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Title: Annular flow synthesis and assembly of two-dimensional materials
Author: Jose, Nicholas Antonio
ISNI:       0000 0004 7968 6163
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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The formation mechanisms of two-dimensional materials are poorly understood, limiting their potential in many applications. Hydrodynamic shear and solvent-surface interactions have recently been suggested to play dominant roles in wet synthesis, but have not been properly explored. Here I developed new methods to both synthesize and analyse inorganic and metal-organic two-dimensional materials, using a combination of microreactor technology and liquid cell transmission electron microscopy (LTEM). To evaluate the effect of hydrodynamic shear, a new microreactor was designed and characterized via high speed fluorescence microscopy and chemical micromixing tests. By operating in the two-phase annular flow regime, it is possible to form microfilms with tuneable shear rates as high as ~1E6 s-1 and sub-millisecond micromixing. By synthesizing layered double hydroxides in this reactor over different shear rates, I found that crystallinity and aspect ratio vary non-monotonically with shear. To investigate the dynamics of particle growth I used LTEM to find that layered double hydroxides (LDH) may crystallize via oriented attachment, which is accelerated by hydrodynamic flow. These observations are used to formulate a mechanism that explains the non-monotonic variation in particle characteristics using characteristic kinetic timescales. I then demonstrated the impact of this method on the synthesis of LDH supercapacitor electrodes, showing that control of shear rate and choice of a dispersion solvent are crucial parameters to fabricate highly capacitve thin films. Applying the same technique to metal organic frameworks, I discovered a new polymorph of copper benzene dicarboxylic acid, which arises from surface energy effects. I used LTEM to analyze the effect of solvent on polymorphism and particle formation, showing that nanosheets may crystallize via oriented attachment, and that the rate and direction of oriented attachment are dramatically influenced by solvent-surface interactions. The CuBDC nanosheets were then applied as adsorbents in organic solvents, in which solvent-induced self-assembly can significantly affect nanomaterial sorption performance.
Supervisor: Lapkin, Alexei Sponsor: Singapore National Research Foundation ; Cambridge Centre for Advanced Research aned Education in Singapore
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Microreactor ; Nanoparticle ; Self-assembly