NANOFLUIDYN

Interfaces and confined liquids play a crucial role in many natural and technological processes, their influence becoming predominant when downsizing. Therefore, many challenging objectives are ahead to understand these effects at nanometer scale that require the development of techniques to confine liquids and study their behavior down to the nanoscale. The aim of this project is to address a wide range of open questions in physics of fluids, especially those concerning the physical origin of the characteristic lengths governing the behavior at nanometer scale. It federates four partners with complementary expertise (CEMES, LPENSL, CBMN and IMFT), involved in the development of non-conventional atomic force microscopy AFM-based methods applied to fluids. The combination of original techniques and probes together with unique theoretical and numerical models will allow us to investigate confined fluids and interfaces under unprecedented solicitation conditions. A new type of AFM-based method has recently been developed to address this issue. It consists in partially immersing, in the liquid of interest, a long cylindrical probe engineered at the end of a cantilever. The pioneering work performed by the partners involved in NANOFLUIDYN has shown that this geometry allows investigating not only bulk liquid properties, but also the liquid interface, the nanomeniscus around the fiber and the contact line, providing a new method to measure the properties of these quantities. In addition, several new instrumental developments have been performed by two members of the consortium: a high-resolution HR-AFM in LPENSL with a very low noise level well adapted for the measurement of thermal fluctuations and a high-frequency HF-AFM setup in CBMN which allows working with picometer amplitudes up to 20MHz. The combination of the instruments available in the consortium provides a range of amplitudes, frequencies and forcing extending over more than five orders of magnitude each, and thus covering an unprecedented range of solicitations. The constructed consortium has a unique capability to take full advantage of this added value, by its expertise in modeling both fluids and instrument responses. The synergy between these expertises provides an opportunity to address a number of fundamental issues on physics of fluids. The numerous questions we anticipate make that the project can lead to important achievements we list below: - The response of fluids to an unprecedented range of solicitations with a special focus on high frequency and small amplitude must lead to a precise determination of characteristic lengths at small scale, on their physical origin and on their interplay. - The measurement of effective static and dynamic interface stiffness, and the spectral response available with HR-AFM by monitoring thermal fluctuations of the interface, will give information on its mechanical properties, on the coupling with the probe and on the role of surfactants, and will design a new method for local probing of interfaces. - The quantification of the sources of dissipation close to the contact line and the role of surface defects at nanometer scale will be an important new result that may lead to a breakthrough in the physics of wetting. It will stimulate new theoretical works to match molecular to macroscopic descriptions that is the main bottleneck in wetting sciences. The project is organized in 5 tasks, one on coordination, one on instrumental aspects, and three tasks corresponding to the issues mentioned above. This project is based on technological advances of the partners who developed AFM methods and original probes, to push beyond the knowledge of liquid at nanometer scale. The new insights brought by the NANOFLUIDYN project on the physics of Newtonian liquids will open large perspectives in the more general fields of complex fluids (polymers, micellar solutions…) and biology which are out of the scope of the present project.