Description du sujet de thèse

Interfacial rheology deals with the response of interfaces against deformations, it has been the subject of research interest during the last decades. A range of devices and methods have been developed to measure the rheological interface properties, such as Langmuir troughs, various rheometers and oscillating drop or bubble . Despite the development of these different, we still face specific challenges to quantifying the interfacial properties; some of these techniques are limited to static measurements and rheological proper-ties are only probed at low frequencies (a few tens of Hz). Recently we have used an atomic force micro-scope (AFM) to probe the thermal capillary oscillation of a hemispherical bubble or drop deposited on polystyrene surface [1-3]. In this method, the nano-metric thermal vibration of the bubble drives the mo-tion of the cantilever. We have shown that the spectrum of the thermal oscillations of the bubble surface presents several resonance peaks corresponding to the different mode of shape oscillations.
In this project, we intend to probe the rheology of the air/water interface formed by an air bubble im-mersed in a solution containing ionic surfactants (examples: sodium dodecyl sulfate SDS, cetrimonium bromide CTAB) and 4-(4-dihexadecylaminostyryl)-N-methylpyridinium iodide DiA). The movement of the bubble or the drop interface will be probed using an AFM cantilever which measures the amplitude of the vibration as a function of frequency. The damping and resonance frequencies of thermal fluctuations will be used to measure the surface tension and surface elasticity of the air/water interface. The obtained frequency and damping will be analyzed to extract the effective surface rheology (surface tension, surface dilatational viscosity and shear surface viscosity). The surface charge of the air/water interface which creates electrostatic barriers and controls adsorption will be studied in detail. We will vary the salt con-centration (example NaCl) in the solutions, to understand the role of electrostatic screening on the adsorp-tion dynamics of the surfactants.



References:
[1] Z. Zhang, Y. Wang, Y. Amarouchene, R. Boisgard, H. Kellay, A. Würger, A. Maali "Near-field probe of thermal capillary fluctuations of a hemispherical bubble" Phys. Rev. Lett. 126, 174503, (2021).
[2] H Zhang, Z Zhang, C Grauby-Heywang, H Kellay, A Maali,"Air/Water Interface Rheology Probed by Thermal Capillary Waves", Langmuir , 39, 3332,(2023).
[3] H. Zhang,B. Gorin, H. Kellay, A. Maali,"Viscoelastic rheology of polymer solution probed by resonant thermal capillary fluctuation",Phys. Fluids 35, 121706 (2023).

Contexte de travail

The research axis “Nanophysics of Fluids at Interfaces” is part of the “Soft Matter & Biophysics” team of the LOMA laboratory. The Laboratoire Ondes et Matière d'Aquitaine (LOMA) is affiliated with the CNRS and the University of Bordeaux. Its research activities aim to explore and characterize the physical properties of matter from both fundamental and applied perspectives, through theoretical and experimental approaches. The laboratory has strong international visibility in Soft Matter Physics and Condensed Matter Physics, Photonics, Materials Science, and Biophysics.