I am interested in theoretical physics and particularly in fluid dynamics, condensed matter and statistical physics.

Below are my past and current subjects of research. 

Study of Flow-Induced Out-of-Equilibrium Interfacial Solids

At the fluid-solid interface the fluid interact with the electrons and phonons of the solid. When imposing a flow, this brings the solid to an out-of-equilibrium state. Under reasonable assumptions the solid is well-described by a quasi-equilibrium state where its different quantum particles still fulfil the fluctuation-dissipation theorem but including a frequency shift. In particular we predict the generation of an electric current which has been measured and studied experimentally. Physically, the liquid transfers momentum to the phonons and the electrons which are respectively the phonon drag and Coulomb drag. In most situations the former is dominant while the latter is negative. The form of the current is tunnable by choosing the internal structure of the solid: this is a quantum effect. Such an flow-induced electric current may have major applications if the solid is well engineered. This opens the door to sense and control the flow velocity at the nanoscales. At larger scales, such a phenomenon could be used to generate electrecity from any fluid flow.

Selected References:

  • Baptiste Coquinot, Lydéric Bocquet, Nikita Kavokine, Quantum feedback at the solid-liquid interface: flow-induced electronic current and negative friction, Submitted (2022)
  • Alice Marcotte, Mathieu Lizee, Baptiste Coquinot, Nikita Kavokine, Karen Sobnath, Clément Barraud, Ankit Bhardwaj, Boya Radha, Antoine Niguès, Lydéric Bocquet, Alessandro Siria, Strong electronic winds blowing under liquid flows on carbon surfaces, Submitted (2022)

 

Quantum Theory of Friction at Fluid-Solid Interface
Credits: Maggie Chiang (Simon’s Foundation)

At nano-scales, the molecules of a flowing liquid are able to interact directly with the electrons of a boundary solid. As a consequence, the resulting interaction can only be explained properly using a quantum formalism. The coupling between the collective modes of the fluid and the electronic excitations at the surface of the solid generate a new kind of friction which is dominant in certain conditions of nanofluidics. In particular, this provides an understanding of the surprising friction in carbon nanotube where the friction vanishes as the radius is reduced . Another consequence is to prodict a different friction on graphene and graphite.  Moreover, when the liquid is confined at the molecular scales, its dynamics changes and so does the associated friction, paving the way to new experimental discoveries. When the solid reach a quasi-equilibrium state dominated by the phonons, the quantum friction becomes negative, reducing the total friction. This opens the door quantum engeenering the friction by controling the internal structure of the solid.

Selected References:

 

Geometric Theory of Mechanics and Thermodynamics

The standard formalism tu study dynamics is the Hamiltonian mechanics which is founded on a symplectic form (or Poisson bracket) and a dynamical funtion: the Hamiltonian. Such a formalism is powerful to study the dynamics of point objects and fluids in many physical situations and is well suited for numerial integration. However, Hamiltonian dynamics does not include dissipation and then can only study systems at the thermodynamic equilibrium. Yet, some dissipative models can be written in a Hamiltonian structure using non-standard formulations of the theory. This is, in particular, the case with b-symplectic geometry which allows singularities in the phase space. These situations are fascinating for numerical and mathematical studies of dynamics but lack generality.  The metriplectic (or GENERIC) framework has been developed to adress these limitations. In this formalism the symplectic form is completed by a pseudo-Riemannian metric and the free energy is used as the dynamical function. Under reasonable assumptions, the two principles of thermodynamics arise from the geometric structure. Such a formalism is well-suited to study close-to-the-equilibrium systems where the thermodynamics is described by Onsager’s linear response. This applies in particular for the majority of models of fluid dynamics. In these models, the metric (or dissipative bracket) contains the microscopic physics and is the geometric realisation of the Onsager’s phenomenological tensor. It can also be derived as a emerging property form grand deviation theory and kinetic theory.

Selected References: