In spite of the tragic conclusion of the scientific mission STS-107 of the
shuttle Columbia, the results of some experiments have been saved, perhaps
making less vain the Astronauts' sacrifice. One of the experiments is FAST
(Facility for Adsorption and Surface Tension), conceived by the Department
of Genoa of IENI and aimed at the investigation of the adsorption process
of surfactants at liquid interfaces, which had a complete success. FAST
houses two Capillary Pressure tensiometers to investigate the surface
rheology, by measuring the response of surface tension of liquid-liquid
and liquid-air interfaces to controlled perturbations of the interfacial
area: expansions and compressions, continuous growing and sinusoidal
variations.
During 15 days, about 6000 single experiments have been performed, by
varying temperature, surfactant concentration and characteristics of the
applied area perturbations. The results show the advantages provided by
microgravity, specifically the purely diffusive conditions in the
surfactant transport and the possibility to investigate surface rheology
in frequency and concentration ranges significant for applications and not
accessible on ground.
The study has been carried out in the framework of the FASES (Fundamental
and Applied Studies in Emulsion Stability) project of the European Space
Agency, for the investigation of emulsion stability. Groups from different
European scientific institutions and industries are partners of the
project which is chaired by IENI-GE.
The additives utilised to control emulsion stability contains mostly
surfactants that, by accumulating at the interface, affect the droplet-droplet interaction, promoting or damping the destabilisation mechanisms:
mainly aggregation and coalescence. Surface rheology plays a fundamental
role in both processes.
In the framework of the project, emulsion stability is studied at all its
detail levels: adsorption at the interface, droplet-droplet interaction,
collective behaviour. The damping of buoyancy and convection provides
instrumental and substantial advantages in the study of all these
processes. Therefore facilities are being developed for the International
Space Station, suitable for the investigation of all detail levels. A new
version of FAST will allow liquid films to be studied and another device
will be devoted to investigate dynamics, interactions and granulometry of
the emulsion droplets.
The project is providing significant scientific results and economical and
social spin-offs in different fields, particularly in those of the
industries involved in the project: crude oil up-stream and separation,
application of emulsions to remediation of chemical and radioactive
contamination, improvement of products and processes in the food and
cosmetic industry.
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