Physics of gas marbles : from granular film to assembly – PhyGaMa

The physical description of these new objects at different scales and for different loading regimes aims at linking the microstructure to the global behavior of the material and at identifying the physical mechanisms dominating the interactions between the grains of the shell: capillarity, contacts between grains and viscous dissipation (in the liquid film and at the liquid/gas interfaces).
To address these issues, we conduct experiments at different scales of the material where the parameters of the continuous and dispersed phases are controlled to reveal the main physical characteristics of these new objects.
At the mesoscopic level, we wish to understand the link between the particle network and the behavior of gas bead membranes subjected to different solicitations: global and local forcing, vibrations and finally classical rheometry. In the quasi-static regime, we study the influence of the capillary pressure on the mechanical behavior of the membrane and on the granular network. In the dynamic regime, the relationship between the contact dissipation between grains and the interfacial or viscous dissipation is discussed.
Finally, on the way to the macroscopic scale, our first objective will be to create gas beads with controlled properties, and our second objective will be to correlate the static behavior of a gas bead and a gas bead assembly to the properties of the membrane and/or the shell.

The first works carried out at the Navier laboratory allowed to probe the effect of the liquid pressure in a granular film (soap film loaded in grains) on its rupture. It has been shown that beyond a threshold liquid depression, the total rupture of the granular film is inhibited, and that the transition from a total rupture state (as for a classical soap film) to a partial rupture state is dependent on the history of the liquid pressure state in the film and on the wetting angle on the particles. For example, an initial cycle of liquid depression subsequently leads to a sharper transition, somewhat «erasing« the initial state of the granular film. The study was conducted for spherical grains of 140µm in diameter and is continuing with grains of different sizes (80-500µm).
The first works carried out in the FAST laboratory, allowed to realize rheograms of granular films. These first studies revealed that the rheology of these systems is much more complex than expected. Indeed, the response to a solicitation depends in a non-linear way on its deformation and its deformation rate, which adds the cumulative deformation as a parameter of the rheological model. The highlighting of this new parameter has forced us to also consider the simpler case of a granular raft (grains held by a single interface while two interfaces confine the grains in a granular film).

Finally, in the perspective of exploring new coupled propagation modes and opening the way to new vibration dampers, the dynamic properties of gas beads and a gas bead stack will be studied by wave propagation and interpreted in terms of the damping properties of the granular films and the gas bead assembly.

in progress ...

Research in line with the pioneer work of Pickering succeeded recently to produce new objects which can be described as gas pockets in air and are named gas marbles. They are made of gas surrounded by a layer of grains constrained by thin liquid film in gas environment. The exceptional mechanical strength of their granular shell promise them to many applications. Among these, we note here that using gas marbles can be relevant for the generation of materials with hierarchical porosity. Moreover, these new hollow marbles offer a promising route to new vibration dampers. In this proposal, our objective is to study the physics of this new material.
In a ternary diagram (solid-liquid-gas), gas marbles share the domain of high gas, low solid and very low liquid fraction with already well-known three phase materials: wet (unsaturated) granular materials, Pickering foams, granular foams. At the microscale of all these materials, three physical mechanisms inducing (possibly multicore) interactions between grains are at play: capillarity, grains contacts and viscous dissipation (in the liquid film and at the liquid/gas interfaces). The time scales, length scales and patterns differs from one systems to another, as the particles and liquid network differ. The main concern common to all dispersed media made of two or three phases are: How microstructure of the dispersed phases and microscale interactions are related and affect the macroscale behavior of the material? Are all these systems one class of material in a sense that they obey the same constitutive laws but with different state parameters defined by the physic at play at the microscale?
Studying gas marbles would help to give new inputs to these questions and propose a unified view to the subject. To tackle these questions, we will carry out experiments at the different scales of the material where the parameters of the continuous phase and dispersed phase will be controlled in order to reveal the main physical features of these new objects.
At the mesoscale, we want to understand the link between the particle network and the behavior of the gas marble membrane when subject to different solicitations: global and local forcing, vibrations and classical rheometry. In the quasi-static regime, we will study the influence of the capillary pressure on the elasticity of the membrane and the granular network in terms of particle fraction, neighbor’s number, aggregation coefficient. In the dynamic regime, the relevance of grains contact dissipation compare to the interfacial dissipation or liquid viscous dissipation will be address.
Finally, on the route to the macroscale, we have the first objective to create a gas marble with controlled properties, the second one is to correlate the static behavior of one gas marble and a gas marbles assembly to the properties of the membrane and/or shell.
Finally, the dynamical properties of one gas marbles and gas marbles assembly will be studied by vibrational waves propagation and interpreted in regards to the damping properties of the granular films and the network assembly of the gas marbles. The multi-scale and ternary structure of the material might reveal different coupling modes of propagation (waves propagation in air and in the granular skeleton).