A new lyotropic liquid crystalline system: Oligo (ethylene oxide) surfactants with transition metal complexes and the synthesis of mesoporous metal sulfides
Author
Çelik, Özgür
Advisor
Dağ, Ömer
Date
2001Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
In this study a new templating method, which can be used to synthesise
mesporous materials, has been developed. The main objective of this work is to form
organic mesophase in the presence of inorganic salts. This is an organic-inorganic
hybrid mesophase, which can be used to template the growth of inorganic materials.
Here for the first time, a new lyotropic liquid crystalline (LLC) system has been
presented from oligo (ethylene oxide) type surfactant and transition metal aqua
complexes.
The temperature and the metal aqua complex concentration range of the
complex/surfactant mixtures have been determined, where the mixtures have a liquid
crystalline (LC) phase. Here, the complex refers to Ni(NO3)2·6H2O, Co(NO3)2·6H2O,
Zn(NO3)2·6H2O, Cd(NO3)2·4H2O, and CoCl2·6H2O and the surfactant is
C12H25(CH2CH2O)10OH, (C12EO10). The addition of the metal aqua complexes
directly to the surfactant produces a LC phase. The LC phase obtained from the
mixture of these two is more stable than the LC phase obtained from a mixture of free
water and surfactant. The FT-IR and UV-Vis absorption, Polarised Optical
Microscopy (POM) and Powder X-ray Diffraction measurements show that the
coordinated water molecules mediate the formation of the LC phase. Our observations
also show that the coordinated water molecules make a stronger interaction with
ethylene oxide (EO) chains than free water molecules.
The LC templating approach, which is demonstrated as a new system has been
used for synthesis of meso-structured metal oxides, metal sulphides and even metal
mesh. From all these studies, it is well known that in order to maintain LC phase the
metal ion concentration should correspond to metal ion to surfactant mole ratio below
0.8. However, this work shows that the amount of metal aqua complex concentration
can be increased up to a 6.5 complex to surfactant mole ratio by maintaining the
integrity of the hexagonal and/or cubic structure of the LC phase. This may open a
new area for the realisation of new mesostructured materials with better qualities and
much higher yields.
In the first part of the thesis, the thermal and structural properties of the new
LLC phase has been established by using polarized optical microscopy (POM) with
an attached hot plate, PXRD, FT-IR and UV-Vis absorption methods. In the second
part, the new phase has been used as a template to synthesise mesoporus metal
sulfides. The second part of the thesis deals mainly with the structure and synthesis of
mesostructured CdS and ZnS. It has been demonstrated that the LC phase of
Zn(NO3)2·6H2O, and Cd(NO3)2·4H2O in oligo(ethylene oxide) surfactant survive
partially during the reaction with H2S to produce the corresponding metal sulfides.
Keywords
Lyotropic liquid crystalmesophases
transition metal aqua complexes
non-ionic surfactants
mesoporous materials
metal sulfides