The interfacial behaviour of two amphiphillic poly iso-butenyl
succinic anhydride (PIBSA)-derived surfactants and the effect
of their interaction with various nitrate salts on the
stability of a water-in-oil type emulsion has been
investigated. The adsorption of the esterification product of PIBSA and
coco-diethanolamide (PICDEA) and of Experse-70 (E-70) at the
equilibrated aqueous-fuel oil interface was investigated via
the measurement of interfacial tension using the ring
detachment method.The interfacial pressure of PICDEA decreased in the presence
of excess unreacted coco-diethanolamide (CDE) and for both
PICDEA and E-70 interfacial pressure decreased with an
increase in the length of the poly iso-butenyl (PIB)
hydrocarbon tail. Interfacial tension-concentration curves and
the Gibbs Equation were used to determine surfactant surface
excess concentration and the packing efficiency of the
surfactant in the interphase. The double hydrocarbon PICDEA
molecule was found to occupy a larger interfacial area than
the single hydrocarbon E-70 molecule. The pH of the aqueous phase effects the interfacial activity
and nature of, PICDEA and E-70 at the interface. PICDEA is
protonated at pH values less than 4.6 and deprotonated at
higher pH values. E-70 is neutral at low pH and deprotonated
at pH values greater than approximately 2.The effect of sodium, calcium and ferric nitrate salts on the
interfacial free energy of the surfactant saturated interface
was also determined. The interfacial tension at the E-70
aqueous nitrate interface was dependent on ionic strength
alone with a general decrease in interfacial free energy as
nitrate concentration was increased. In the case of PICDEA,
however, a surfactant-cation orientation effect was observed.
The divalent Ca2+ cation attracts two adjacent PICDEA anions
resulting in the adverse interaction of hydrocarbon tails in
the interphase. This produces an interface with a higher than
expected interfacial free energy. The Na+ cation produces an
interface with a more energetically stable orientation.
PICDEA in the presence of a ferric nitrate solution (pH 1 to
2) is protonated and therefore the univalent nitrate anion
forms the counterion layer at the positively charged
surfactant interface. Stability studies were carried out on aqueous nitrate salt in
diesel emulsions using PICDEA as the stabilizing surfactant.
Droplet coalescence rates were determined from droplet size
distribution data in the presence of varying concentrations of
sodium, calcium and ferric nitrate salts. Droplets were sized
microscopically at progressive time intervals and the rate of
coalescence determined from the change in droplet
concentration with time. Coalescence was found to follow two or more consecutive first
order reactions. After an initial period of rapid droplet
coalescence, involving small droplets with diameters of 5~m
and less, a droplet distribution is attained conducive to a
more stable emulsion which then undergoes a slower rate of
coalescence involving larger droplets.
The effect of the nitrate salt type on the initial droplet
coalescence rate (in order of increasing rate) is as follows:
Ca2+< Na+< Fe3+. The opposite trend was observed for the
slower long term rate of coalescence, i.e. Fe3+< Na+< Ca2+.
These trends are explained in terms of the surfactant cation
orientation effect, the effect of the droplet's radius of
curvature on the potential energy barrier against coalescence
and the effect of the droplet distribution of the emulsion
system. / Thesis (M.Sc.)-University of Natal, Durban, 1990.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/7806 |
| Date | January 1990 |
| Creators | Rutherford, Christine Elizabeth. |
| Contributors | Salter, L. F. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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