Dual thermo-responsive and ion-recognizable monodisperse microspheres

A novel type of dual stimuli-responsive microspheres that simultaneously exhibit ion-recognition property based on the supramolecular host-guest complexation of crown ether receptors (benzo-18-crown-6-acrylamide) (BCAm) with specific ions and thermo-sensitivity based on the phase transition of poly(N-isopropylacrylamide) (PNIPAM) is fabricated in this study. The prepared poly(N-isopropylacrylamide-co-benzo-18-crown-6-acrylamide) (P(NIPAM-co-BCAm)) microspheres are characterized by FT-IR spectroscopy, UV-vis absorption spectroscopy, scanning electron microscopy (SEM), and dynamic light scattering (DLS). SEM images and DLS data show that the synthesized microspheres exhibit nearly perfect spherical shape and high monodispersity. Moreover, according to the DLS results, P(NIPAM-co-BCAm) microspheres exhibit satisfactory thermo-responsive behavior and ion-recognition property. In K+ solutions, due to the formation of crown ether/K+ complexes, the LCST of P(NIPAM-co-BCAm) microspheres shifts to a higher temperature and the colloidal stability is increased. The P(NIPAM-co-BCAm) microspheres undergo a volume change from shrunken state to swollen network isothermally at a certain temperature by the addition of metal ions. Due to dual thermo-responsive and ion-recognition behaviors, this kind of microspheres would serve as promising candidates for sensors, controlled drug delivery systems and possibly new biomaterials.