# A Versatile Route to Shape Polymer Nanoparticles by Deforming Nanoreactors Made from Magnetic Surfactants

## TL;DR

A new method uses magnetic surfactants and a magnetic field to create rod-shaped polymer nanoparticles, which are usually spherical, offering a sustainable and versatile approach.

## Contribution

A novel, nontoxic, and sustainable method to produce rod-shaped polymer nanoparticles using magnetic surfactants and a magnetic field.

## Key findings

- Applying a weak magnetic field to magnetic surfactants during emulsion polymerization creates rod-like polymer nanoparticles.
- The method works for various polymers, including polystyrene, polymethylmethacrylate, and polythiophene.
- The magnetic surfactant can be recovered and reused, making the process sustainable.

## Abstract

Directions are equivalent in an amorphous system, so anisotropy cannot emerge of its own accord, resulting in a gap for preparing polymer nanoparticles deviating from a spherical shape. Unlike inorganic nanocrystals for which faceting controls shape, polymers are not directly available as rod‐like particles, for instance. Here, we show a highly versatile, nontoxic, novel approach to break this paradigm and obtain polymer nanorods by emulsion polymerization using a unique surfactant comprising a magnetic head group. Surprisingly, even applying a weak magnetic field to the magnetic surfactant within an emulsion polymerization transforms diamagnetic polymers into rod‐like nanoparticles instead of their usual spherical shapes. The polarization in a magnetic field exerts a torque on the molecular structure, and as a result, the emulsion droplets deform. The method can be applied to different polymers such as polystyrene, polymethylmethacrylate, or polythiophene. The magnetic surfactant is recovered quantitatively and can be reused; one obtains metal‐free polymer particles, and the process is sustainable. The straightforward approach presented here will unlock several applications of these previously inaccessible polymer nanorods, particularly in the case of conducting polymers.

Shaping up! Polymer nanoparticles are typically spherical, constrained by their structures. Now, a unique magnetic surfactant enables rod‐shaped polymer nanoparticles. Through emulsion polymerization and a magnetic field, the surfactant elongates nanoreactor droplets. Nanorods of polystyrene, polymethylmethacrylate, and polythiophene demonstrate versatility. This recyclable surfactant offers a sustainable path to polymer nanorods for many uses.