Surface activity and micelle formation of alkylguanidinium chlorides, containing 10, 12, 14, and 16 carbon atoms in the hydrophobic tail have been studied by combining conductivity and surface tension measurements with isothermal titration calorimetry. The purity of the resulting surfactants, their temperatures of Cr → LC and LC → I transitions, as well as their propensity of forming birefringent phases were assessed based on the results of 1H and 13C NMR, differential scanning calorimetry (DSC), and polarizing microscopy studies. Whenever possible, the resulting values of Krafft temperature (TK), critical micelle concentration (CMC), minimum surface tension above the CMC, chloride counter-ion binding to the micelle, and the standard enthalpy of micelle formation per mole of surfactant (micH°), were compared to those characterizing alkyltrimethylammonium chlorides or bromides with the same tail lengths. The value of TK ranged between 292 and 314 K and increased strongly with increase in the chain length of the hydrophobic tail. Micellization was described as both entropy and enthalpy-driven. Based on the direct calorimetry measurements, the general trends in the CMC with the temperature, hydrophobic tail length and NaCl addition were found to be similar to those of other types of cationic surfactants. The particularly exothermic character of micellization was ascribed to the hydrogen-binding capacity of the guanidinium head-group.

Material failure is ubiquitous on length scales ranging from a few nanometers, as in fracture of atomic or molecular systems, up to geological scales, as in earthquakes. The detection of any precursors that may point to incipient failure is the Holy Grail in many disciplines, from material science to engineering and geology. Material failure is particularly relevant to soft matter systems (colloids, emulsions, polymers etc.), which are an ideal benchmark to investigate how mechanical stress impacts condensed matter. Indeed, soft matter is very susceptible to even modest mechanical loads and most soft materials can be conveniently investigated by powerful optical methods such as microscopy or light scattering.We have built up a shear-cell that allows us to couple rheology to light scattering measurements on soft solids. In this talk I will focus on a fractal colloidal gel produced by in-situ aggregation of silica nanoparticles in water and show how reversible and irreversible (microscopic and macroscopic) deformations, build up when the gel is submitted to a shear stress. Thanks to our set-up, we are able to elucidate the physical processes at play at the onset of yielding.

Liquid sheets that freely expand in air can be produced by the impact of a small drop of liquid on a cylindrical target of size comparable to that of the drop. In this talk I will illustrate with two examples how the imaging with a fast camera of the dynamics of the sheets thus formed can shed light on fundamental and industrial issues. On the one hand, we quantify the interplay between elasticity and viscosity and the effects of a strong and fast deformation on viscoelastic droplets. On the other hand, we rationalize the role of dilute emulsions in the destabilization mechanism of liquid sheets and its consequence for anti-drift phenomena in agricultural sprays.

Liquid sheets that freely expand in air can be produced by the impact of a small drop of liquid on a cylindrical target of size comparable to that of the drop. In this talk I will illustrate with two examples how the imaging with a fast camera of the dynamics of the sheets thus formed can shed light on fundamental and industrial issues. On the one hand, we quantify the interplay between elasticity and viscosity and the effects of a strong and fast deformation on viscoelastic droplets. On the other hand, we rationalize the role of dilute emulsions in the destabilization mechanism of liquid sheets and its consequence for anti-drift phenomena in agricultural sprays.

The structure of polymer nanocomposites has important consequences on final properties, like for instance mechanical reinforcement. While the structure of the hard filler phase is usually characterized by electron microscopy and small-angle X-ray scattering, the chain conformation can only be measured by small-angle neutron scattering (SANS).

Several techniques to assemble artificial lipid bilayers involve the zipping of monolayers. Theirefficiency is determined by the renewal of the saturated monolayers to be zipped and this proceeds byadsorption of lipids dispersed in oil as aggregates. The size of these lipids aggregates is a key parameterto ensure both the stability of the suspension and a fast release of lipids at the interface. We proposea new method inspired from the solvent-shifting nucleation process allowing to control and tune thelipid aggregates size and that improves the production of artificial membranes. It is simpler and fasterthan current methods starting from a dry lipid film, which are highly sensitive to environmental conditions.This method opens the route to bilayer production processes with new potentialities in membranecomposition.