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Title: Synthesis of inorganic nanoparticles using microfluidic devices
Author: Baber, M. R.
ISNI:       0000 0004 8499 7775
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2017
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The well-known benefits of using micro-scale flow are associated with controlled mass transfer because of the reduced dimensions of microfluidic devices. The improved mass transfer characteristics make microfluidic devices an ideal candidate for synthesis of nanoparticles (NPs). In this study, mass transfer characteristics are investigated for microfluidic devices such as the coaxial flow reactor (CFR) and the impinging jet reactor (IJR), through the use of the interaction by exchange with the mean mixing model, Villermaux-Dushman reaction scheme, high speed camera images and flow visualization using dye and water. These reactors are contrasting in that the CFR has slower mixing because of its laminar flow profile whereas as the IJR has mixing time in the order of a few ms. The importance of mixing time as well as manipulation of hydrodynamics at the micro scale is shown through the use of these types of reactors for NP synthesis. Both types of reactors have beneficial properties for the synthesis of NPs. NPs were characterized using UV-Vis spectroscopy, DCS and TEM. Longer residence times and a higher consumption of reagents in the CFR led to reduction of size of silver NPs, leading to reductions in size from 9.3 ± 3 nm to 3.7 ± 0.8 nm. The IJR showed a reduction in NP size with increasing mixing efficiency, with a reduction in size from 7.9 ± 5.8 nm to 3.4 ± 1.4 nm using citrate as a ligand and from 5.4 ± 1.6 nm to 4.2 ± 1.1 nm using PVA as a ligand. A system to control nucleation and growth periods was developed by combining the CFR with a coiled flow inverter (CFI). Size control over gold NPs was achieved simply by changing the flow rate of reagents, with a reduction in size from 23.9 ± 4.7 nm to 17.9 ± 2.1 nm. Various hydrodynamics within the CFR were also tested. Vortex flow at higher Reynolds numbers did not give good control over NP size and dispersity, while reducing the inner tube internal diameter resulted in a decrease in NP size from 10.5 ± 4.0 nm to 4.7 ± 1.4 nm. Silver and gold NP synthesis was also performed in a batch reactor. Two different mixing configurations and variation in the order of reagent addition was investigated, and confirmed the importance of mass transfer conditions in determining size and dispersity. In both cases, fast and efficient mixing of the reducing agent to the precursor resulted in the smallest NPs. The range of sizes obtained were 6.7 ± 1.7 nm to 11.5 ± 2.4 nm and 13.1 ± 2.2 nm to 18.0 ± 4.8 nm for silver and gold NPs respectively. All these results show a strong link between mass transfer and NP size and dispersity for the systems tested, showing the need for well controlled and carefully considered mass transfer conditions.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available