The infrared signatures of very small grains in the Universe seen by
  JWST
  The near- and mid-IR spectrum of many astronomical objects is dominated by
emission bands due to UV-excited polycyclic aromatic hydrocarbons (PAH) and
evaporating very small grains (eVSG). Previous studies with the ISO, Spitzer
and AKARI space telescopes have shown that the spectral variations of these
features are directly related to the local physical conditions that induce a
photo-chemical evolution of the band carriers. Because of the limited
sensitivity and spatial resolution, these studies have focused mainly on
galactic star-forming regions. We discuss how the advent of JWST will allow to
extend these studies to previously unresolved sources such as near-by galaxies,
and how the analysis of the infrared signatures of PAHs and eVSGs can be used
to determine their physical conditions and chemical composition.
