Accueil > Propositions de stages et thèses > Propositions de thèses > Hydrodynamics at molecular scales : probing ultra-thin liquid films Date limite de dépôt du dossier 28/09/2017

Hydrodynamics at molecular scales : probing ultra-thin liquid films Date limite de dépôt du dossier 28/09/2017

Sciences et Ingénierie de la Matière Molle (SIMM),
UMR 7615
Adresse  : ESPCI – 10 rue Vauquelin – 75231 Paris Cedex 05
Directeur de l’Unité : Christian Fretigny
Etablissement de rattachement : ESPCI/UPMC/CNRS
Encadrement : Laurence Talini, +33 1 40 79 46 79 mail et Christian Fretigny
 
In the vicinity of a solid wall, the structure of a liquid may be modified at a molecular scale : for instance, in some liquids, a layering has been observed at nanometric distances from a wall. The resulting dynamics of the liquid at those distances remains a matter for debate. One difficulty is that the formed structure may be disturbed by an applied shear.
We have developed an optical technique in order to form thin liquid films lying on solid substrates and study their properties in a non invasive way. We use the spontaneous thermal fluctuations of the free surface of liquids to probe them. In a recent work, we have evidenced a layer of immobile molecules within molecular distances from the wall [Phys. Rev. Lett., 114, 227801 (2015)]. The thesis will consist in using a similar experimental system in order to address different questions on nanometric liquid films ; for instance, how does the immobile layer evolve close to the solidification temperature of the liquid ? or how does an induced flow modify that layer ? The results will shed new light on the confinement-induced structures of liquids.

Evidence for a 4nm-thick immobile layer close to a glass wall in hexadecane. A quantity obtained from the spectrum of the surface fluctuations of the film is shown as a function of the film thicknesses, at different frequencies. The dotted line represents what is expected for a zero slip velocity boundary condition, whereas the full line corresponding to to a slip length of -4nm better describes the experimental data.