A monolayer film of methyl stearate was compressed until catastrophic film collapse took place. Surface pressure relaxation was then followed as a function of time. Investigation involving the effects of film compression beyond the collapse pressure revealed an important process involved in the surface pressure relaxation mechanism. When the monolayer is compressed beyond the collapse pressure and then held at a constant area, the surface pressure relaxation, in a plot of surface pressure vs time, was delayed during the initial stage of the process. A similar delay in the surface pressure relaxation was also observed for a monolayer film of methyl stearate when it was compressed and held at 40 mN/m, below the collapse pressure, for some time before allowing it to relax under a constant area condition. A relaxation mechanism has been proposed to explain the delay phenomenon observed during the surface pressure relaxation at constant area: At collapse, the monolayer film buckles and folds over to form bilayer molecular channels (ridges and ribbons). The ridges and ribbons act as a reservoir for monolayer material to make up for lost molecules at the air/water interface due to the growth of a bulk (crystalline) phase under a constant area condition.
The results from temperature dependence studies as well as from the area-relaxation experiments strongly support the proposed relaxation mechanism. The Langmuir-Blodgett films of methyl stearate, deposited before and after the catastrophic film collapse, revealed interesting structural features of the collapsed film.
The experimental results from the pressure-time, area-time, and pressure-area isotherms strongly suggest that the methyl stearate monolayer film undergoes an organized film collapse. This work helps to better understand the relaxation mechanism in monolayer films at the air/water interface. / Master of Science
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/43161 |
| Date | 11 June 2009 |
| Creators | Tiwari, Rajesh Kumar |
| Contributors | Chemistry |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | xi, 73 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 32378471, LD5655.V855_1994.T593.pdf |
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