Intrinsic dynamics of emulsions: Experiments in microgravity on the International Space Station

[Display omitted] In order to understand the basic mechanisms affecting emulsion stability, the intrinsic dynamics of the drop population must be investigated. We hypothesize that transient ballistic motion can serve as a marker of interactions between drops. In 1G conditions, buoyancy-induced drop...

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Bibliographic Details
Published in:Journal of colloid and interface science 2025-01, Vol.677 (Pt A), p.231-243
Main Authors: Lorusso, V., Orsi, D., Vaccari, M., Ravera, F., Santini, E., Chondrou, A.P., Kostoglou, M., Karapantsios, T.D., McMillin, R., Ferri, J.K., Vincent-Bonnieu, S., Liggieri, L., Cristofolini, L.
Format: Article
Language:English
Subjects:
Ballistic motion
Brownian dynamics
Coalescence/aggregation
Diffusing Wave Spectroscopy (DWS)
Drop size distribution
Dynamic transition
Emulsions
Microgravity
Non-ionic surfactants
Optical Monte Carlo simulations
Soft matter dynamics
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Summary:[Display omitted] In order to understand the basic mechanisms affecting emulsion stability, the intrinsic dynamics of the drop population must be investigated. We hypothesize that transient ballistic motion can serve as a marker of interactions between drops. In 1G conditions, buoyancy-induced drop motion obscures these interactions. The microgravity condition onboard the International Space Station enable this investigation. We performed Diffusing Wave Spectroscopy (DWS) experiments in the ESA Soft Matter Dynamics (SMD) facility. We used Monte Carlo simulations of photon trajectory to support data analysis. The analysis framework was validated by ground-based characterizations of the initial drop size distribution (DSD) and the properties of the oil/water interface in the presence of surfactant. We characterized the drop size distribution and found to be bi-disperse. Drop dynamics shows transient ballistic features at early times, reaching a stationary regime of primarily diffusion-dominated motion. This suggests different ageing mechanisms: immediately after emulsification, the main mechanism is coalescence or aggregation between small drops. However at later times, ageing proceeds via coalescence or aggregation of small with large drops in some emulsions. Our results elucidate new processes relevant to emulsion stability with potential impact on industrial processes on Earth, as well as enabling technologies for space exploration.
ISSN:0021-9797
1095-7103
1095-7103
DOI:10.1016/j.jcis.2024.07.205