A facile approach to prepare strong poly(acrylic acid)/LAPONITE® ionic nanocomposite hydrogels at high clay concentrations

A facile strategy was developed to prepare mechanically strong LAPONITE (R)-based ionic nanocomposite (NC) hydrogels at high clay concentrations. Based on the thixotropy of an acrylic acid (AA)/LAPONITE (R) dispersion, a series of ionic poly(acrylic acid) (PAA)/LAPONITE (R) NC hydrogels were successfully prepared without the addition of additional dispersing monomers. Fourier transform infrared (FTIR) spectroscopy and thermogravimetric (TG) analysis demonstrated the composition and thermostability of the NC hydrogels, respectively. The network of the hydrogels was examined by scanning electron microscopy (SEM), and the dispersion of LAPONITE (R) nanoplatelets in the ionic hydrogels was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The hydrogels exhibited viscoelastic solid-like properties, as revealed by dynamic mechanical analysis (DMA) within a linear viscoelasticity region, and demonstrated that the network structure was formed with the junction of the ionic AA monomer and the LAPONITE (R) platelets. The hydrogels showed improved mechanical properties (i.e. tensile strength: 308 kPa, elongation at break: 1110%), which were due to more effective cross-link points provided by the high content of LAPONITE (R) and the entanglements among the PAA chains. This approach is synthetically simple and dramatically increases the choice of strong hydrogels for applications.