Study on novel exfoliated polyampholyte nanocomposite hydrogels based on acrylic monomers and Mg-Al-Cl layered double hydroxide: Synthesis and characterization

Abstract

Novel exfoliated polyampholyte nanocomposite hydrogels (NH-LDHs) based on acrylic acid (AA), 2(diethylamino) ethyl methacrylate (2-DEAEMA), N,N-methylenebisacrylamide (NMBA) and layered double hydroxide (Mg-Al-CI LDH) were synthesized using an in situ free radical addition polymerization method in aqueous media. First, Mg-Al-CI LDH with a highly crystalline structure was prepared and characterized using FTIR, XRD, TGA and SEM analyses. The formation of NH-LDHs was confirmed by FTIR and XRD analyses. The morphological structure and select properties, such as the thermal, swelling and mechanical properties, of the NH-LDHs were also investigated. NH-LDHs have an exfoliated structure and smooth and nonporous surface morphologies. They can also be used as thermally stable nanocomposite hydrogels. The results revealed that adding a small amount of exfoliated Mg-Al-CI LDH could effectively increase the compressive modulus of the polyampholyte gels. When the Mg-Al-CILDH was incorporated into the polyampholyte hydrogel matrix, two synergic effects, additional co-crosslinking and additional hydrophilicity, occur in the swelling behaviors of the gels. All NH-LDHs are sensitive to pH, and they have zwitterion characteristics at pH 5.5. It was concluded that the NH-LDHs synthesized in this study might be used as alternative water absorbents in solutions with different pH. The diffusion of water into the NH-LDHs gel systems in deionized water at room temperature is assumed to be a non-Fickian behavior. (C) 2013 Elsevier B.V. All rights reserved.