Jeudi 6 octobre 2016
à 11h15 en salle C. BROT
Gabriela RAMOS CHAGAS
Encadrants : Thierry Darmanin et Frédéric Guittard
Hydrophobicity and water adhesion from nanotubes to nanospheres of structured polymeric surfaces
Controlling surface hydrophobicity and water adhesion is fundamental for various applications including anti-bacterial or anti-corrosion coatings, oil/water separation membranes, water transport and harvesting or for optical sensors. Superhydrophobic and parahydrophobic surfaces can be obtained by controlling surface roughness and energy, and these two types of surfaces yield different tendencies toward water adhesion. Here, we show that by differing by the chemical structure of a monomer, varied surface morphologies are produced by a direct electropolymerization process. Different nanostructures are obtained by manipulating not only the polymerizable core, but also the electrochemical parameters and the substituent groups. Nanotubes and tree-like structures can be obtained using thiophene as the polymerizable core. Here is observed that the electrochemical method plays an important role on the surface structuration. The polypyrenes with various substituents differing by their hydrophobicity, size or rigidity/flexibility can lead to surfaces with tunable hydrophobicity, water adhesion and fluorescent properties. This work used an innovative strategy to show a combination of superhydrophobicity with fluorescence properties on polypyrenes surfaces. The study with different molecules opens new doors to explore this domain of materials science since the control of surface wettability and water adhesion is extremely important for various applications. With this aim, more studies with different copolymers will be done in order to better evaluate the morphology, wettability and water adhesion.
Encadrant : Xavier Noblin
Bubbles cavitation dynamics in micro-confined systems
Among numerous fascinating features, water is able to sustain high negative pressure. It can eventually relax its stretched state by rupturing into vapor cavities, a process named cavitation. My PhD thesis focuses on water pressure decreasing and bubble cavitation occurring in bio-inspired devices we fabricate through soft-lithography. These devices are made up of 2D arrays of cubic cells containing water that evaporates if the system is placed in a sub-saturated environment. Evaporation leads water into a stretched state and, once the tension reaches a threshold value, bubbles appear. It has been observed that one bubble nucleation can trigger up to hundreds cavitation events in neighboring cells, resulting in an avalanche-like phenomenon. Our setup allows for the simultaneous recording of images –by the means of a high-speed camera- and acoustic signals employing a hydrophone. I will show bubbles dynamics and their acoustic emissions whose frequency can reach up to 3 MHz in case of single-nucleation and avalanche-like events. Finally, I will present the present work under progress in order to measure the negative pressures in static (cavitation threshold) and dynamic conditions (time-dependent pressure profile). Both methods require new fabrication procedure for the micro-devices and optical setups.
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