Preparation of Chitosan Based Polymer Microgels, Their Composites with Zinc Oxide Nanoparticles, and Physicochemical Investigation

The combination of inorganic nanoparticles and organic microgels can lead to the formation of novel hybrid materials with multifunctional properties; such hybrid materials reflect the properties of all of its individual components and may show synergetic effects due to the interaction between inorganic nanoparticles and microgels. Applying this concept, a new type of (zinc oxide)-poly(N-isopropylacrylamide)-(chitosan)-poly(acrylic acid), abbreviated as ZnO-(PNIPAAm-CS-PAA), hybrid polymer microgels were fabricated, characterized, and its physicochemical properties were studied. In the first step, the polymeric gel (PNIPAAm-CS-PAA) and ZnO particles were prepared separately. Polymer microgels were synthesized from N-isopropylacrylamide (NIPAM), chitosan (CS), acrylic acid (AA), and N,N '-methylene bisacrylamide (MBAm) using the free radical emulsion polymerization method. Likewise, the ZnO NPs were prepared using zinc acetate dihydrate in alcoholic medium and then centrifuged. Then, ZnO-(PNIPAAm-CS-PAA) hybrid material was prepared and purified. The hybrid materials as well as their individual components were characterized by Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy, scanning electron microscopy (SEM), dynamic light scattering (DLS) and thermogravimetric analysis (TGA). Presence of the absorption bands characteristic to ZnO particles in the hybrid gel samples was confirmed by both FTIR and UV-Vis spectroscopy. Similarly, differences in the surface morphology, changes in hydrodynamic diameter (D-h) of gels particles as well as in the D-h-temperature and TGA profiles of individual components compared to those of the hybrid samples provided a good proof of successful fabrication of PNIPAAm-CS-PAA microgels with nanostructured ZnO. In addition to the fundamental characterization, an overall physicochemical behavior of both pure and hybrid colloids was found to be dependent on the temperature and pH of the solution. Hence, it can be concluded that the hybrid microgel possess the combined features of incorporated components with improved stimuli-sensitive properties.