The objective of the FOAM (Foam Optics And Mechanics) flight experiment is to study the characteristics of wet foams in the absence of gravity. The microgravity environment on the ISS will eliminate drainage of liquid out of the wet foams at high liquid contents. This experiment is a joint collaborative project between the European Space Agency (ESA) and NASA. As part of the ISS Non-Exploration Program, Professor Douglas Durian, University of Pennsylvania, Department of Physics, participates as the U.S. principal investigator, and is supported by NASA. Professor Dominique Langevin of the University of Paris South (UPS) leads the flight project. As part of the international science team, ESA also supports several additional scientists from Germany, Ireland, France, Belgium and Sweden, mostly from universities.
ESA is currently designing the FOAM flight hardware with the lead contractor ASTRIUM (Germany). The FOAM hardware is being integrated into the Microgravity Science Glovebox (MSG) facility. The FOAM Preliminary Design Review (PDR) was held at the contractor’s facility in Germany and successfully completed during the 3rd week of December 2006. As recently proposed at the PDR by Prof. Durian, ESA and the European contractors are planning to integrate Speckle Visibility Spectroscopy, a newly developed technique by Professor Durian, to further elucidate how foam structures evolve over time in a microgravity environment. The flight module is expected to be delivered in late 2008. The tentative flight date is July 2009.
• Science Objectives: To exploit microgravity conditions to quantify and elucidate the unusual elastic character of foam structure and dynamics. To observe how the foam melts into a simple viscous liquid as a function of both increasing liquid content and shear strain rate.
• Relevance/Impact: The proposed flight research generate valuable fundamental guidance for the development of materials with more desirable rheology and better stability. On board Rheometry and light scattering techniques will provide the rheology and coarsening in terms of microscopic structure and dynamics.
• Justification for Microgravity: Microgravity environment will eliminate drainage of liquid out of the wet foams at higher liquid content.
• Joint collaborative project between NASA and ESA. European P.I.s: Langevin , Saint-Jalmes, Adler (France,), Vanderwalle (Belgium), Waiere (Ireland), Odenbach, Banhardtn (Germany), Kronberg (Sweden)
To exploit rheological and multiple-light scattering techniques, and ultimately microgravity conditions, in order to quantify and elucidate the unusual elastic character of foams in terms of their underlying microscopic structure and dynamics. Special interest is in determining how this elastic character vanishes, i.e., how the foam melts into a simple viscous liquid as a function of both increasing liquid content and shear strain rate.
The unusual elastic character of foams will be quantified macroscopically by measurement of the shear stress as a function of static shear strain, shear strain rate, and time following a step strain; such data will be analyzed in terms of a yield stress, a static shear modulus, and dynamical time scales. Microscopic information about bubble packing and rearrangement dynamics, from which these macroscopic non-Newtonian properties presumably arise, will be obtained non-invasively by novel multiple-light scattering diagnostics such as diffusing-wave spectroscopy (DWS). Quantitative trends with materials parameters, such as average bubble size, and liquid content, will be sought in order to elucidate the fundamental connection between the microscopic structure and dynamics and the macroscopic rheology.
The utility and fascination of foams are derived largely from the surprising fact that they have a solid-like elastic character in spite of being mostly gas with a few percent volume fraction of liquid, but can nevertheless flow under shear. The physical origin of such unusual rheology in terms of microscopic structure and dynamics is poorly understood. The flight experiment promises important new insight into these issues, and could also have significant consequences for our understanding of flow in other dense randomly-packed systems such as emulsions, colloidal suspensions, slurries, bubbly liquids, and granular materials. Furthermore, all foam applications are empirically based and the proposed research may generate valuable fundamental guidance for the development of materials with more desirable rheology and better stability.
The FOAM is dedicated to the study of aqueous and non-aqueous foams in the microgravity environment onboard the International Space Station (ISS). In particular, “wet” foams which cannot be stabilized on earth because of drainage will be investigated under microgravity conditions.
The Foam Experiment Assembly (FEA) will provide the possibility to perform three different types ofexperiments:
• Rheometry, to quantify and elucidate the visco-elastic character of foams in terms of their underlyingmicroscopic structures and dynamics
• Drainage, to better describe the hydrodynamics of foams at high liquid fraction, and thus to advance thedevelopment of simulation tools
• Stability, to define physico-chemical aspects of unstable foams.
To carry out these experiments, the FEA, hosted by the Microgravity Science Glovebox (MSG) will have 5 functional units:
• Stability, Drainage and Rheometry Insert (SDRI)
• Electrical Subsystem (ESS FEME)
• Gas Mixing Unit (GMU)
• Solution Cartridge
• Liquid-Gas Cartridge
The FOAM Experiment Assembly (FEA) designed to perform FOAM experiments can be broken down into two major scientific instrumentation assembly, together known as SDRI (Stability Drainage Rheometry Insert):
In the SDRI:
(1) The Stability experiment Unit (STU) including the following subunits:
– Foam generation subunits (translation grid mechanism)
– Two Stability experiment cells
– Scientific diagnostic devices
– STU internal structure
(2) The Drainage rheometry experiment unit (DRU) including the following subunits:
– Foam generation subunit (close loop)
– Rheometer compressor
– Drainage Rheometry experiment cell
– Scientific diagnostic devices
– DRU internal structure