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Univ. Paris-Saclay

Sujet de stage / Master 2 Internship

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Microfluidic detection of crystal nucleation Intermediates during yttrium vandate (YVO4) nanoparticle synthesis in water

Contact: CHEVALLARD Corinne, , corinne.chevallard@cea.fr, +33 1 69 08 52 23
The synthesis of yttrium vanadate nanoparticles in water is characterized by the transient existence of an amorphous network that appears within the first few ms, prior to crystal nucleation. In order to track the appearance of this transient network, we will carry out microfluidic syntheses using a device which allows mixing salt solutions in a few 100 µs, as well as on-chip x-ray scattering measurements.
Possibility of continuation in PhD: Non
Deadline for application:25/06/2021

Full description:
A proper understanding of crystal nucleation from supersaturated salt solutions crucially determines our ability to tailor nanomaterials, or to capture geological and biomineralization processes [1]. Despite this importance, crystal nucleation is poorly captured by the so-called “classical nucleation theory” (CNT), which can be off by ten orders of magnitude in the predicted nucleation rates [2]. An acknowledged reason for this failure is that the CNT overlook the existence of transient disordered states, that is, liquid or solid amorphous states. However, to date, quantitative data are scarce and limited as detecting small and transient structures (< nm, << 1s) is very challenging.
We have recently developed microfluidic mixers that provide reaction times after mixing (~ 100 µs) which are ten times shorter than those available with commercial mixers [3]. The use of these ultra-fast mixers will allow us to characterize, by X-ray scattering on a synchrotron source, the very first steps of YVO4 crystal nucleation, even before the formation of the amorphous network already observed with a commercial mixer [4]. The first experiments carried out in February 2020 at the DIAMOND synchrotron (United Kingdom) confirmed the feasibility of these measurements and provided first scientific results. It is now necessary to certify the reproducibility of the measurements and generalize the use of the microfluidic mixer to other experimental conditions (salt concentrations, pH value, nature of the salts) in order to prepare or consolidate the next experiments planned during spring 2021 at SOLEIL synchrotron.
This Master 2 internship corresponds to an experimental work, which will consist in producing the microfluidic chips in a clean room environment, then characterizing their typical mixing time according to the chosen flow rates, and carrying out crystallization experiments on chips, with optical microscopy monitoring. Additional laboratory experiments will be performed in order to characterize the final products, through the use of stationary luminescence spectroscopy, X-ray scattering measurements or TEM microscopy.
Technics/methods used during the internship:
Soft-lithography, microfluidics, optical microscopy, x-ray scattering

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