ESPCI web site
ESPCI Paris
Lieu de travail
Paris - Ile-de-France - France
Intitulé du sujet
Flows at molecular scales : probing and manipulating ultra-thin liquid films
Champs scientifiques
Chimie
Physique
Description
A hydrodynamical description of a liquid down to molecular scales has to consider the effects that are specific to those very small scales. For instance, at molecular distances from a solid wall, phenomena such as slip or confinement-induced molecular layering have been observed with liquids in both experiments and numerical simulations. The ability to predict those effects is crucial in many fields involving flows at small scales close to a solid, such as colloidal science, micro and nanofluidics or flows in mesoporous media. However, a unifying picture of the different reported features is still lacking, partly because their manifestation critically depends on the chemical nature of both the liquid and solid media. Therefore, a full hydrodynamic description at a molecular scale must take the specific physical-chemical properties into account. The PhD project aims at understanding the dynamical behaviour of a liquid close to a solid wall, and at shedding new light on the link between the physical-chemistry and the dynamics of a liquid close to a solid surface.
Experimentally, the study of such effects requires either measurements of the dynamics on the very vicinity of the interfaces, or the generation and control of flows in nanometric liquid films. We have developed a fully non invasive optical technique (awarded in 2015 and 2016) in order to characterize the dynamics of a liquid by measuring the spontaneous thermal fluctuations of its free surface. Liquid films lying on solid substrates are formed with a thickness down to 10 nm using a Marangoni (surface tension gradient induced) flow. In a recent work, we have used those techniques to evidence a negative slip length in n-hexadecane consistent with the presence of a few layers of molecules at nanometric distances from the wall [Phys. Rev. Lett., 114, 227801 (2015)].
The PhD project will address the more general question of the hydrodynamic behavior of liquids at molecular distances from a solid wall and its link with the physical-chemical properties. Techniques already developed will be used and further improved in order to allow a fully controlled manipulation of the liquid films, in particular by applying thermal gradients to induce and control Marangoni flows. Complementary techniques, such as ellipsometry that allows for static thickness measurements, will be used. Measurements of small scale properties together with the ability to manipulate ultra thin films will also provide tools to better understand the forced dewetting dynamics of a liquid, in which the role of precursor films has been evidenced. Finally, the project will shed new light on how the classical zero-velocity boundary condition breaks down at very small scales.
3i Aspects
The aim of the PhD subject is to understand the behavior of liquids at molecular distances from a solid wall. The questions at stake are in particular crucial for transport properties at small scales, involved e.g. in flows through nanoporous materials or in nanofluidic devices. The project aims at making a link between macroscopic or mesoscopic flow properties and the physical-chemical properties. It therefore crosses the frontier between a purely hydrodynamic description of the flows and the details at a molecular scale of the liquids and solids at stake. The PhD student will benefit from scientific exchanges and visits to the group “Dynamics of Fluid and Biological Interfaces” headed by Dr Oliver Bäumchen (Max Planck Institute Göttingen, Germany), which has in particular developed a scientific focus on the physics of soft matter at interfaces.
PhD supervisor(s) Laurence Talini and Christian Frétigny (co-supervisor)
Présentation établissement et labo d’accueil
ESPCI Paris
The Hosting Lab
SIMM (Science and Engineering of Soft Matter) is a joint research unit of ESPCI, CNRS and UPMC. The laboratory develops its activity in science (physics and chemistry) and soft matter engineering, by using the really multidisciplinary competences of its members which include the design of systems and of original techniques and the mastering of the measurement of the properties (especially of mechanical ones). The lab aims at developping new concepts, inspired in particular by industrial problems and situations.
Site web :
https://www.upto.paris/
Profil du candidat
The candidate should be specialized in physics of liquids and/or physical-chemistry and have experimental skills.
Date limite de candidature
28/02/2018
Date de début de thèse
01/09/2018
Eléments à fournir pour la candidature
Applications must be submitted on the UPtoPARIS
More information is available in the "How to apply" section of the website.