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

## TL;DR

This paper studies how charged polymers interact in solution, showing how their mixtures can change shape and phase, which is important for designing soft materials.

## Contribution

The study introduces a new model to explore how oppositely charged polymers affect each other's structure and phase behavior.

## Key findings

- Adding linear polyelectrolytes can shrink or expand star-shaped polyelectrolytes depending on concentration and length.
- Long linear polyelectrolytes cause clustering and phase separation, leading to a glass-to-coacervate transition.
- Rheological experiments confirm simulations showing viscosity changes and phase separation.

## Abstract

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.