Dissertation/Thesis Abstract

Phases, line tension and pattern formation in molecularly thin films at the air-water interface
by Mandal, Pritam, Ph.D., Kent State University, 2013, 384; 3618868
Abstract (Summary)

A Langmuir film, which is a molecularly thin insoluble film on a liquid substrate, is one practical realization of a quasi-two dimensional matter. The major advantages of this system for the study of phase separation and phase co-existence are (a) it allows accurate control of the components and molecular area of the film and (b) it can be studied by various methods that require very flat films.

Phase separation in molecularly thin films plays an important role in a range of systems from biomembranes to biosensors. For example, phase-separated lipid nano-domains in biomembranes are thought to play crucial roles in membrane function. I use Brewster Angel Microscopy (BAM) coupled with Fluorescence Microscopy (FM) and static Light Scattering Microscopy (LSM) to image phases and patterns within Langmuir films. The three microscopic techniques — BAM, FM and LSM — are complimentary to each other, providing distinct sets of information. They allow direct comparison with literature results in lipid systems.

I have quantitatively validated the use of detailed hydrodynamic simulations to determine line tension in monolayers. Line tension decreases as temperature rises. This decrease gives us information on the entropy associated with the line, and thus about line structure. I carefully consider the thermodynamics of line energy and entropy to make this connection. In the longer run, LSM will be exploited to give us further information about line structure. I have also extended the technique by testing it on domains within the curved surface of a bilayer vesicle. I also note that in the same way that the presence of surface-active agents, known as surfactants, affects surface energy, the addiction of line active agents alters the inter-phase line energy. Thus my results set to stage to systematically study the influence of line active agents —'linactants' — on the inter-phase line energy.

Hierarchal self-assembled chiral patterns were observed as a function of temperature. I found that the appearance of these domains could be explained with a simple uniaxial optical axis in the underlying structure, which is the first critical step to understanding the origin of these patterns.

Indexing (document details)
Advisor: Mann, Elizabeth
Commitee: Allender, David, Balci, Hamza, Mann, Elizabeth, Mann, J., Wei, Qi-Huo, Yokoyama, Hiroshi
School: Kent State University
Department: Physics
School Location: United States -- Ohio
Source: DAI-B 75/08(E), Dissertation Abstracts International
Subjects: Molecular physics, Biophysics
Keywords: Bilayer, Brewster angel microscopy, Chirality, Fluorescence microscopy, Langmuir film, Line entropy, Line tension, Lipid monolayer, Pattern formation, Phases, Static light scattering microscopy, Vesicles
Publication Number: 3618868
ISBN: 978-1-303-87393-5
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