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

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.