monolayers. The different regions of the isotherm curves were interpreted to signify specific phases of the monolayers throughout the compression. The goal was to find a monolayer that displayed a highly reproducible isotherm. This monolayer could then be examined with a bound porphyrin in the subphase, as a possible template for future two-dimensional aggregation studies. Both DPPC and STA displayed highly reproducible isotherms. The decision was made to use STA as the first subject with porphyrin in the subphase. The porphyrin molecule that was added to the subphase was tetrakis (N-methylpyridinium-4-yl) porphine (abbreviated H₂T4). This porphyrin was chosen because it would ionically bind to the deprotonated carboxylic acid head group of the stearic acid monolayer. A number of trials were run with various concentrations of H₂T4 in the subphase. It was hypothesized that the binding of porphyrin to the monolayer would occur in a manner leading to an "S" shaped binding curve. Unfortunately, quantitative results did not verify the hypothesized shape of the binding curve. Qualitatively, the study found evidence that the H2T4 molecules were binding to the stearic acid molecules, but further studies must be done to establish the exact manner in which the porphyrin binds to the Langmuir monolayer.