Periodic Reporting for period 1 - NANOSLIP (Shear at the liquid/nano-fluid interface: Drag, slip, and friction.)
Berichtszeitraum: 2021-09-01 bis 2023-08-31
Aqueous Nanofluids are typically comprised of like-charged nanoparticles of silica suspended in water at high concentrations. These Nanofluids possess improved spreading properties over surfaces compared to standard liquids due to the structuring of the nanoparticles within, whereby the nanoparticles organize into layers, which are more tightly bound as they approach the surface in contact with the Nanofluid. The more stable configuration of the layers of nanoparticles nearest to the surface encourages the propagation of a nanofilm of the Nanofluid over the surface, containing 2-3 layers of nanoparticles. The Nanofluid nanofilm is capable of displacing immiscible liquids in contact with surfaces and has been a subject of research for its use in Enhanced Oil Recovery (EOC), and soil remediation. Existing methods to study the Nanofluid nanofilm confined between a surface and oil have been limited to indirect approaches, such as white light interferometry, which only enable the visualisation of the Nanofluid nanofilm, alongside determining its thickness. The objective of this project was to perform the first direct measurements of the Nanofluid nanofilm, using atomic force microscopy (AFM) at the nanofilm/oil interface. Here, the thickness of the Nanofluid nanofilm could be directly determined, and then further probed in response to shear forces which are relevant in its use in EOC and soil remediation. Through the development of this experimental platform via AFM, further investigations could be performed, enabling a deeper understanding of Nanofluids spreading properties. This project has successfully measured the presence and thickness of the Nanofluid nanofilm confined between a mica surface and fluorinated oil for the first time via AFM. The thickness of the nanofilm was larger than expected, upwards to a factor of 10, which is suspected to be due to the specific experimental set up required to achieve this feat. While there is further development required to reconcile the unexpected nanofilm thickness, this project has successfully established an experimental platform via AFM to directly study the Nanofluid nanofilm at the nanofilm/oil interface.
This project undertook the following work during its lifetime:
Characterisation of the Nanofluid – Here the Nanofluid chosen for the project, a highly concentrated suspension of silica nanoparticles (LUDOX HS40) was prepared following existing experimental protocol prior to undertaking further experiments. The Nanofluid was purified of excess salt via dialysis with Milli-Q water, had its nanoparticle particle size and polydispersity determined via AFM imaging, and the presence of nanoparticle layering toward a smooth mica surface, necessary for the formation of the desired Nanofluid nanofilm, was confirmed via AFM force measurements and compared to existing literature.
Direct measurements of the Nanofluid nanofilm via AFM – Here, an experimental set up to enable using AFM to directly probe the nanofilm/oil interface was established. A fluorinated oil was deposited onto a smooth mica surface in a liquid cell while surrounded by the Nanofluid. AFM force measurements were performed through the oil phase, towards the mica surface, and revealed the presence of the Nanofluid nanofilm through the presence of the attractive capillary force generated upon contact with the nanofilm/oil interface. The thickness of the nanofilm was found to be larger than expected based on existing reports in literature, which was suspected to be due to the experimental configuration required to perform the AFM force measurements.
Studying the interfacial properties of the Nanofluid and fluorinated oil – Here, the surface tension of the Nanofluid and the fluorinated oil was studied using the pendant drop method, undertaken primarily by an undergraduate project student under the supervision of the project lead. A series of experiments were performed to confirm the reproducibility of experimental technique through using Milli-Q water against silicone oil and the fluorinated oil, obtaining values reported in literature. The surface tension of the Nanofluid against the fluorinated oil was found to be comparable to that of the values obtained using Milli-Q water, indicating the nanoparticles in the Nanofluid were not interface active. The properties of the Nanofluid/fluorinated oil interface were probed in response to the inclusion of a surfactant (SDS) at low concentrations, helping reinforce the understanding of the experimental system used in the prior mentioned AFM force measurements at the Nanofluid nanofilm/oil interface.
The findings of this project were presented at the following durng it's lifetime:
Department of Theoretical Physics at Jožef Stefan Institute, Ljubljana, Slovenia, 2023.09 (Invited seminar)
9th Bubbles & Droplets Conference, Lublin, Poland, 2023.06 (Oral presentation)
Postgraduate Research Associate Seminar, University of Bristol, UK, 2022.10 (Invited talk)
17th Conference of the International Association of Colloid and Interface Scientists, Brisbane, Australia, 2022.06 (Oral presentation)
Peter Tims Symposium, University of Bristol, UK, 2022.05 (Invited poster presentation)
Colloids Talk at the University of Bristol, UK on 2021.11 and 2023.02 (Oral presentation)
A publication is in preparation combining the above, whereby the developed platform for using AFM to directly probe the Nanofluid nanofilm/oil interface will be described, enabling further research into deepening our understanding this system.
Characterisation of the Nanofluid – Here the Nanofluid chosen for the project, a highly concentrated suspension of silica nanoparticles (LUDOX HS40) was prepared following existing experimental protocol prior to undertaking further experiments. The Nanofluid was purified of excess salt via dialysis with Milli-Q water, had its nanoparticle particle size and polydispersity determined via AFM imaging, and the presence of nanoparticle layering toward a smooth mica surface, necessary for the formation of the desired Nanofluid nanofilm, was confirmed via AFM force measurements and compared to existing literature.
Direct measurements of the Nanofluid nanofilm via AFM – Here, an experimental set up to enable using AFM to directly probe the nanofilm/oil interface was established. A fluorinated oil was deposited onto a smooth mica surface in a liquid cell while surrounded by the Nanofluid. AFM force measurements were performed through the oil phase, towards the mica surface, and revealed the presence of the Nanofluid nanofilm through the presence of the attractive capillary force generated upon contact with the nanofilm/oil interface. The thickness of the nanofilm was found to be larger than expected based on existing reports in literature, which was suspected to be due to the experimental configuration required to perform the AFM force measurements.
Studying the interfacial properties of the Nanofluid and fluorinated oil – Here, the surface tension of the Nanofluid and the fluorinated oil was studied using the pendant drop method, undertaken primarily by an undergraduate project student under the supervision of the project lead. A series of experiments were performed to confirm the reproducibility of experimental technique through using Milli-Q water against silicone oil and the fluorinated oil, obtaining values reported in literature. The surface tension of the Nanofluid against the fluorinated oil was found to be comparable to that of the values obtained using Milli-Q water, indicating the nanoparticles in the Nanofluid were not interface active. The properties of the Nanofluid/fluorinated oil interface were probed in response to the inclusion of a surfactant (SDS) at low concentrations, helping reinforce the understanding of the experimental system used in the prior mentioned AFM force measurements at the Nanofluid nanofilm/oil interface.
The findings of this project were presented at the following durng it's lifetime:
Department of Theoretical Physics at Jožef Stefan Institute, Ljubljana, Slovenia, 2023.09 (Invited seminar)
9th Bubbles & Droplets Conference, Lublin, Poland, 2023.06 (Oral presentation)
Postgraduate Research Associate Seminar, University of Bristol, UK, 2022.10 (Invited talk)
17th Conference of the International Association of Colloid and Interface Scientists, Brisbane, Australia, 2022.06 (Oral presentation)
Peter Tims Symposium, University of Bristol, UK, 2022.05 (Invited poster presentation)
Colloids Talk at the University of Bristol, UK on 2021.11 and 2023.02 (Oral presentation)
A publication is in preparation combining the above, whereby the developed platform for using AFM to directly probe the Nanofluid nanofilm/oil interface will be described, enabling further research into deepening our understanding this system.
This project has developed an experimental system to directly probe a Nanofluid nanofilm confined between oil and a mica surface using AFM for the first time. In doing so, the potential to study nanofilm/oil interfaces via direct force measurements has been unlocked, enabling a deeper understanding of the enhanced spreading properties of Nanofluids and their use in EOC and soil remediation. Through the new insight gained in this domain, new uses for Nanofluids which utilise their unique interfacial properties could be possible, alongside further development in our understanding of how nanofilms of liquids can be tuned, which are necessary for coating technologies spanning multiple industries.