A microscopic technique based on digital holography is proposed to investigate blood microcirculation and vascular development in model organisms such as zebrafish larvae. Recent achievements in 3D imaging of blood flow in vessels are presented.

The addition of nanoparticles to a polymermatrix is a well-known process to improve the mechanicalproperties of polymers. Many studies of mechanical reinforcementin polymer nanocomposites (PNCs) focus on rubberymatrices; however, much less effort concentrates on thefactors controlling the mechanical performance of thetechnologically important glassy PNCs. This paper presentsa study of the effect of the polymer molecular weight (MW)on the overall mechanical properties of glassy PNCs withattractive interaction by using Brillouin light scattering. Wefound that the mechanical moduli (bulk and shear) have anonmonotonic dependence on MW that cannot be predictedby simple rule of mixtures. The moduli increase with increasing MW up to 100 kg/mol followed by a drop at higher MW. Wedemonstrate that the change in the mechanical properties of PNCs can be associated with the properties of the interfacialpolymer layer. The latter depend on the interfacial chain packing and stretching, as well as polymer bridging,which vary differently with the MW of the polymer. These competing contributions lead to the observed nonmonotonicvariations of the glassy PNC moduli with MW. Our work provides a simple, cost-effective, and efficient way to control themechanical properties of glassy PNCs by tuning the polymer chain length. Our finding can be beneficial for the rational designof PNCs with desired mechanical performance.

We investigate the dynamics of thin sheets freely expanding in air. The sheets are produced by impacting a drop onto a small solid target or onto a cushion of liquid nitrogen, in order to suppress any dissipation process. To disentangle the role of capillary, viscous and elastic forces in the dynamics of the sheets several materials are used, whose rheological characteristics are tuned over several orders of magnitude: viscous liquids, viscoelastic Maxwell fluids and ultrasoft solids. In this talk, I will present our approaches to rationalize the spreading of sheets for viscous, viscoelastic and elastic materials by taking into account surface tension, elastic deformation and shear and biaxial viscous dissipations.

Evening student presentation at the Bombannes summer school

A gel is a dispersed system which consists of at least two different components: a solid or flexible mesh and a fluid (water in the present case). Microgels are gels in the size range of 10 nm to 1 μm and can be used in a wide range of applications like drug delivery and smart surface coatings. If the microgel consists of acrylamides like N-isopropylmethacrylamide (NIPMAM) or N-n-propylacrylamid (NNPAM) as network component, they show a volume phase transition (VPT) at a certain temperature, the volume phase transition temperature (VPTT). An increase in temperature above the VPTT leads to an abrupt decrease in size and a decrease in temperature leads to an abrupt increase in size. The VPTT is specific for each monomer. To use microgels in sensors or for nanoactuators the thermoresponse has to be precise. That is why we investigated microgels with a core-shell architecture containing NIPMAM and NNPAM. These particles show a tunable linear change in size between 22 °C and 43 °C. Furthermore, we deposited these microgels on surfaces and investigated the properties of the coating. The properties of these particles and coatings can be adjusted by selecting specific synthesis conditions. We then did small angle neutron scattering (SANS) to determine the internal structure of the core-shell microgel.

Proposition d'une modélisation numérique