Hydrogels are considered as an ideal material for bioelectronic devices to fulfill the requirements of various applications. However, integrating self-adhesion properties, high stretchability, good sensing performance, and direction-aware functionality into a single hydrogel strain sensor remains a significant challenge and has been seldom reported. In this study, through the characteristics of montmorillonite (MMT) adsorption, we designed a gradient intersecting strategy based on bifunctional MMT nanoparticles. These nanoparticles act as both cross-linking agents and conductive components to strongly intersect the hydrogel and the conductive networks, preventing them from sliding against each other. Thus, the hydrogel sensor had a wide range of adjustable mechanical properties and good adhesion on various substrates. Moreover, the hydrogel sensor can detect both large- and small-scale human activities and achieves direction awareness. Importantly, the hydrogel sensor can be used to construct a wireless sensor system to monitor human movement in real time. This work provides a strategy for the design of the next-generation flexible strain sensors and a method for the development of multifunctional MMT materials, expanding the application of both MMT materials and hydrogel sensors.
Jian Liu,Weizhong Xu,Zhongwen Kuang,Pengli Dong,Youxing Yao,Huaping Wu,Aiping Liu,Fangmin Ye
Smart hydrogels play a vital role in fundamental research and industrial applications in the fields of biosensors, flexible devices and intelligent human–machine technologies; however, developing a simple, low-cost and large-scale method to obtain hydrogel actuators with rapid response and robust and steadily controllable motion remains a big challenge. In this work, a temperature-responsive, gradient structured hydrogel with quick bending and adjustable actuation was fabricated by the copolymerization of the N-isopropylacrylamide (NIPAM) monomer with dispersed montmorillonite (MMT) via a facile precipitation method. The introduction of MMT with good thermal conductivity made the volume phase transition of the PNIPAM-based hydrogel occur earlier, and the deformation degree and bending direction could be adjusted by changing the MMT content. The representative composite hydrogel with 0.2 g MMT in the precursor presented bidirectional bending characteristics with a bending amplitude of about 289° and an average bending speed of about 36.0° s−1, while the composite hydrogel with 0.3 g MMT in the precursor only possessed a unidirectional bending ability with a bending amplitude of about −259° and a bending velocity of about −28.8° s−1 due to the great difference in the shrinking capacity between the top and bottom sides of the composite hydrogel. In addition, flexibly controllable deformation was specially realized by a well-designed patterned hydrogel with a local component and a thickness difference. Our work provides a practical method for the ingenious design of a hydrogel for further development of programmable and versatile hydrogel-based smart actuators and soft robots.
Bao Guo,Xinlei Zhan,Kaixi Jiang,Hongzhen Xie,Rongdong Deng
Sedimentation of ultrafine silica particles that exist in acid leaching pulp and their separation from Pregnant Leach Solution largely determines the efficiency of a hydrometallurgical process utilizing copper oxide ore. Thickener on a larger scale can allow longer sedimentation, generating low overflow turbidity but high economic input. In this paper, the flocculation behavior of quartz particles in sulfuric acid solution using nonionic flocculants polyethylene oxide (PEO) and polyacrylamide (PAM), as well as ionic cofactor montmorillonite (MMT) and nonionic cofactor tannic acid (TA), were investigated, with the dynamic size of flocs and counts of fines being monitored using an in situ particle size measurement technique, namely the focused beam reflectance measurement (FBRM), under turbulent conditions. Attention was paid to variables affecting quartz flocculation properties from both physicochemical and hydrodynamic aspects such as shear intensity. The flocculation mechanism was investigated using zeta potential and dynamic light scattering measurements. It was found that the TA promotes the bridging flocculation of PEO-quartz by forming associative complexes with larger clusters in solution, while MMT electrostatically adsorbs on the quartz surface, enhancing its bridging with PAM. Low turbidity benefited from the higher shear resistance of the compact flocs structure provided by PEO/PEO + TA/PAM + MMT. Efficient solid–liquid separation was achieved by using the synergistic flocculation of small molecule cofactors and polymer flocculants.Keywords:acid leaching;thickening;quartz;flocculation
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