Stimuli-Responsive Nanocomposite Gels and Soft Nanocomposites Consisting of Inorganic Clays and Copolymers with Different Chemical Affinities

A novel series of nanocomposite hydrogels (MD-NC gels), consisting of inorganic clay (hectorite) and specific copolymers with different chemical affinities for water, i.e., copolymers composed of hydrophobic (2-methoxyethyl acrylate: MEA) and hydrophilic ( N,N -dimethylacrylamide: DMAA) units, were prepared by in situ free-radical polymerization in aqueous media at 20 °C. MD-NC gels showed outstanding stimuli sensitivities in response to changes in temperature, pH, salt concentration, and solvents in the surrounding aqueous solution as well as excellent, composition-dependent mechanical properties, such as a large elongations at break (≥1000%) and high strengths and moduli. After drying, the gels were changed into transparent, soft nanocomposites (MD-NCs) with high mechanical toughness and safety in in vitro cytotoxicity tests. The clay morphology in MD-NCs gradually changed on increasing the molar ratio of DMAA from a clay shell network of 20 nm thickness to a uniform dispersion of exfoliated clay platelets in a polymer matrix.