Homogeneous hydrogels made with acrylic acid, acrylamide and chemically functionalized carbon nanotubes

Carbon nanotubes (CNTs) chemically functionalized were used to synthesize a series of novel nanocomposite hydrogels by in situ polymerization with acrylic acid (AA) and acrylamide (AM). A novel strategy was developed to prepare these hydrogels. CNTs were functionalized following a three-step chemical procedure: (i) purified carbon nanotubes (CNTsp) were partially surface oxidized to obtain CNTs with hydroxyl, carbonyl and carboxyl groups on their sidewalls (CNTsoxi), (ii) CNTsoxi were reacted with oxalyl chloride to obtain CNTs functionalized with acyl chloride groups (CNTsOCl), and (iii) CNTsOCl were reacted with acrylic acid (AA). The product, AA modified CNTsOCl (CNTsOCl-AA) was used to prepare the (CNTsOCl-AA-AM) nanocomposite hydrogels, where anhydride groups were tethered to the surface of the CNTsOCl-AA. The swelling process in water was evaluated as a consequence of the anhydride group hydrolysis, which broke some chemical links between CNTsOCl-AA and crosslinked AA-AM network. Equilibrium-swelling values of all hydrogels increased as the content of AA increased and were larger for AA-AM hydrogels than for CNTsOCl-AA-AM nanocomposite hydrogels. Young's moduli of CNTsOCl-AA-AM nanocomposite hydrogels prepared with 1 or 2 wt.% AA, reached larger values than those measured for AA-AM hydrogels. This tendency was reversed when the AA content was raised to 3 wt.%.