Khedr, Abeer Mohamed Safwat Salah;
(2020)
Predicting the Stability of Emulsions in the Presence of Surfactants and Nanoparticles Using Coarse-Grained Simulations.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Understanding the molecular mechanisms and processes that control the stability of emulsions is of great interest for many practical applications. Both surfactants and particles have been developed and optimised to control the emulsions stability. Due to the complexity of the emulsion system, it is challenging to understand the effect of these emulsifiers on the various demulsification processes, which can occur simultaneously or consecutively during phase separation. Molecular dynamics simulations are useful to identify some of the molecular mechanisms responsible for emulsions stability by providing algorithms designed to study the phenomena of interest. This work presents advances obtained via the implementation of the coarse-grained Dissipative Particle Dynamic simulation framework, DPD. First, a systematic approach was conducted to estimate the parameters to describe immiscible liquids containing surfactants. Starting from the Hansen theory of solutions, the model proved its ability to reproduce experimental water/oil interfacial tension as well as the micellar properties of aqueous non-ionic surfactants representative of the octyl polyethylene oxide family. Using this model, an algorithm was designed to study the Ostwald ripening phenomenon in an oil-in-water emulsion. The DPD simulation results are consistent with theoretical expectations, as well as with experimental observations. When surfactants were introduced to the system, the results show an enhancement in the emulsion stability due to the reduction in the interfacial tension, with a possible effect of the surfactant film properties on the Ostwald ripening rate. Finally, the effect of particle size on the arrangement of nanoparticles (NPs) on a curved oil/water interface was investigated. The arrangement of NPs showed a dependency on the particle size when the emulsion was subjected to a change in the NP-NP interaction, with a prompt self-organization of the smaller NPs. When a mixture of NPs of different sizes were introduced to the system, the NPs self-assembly on the droplet surface showed a dependency on the initial configuration. These findings could prove useful to understand the morphological changes occurring in Pickering emulsions affecting their stability, when subjected to a change in the interaction between its constituents.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Predicting the Stability of Emulsions in the Presence of Surfactants and Nanoparticles Using Coarse-Grained Simulations |
| Event: | University College London |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2020. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10108305 |
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