Functional Microcapsules with Ion-Recognizable Properties

In this chapter, the design, fabrication, and performance of the ion-recognizable functional microcapsules with crown ether as ion-recognition receptor and poly(N-isopropylacrylamide) (PNIPAM) as actuator are introduced. The microcapsules with different capsule structures and/or different crown ether receptors are developed for different purposes. For the porous microcapsule with ion-recognizable smart gates using 18-crown-6 as the ion receptor, the functional gates in the pores can close by recognizing Ba2+. For the microcapsule with ion-recognizable cross-linked hydrogel membrane using 15-crown-5 as the ion receptor, the microcapsule shrinks isothermally by recognizing K+. For the microcapsule with ion-recognizable cross-linked hydrogel membrane using 18-crown-6 as the ion receptor, the microcapsule swells isothermally by recognizing Ba2+ or Pb2+. These ion-recognizable microcapsules provide new modes for smart controlled-release systems, which are highly attractive for drug delivery systems, chemical carriers, sensors, and so on.