<p>Emulsions are advantageous
in many applications including healthcare, food science, and detergency due to
their ability to disperse one fluid in another, otherwise immiscible fluid. For
the same reason, emulsions are also problematic when mixtures of oil and water
are undesirable like in industrial wastewater pollution and fuel systems. Whether
an emulsion is desirable or not, both benefit from understanding the
fundamental relationship of emulsion formation and stability to the physical
and chemical properties of the oil-water-surfactant mixture. This work
identifies the formation and stability mechanisms of model emulsion systems
through the perspective of emulsion prevention for applications in shipboard
wastewater (bilge water) treatment. Although experiments in this study were
designed to model bilge water systems, their fundamental approach makes them
practical for many different applications like food science, pharmaceuticals,
and detergency.</p>
<p>The impact of salts on
emulsion formation and stability to coalescence were studied to understand how
emulsions stabilized by ionic surfactant behave in saltwater environments. Droplet
size analysis revealed that emulsion stability to coalescence improved with
salt concentration. Through interfacial tension and zeta potential
measurements, it was found that the addition of salt promoted close surfactant
packing and faster surfactant adsorption kinetics at the oil-water interface.
This aided in preventing coalescence and created conditions favorable for the
formation of a stable Newton black film. Extended DLVO calculations were used
to model the interaction energy between droplets and suggested that hydration
forces play an important role in stabilizing these systems. These emulsions
were then studied under dynamic ageing conditions to observe the impact of
motion on emulsion stability. While statically aged emulsions were stable to
coalescence, dynamic ageing induced coalescence (increased droplet size) or
emulsified the oil droplets (decreased droplet size) depending on the
surfactant concentration and energy input during ageing.</p>
Formation mechanisms
and stability of spontaneous emulsion systems were also investigated. Low
molecular weight oils (e.g., toluene, xylenes, and cyclohexane) were found to
spontaneously emulsify with nonylphenol polyethoxylated (NPE) and sodium dodecylbenzene
sulfonate (SDBS). NPE emulsions spontaneously emulsified via diffusion and
micelle swelling and displayed limited stability due to Ostwald ripening. SDBS
emulsions also spontaneously emulsified with toluene but only in saltwater
environments. As the concentration of salt in the aqueous phase increased, the
spontaneity of these emulsions also increased. These systems were analyzed
using the hydrophilic lipophilic difference (HLD) theory to evaluate its efficacy
for predicting the conditions favorable for spontaneous emulsification.
Limitations and practicality of using the HLD model for these systems were also
explored.
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/14960043 |
| Date | 22 July 2021 |
| Creators | Cole R Davis (11113473) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Relating_the_Formation_Mechanisms_and_Kinetic_Stability_of_Complex_Shipboard_Emulsions_to_the_Physical_and_Chemical_Properties_of_Model_Surfactant-Oil-Water-Salt_Systems/14960043 |
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