  We demonstrate in this paper the influence of solvent quality on the
structure of the semi-dilute solution of a hydrophobic polyelectrolyte,
partially sulfonated Poly-Styrene Sulfonate. Two solvents are used: (i) one
mixture of water and an organic solvent: THF, which is also slightly polar;
(ii) DMSO, a polar organic solvent. In case (i), it is shown by SAXS study that
the structure - namely the scattering from all chains, characterised by a
maximum ("polyelectrolyte peak"), of the aqueous hydrophobic polyelectrolyte
solutions (PSS) depends on the solvent quality through the added amount of
organic solvent THF. This dependence is more pronounced when the sulfonation
rate is low (more hydrophobic polyelectrolyte). It is proposed that when THF is
added, the chain conformation evolves from the pearl necklace shape already
reported in pure water, towards the conformation in pure water for fully
sulfonated PSS, which is string-like as also reported previously. On the
contrary, for a hydrophilic polyelectrolyte, AMAMPS, no evolution occurs with
added THF in the aqueous solution. In case (ii), it is shown directly by SANS
study that PSS can behave as a classical solvophilic polyelectrolyte when
dissolved in an organic polar solvent such as DMSO: the structure (total
scattering) as well as the form factor (single chain scattering measured by
SANS using the Zero Average Contrast method) of the PSS chains is independent
of the charge content in agreement with Manning condensation, and identical to
the one of a fully charged PSS chain in pure water, which has a classical
polyelectrolyte behaviour in the semi-dilute regime.
