  Water, ethanol, and ammonia are the key components of the mantles of Uranus
and Neptune. To improve structure and evolution models and give an explanation
of the magnetic fields and luminosities of the icy giants, those components
need to be characterised at planetary conditions (some Mbar and a few $10^3$
K). Those conditions are typical of the Warm Dense Matter regime, which
exhibits a rich phase diagram, with the coexistence of many states of matter
and a large variety of chemical processes. H$_2$O, C:H:O, and C:H:N:O mixtures
have been compressed up to 2.8 Mbar along the principal Hugoniot using
laser-driven decaying shocks. The experiments were performed at the GEKKO XII
and LULI 2000 laser facilities using standard optical diagnostics (Doppler
velocimetry and pyrometry) to characterise equation of state and optical
reflectivity of the shocked states. The results show that H$_2$O and the
C:H:N:O mixture share the same equation of state with a density scaling, while
the reflectivity behaves differently by what concerns both the onset pressures
and the saturation values. The reflectivity measurement at two frequencies
allows to estimate the conductivity and the complex refractive index using a
Drude model.
