A novel synthesis of nanocapsules using identical polymer core/shell nanospheres

Abstract

Polymer nanocapsules were synthesized using core/shell nanospheres composed of an identical polymer. Linear polypyrrole (PPy)/crosslinked PPy core/shell nanospheres were synthesized stepwise by microemulsion polymerization using two oxidants with different chemical oxidation potentials, i.e. copper(II) chloride and iron(III) chloride. Coupled with the characteristics of the O/W microemulsion polymerization, the hydrophilic oxidants with different chemical oxidation potentials produced PPys with different solubility in alcohol. The linear PPy core and cationic surfactants could be removed by one-step solvent etching process simultaneously, and crosslinked PPy nanocapsules were obtained. The pore size and shell thickness of PPy nanocapsules were tunable by controlling the feeding amount of monomers in each synthetic step. The pore size of PPy nanocapsules was controllable from 19 to 33 nm by changing the monomer amount from 5.4 to 20.2 mmol in the first synthetic step. The shell thickness also increased gradually from 5.0 to 12.5 nm with increasing the feeding amount of monomers from 14.9 to 48.5 mmol in the second synthetic step. The average diameter of polymer nanocapsules could also be controllable by changing the surfactant concentration and surfactant spacer length. PPy nanocapsules had two mesopores, that is, the inner cavity and the mesochannel in the wall. In addition, PPy hollow nanospheres could be transformed into carbon nanocapsules through the carbonization process. The structural development of graphene layers in the carbon nanocapsule wall was investigated using XRD measurement, Raman spectroscopy, and HRTEM analysis. The ability to selectively encapsulate and release guest molecules was examined by introducing a photochromic dye (pyrene) solution into the polymer and carbon nanocapsules in a different environment.