Thermosensitive poly(N-isopropylacrylamide)-clay nanocomposites with enhanced temperature response

This paper reports a thermosensitive polymer-clay nanocomposite with enhanced temperature response based on organically modified clay-poly(N-isopropylacrylamide) (PNIPAAm) nanocomposites. Compared with previously reported polymer-clay nanocomposites, the interfacial chemistry between the clay minerals and the polymer in the new nanocomposite is modified through a coupling agent to favor a more efficient thermal transition. This material exhibits an unusually large thermal volumetric change and faster transition kinetics as compared to conventional PNIPAAm gels. These results are contrary to what has been observed in a PNIPAAm-clay nanocomposite, in which the polymer molecules interact directly with the hydrophilic silicate clays. X-ray diffraction and transmission electron microscopy suggest that the clay minerals in the nanocomposite are partially intercalated and partially exfoliated in the dried state and mostly exfoliated in the swollen state. The enhanced thermal response and increased release rate are desirable for a range of applications, including sensors, actuators, regulators, and controlled release devices. The different results obtained in different nanocomposites point to a new approach to finely tune the thermal transition by controlling the interfacial interactions between the polymers and the nanophase materials.