High-strength and physical cross-linked nanocomposite hydrogel with clay nanotubes for strain sensor and dye adsorption application

A high-strength nanocomposite hydrogel composed with polyacrylamide (PAAm) is fabricated via in-situ free radical polymerization of acrylamide in presence of halloysite nanotubes (HNTs) and then by ethanol immersing. HNTs act as physical cross-linkers for PAAm chains via hydrogen bonding interactions, while ethanol makes the crosslinking network denser by release of water. The mechanical properties of hydrogels are significantly increased by addition of HNTs and ethanol treatment. The structure of the composite hydrogel was studied by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Interestingly, the composites hydrogels show good conductivity, which is attributed to the presence of the potassium ion in hydrogel network originated from initiator. Therefore, the composite hydrogels can be applied in strain sensor, which can monitor human activities such as bending and releasing the finger, elbow, knee as well as detecting walking pace with high sensitivity. Moreover, the freeze-dried gels show superior removal efficiency of methylene blue dye from water in short time. This work developed a simple, economical, and practical way to synthesize high-strength nanocomposite hydrogel using natural nanotubes, which shows promising applications in strain sensor and environmental restoration.