Thermoresponsive hollow polymeric shell nano/microparticles with interconnected nanoholes

PNIPAAm-grafted thermoresponsive hollow nano-holed polymeric-shell (HHPS) particles were fabricated from surface-modified colloidal silica (CS) with poly(ethylene glycol) methyl ether-3-(triethoxysilyl)propyl isocyanate (PEGME-IPTES) and 3-(trimethoxysilyl) propyl methacrylate (MPS) as templates. The polymeric shells were then synthesized through a "grafting-through" approach via surface-initiated polymerization of N-isopropyl acrylamide (PNIPAAm) using potassium persulfate (KPS) as an initiator, followed by the etching of CS with hydrofluoric acid to remove the CS core templates. CS nanoparticles and PEGME-IPTES were presynthesized using tetraethoxysilane (TEOS) and distilled water in methanol with ammonia solution as a catalyst by the sol-gel method and using 3-(triethoxysilyl) propyl isocyanate (IPTES) with poly(ethylene glycol) methyl ether (PEGME) in the presence of dibutyltin dilaurate. The chemical structures of bare and modified CS, PNIPAAm, PNIPAAm-CS, and HHPS particles were characterized by FT-IR and NMR spectroscopies. SEM and TEM images confirmed that the resulting HHPS particles had a significant number of interconnected nanoholes. To evaluate the LCST behaviors of HHPS particles, the transition of transmittance and the changes in particle diameter according to the temperature change were measured through UV-vis spectroscopy, DLS, and microscopy.