Investigation of two new lyotropic liquid crystalline systems : [Zn (formula) and [Zn (formula)
Author
Albayrak, Cemal
Advisor
Dağ, Ömer
Date
2008Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
The transition metal aqua complex salts (TMS) can be dissolved in oligo
(ethylene oxide) type non-ionic surfactants (CnH2n+1(CH2CH2O)mOH, denoted as
CnEOm) with very high salt/surfactant ratios to form lyotropic liquid crystalline (LLC)
mesophases. In this study we show that addition of charged surfactants, such as
cethyltrimethylammoniumbromide (CTAB) or sodiumdodecylsulfate (SDS) results a
new type of LLC in which the solubility of the salts in the LC mesophase of TMS:
C12EO10 is enhanced. The LC phase of a [Zn(H2O)6](NO3)2:C12EO10 is hexagonal
between 1.2 and 3.2 and cubic (liquid like) above 3.2 salt/ C12EO10 mole ratios.
Addition of CTAB or SDS increases the same salt/surfactant mole ratio to 8.0-9.0,
which is a record salt amount for a lyotropic liquid crystalline system. The mixed
surfactant mesophases have birefringent hexagonal mesophase between 2.0 and 8.0
salt/C12EO10 mole ratios The new mixed surfactant systems can also accomodate high
TMSs in the presence of excessive amounts of water (35.0 water:C12EO10 mole ratio). Both systems have similar thermal properties. Izotropisation Temperature (IT) values
of the new systems go down with increasing salt and charged surfactant
concentrations. The mesophases are stable at high salt concentrations in the presence
of high CTAB or SDS concentration in the expense of the stability of the LLC
mesophase. The IT values changes from around 80o
C down to 32o
C with increasing
composition of the LLC mesophase. The new mesophase have 2D or 3D hexagonal
structure that responds to water content of the phase. A 3D hexagonal phase
transforms to 2D hexagonal phase with the evaporation of excess water in both
[Zn(H2O)6](NO3)2:C12EO10-CTAB-H2O and [Zn(H2O)6](NO3)2:C12EO10-SDS-H2O
systems. The new mesophases were investigated using POM (Polarised optical
microscope), and a hot stage under the POM, XRD (X-ray Diffraction), FT-IR
(Fourier Transform Infrared Spectroscopy) and Raman techniques. These new LLC
systems are good candidates for metal containing mesostructured material synthesis
due to their high salt content.
Keywords
Transition metal aqua complex saltsIzotropisation Temperature
Lyotropic liquid crystals
Hexagonal and cubic mesophases
Mixed Surfactants
CTAB
SDS
C12EO10