Ultra-high hydrophobicity on the surface of nanocomposite hydrogels with a poly(n-isopropylacrylamide)/clay network

Surface wettability is one of the most important properties of all materials, since it reflects the real structure and chemical composition at the outer-most surface, and is a decisive factor in many properties. As readily expected from their compositions, soft polymeric hydrogels, which consist largely of water and a hydrophilic polymer network, are naturally hydrophilic, and their surfaces generally show very low theta(w). Here, we report extraordinarily high hydrophobicity, i.e. abnormally high values of theta(w), (e.g. 120 degrees), observed at the cross-sectional surfaces of nanocomposite hydrogels (NC gels) consisting of poly(N-isopropylacrylamide) (PNIPA) / clay network. Also, characteristic surface properties such as the reversible change of theta(w) by altering the circumstances and their stability are discussed.