Fabrication of Thermoresponsive Cross-Linked Poly(N-isopropylacrylamide) Nanocapsules and Silver Nanoparticle-Embedded Hybrid Capsules with Controlled Shell Thickness

Hollow polymeric nanocapsules have attracted great interest in recent years due to their broad applications in controlledrelease carriers, catalysis, nanoreactors, and encapsulation of guest molecules. Polymeric nanocapsules have been typically fabricated via the selfassembly of block copolymers, 5 polymerization within lipid vesicles, emulsion polymerization, 14 and the sacrificial core-template approach. 32 The latter can provide extra advantages such as ease of fabrication and tunable sizes of the hollow void. The sacrificial core-template approach typically involves the covalent or noncovalent attachment of polymer shells onto the surface of inorganic or organic core templates, followed by the subsequent core etching step. Core templates can be coated with polymer shells via layer-bylayer (LBL) adsorption or surface polymerization techniques. In the latter case, precipitation polymerization in the presence of core templates were commonly employed for the preparation of hollow polymeric nanocapsules. 21,24,27,29,33 35 However, the accurate control over shell thickness of hollow nanostructures is difficult as the free radical polymerization process can not be solely restricted at the surface of core templates. Developments in the field of controlled radical polymerization (CRP) in the past 20 years have rendered surfaceinitiated CRP as an indispensible approach for the fabrication of hybrid nanoparticles coated with polymer brushes of uniform thickness and predetermined chemical structures, 39 which in turn has allowed for the facile preparation of uniform polymeric nanocapsules with controlled shell thickness. In a typical