Organic versus Hybrid Coacervate Complexes : Co-Assembly and Adsorption Properties

TL;DR

This study compares the assembly and adsorption behaviors of organic and hybrid coacervate complexes formed from polyelectrolyte-neutral block copolymers with nanocolloids, revealing differences in stability, microstructure, and substrate adhesion.

Contribution

It provides new insights into the structural and adsorption properties of organic versus hybrid coacervate complexes, highlighting the role of nanoparticle clustering and critical association concentrations.

Findings

Cerium oxide complexes form nanoparticle clusters with dense cores.

Surfactant-based complexes exhibit a critical association concentration.

Adsorption stability differs: surfactant complexes desorb upon rinsing, hybrid complexes do not.

Abstract

We report the co-assembly and adsorption properties of coacervate complexes made from polyelectrolyte-neutral block copolymers and oppositely charged nanocolloids. The nanocolloids put under scrutiny were ionic surfactant micelles and highly charged 7 nm cerium oxide (CeO2) nanoparticles. Static and dynamic light scattering was used to investigate the microstructure and stability of the organic and hybrid complexes. The microstructure of the CeO2-based complexes was resolved using cryogenic transmission electronic microscopy (Cryo-TEM), and it revealed that the cores were clusters made from densely packed nanoparticles. In the concentration range of interest, c = 10-4 - 1 wt. %, the surfactant-based complexes were shown to exhibit a critical association concentration (cac) whereas the nanoparticle-polymer hybrids did not. The adsorption properties of the same complexes were investigated above the cac by stagnation point adsorption reflectometry. The adsorbed amount was measured as a function of time for polymers and complexes using anionically charged silica and hydrophobic poly(styrene) substrates. It was found that all complexes adsorbed readily on both types of substrates up to a level of 1 - 2 mg m-2 at stationary state. Upon rinsing however, the adsorbed layer was removed for the surfactant-based systems, but not for the cerium oxide clusters. As for the solution properties, these finding were interpreted in terms of a critical association concentrations which are very different for organic and hybrid complexes.