Complex coacervates, the rheologically manageable complex fluids that result from combination of aqueous polyanionic and polycationic solutions, have found use in applications from coatings and adhesives to hygiene and pharmaceuticals.  Complex coacervates can usually be described, at the continuum level, by thermodynamic phase diagrams where compositions along tie lines adhere to the mass balance of the lever arm rule.  In these phase diagrams, where added salt plays the role as temperature through its influence on polymer-polymer interactions, critical phenomena are reported and a single fluid phase occurs at the highest salt concentrations.  This coacervation behavior provides a sharp contrast to the kinetically-trapped and aggregated structures that are produced from the combination of electrostatically charged colloidal- or nano- particles and oppositely charged polymer.  We find, however, that engineering nanoparticles to present a brushy charged layer extending nanometers from the fluid-solid surface enables the production of a coacervate through complexation with oppositely charged polyelectrolyte. The charge proportions in the particle-based coacervates are similar to those of analogous classical polymer complex coacervates, as is the appearance of fluid-droplets signifying fluid-fluid phase equilibria.  The particle-based coacervates resemble classical coacervates in other measures such as macroscopic polymer content; however, important differences are observed.  These include a larger coacervation two-phase region. Further, estimates of the interstitial polymer distribution reveal a puzzle of how charged polymer can be arranged near an interface and still form a space filling complex with macroscopic properties similar to classical complex coacervates.  This talk highlights the similarities and differences between classical and particle-integrated complex coacervates.

Particle-integrated complex coacervates and the role of surface brushes

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.