  Numerous formulation processes of materials involve a drying step, during
which evaporation of a solvent from a multi-component liquid mixture, often
confined in a thin film or in a droplet, lead to concentration and assembly of
non volatile compounds. While the basic phenomena ruling evaporation dynamics
are known, a precise modeling of practical situations is hindered by the lack
of tools for local and time-resolved mapping of concentration fields in such
confined systems. In this article, the use of Fluorescence Lifetime Imaging
Microscopy and of Fluorescent Molecular Rotors is introduced as a versatile,
in-situ and quantitative method to map viscosity and concentration fields in
confined, evaporating liquids. More precisely, the cases of drying of a
suspended liquid film and of a sessile droplet of mixtures of fructose and
water is investigated. Measured viscosity and concentration fields allow to
characterize drying dynamics, in agreement with simple modeling of the
evaporation process.
