Temperature-Directed Formation of Anisotropic Kettlebell and Tadpole Nanostructures in the Absence of a Swelling-Induced Solvent.

Anisotropic Janus ("snowman") nanoparticles with a single protrusion are currently made via the solvent swelling-induced method. Here, we demonstrate without the aid of toxic solvents a generally applicable method for the formation of anisotropic polymer nanoparticles directly in water by controlling polymer mobility through tuning its glass transition temperature (T ). Spherical structures, formed immediately after the emulsion polymerization, transformed into uniform tadpoles (with head diameter ≈60 nm and tail length ≈130 nm) through the protrusion of a single cylindrical tail when cooled to a temperature above the T of the polymer. Cooling the spheres to below the T produced kinetically trapped kettlebell structures that could be freeze-dried and rehydrated without any structural change. These unique kettlebells could transform into uniform tadpoles by heating above the T , representing a triggered and on-demand structural reorganization.