Electric field-induced gradient strength in nanocomposite hydrogel through gradient crosslinking of clay.

In this paper, mechanically strong organic-inorganic nanocomposite (NC) gradient hydrogels were successfully prepared by the in situ polymerization of acrylamide (Am) and N,N-dimethyl aminoethyl methacrylate (DMAEMA) using an electrophoresis method. Due to its specific colloidal properties, LAPONITE® showed directional movement in direct-current (DC) electric field and thus formed a gradient distribution in the hydrogel. The concentration gradient of LAPONITE® was characterized by UV-vis absorption, FTIR and TGA. The network structures of lyophilized gradient hydrogels were observed from SEM images. The TEM morphology indicated that LAPONITE® had a good gradient dispersion in the NC gradient hydrogel. As a physical crosslinker, LAPONITE® can regulate the cross-linking density of the hydrogel, thus affecting its mechanical properties. The NC gradient hydrogel exhibited a high mechanical strength (a gradient tensile strength ranging from 43.4 to 135.3 kPa and a gradient compression strength ranging from 116 kPa to 1100 kPa, depending on the distance from the anode). This work provided a facile method to develop NC gradient hydrogels with improved mechanical performance. The NC gradient hydrogels can be used as potential candidates in the field of biological and chemical materials.