  The temporal and spatial evolution of dispersed media is a fundamental
problem in a wide range of physicochemical systems, such as emulsions,
suspensions and aerosols. These systems are multiphasic and involve compounds
of different densities. They are therefore subject to the influence of gravity
which determines the sedimentation rate of their dispersed phase. This effect
can be dominant and prevent a detailed study of the phenomena occurring between
the constituents themselves, such as the coalescence of drops in emulsions, the
evaporation of droplets or the flocculation in suspensions. In this context,
the Centre National d'Etudes Spatiales (CNES) has recently supported the
development of a new instrument to produce populations of droplets, a few
micrometers in radius, under controlled conditions with the objective of
allowing a detailed study of their properties in microgravity conditions. The
principle of this instrument is to generate, by a fast compression/expansion of
air, populations of water droplets and to track their evolution by optical
scanning tomography in transmission mode within a volume of approximately 2
mm3. Parabolic flight experiments have shown the possibility to generate and
accurately follow the evolution of populations of several hundred droplets for
more than 20 seconds. The first experimental results show that it is possible
to study their evaporation kinetics or their motion when imposing Von Karman
swirling flows. This work is part of the AEROSOL project of DECLIC-EVO
supported by CNES and aims to help the understanding of cloud microphysics
which remains a critical open problem in the context of global warming.
