Mitrou, Stamatina;
(2025)
Rheological characterisation of bubble suspensions: insights for complex oral health formulations.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Bubble suspensions are complex systems with applications across various industries. Despite their prevalence, experimental data for understanding their rheology and validating existing models remain sparse. This thesis aims to provide a detailed experimental characterisation of the rheological behaviour of bubble suspensions, particularly to aid the oral care industry in understanding how bubbles influence the rheological properties of their formulations. The dissertation begins by examining the effect of bubbles on the rheology of a Newtonian matrix, progressing to explore their impact on more complex matrices. Alongside conventional rheological tests, a novel rheo-optical set up was employed to visualise the suspension behaviour under shear. First, the steady shear viscosity of bubble suspensions in Newtonian media was investigated. Rheo-optical experiments revealed the shear-induced formation of bubble clusters and threads, suggesting that the shear-thinning behaviour of bubble suspensions originates from both bubble clustering and deformation, rather than solely deformation. The research then delved into the linear viscoelastic properties of bubble suspensions in Newtonian media, crucial for various industrial applications. SAOS results showed that bubble fluid dynamic interactions affected suspension elasticity by introducing additional relaxation modes at low oscillation frequencies. Building on the results obtained in Newtonian media, the final part of the research focused on the influence of bubbles on more intricate matrices typically used in oral care formulations. This study examined the steady shear viscosity of bubble suspensions in a shear thinning Carbopol dispersion, followed by the addition of surfactant to increase matrix complexity. Bubbles induced additional shear-thinning effects in both matrices. In the pure Carbopol matrix, significant bubble coalescence resulted in the formation of bubble clusters and threads as larger bubbles, confined by the flow, aligned with the fluid streamlines. Adding surfactant mitigated bubble coalescence, showing less pronounced bubble clustering compared to both the pure Carbopol and the Newtonian matrices.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Rheological characterisation of bubble suspensions: insights for complex oral health formulations |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/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 BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10217291 |
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