Shaping fluid-fluid interfaces

In this thesis, we present studies on the regular structuring of fluid/fluid interfaces. In Chapter 1 through 3, we investigate the spreading of droplets and the impact of liquid jets on microtextured solid substrates. We show that the liquid films produced adopt the symmetry of the substrate topography, despite the different physical mechanisms involved in the film formation. When a droplet of partially wetting fluid spreads on a regular lattice of microposts, the shape of the resulting film depends on the dynamics of the spreading/imbibition, i.e. the geometrical features of the substrate and the contact angle of the fluid (Chapter 1). When a jet impacts a microtextured substrate, at high Reynolds number, the velocity field is no longer isotropic. The angular dependence results in the formation of polygonal hydraulic jumps (Chapter 2) and polygonal liquid sheet (Chapter 3). In Chapter 4 and 5, we study a highly stable dispersion of micron scale bubbles. We show that each bubble is coated with an insoluble layer of condensed surfactant molecules. Under compression, the shell initially buckles into nanometer scale hexagonal domains. The nanopatterned interface resists further shrinkage of the bubble and the gas dispersion is stable over a year. We rationalize the surface structure by considering the mechanical features and the chemical composition of the interface. Finally, in Chapter 6, we present an experimental study on the clogging of microchannels by colloidal suspensions and document the role of the interaction between particles and the flow properties.