Expanding the regular atomic world at the colloidal level using valence-endowed particles – ENLARgER

The work program is in the form of 4 workpackages, divided into tasks and deliverables:
WP0 - Coordination and dissemination / protection of results activities.
WP1 - Design and synthesis of elementary bricks (CAs): preparation of the patch and / or dimpled particles from silica / PS multicode particles obtained by seed polymerization of styrene. The stakes will consist in i) preparing batches (5 g) of ACs whose purity, ie valence (1, 2, 3 or 4), will be at least 80%, ii) control the patch-to-particle size ratio and iii) to develop an effective chemistry of the PS to chemically activate the patches.
WP2 - Assembly of CAs to synthesize new «colloidal molecules« and «covalent« 2-D and 3-D colloidal crystals: we will have to explore several roads in order to synthesize from CAs «colloidal molecules «For example, the H2O molecule (made of a tetravalent CA combined with two monovalent CAs) or a chiral molecule (made of a tetravalent CA coupled with four monovalent CAs of different chemicals or sizes), as well as crystals Two-dimensional imitation of graphene sheets (based on trivalent CAs) and 3D crystals of diamond structure (based on tetravalent CAs).
WP3 - Theoretical studies of concentrated dispersions of CAs: simulations will be carried out using simultaneously the Monte Carlo technique and the integral equations technique, or a combination of the two, to simulate the diffusion spectra obtained by USAXS or diffusion of Neutrons and help predict the optimal design of CAs (patch / CA diameter ratio, polydispersity in size and / or valency of CAs, relative proportions, etc.) to achieve targeted assemblies.

- WP1: it appears that the method of synthesis of the particles with patches does not lead spontaneously to batches of sufficient purity; We are currently developing a complementary purification route. We have developed effective protocols to make the patches sticky, either by covalent bonds or hydrophobic interactions;
- WP2: we obtained assemblies of type «CF4«, «H2O« and «carbyne«. Our current efforts are focused on «chiral«, «polyethylene« and «graphene« type assemblies. The Poseidon select liquid microscopy cell, which will allow the observation of nanoparticles in liquid phase and consequently to follow their assembly, will be operational in September;
- WP3: the first molecular dynamics simulations were carried out for solutions of colloidal molecules of the «H2O« type. Correlations and structures depend very closely on Coulomb interactions between peripheral and dimple sites.

The conditions are assembled to consider serenely the continuation of the work plan: as soon as the batches of particles with patches can be obtained pure, we can thus realize extended assemblies with fewer defects and consequently of greater volume and dimension (ex: Diamond «). Numerical experiments will allow us to optimize the experimental parameters more quickly. In situ monitoring by electron microscopy, dynamic light scattering, and neutron or X-ray scattering will combine original methods to confirm these simulations.

One review paper has been published:
1. Synthesis and assembly of patchy particles: Recent progress and future prospects. S. Ravaine et E. Duguet, Curr. Opin. Colloid Interface Sci., 30, 45-53 (2017).

ENLARgER aims to design, fabricate and assemble submicronic particles whose surface parts are regioselectively modified (patches) and/or present topological discontinuities (dimples) endowing them with the capability to interact with only a few other particles in specific directions.
The challenge is to reproduce at the scale of submicrometric particles the notion of valence, which is well-known at the level of atoms and which is at the origin of the diversity of all molecules, macromolecules and other covalent compounds. These particles are called "colloidal atoms" (CAs) and will be obtained by chemical modification of silica colloids holding polystyrene (PS) nodules, whose number (1, 2, 3 or 4) will be equal to the valence of the CA. The patches (or the bottom of the dimples) will thus be made of grafted PS macromolecules.
"Covalent bonds" within CAs aggregates will be generated by an assembly process controlled by hydrophobic interactions (directly from PS macromolecules), chemical bonding (after chemical modification of PS chains) or depletion forces (interaction between spherical particles and dimples). It will therefore be considered in order to fabricate at the colloidal scale analogues of molecules, macromolecules and 2-D and 3-D covalent crystals, as discrete aggregates or assemblies extended in one, two or three dimensions, respectively. We will aim in particular to build from CAs "colloidal molecules" imitating the H2O molecule (made of a tetravalent CA combined with two monovalent CAs) or a chiral molecule (made of a tetravalent CA associated with 4 monovalent CAs of different chemical compositions or sizes), and "colloidal crystals" imitating graphene sheets (based on trivalent CAs) or diamond crystal structure (based on tetravalent CAs).
The study of the assembly mechanisms and characterization of the colloidal structures obtained will require the use of advanced techniques such as static and dynamic light scattering, ultra-small-angle X-ray scattering, neutron scattering, transmission electron microscopy (especially in liquid cell) and electron tomography.
Finally, Monte Carlo and Integral Equations techniques will be used to simulate the scattering spectra and help in predicting the optimal design of CAs (patch-to-CA diameter ratio, size and/or valence polydispersity, relative fractions, etc.) in order to achieve the target assemblies.
To reach these aims, three partners with complementary skills form the ENLARgER consortium: colloidal chemists (Partner 1), physical chemists (Partner 2 and 3), and physicists (Partner 3). Partner 1 will take charge of the synthesis and characterization of the CAs. Partners 1 and 2 and 3 will be in charge of the assembly of the CAs and the comparison of the results with the numerical experiments carried out by Partner 3. Grants for one PhD student and two Master students, and fellowships for two one-year postdocs with complementary skills are required.