ED Sciences Physiques et de l'Ingénieur
Thermophoretic nanomotors: individual dynamics and ensemble effects under optical heating
by Yoann DE FIGUEIREDO (Laboratoire Ondes et Matière d'Aquitaine)
The defense will take place at 14h00 - Amphithéâtres D, A29 351 Cr de la Libération, Bâtiment A29, 33400, Talence.
in front of the jury composed of
- Antoine AUBRET - Chargé de recherche - Université de Bordeaux - Directeur de these
- Antonio STOCCO - Directeur de recherche - Institut Charles Sadron - Rapporteur
- Christophe YBERT - Directeur de recherche - Université Lyon 1 - Rapporteur
- Jean-Pierre DELVILLE - Directeur de recherche - Université de Bordeaux - CoDirecteur de these
- Damien BAIGL - Professeur - ENS Paris - Examinateur
- Aurélie DUPONT - Chargée de recherche - Université Grenoble Alpes - Examinateur
- Laura ALVAREZ - Maîtresse de conférences - Université de Bordeaux - Examinateur
- Pierre NASSOY - Directeur de recherche - Université de Bordeaux - Examinateur
Active matter consists of elementary building blocks capable of converting energy locally into work. A typical example is provided by living organisms, which are capable of organising themselves dynamically across multiple spatial scales. Understanding the dynamics of these non-equilibrium processes is a central issue in physics and biology. In this context, numerous synthetic active systems have been developed, enabling the study of emergent behaviours and the construction of controlled active machines. The vast majority of studies have focused on the use of micrometre-sized active colloids. However, these systems present limitations, particularly due to sedimentation effects inherent to this scale. In contrast, the collective dynamics of active nanoparticles remain largely unexplored, despite their potential for the design of active processes at a very small scale and in three dimensions. This project is set within this context and aims to study the dynamics of artificial active nanoparticles. To this end, we have synthesised and developed nanomotors based on gold-silica nanoheterodimers, whose self-propulsion relies on their asymmetrical shape and the mechanism of thermophoresis. These nanoparticles are activated by the photothermal effect via the optical absorption of gold, enabling spatiotemporal control of their activity. To study their dynamics, we have developed an experimental setup based on optical correlation and statistical analysis techniques in confocal microscopy. The methods employed provide insight into their 3D dynamics across a wide range of concentrations, within volumes on the order of the optical wavelength. Our results highlight collective effects, with propulsion strongly dependent on concentration. The speeds, which are extremely fast (several hundred µm/s) by state-of-the-art standards, result from macroscopic optothermal effects coupled with non-linearities in the propulsion effects. These effects are quantified and modelled as a function of concentration and optical parameters. The coupling between concentration and active dynamics reveals thermal self-regulation of the velocity. This behaviour represents a first step towards the study of the collective behaviour of active baths of synthetic nanomotors.