  The combination of two techniques (Small Angle X-ray Scattering and Atomic
Force Microscopy) has allowed us to measure in reciprocal and real space the
correlation length $\xi$ of salt-free aqueous solutions of highly charged
hydrophobic polyelectrolyte as a function of the polymer concentration $C_p$,
charge fraction $f$ and chain length $N$. Contrary to the classical behaviour
of hydrophilic polyelectrolytes in the strong coupling limit, $\xi$ is strongly
dependent on $f$. In particular a continuous transition has been observed from
$\xi \sim C_p^{-1/2}$ to $\xi\sim C_p^{-1/3}$ when $f$ decreased from 100% to
35%. We interpret this unusual behaviour as the consequence of the two features
characterising the hydrophobic polyelectrolytes: the pearl necklace
conformation of the chains and the anomalously strong reduction of the
effective charge fraction.
