Mihaylov_Miroslav.pdf (4.44 MB)
Download fileX-ray Investigations of Mixed Charge Amphiphilic Systems
thesis
posted on 2016-02-16, 00:00 authored by Miroslav N. MihaylovThe liquid vapor interface is of a fundamental importance for a wide range of
applications from physics, chemistry and biology to material science and
nanotechnology. Soft matter thin films composed of mixture of cationic and
anionic surfactants are of great interest because of their unique interfacial
properties that arise from the strong electrostatic interactions between the
oppositely charged headgroups. In order to exploit these properties a better
understanding of the molecular scale structure of these catanionic systems is
needed.
Surface sensitive synchrotron X-ray scattering techniques at room temperature
were used to study structural properties of a catanionic system composed of the
phospholipid PIP2 and Trimethyloctadecylammonium bromide.
Through a series of surface pressure versus time and surface pressure - area
isotherm measurements it was established that the catanionic mixture is more
surface active compared to its individual components. Furthermore, the surface
pressure - area isotherm of the mixed charge system was monotonous without any
phase transition indicating that the film is in a liquid expanded phase. The
monlayer stability compression-decompression cycles showed that the formed
Langmuir film was stable over the course of many days.
Specular X-ray reflectivity measurements determined the electron density profile
in the direction normal to the interface averaged over the inplane region of the
interface. X-ray reflectivity, normalized to the Fresnel reflectivity of an
ideal flat interface, was fit to a model system consisting of 2 layers. The
occupancy of the components obtained from the electron density profile analysis
gave an estimate which was in excellent agreement with the macroscopic
calculation from the molecular weight, amount deposited and available area of
the film.
Another independent technique, Grazing Incidence Diffraction, probed for an
inplane ordering of this two dimensional structure. It showed highly ordered
domains composed of untitled acyl chains with hexagonal unit cell. Bragg rod
analysis of the variation of the scattered intensity along the specular
direction was in agreement with the findings from the X-ray reflectivity
analysis.
X-ray data showed a stable ordering of this soft matter system with the same
regularity as that of a solid crystal. What makes this type of ordering so special is that none
of the individual components of the system on their own can form such a state but, because of their cooperative and
collective behavior, it becomes possible to achieve a very stable configuration in this catanionic system.
History
Advisor
Schlossman, Mark L.Department
PhysicsDegree Grantor
University of Illinois at ChicagoDegree Level
- Doctoral
Committee Member
Ansari, Anjum Ogut, Serdar Cavanaugh, Richard Sharma, VivekSubmitted date
2015-12Language
- en