CE30 - Physique de la matière condensée et de la matière diluée

Direct Visualisation of Nucleation: from Fundamentals to New Materials – DiViNew

Submission summary

Understanding the nucleation of crystals is of profound importance both for fundamental and technological reasons. In the simplest material known to self—assemble to form a crystal, hard spheres, state-of-the-art predictions and experimental measurements of nucleation rates differ by over ten orders of magnitude. As well as challenging our understanding of crystallisation, this confounds attempts to use self—assembly to realise new materials.

Beyond hard spheres, soft particles in the form of colloidal microgels exhibit a wide range of predicted colloidal crystal structures, which to date have proven hard to realise. And binary systems with two species of colloids offer even more possibilities.

Here we propose a combined experiment—computer simulation approach to address the challenges of nucleation and realisation of crystal structures in colloids. The platform we shall develop rests on three pillars.

1) A new experimental technique, nano-real space analysis, developed by the team which will address the challenge of the nucleation rate discrepancy and form the basis for the experimental part of the project. Real space analysis of colloidal systems with confocal microscopy has until now required particles of 2 or 3 microns in size. STimulated Emission via Depletion (STED) “nanoscopy” changes that enables us to image much smaller colloids. This is important because these smaller particles diffuse faster and so for the first time rare events like crystal nucleation can be directly imaged at state points where the discrepancy between simulation predictions and previous experiments is found.

2) We shall develop a novel feedback method where nano-real space analysis is combined with computer simulation. Uniquely, this is built on analysis of higher—order structure (such as geometric motifs like icosahedra) and matching the populations of these structures between experiment and simulation allows a far closer degree of mapping than has been possible until now. We shall develop our combined simulation—experiment methodology to direct the assembly of a novel colloidal system which will form a variety of new crystal structures with applications e.g. in photonic crystals.

3) Assembly of soft particles is predicted to massively enhance the range of possible crystal structures that the system can access. However, this has yet to be realised, and in the case of colloidal microgels, little is known of their interactions at high concentration. This gap in knowledge we propose to address by the development of a microgel system based on polymethyl methacrylate colloids, which can be refractive index matched to the solvent. This enables better imaging than has been possible until now with microgel systems, and means that our methodology may be applied to microgels and thus detailed understanding of their interactions and hence their self—assembly at high concentration will then be possible.

With these developments, our objectives are to
1) Implement nano–real–space analysis to study nucleation in the discrepancy regime.
2) Optimise a tuneable colloidal microgel model system with a core–shell architecture.
3) Design simulation models to match the higher–order structure found in experiments and develop a feedback methodology, where in–situ analysis of self–assembly in experiments feeds back through simulations to optimize interactions for the crystallization of a target structure.
4) Use the insight and methodology gained to investigate manipulation of crystallisation in binary systems.

Project coordination

Paddy ROYALL (GULLIVER)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LPS Laboratoire de Physique des Solides
GULLIVER GULLIVER

Help of the ANR 507,159 euros
Beginning and duration of the scientific project: March 2022 - 48 Months

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