Fluidization of concentrated emulsions in herringbones decorated microfluidic channels

In this thesis we study the flow of concentrated emulsions in microfluidic channels with herringbone structured grooves on the walls. Concentrated emulsions are a model for yield stress fluids, an interesting class of materials that includes also foams, gels, and colloidal suspensions. If a stress below the yield value is applied, these materials behave like a solid, but if the applied stress overcomes the threshold, the fluid starts to flow like a liquid. Recent studies showed that this transition could be influenced by the material confinement and by microstructures on the surfaces. These works always considered a symmetrical patterning with respect to the possible flow directions. In this thesis we extended these works, by studying and characterizing the flow of concentrated emulsion in microfluidic channels, patterned with herringbones microstructures. The asymmetric roughness allowed us to define a favourite direction for the flow, called forward direction, while the other was called backward direction.Results showed that the flow strongly depend on the chosen direction. We focused on the difference between velocities in forward and backward flows, observing how this value could change as a function of the angle and of the herringbone structures and of the distance between them. Moreover we observed how the flow changes as a function of the pressure drop.