  Aggregation and other interactions are suppressed for a biological
semiflexible polyelectrolyte, hyaluronan (HA), when it is embedded in a mixture
with another negatively charged and flexible polyelectrolyte chain, sodium
polystyrene sulfonate. We see directly HA only in the mixture using Small-Angle
Neutron Scattering, isotopic labelling and contrast matching. At low ionic
strength, for which aggregation is usually seen for pure HA solutions, an
unambiguous set of experimental results shows that we neither observe HA
aggregation nor a polyelectrolyte peak (observed for solutions of single
species); instead we observe a wormlike chain behaviour characteristic of
single chain with a variation of the persistence length with the square of the
Debye screening length, Le~\kappa^-2, as formerly predicted by Odijk and not
yet observed on a polymer chain.
