Résumé
Solid micron- and nano- particles have been extensively used to stabilize dispersions such Pickering emulsions and particle-stabilized foams. In many cases, particle's adsorption onto the fluid interfaces represents a limiting step for the stability of the dispersion since adsorption can be very slow or even hindered by interfacial potential barriers. In the first part of the talk, I will show experimental evidences on the slow dynamics of nanoparticles at the interface and the role of colloidal forces and wetting on the free energy profile across the interface. A step beyond the understanding of particle's adsorption onto the interface is the control of nanoparticle crossing of liquid-liquid interfaces. The second part of the talk discusses experiments and models describing the adsorption-desorption phenomena, which result in the phase transfer of nanoparticles from oil to water and viceversa . Gold nanoparticles coated with stimuli-responsive polymer transfer from water to oil and from oil to water across the planar interfaces when environmental parameters are slightly changed. The oil to water transfer occurs when the temperature is reduced below 5 °C, while they transfer from salty water to oil when the environmental temperature returns to room temperature. The water-to-oil particle transfer is dictated by the ionic strength of the aqueous phase. In contrast, the oil-to-water particle transfer is correlated with the hydration interaction. The transfer mechanism disparity for the two directions during NP crossing of oil-water interfaces result from an intricate interplay of interfacial interactions and transitions. Among the different experimental tools used for the investigation, multiple angle of incidence ellipsometry was applied to in situ assess the contact angle and surface coverage of nanoparticles as small as 18 nm at water-oil and water-air interfaces.