PhD defence by Lilian Magermans

Congratulations to Lilian for her PhD defence (30th October 2024). Lilian will start a new academic adventure as postdoc at Institut Fresnel with Dr. Hervé Rigneault

Thesis title: Orientation Tomography in Liquid Crystals & Shearmetry in Hydrovoltaic Systems by Spectroscopy of Polarized Luminescence of LaPO4:Eu Nanorods

Abstract: The ability to measure the orientation of objects at the micro- or nanoscopic scale is of great importance for a wide variety of research fields. We previously demonstrated that spectroscopy of the polarized emission of lanthanide doped nanocrystals is an effective and straightforward way to determine their three-dimensional (3D) orientation. In this work, the methodology is further developed to be applicable to assemblies of such nanorods. Two different aligned systems are explored:

1) Spontaneously formed self-assemblies.

2) Actively aligned ensembles under flow.

To address the first system, a colloidal liquid crystal (LC) of LaPO4:Eu nanorods is used. When confined between rigid walls, such an LC suspension undergoes a remarkable morphogenesis, with conventional nematic tactoids evolving into streak-like patterns and finally never-before-seen flower-like structures. Using the developed spectroscopic analysis, the 3D orientation in these structures is characterized, revealing the relative impact of volume and surface energies.

As a second application, LaPO4:Eu nanorods are used as shear-probes by measuring their local alignment under flow. A method for obtaining the experimental relationship between the degree of alignment and the local shear rate is further developed. We aim to apply this approach to characterize the impact of flow shear on the electrochemical response of a hydrovoltaic system based on selective ion sweeping on capacitive electrodes.