الفهرس 
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Abstract
The present thesis deals with microemulsion characterization and microemulsion
application as media for electrochemical reactions. The effect of microemulsion as a local
environment in comparison to pure aqueous medium on the electrode process, kinetics
and thermodynamics were recorded for a model quinone, nucleic acids and for two
different series of azo compounds, in both aqueous and microemulsion media.
Also, the charge transfer switching reactions of polypyrrole and polyaniline
conductive composites were recorded for polymer composites prepared at different
potential steps and different amounts of charge passed during the electropolymerization
process. This work comprises three chapters:
Chapter (I) includes an introduction and background on microemulsions and a
literature survey on the electrochemical investigations in microemulsion media.
Extension of chapter (I) was a background on the electrochemical techniques used in
these investigations.
Chapter (II) includes preparation of azo compounds derived from 6,7-
dihydroxycoumarin and those derived from 2-hydroxy-6-naphthalenesulfonic acid,
instruments and solutions which were used for the measurements using different
techniques. It also includes the methods of preparation of nonconductive coatings by
microemulsion copolymerization in the presence of SDS and polymerizable surfactant.
Chapter (III) is divided into two main parts. Part (A) includes microemulsion
characterization by using different electrochemical techniques and the use of
microemulsion and micelles as media in the electrochemical investigation of electrode
reactions. It is subdivided into eight parts: 1- Electrochemical characterization of three different microemulsion systems
usmg ferrocene as a standard probe. Cetyltrimethylammonium bromide, CTAB, sodium
dodecyl sulphate, SDS and octylphenoxypolyoxyethylene, Triton X-IOO model
surfactants were used in this investigation. Cyclic voltammograms of 1 roM of ferrocene
were recorded in the different surfactant systems. It was found that ferrocene has only a
single redox couple of peaks. The peak separation AEp is around 60 mV indicating a
single electron transfer. The peak current ratio of Ip.”IIp.c was found not to exceed 1.15
indicating that adsorption of surfactants on the electrode surface is negligible and it was
confirmed by using the double potential step chronocoulometry technique. The plots of
the anodic peak current (Ip .a) versus u 1/2 showed linear correlations passing through the
origin indicating that the electrode process is diffusion controlled. The apparent diffusion
coefficients of microemulsion droplets were determined from the slope. By using the
Stoke’s-Einstein equation, the radius of micro emulsion droplets was calculated to be 123,
44 and 72 AO for CTAB, SDS and Triton X-IOO, respectively. These results were
confirmed from the rotating disc electrode study in these media. The effects of
temperature and hydrocarbon content on the microemulsion droplet size were determined.
It was found that the size of microemulsions is increased on increasing the percentage of
n-octane, while it decreased with increasing temperature ..
2- The electrochemical behaviour of a model qumone l-amino-9,10-
anthraquinone (IAAQ) was observed in micelles and microemulsions of three different
surfactant types as well as in aqueous solution using cyclic voltammetry. The
voltammograms showed a single reduction step in all media, except in CTAB micelles a
shoulder appears and becomes a peak on increasing the sweep rate. In general, the peak separation ~p is 30 mV at lower sweep rates indicating a 2-electron transfer and
increases on increasing sweep rate up to 55 mY. Generally, the ratio of peak current
(lp,alIp.c) is less than unity in microemulsions and much less in micellar solutions. These
electrochemical results indicate that a chemical reaction has to take place, the
disproportionation of lAAQ-’ anionic radical to the original quinone (lAAQ) and
hydroquinone (lAAQHz) . Differences in Ep, ~Ep and the Ip,alIp.c values is explained in
terms of stabilization mechanisms. Stabilization is imparted by electrostatic and! or
hydrophobic interactions. The surfactant present affects the stability of lAAQ-’ and thus
the equilibrium of the disproportionation reaction to different extents, It was found that
CTAB stabilizes lAAQ more than SDS and Triton X-I 00 by electrostatic interactions
and tends to inhibit the disproportionation of IAAQ. SDS and Triton X-I 00 systems also
stabilize lAAQ by surface interaction. This leads to a slower disproportionation of lAAQ
and the reduction of lAAQ becomes chemically quasi-reversible with a net transfer of
two electrons. Diffusion coefficient values of oxidized and reduced forms indicate the
partitioning of lAAQ between oil droplet, surfactant film and aqueous domain.
There is no adsorption on the electrode in micellar solutions and microemulsions
compared to aqueous media. This was confirmed by chronocoulometry since the amount
of adsorption of lAAQ on the electrode surface was found to be in the order of 10,12
moles which is negligible. These results confirmed that the reactivity of the quinoid
moiety in biological systems is critically dependent on its location and the surrounding
environment.
3- The cyclic voltarnmograms of nucleic acids (adenine and cytosine) were
recorded in micelles and microemulsion media of three different surfactant types and in aqueous solution. CTAB, SDS and Triton X-IOO model surfactants were used. The
voltammograms showed a single reduction step for adenine and cytosine in all media.
The absence of any anodic peaks in the reverse scan as well as the values of an. indicate
the irreversible nature of the electrode process. The peak potential (Ep) displayed a
cathodic shift on increasing the sweep rate which further confirms the irreversible
reduction process. Complications observed in aqueous media due to adsorption and
catalytic activity on the electrode surface were eliminated in microemulsions. It is
postulated that surfactant stabilization of reactant, intermediate and products purine and
pyrimidine moities were partitioned into microemulsions.
4- The cyclic voltammograms of two series of azo compounds [coumarin azocompounds
(series I), and Schiffer azodyes (series II)] were recorded in microemulsion
media of three different surfactant types (CTAB, SDS and Triton X-I 00) using a GCE.
The CV was also observed using a HDME in aqueous buffered solutions of different pH
values containing 40% (v/v) ethanol for compounds of series (1) and in pure aqueous
solution for compounds of series (II). The voltammograms showed a single reduction step
in all microemulsions and aqueous solutions. The peak potential displayed cathodic shift
on increasing both sweep rate and pH of solution, indicating that irreversible reduction
takes place and the reduction includes the consumption of protons. The plots of peak
current (lp) versus u \/2 showed linear correlations intersecting the origin in microemulsion
media indicating that the electrode process is diffusion controlled. However, such plots
for pure aqueous buffered solutions showed some adsorption on the electrode. The values
of the transfer coefficient (a) were obtained from the Ep-ln(u) plots in all media for the compounds of the two series and were found to be less than unity indicating the
irreversible nature of the electrode process.
5- The different kinetic parameters of the various electrode reactions and the
substituent effect on the reduction mechanism were determined. It was found that the
heterogeneous rate constant (kof,h) in cationic CTAB systems is higher than in aqueous
solutions or anionic, SDS, and nonionic, Triton X-I 00 systems.
6- Thermodynamic parameters, such as I’1G#, I’1It and I’1S# of the electrode
reactions were determined for cytosine, adenine and coumarin azodyes in both aqueous
and microemulsion media. Also, the activation energy (E.) of the reduction of lAAQ was
determined. Inspection of the values revealed a positive enthalpy changes indicating the
irreversible nature of the electrode process. Negative entropy change means an ordered
electrode reaction becomes less ordered on increasing temperature. Values of the
activation energy indicate that the electrode reaction in CTAB systems is less ordered
compared to Triton X-IOO and SDS systems.
7- The electrode mechanisms of lAAQ, adenine and cytosine as well as the two
series of dyes were determined from the obtained data and the total number of electrons
determined from the controlled potential electrolysis and found to be 2 in case of IAAQ,
4 in case of adenine, 3 in case of cytosine and 4 for the azodye compounds of the two
series.
8- The effect of complex formation of Schiffer azodye compounds on the
voltamrnetric behaviour of Cu(II) and Zn(II) ions was recorded. The stoichiometry of
complexes formed in solution were determined as well as their stability constants. Part (B) includes the preparation of conductive composite polymers such as
polypyrrole and polyaniline films. The method of preparation of conductive composites is
a two-step process combining chemical and electrochemical methods. The chemical step
includes the copolymerization ofMMAIHEA from SDS microemulsion and MMAlAA in
the presence ofNa II-AAU to obtain hydrophilic porous nonconductive coatings.
The second step is electrochemical polymerization of either pyrrole or aniline
monomer through the noncondutive coating in the presence of a dopant anion such as 0.1
M of either 1,3-benzenedisulfonate or toluenesulfonate in case of pyrrole or 1M of
perchloric acid in case of aniline electropolymerization.
The chronoamperometric responses of electropolymerized films obtained
potentiostatically at 650, 800, 1000, 1500 and 2000 mV indicate overoxidation for
conductive polymer composites prepared at potentials > 1000 mY. Cyclic
voltammograms were recorded for polypyrrole composite films prepared at different
potential steps by passing 30 mC. At potentials less than 800 mY, the anodic peak
currents of polypyrrole composite films incorporating either toluenesulfonate or 1,3-
benzenedisulfonate showed linear dependence on the sweep rate indicating that the rate
controlling step is the electron transfer process from or into the polymer chains.
In general, an emperical correlation was used to determine the rate controlling
reaction of the polymer composites by studying the effect of the amount of charge passed
during electropolymerization on the cyclic voltammetric responses of polymer composite
films prepared by applying different potential steps. The thermal and mechanical properties of the polymer coatings were discussed
and the morphology of different polymer composites was observed by scanning electron
microscopy (SEM). The effects of potential of polymerization and the amount of charge
passed on the morphology and sheet resistivity were determined.