Sylvain Prévost

All molecules have their own interaction potential, hence upon mixing different compounds one should rarely if ever expect achieving a homogeneous mixture down to the molecular level. Indeed density fluctuations are observed by Small Angle Scattering in many liquids resulting from combining two or more components. While the self-assembly of surfactants has been extensively studied over the last century, the weak association of molecules resulting in nanometer-scale clusters has mostly been ignored. Yet the existence of these clusters can be linked to non-ideality in solutions and has major applications throughout everyday products. Such behavior is illustrated with the ternary water/ethanol/octanol, where octanol clusters can be used to dissolve highly hydrophobic molecules such as squalene. Due to the existence of two domains of different composition, with no molecular interfacial film and a curvature energy that is practically zero, we dubbed these solutions Ultra Flexible MicroEmulsions (UFME).

This PhD thesis has been funded by ILL and Keele University. The position is still opened.

Project description:
Protein quality control is an essential mechanism by which the cell ensures its viability and growth. Defects in protein quality control lead to the accumulation of damaged proteins, which plays a role in many diseases (e.g. cancer, diabetes, various neurodegenerative diseases) and ageing. This PhD studentship will be part of a larger project that aims to elucidate prohibitins’ role in premature cellular ageing by investigating how prohibitins interact with m-AAA proteases at a molecular level, and thus help to maintain healthy mitochondrial morphology and cellular metabolic capacity. Interactions between the proteins as well as their assembly in the membrane will be investigated using in-solution and soft matter techniques such as Small Angle Neutron and X-ray Scattering, lipid monolayer techniques, as well as biochemical assays. Data analysis with different pieces of software will be an important part of the PhD work. 

Cluster formation of colloids has historical, practical, fundamental and forecasted relevance. Historically, colloids (‘glue’ in greek) were invented to explain sedimentation due to aggregation of ‘amicroscopic’ particles. Practically, many phenomena from cheese making to wastewater treatment are based on coagulation and flocculation of particles (often negatively charged), typically via adjunction of a polycation. Fundamentally, cluster formation occurs due to a complex balance between interaction potentials, repulsive and attractive, at short and long range, resulting in cluster growth of different fractal dimension and branching, and at various time and space scales – including aggregates sufficiently small or dynamic to be long-term stable. One expects that the tuning of these forces will lead to self-organized complex structures, allowing large-scale production of specifically designed hierarchical colloids at and beyond equilibrium, such as highly anisometric (1D) nanorods.

The PhD thesis of Oonagh Mannix uses (Ultra-) Small Angle X-ray Scattering on ID02@ESRF to study the entire process covering the relevant spatial scales from nm to µm and time scales from ms to months, in order to elucidate the formation pathway and long-term equilibrium of structures. This work focusses on technical-grade materials: nanoparticles (silica) and a bio-sourced polycation (chitosan), as it aims at uncovering general mechanisms relevant for practical applications; it must therefore accounts for the lack of ideality of components. A comparison to finely controlled laboratory-grade colloids helps generalizing our findings and deepening our analysis of the experimental observations.

• simSAS 2019, "Perspectives and Challenges in Modeling of Small Angle Scattering data in Soft Matter and Life Sciences"
  8-12 April 2019 at ILL. Bridging the gap between Small-Angle Scattering users and experts in simulations of Soft Matter and Life Sciences.
• PolySolvat-12, "12th conference on polymer-solvent complexes and intercalates"
  4-7 Septembre 2018 at ILL. Formation mechanisms, the morphology, the molecular structure, and the properties of compounds formed between solvent molecules and/or small molecules with synthetic polymers, biopolymers, proteins, and supramolecular polymers.
• ChemWood, "Chemical Engineering and Mechanics in Wood: X-ray and neutron scattering, microscopy and modeling"
  23-24 March 2017 at ILL. Experimental possibilities to follow adsorption of water, salts or reactives in wood and cellulose-based materials in link with open questions from theory to current applications.