# Shape characteristics of the aggregates formed by amphiphilic stars in water: dissipative particle dynamics study

## TL;DR

This study uses dissipative particle dynamics simulations to analyze how the molecular architecture of amphiphilic star polymers influences the shape of water-formed aggregates, revealing shape phase boundaries and transition behaviors.

## Contribution

It provides new insights into the relationship between molecular architecture and aggregate shape in amphiphilic star polymers in water.

## Key findings

- Identified four aggregate shapes: spherical, rod-like, disc-like micelles, and vesicles.
- Mapped phase boundaries between different aggregate shapes.
- Observed sharp shape transitions and oscillations near phase boundaries.

## Abstract

We study the effect of the molecular architecture of amphiphilic star polymers on the shape of aggregates they form in water. Both solute and solvent are considered at a coarse-grained level by means of dissipative particle dynamics simulations. Four different molecular architectures are considered: the miktoarm star, two different diblock stars and a group of linear diblock copolymers, all of the same composition and molecular weight. Aggregation is started from a closely packed bunch of $N_{\text a}$ molecules immersed into water. In most cases, a single aggregate is observed as a result of equilibration, and its shape characteristics are studied depending on the aggregation number $N_{\text a}$. Four types of aggregate shape are observed: spherical, rod-like and disc-like micelle and a spherical vesicle. We estimate "phase boundaries" between these shapes depending on the molecular architecture. Sharp transitions between aspherical micelle and a vesicle are found in most cases. The pretransition region shows large amplitude oscillations of the shape characteristics with the oscillation frequency strongly dependent on the molecular architecture.