Evaluation of temperature responsive swelling of (inorganic nanofiber/poly(N-isopropylacrylamide)) hybrid hydrogel

Imogolite is a natural tubular aluminosilicate with an outer diameter of 2.5 nm and length of several micrometers. Al-OH groups at the outer surface of imogolite interact specifically with phophoryl group. The hybrid hydrogel composed of imogolite and poly(N-isopropylacrylamide-co-phosphorylated 2-hydroxyethyl methacrylate) (poly(NIPAAm-co-p-HEMA)) was prepared by free radical copolymerization of NIPAAm and p-HEMA, which is vinyl monomer with phosphoryl group, in the presence of imogolite. The temperature-dependent light transmittance confirmed that the lower critical solution temperature (LCST) of hybrid hydrogel was 33°C, which is nearly consistent with LCST of conventional PNTPAAm hydrogel. Furthermore, the hybrid hydrogel showed high swelling ratio and improved swelling behavior compared with PNIPAAm hydrogel due to the presence of imogolite and p-HEMA, which have hydrophilic groups.