Location:  Rennes University, FrancePosition:PhD

Title: Use of the electrokinetic leakage phenomenon as a tool for advanced characterization of membrane materials

Keywords: Membranes, polymers, surface characterization, zeta potential, electrokinetic phenomena

Membrane separation processes are recognized worldwide as unavoidable alternatives to conventional energy-intensive separation techniques such as distillation or evaporation. Membrane separations are indeed capable of responding to many of the problems of our modern societies in a process intensification logic, i.e. by reducing the use of raw materials, energy consumption, the size of equipment and the generation of waste.
Whatever their chemical nature (polymers or ceramics), the synthetic membranes used in liquid phase separation processes have a surface charge density resulting from the ionization of surface functional groups and/or adsorption phenomena. It is clearly established that this surface charge density has a direct impact on the capacity of the membrane material to reject charged species in solution (ions, natural organic matter, etc.) as well as on the propensity of the material to fouling (accumulation of matter on the membrane surface and in the pores leading to a reduction in the amount of liquid treated per unit of time) or on its chemical resistance to certain oxidants (e.g.: ozone).
The charge density of a membrane material can be estimated from the measurement of electrokinetic quantities such as streaming potential or streaming current. These techniques make it possible to determine, via an appropriate solid/liquid interface model, the zeta potential of the material, which is a marker of the intensity of electrostatic interactions between the membrane surface and the surrounding medium. The value of electrokinetic techniques has been demonstrated in a wide range of applications from surface functionalization to the study of membrane chemical resistance and degradation. Since the late 2000s, the measurement of tangential streaming current has attracted increasing interest in characterizing the surface properties of membrane materials. However, a parasitic phenomenon, called electrokinetic leakage, has been highlighted in the case of macro/mesoporous materials. It corresponds to a leakage current passing through the porosity of the material and likely to bias the interpretation of experimental measurements. Recent work has led to the development of experimental protocols that make it possible to correct electrokinetic measurements flawed by this parasitic signal, or even to be free of it directly.
This thesis aims at understanding the phenomenon of electrokinetic leakage from another point of view by taking advantage of this parasitic signal to extract the information it contains. Indeed, the electrokinetic leakage crossing the porosity of the material (partially or totally), the variation of its intensity reveals a modification of the solid/liquid interface in the pores of the material. The objective of the thesis will therefore be to explore the potential applications of this phenomenon in the field of membrane science by attempting to apply it to the early detection of internal fouling (target applications: microfiltration and ultrafiltration) and surface wetting in
membrane contactors (target application: membrane distillation). This will require the synthesis of a set of membranes with different properties of charge density, hydrophilicity, porosity and pore size. These membranes will be developed by phase inversion (induced by non-solvent or by evaporation) from various polymers (polyacrylonitrile, polyethersulfone, polyimide, polyvinylidene fluoride, etc.).
This thesis, by the perspectives it will open, should represent an important milestone in the field of characterization of electrical surface properties of porous materials and more particularly of synthetic membranes. It will also provide the necessary proof of concept for the future development of in-line electrokinetic sensors.

Required qualifications
✓ 5 years of higher education (engineering school and/or Master’s degree) in physical chemistry, materials chemistry or process engineering
✓ Motivation for research
✓ Good English skills (minimum level B2)
✓ Ability to present results (orally and in writing)

Applications may be submitted until 14 June 2022 to the following address:

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