  We investigate the dynamical properties of asymmetric nuclear matter at low
density. The occurrence of new instabilities, that lead the system to a
dynamical fragment formation, is illustrated, discussing in particular the
charge symmetry dependence of the structure of the most important unstable
modes. We observe that instabilities are reduced by charge asymmetry, leading
to larger size and time scales in the fragmentation process. Configurations
with less asymmetric fragments surrounded by a more asymmetric gas are
favoured. Interesting variances with respect to a pure thermodynamical
prediction are revealed, that can be checked experimentally. All these features
are deeply related to the structure of the symmetry term in the nuclear
Equation of State (EOS) and could be used to extract information on the low
density part of the EOS.
