ED Sciences Chimiques
Stabilisation of oil-in-water Pickering emulsions with cellulose nanocrystals for encapsulation and oxidative protection
by Mohd Azmil MOHD NOOR (Laboratoire de Chimie des Polymères Organiques)
The defense will take place at 9h30 - Amphithéâtre 2 ENSMAC, Bât. A, 16 av. Pey-Berland 33607 Pessac
in front of the jury composed of
- Gilles SEBE - Maître de conférences - Université de Bordeaux - Directeur de these
- Chrystel FAURE - Professeure des universités - Bordeaux INP - CoDirecteur de these
- Henri CRAMAIL - Professeur des universités - Université de Bordeaux - Examinateur
- Isabelle CAPRON - Directrice de recherche - INRAE Nantes - Rapporteur
- Audrey DRELICH - Maîtresse de conférences - Université de Technologie de Compiègne - Rapporteur
- Cécile JOSEPH - Ingénieure de recherche - ITERG - Examinateur
In this Ph.D. work, oil-in-water (O/W) Pickering emulsions stabilized by unmodified and chemically modified cellulose nanocrystals (CNCs) were prepared using different oils & salt concentrations, and investigated in terms of stability, surface coverage, encapsulation/release properties, and oxidative protection. Regardless of the oil investigated, a linear dependence of the inverse droplet diameter on CNCs concentration was observed, in line with the limited coalescence process expected for Pickering emulsions. The surface coverage by the particles around the droplets was estimated by calculating the coverage percentage C and specific surface area S, based on the slope of the limited coalescence domain. A linear dependency of C and S with the ionic strength was demonstrated, showing that the surface coverage by the particles can be monitored by the salt concentration. When resveratrol (RSV) was incorporated in the internal phase of the emulsion, salt was not required anymore to stabilize the emulsion and the C value was now correlated to the RSV concentration instead of the ionic strength, the RSV molecules acting as co-stabilizers at the interface. Release experiments showed a linear dependency of the interfacial release rate with the surface coverage around the droplets. Finally, the linseed oil-in-water emulsions stabilized with unmodified CNCs, were shown to partially protect the oil from lipid oxidation in comparison to SDS. The protective properties of the CNCs were later further improved, by functionalizing the nanoparticles surface with polydopamine, using a simple process in water.
ED Sciences Physiques et de l'Ingénieur
A study of the winds of evolved cold stars: understanding the properties and the chemistry of the wind forming region and the more extended CSE through high angular resolution observations and modeling
by Louise MARINHO (Laboratoire d'Astrophysique de Bordeaux)
The defense will take place at 10h00 - Salle Univers Laboratoire d'Astrophysique de Bordeaux Observatoire Aquitain des Sciences de l'Univers Université de Bordeaux - Bât. B18N Allée Geoffroy Saint-Hilaire CS 50023 33615 PESSAC CEDEX
in front of the jury composed of
- Fabrice HERPIN - Astronome - Université de Bordeaux - Directeur de these
- Anna PALACIOS - Astronome - LUPM - Rapporteur
- Juan RAMON PARDO CARRION - Full professor - IFF (Instituto de Física Fundamental) au CSIC (Consejo Superior de Investigaciones Científicas) - Rapporteur
- Agnès LEBRE - Directrice de recherche - LUPM - Examinateur
- Arturo LOPEZ ARISTE - Directeur de recherche - IRAP - Examinateur
- Helmut WIESEMEYER - Full professor - Max-Planck-Institut für Radioastronomie - Examinateur
- Caroline SOUBIRAN - Directrice de recherche - Université de Bordeaux - Examinateur
Intermediate-mass stars, like the Sun, will evolve into AGB (Asymptotic Giant Branch) stars, which have a much larger radius than the Sun and are a thousand times brighter than it. These evolved stars play a major role in stellar evolution. Evolved cool stars have a high mass loss rate, which contributes to the enrichment of the interstellar medium and so, to the recycling of matter in the Universe, through strong winds propagating in the star's circumstellar envelope (CSE). The physics of these winds and the origin of these mass-loss phenomena are still poorly understood, but can be constrained by observations of various molecular transitions in the CSE. Using ALMA observations from the large program ATOMIUM, we will attempt to describe and understand the dynamics of the winds through the envelope. It has recently been observed that most evolved stars have a close companion that impacts on the gas dynamics around the star and on the winds dynamics. Using a radiative transfer code (MCFOST), we aim to reproduce ALMA observations, adding a binary to the model. We will try to explain the observed spiral shapes and constrain stellar parameters (such as the distance and the radius), dust components and molecular abundances. This thesis will also focus on the emission of the SiO maser line from a sample of recently observed evolved stars, in order to probe the presence of a magnetic field in the inner gas region of the envelope, up to 2-4 stellar radii from the photosphere. It is emitted by gas cells in the CSE and is strongly polarized. From mm-wave radio observations, we can derive the Stokes parameters and after careful calibration, determine the circular polarizations, which, according to theoretical predictions, can lead to a characterization of the environment of the emitting cells, like an estimate of the sightline-projected magnetic field strength. If there is a magnetic field and if the maser line is saturated, we should observe an « S » shape Zeeman signature in Stokes V. Using the rvm code, we search for this specific pattern in our data. We work with two theories, one for the saturated and one for the strongly saturated maser. In both cases, we can relate the observed Stokes V line profiles to the magnetic field strength. There are still open questions about the origin of the magnetic field (e.g. a solar-type dynamo, a turbulent dynamo, etc.) and its evolution. We can try to answer these with future observational projects that will be described in the thesis.