The anomalously fast growth of the silicon oxide layer at room temperature has been reported for the Cu/Si system. However, the systematical exploration of such a reaction under humidity conditions has not yet been carried out. Through one combination of the experiments and first-principle density functional theory (DFT) simulations, here, we investigate the influence of the imparted Cu atoms in Cu/Si on the oxidation of Si with the presence of H2O. The Cu addition causes the geometric distortion of the Si lattice, which alters the charge transfer to absorbed H2O and decreases its dissociation energy. This results in the experimental formation of much defective SiO x for the Cu/Si system than bare Si under humidity conditions. Furthermore, the presence of such an oxide structure and the catalytic effect of Cu provide the suitable diffusion channels and adsorption sites for the H2O transport and its dissociation. This enhances the oxidation rate of Si consequently and results in the fast growth of the oxide layer on Cu/Si at room temperature.

An operative and straightforward precipitation-driven approach was reported to fabricate an anisotropic hydrogel actuator with temperature response. Through in situ deposition of lignin nanoparticles in the process of polyacrylamide (PAM) polymerization with the presence of hydroxypropyl cellulose (HPC), an inhomogeneous hydrogel network (polyacrylamide/hydroxypropyl cellulose/lignin hydrogel, PHL hydrogel) with distinct gradient porous structure was achieved that could be tailored to form a hydrogel actuator. The PHL hydrogels exhibit faster shape deformation as responding to temperature and higher mechanical properties caused by introducing the lignin nanoparticles and HPC chains. The deformation direction and rate of the hydrogel actuator could be influenced by the lignin content, temperature, and as well as their shape. The maximum bending angle could reach near 360o with 60s as it was exposed to 60 oC. Due to the excellent bending behavior of the PHL hydrogel, the potential applications as grippers and valves were studied, and the results showed its sensitive response to temperature, suggesting its potential application as an intelligent actuator in the future.