Tesis: "Mechanical stability of a granular interface: hydrophobic monolayer of particles on a water-air interface"
Dr. Francisco Melo
The aggregate particles on a liquid-fluid interface have the ability to stabilize emulsions and increase the lifetime of foam bubbles. It has been shown that partcles-coated interfaces do not obey the minimization of surface energy and can exist in a metastable-like state by acquiring non-spherical configurations. In addition, they have behaviors such as buckling or wrinkling, which are typical behaviors of an elastic solid.
The objective of this research is to determine the conditions that influence the granular interfaces stabilizing mechanism, composed of hydrophobic particles (lycopodium spores of 20 microns in diameter), deposited on a water-air interface. We have developed an experimental methodology that allows us to study and offer a phenomenological description of the mechanical behavior with this type of systems.
Through image adquisition, we can determine the profile and the packing fraction of particles covering a drop, by controlling the liquid surface. Preliminary (figure 1) results show that, depending on the packing fraction of particles at the liquid surface, the stability of the granular interface is not described completely by the Laplace relationship from granular interactions in the system.
By compressing a planar granular interface, wrinkles appear on the surface. We have developed a Langmuir system for compressing the granular interface by controlling from one end, while at the another extreme we check the stress applied with a force sensor (figure 2). The vertical deformation after the buckling appears is determined with the FTP (Fourier Transform Profilometry) technique. Analyzing the hysteresis of the stress-strain curve makes possible to distinguish the influence of force chains between the grains in the system.
NonLinear Physics Laboratory, Physics Department.
Universidad de Santiago de Chile
Av. Ecuador 3493, Estacion Central, Santiago Chile
Teléfono: (56-2) 7181298