Positron Annihilation Lifetime Study of the Cubic Phases in The Ternary System of Didodecyldimethylammonium Bromide/ Water/ Hydrocarbon
Positron annihilation lifetime technique (PAL) has become a standard technique especially for the investigation of defects in solids, fermi surface, phase transitions etc. The effectiveness of the method lies on the ability of the positron to sample selectively electron states in the media and hi...
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| 格式: | Thesis |
| 语言: | English English |
| 出版: |
1999
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| 主题: | |
| 在线阅读: | http://psasir.upm.edu.my/id/eprint/9471/1/FSAS_1999_18_A.pdf |
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| 总结: | Positron annihilation lifetime technique (PAL) has become a standard
technique especially for the investigation of defects in solids, fermi surface, phase
transitions etc. The effectiveness of the method lies on the ability of the positron
to sample selectively electron states in the media and highlighting them via its
annihilation photons. It is now known that in amphiphilic system positron forms
para and ortho-positronium atoms. The former has a lifetime of 125 ps and
annihilates via two photons while the ortho-positronium atom has a lifetime of
140 ns and annihilates via three photons. Any localised factors such as those
found during rearrangement of microstructures in amphiphilic systems can
influence the ortho-positronium to annihilate prematurely. In this project Positron Annihilation Lifetime Method was used to study
the cubic phases in the ternary system of didodecyldimethylamrnonium bromide
(DDAB)/water /hydrocarbon. Three different systems of DDAB were measured
i.e DDABI D201 Octane, DDABI D201 Tetradecane, and DDABI D201 Toluene.
These systems were expected to provide information on the effect of molecular
size and degree of penetration of the oil into the hydrophobic tail region and to
influence the structure of the cubic phase. A fast-slow coincidence technique was
used to measure the lifetime of positron that interacts with the surfactant medium.
The result was analysed using POSITRONFIT programme. An attempt was made
to identify the various symmetries by referring to alternative work on the same
system.
The inhibition constants, k' for the D -Schwarz of the mixtures of DDABI
D201 Octane and DDABI D201 Toluene were found to be 2.54 and 0.92
respectively. On the other hand the P-Schwarz minimal surfaces for the mixtures
ofDDABI D201 Octane gave an inhibition constant of 1.89 and for the mixtures
of DDABI D201 Tetradecane an inhibition constant is 1.63. For other space
groups such as the Ia3d space group in the DDABI D201 Toluene mixtures, k' was
found to be 5.03 . Although the results is not constant from one sample to another,
the positron method shows the sensitiveness of the changes in the microstructure
phases. Thus the Positron Annihilation Lifetime Technique can be used as an
alternative method in resolving phases in ternary surfactant systems. |
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