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Theme 2 : Thermodynamic approaches

Contact : Yannick HALLEZ

The issues dealt with in this theme are related to fields such as soft materials, complex fluids, phase transitions or solvation, for which there is a close link between macroscopic behavior and interactions at smaller scales. What are the numerical methods relevant for this change of scale? Why are certain crystals stable in microdroplets but not in standard reactors? How does the ionic specificity affect mass flow through a filtration or electrodialysis membrane? How can the equation of state of an anisotropic colloidal dispersion be predicted?

The contribution of supercomputing

- Numeric approaches based on supercomputing have been introduced in parallel to the experimental approaches already well practiced in the department. For instance, it was experimentally demonstrated that mass transfer through an ion exchange membrane during electodialysis is influenced by the type of the ions in the electrolyte (PhD: Julie Savignac 2010). Hybrid methods involving mechanics, quantum mechanics and molecular mechanics have been implemented to determine the solute-electrolyte, solute-membrane, and membrane-electrolyte interaction energies in this system (PhD: under co-supervision with ITM-CNR, University of Calabria). Another example is the determination of the equation of state equation of a colloidal dispersion – variation of the osmotic pressure versus the volume fraction of nanoparticles. It enables both the prediction of the characteristics of a dispersion at equilibrium or the type of phase obtained and the transport properties of colloids.
- The equation of state can be determined by means of osmotic compression experiments (PhD: Marie-Laure Rami 2009) or by small-angle light scattering, techniques familiar to the laboratory. Moreover, an approach was developed involving the calculation of the Brownian dynamics linked to the resolution of multi-body electrostatic interactions between anisotropic colloids (PhD: Joseph Diatta 2014).

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Simulation of the structure of a dispersion of platelets under the effect of electrostatic interactions.

Lab-on-a-chip microfluidics at the service of thermodynamics

- Determining the conditions required for the existence of a phase and the kinetics of a phase change is essential for applications such as crystallization or the production of polymeric filtrations membranes.
- Microfluidics chips efficiently respond to both these issues. Miniaturization enables excellent control of the operational parameters and provides an extremely high level of reproducibility. It also enables a scan through of the parameters on a single chip. Thus, metastable solid and liquid phases, impossible to reveal in a normal sized reactor, were generated using these chips.

Simulation of the structure of a dispersion of platelets under the effect of electrostatic interactions.

Molecular interactions with macroscopic properties in processes

- In an organic medium, intra/extra molecular interactions (hydrogen bonding), the effects of solvation, and self-association at the molecular level have a primordial influence on the thermodynamic macroscopic quantities that control a process. Investigations based on various thermodynamic approaches at different levels enable connections to be established between properties at the molecular scale and those at the scale of the process.
- By modifying existing models, we have taken into account interactions such as hydrogen bonds leading to a much finer description of the solubility equilibria of complex systems..

Crystallization of an active pharmaceutical in a confined environment.