Why Single‐Chain Nanoparticles from Weak Polyelectrolytes Can Be Synthesized at Large Scale in Concentrated Solution?

Abstract

AbstractHere, the unresolved question of why single‐chain nanoparticles (SCNPs) prepared from a weak polyelectrolyte (PE) precursor can be synthesized on a large scale in a concentrated solution is addressed, unlike SCNPs obtained from an equivalent neutral (nonamphiphilic) polymer precursor. The combination of the standard elastic single‐chain nanoparticles (ESN) model −developed for neutral chains− with the classical scaling theory of PE solutions provides the key. Essentially, the long‐range repulsion between electrostatic blobs in a weak PE precursor restricts the cross‐linking process during SCNPs formation to the interior of each blob. Consequently, the maximum concentration at which PE‐SCNPs can be prepared without interchain cross‐linking is not determined by the full size of the PE precursor but, instead, by the smaller size of its electrostatic blobs. Therefore, PE‐SCNPs can be synthesized up to a critical concentration where electrostatic blobs from different chains touch each other. This concentration can be 30 times higher than that for non‐PE polymer precursors. Upon progressive dilution, the size of PE‐SCNPs synthesized in concentrated solution increases until it reaches the bigger size of PE‐SCNPs prepared under highly diluted conditions. PE‐SCNPs do not adopt a globular conformation either in concentrated or in diluted solution. It shows that the main model predictions agree with experimental results.