On the pearl size of hydrophobic polyelectrolytes

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Hydrophobic polyelectrolytes have been predicted to adopt an unique pearl-necklace conformation in aqueous solvents. We present in this Letter an attempt to characterise quantitatively this conformation with a focus on Dₚ, the pearl size. For this purpose polystyrenesulfonate (PSS) of various effective charge fractions feff and chain lengths N has been adsorbed onto oppositely charged surfaces immersed in water in condition where the bulk structure is expected to persist in the adsorbed state. In situ ellipsometry has provided an apparent thickness happ of the PSS layer. In the presence of added salts, we have found: happ aN⁰feff⁻²/³ (a is the monomer size) in agreement with the scaling predictions for Dₚ in the pearl-necklace model if one interprets happ as a measure of the pearl size. At the lowest charge fractions we have found happ aN¹/³ for the shorter chains, in agreement with a necklace/globule transition.