Correlation length of hydrophobic polyelectrolyte solutions

TL;DR

This study measures the correlation length of salt-free hydrophobic polyelectrolyte solutions using X-ray scattering and microscopy, revealing a unique dependence on charge fraction and concentration linked to chain conformation.

Contribution

It provides the first detailed experimental analysis of correlation length dependence on charge fraction and concentration in hydrophobic polyelectrolytes, highlighting the impact of pearl necklace conformation.

Findings

Correlation length varies from $C_p^{-1/2}$ to $C_p^{-1/3}$ with decreasing charge fraction.

Correlation length strongly depends on the charge fraction, contrary to hydrophilic polyelectrolytes.

Chain conformation influences the correlation length behavior.

Abstract

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.