Structure and Dynamics of Hybrid Colloid–Polyelectrolyte Coacervates: Insights from Molecular Simulations

Abstract

Electrostatic interactions in polymeric systems are responsible for a wide range of liquid−liquid phase transitions that are of importance for biology and materials science. Such transitions are referred to as complex coacervation, and recent studies have sought to understand the underlying physics and chemistry. Most theoretical and simulation efforts to date have focused on oppositely charged linear polyelectrolytes, which adopt nearly ideal-coil conformations in the condensed phase. However, when one of the coacervate components is a globular protein, a better model of complexation should replace one of the species with a spherical charged particle or colloid. In this work, we perform coarse-grained simulations of colloid−polyelectrolyte coacervation using a spherical model for the colloid. Simulation results indicate that the electroneutral cell of the resulting (hybrid) coacervates consists of a polyelectrolyte layer adsorbed on the colloid. Power laws for the structure and the density of the condensed phase, which are extracted from simulations, are found to be consistent with the adsorption-based scaling theory of hybrid coacervation. The coacervates remain amorphous (disordered) at a moderate colloid charge, Q, while an intra-coacervate colloidal crystal is formed above a certain threshold, at Q > Q*. In the disordered coacervate, if Q is sufficiently low, colloids diffuse as neutral nonsticky nanoparticles in the semidilute polymer solution. For higher Q, adsorption is strong and colloids become effectively sticky. Our findings are relevant for the coacervation of polyelectrolytes with proteins, spherical micelles of ionic surfactants, and solid organic or inorganic nanoparticles.

Polyelectrolytes for Environmental, Agricultural, and Medical Applications

“…Moreover, the trends in formulation methods such as hydrogels, layer-by-layer assembly, nanoparticles, and microencapsulation were determined. On the other hand, the main keywords were determined based on their co-occurrence, where polyelectrolytes (150), layer-by-layer assembly (47), chitosan (46), full cells (43), and polyelectrolyte complexes (36) were the words most closely associated in the published research according to the data extracted from Scopus.…”

“…The interaction between the opposite charges of the functional groups in the polymer and the ions in the surrounding medium influences their three-dimensional structure. For example, in environments with a high concentration of ions, polyelectrolytes can adopt more extended configurations due to electrostatic repulsion [35,36].…”

Surface-Immobilized Interpolyelectrolyte Complexes Formed by Polyelectrolyte Brushes

“…In recent years, the renewed interest in interpolyelectrolyte complex (IPEC) coacervates has resulted in combined experimental, theoretical, and computational studies, which provided a deep and consistent description of the internal structure of these phases and the mechanisms underlying their formation. − These results provide a fundamental background for studying complexation in more complex systems. While important steps toward understanding scaling laws controlling micelles with complex coacervate cores − and “hybrid” coacervates formed from linear polyelectrolytes with charged nanoparticles , have already been made, complexation in polyelectrolyte brushes remains completely unexplored. The PE brushes serve as ultrathin coatings in the fabrication of smart interfaces with adhesive and tribological properties controlled by external stimuli. − We anticipate that, because of the planar geometry and lack of chains’ translational mobility, the IPE complexation in brushes should obey more complex regularities than in the bulk, and this work is aimed at deciphering them.…”