Characterizing the Structural Conformation of Highly Charged Star-Linear Polyelectrolyte Mixtures in Solution

Long-range electrostatic interactions provide unique opportunities to tune the conformation and phase behavior of polymeric micelles and soft colloids in solution, but their effects remain understudied due to the higher synthesis, characterization, and simulation complexity. We recently showed that micelles with long, charged polymer arms exhibit unique softness and glassy behavior at varying concentrations due to long-range electrostatic interactions, and developed a molecular dynamics model to validate the experimental results. Here we further explore our new system, and we investigate mixtures of highly charged star polyelectrolytes (SPEs, mimicking spherical micelles) and oppositely charged linear polyelectrolytes (LPEs) using molecular dynamics simulations and rheological validation. SPE size and conformation are strongly affected by LPE addition, which introduces charge neutralization within the SPEs' bounding spheres, leading to shrinkage or expansion depending on the LPE length and concentration. Long LPEs form bridges between multiple SPEs, inducing clustering and promoting liquid-liquid phase separation at high charge ratios, triggering a glass-to-coacervate transition. Experimental rheology confirms that increasing the LPE initially decreases, then drastically increases viscosity, together with visual phase separation of the system, validating the simulation results. These findings highlight the interplay between electrostatic interactions, chain entropy, and packing effects, offering insights into how polyelectrolyte mixtures can be tuned for controlled complexation and phase behavior in soft materials design.