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Polymer hydrogels synthesized by chemical cross-linking of acrylate or acrylamide monomers can absorb more than 100 times their weight in water. However, such gels are usually fragile and rupture when stretched to moderate strains (∼50%). Many strategies have been developed to create tougher gels, including double-networking, incorporation of nanoparticles as cross-linkers, etc., but these strategies typically retard the water absorbency of the gel. Here, we present a new approach that gives rise to superabsorbent hydrogels having superior mechanical properties. The key to our approach is the self-cross-linking ability of N,N-dimethylacrylamide (DMAA). That is, we conduct a free-radical polymerization of DMAA (along with an ionic comonomer such as sodium acrylate) but without any multifunctional monomers. A hydrogel still forms due to interchain covalent bonds between the growing linear polymer chains. Gels formed by this route can be stretched up to 1350% strain in the unswollen state. The same gels are ...

A systematic electrical and rheological characterization of percolation in commercial polydisperse polystyrene (PS) nanocomposites containing multiwall carbon nanotubes (MWCNTs) is presented. The MWCNTs confer appreciable electrical conductivities (up to ca. 1 S/m) to these nanocomposites at a concentration of 8 vol %. In addition to enhancing the electrical properties, even at small concentrations (ca. 2 vol %), MWCNTs significantly enhance the rheological properties of PS melts. At concentrations exceeding 2 vol %, a plateau appears in the storage modulus G‘ at low frequencies, indicating the formation of a percolated MWCNT network that responds elastically over long timescales. Network formation, in turn, implies a diverging complex viscosity vs complex modulus curve. A focus of this study is on the correlation between electrical and rheological properties at the onset of percolation. The experimental results indicate that the elastic load transfer and electrical conductivity are far more sensitive to ...