Thesis in the Micromégas team (LPENS - CNRS)

In this experimental thesis, we will explore the effects of flow tunneling induced by excitation transport through solids. Application to spectral separation will be explored.

This experimental thesis aims to comprehensively explore "hydro-electronic couplings" in ultra-confined fluids. To this end, we will consider the flow of various fluids through nano-channels made from two-dimensional materials based on multi-layer graphene, hBN, MoS2 or MXene. The nanofabrication of these systems relies on the van der Waals assembly of these materials, a method we have mastered in the Micromégas team. Confinement ranges from tens of nanometers down to a few Angstroms.

On the basis of these nanoconfined systems, the thesis project will include several objectives which will constitute milestones for the work:

- Circuitry based on gel channels: A first step will aim to develop a hybrid connector system, coupling nano-channels based on two-dimensional systems, and a circuitry based on gel channels. The aim of this technical stage is to interface 2D nano-channels deposited on surfaces, using ionic transfer within nanogels to create ionic connectivity. These gel microchannels will be deposited via a technique introduced in the laboratory using micro-pipettes controlled by an AFM-type system. The advantage of this novel approach is the ability to create a completely two-dimensional nanofluidic circuitry.

- Flow tunneling: we have very recently predicted that the flow of one liquid can induce the flow of another liquid placed behind a solid wall. This phenomenon is based on the transmission of excitation between fluids and solids. It runs counter to the predictions of continuum hydrodynamics. We call it "flow tunneling", because it relies on a "tunneling" effect for hydrons, which are fluctuations in elementary charge within the liquid. The extent of this tunneling can be modified by the electronic excitations of the solid, the maximum being reached when these excitations are in resonance with the hydron modes. This result provides the guideline for the experimental realization of the effect, which will therefore be one of the main objects of this thesis. The aim is to study flow transfer through the wall, using nanochannels whose upper wall is made of a graphene multi-layer, separating one nanochannel from a second fluid. The thickness will be varied, enabling predictions to be tested. A second essential parameter will be the coupling parameter quantifying the spectrum overlap between fluid and solid excitations. To this end, we will consider a variety of fluids and solids, with different spectral properties. These experiments will enable us to explore in detail the mechanisms of fluid-induced transport of quantities of motion through solids.

- spectral separation: beyond these experiments, a direct application of these behaviors concerns an unconventional fluid-fluid separation method. We will extend the experimental results of flow tunneling to fluid mixtures, and in particular to water-glycerol mixtures as a model system. The aim will be to study fluid separation induced by a difference in the overlap parameter between the excitations of the solid and those of each of the two fluids. Depending on the overlap, the interaction of each fluid will be differentiated and may lead to dynamic fluid separation. As before, experiments will explore various materials and fluids within the nanochannels to quantify the power of separation. Finally, generalization to ionic mixtures will be investigated.

The work of this experimental thesis will be supported by the theoretical activities of the Micromégas team.