“Crocodile skin” ultra-tough, rapidly self-recoverable, anti-dry, anti-freezing, MoS2-based ionic organohydrogel as pressure sensors

Nanofiber Composite Reinforced Organohydrogels for Multifunctional and Wearable Electronics

Composite organohydrogels have been widely used in wearable electronics. However, it remains a great challenge to develop mechanically robust and multifunctional composite organohydrogels with good dispersion of nanofillers and strong interfacial interactions. Here, multifunctional nanofiber composite reinforced organohydrogels (NCROs) are prepared. The NCRO with a sandwich-like structure possesses excellent multi-level interfacial bonding. Simultaneously, the synergistic strengthening and toughening mechanism at three different length scales endow the NCRO with outstanding mechanical properties with a tensile strength (up to 7.38 ± 0.24 MPa), fracture strain (up to 941 ± 17%), toughness (up to 31.59 ± 1.53 MJ m-3) and fracture energy (up to 5.41 ± 0.63 kJ m-2). Moreover, the NCRO can be used for high performance electromagnetic interference shielding and strain sensing due to its high conductivity and excellent environmental tolerance such as anti-freezing performance. Remarkably, owing to the organohydrogel stabilized conductive network, the NCRO exhibits superior long-term sensing stability and durability compared to the nanofiber composite itself. This work provides new ideas for the design of high-strength, tough, stretchable, anti-freezing and conductive organohydrogels with potential applications in multifunctional and wearable electronics.

Anti-freezing, recoverable and transparent conductive hydrogels co-reinforced by ethylene glycol as flexible sensors for human motion monitoring

Wearable flexible sensors based on conductive hydrogels have received extensive attention in the fields of electronic skin and smart monitoring. However, conductive hydrogels contain a large amount of water, which greatly affects their performances in harsh environments. It is therefore necessary to prepare hydrogel sensors that are stable at low temperatures. Herein, metal ions (MgCl₂) and ethylene glycol (EG) were combined with polyvinyl alcohol (PVA) to obtain a conductive PVA/EG hydrogel with tensile strength and elongation at break of 1.1 MPa and 442.3 %, respectively, which could withstand >6000-fold its own weight. The binary solvent system composed of water and EG contributed to the excellent anti-freezing properties and long-term storage (>1 week), flexibility, and stability of the hydrogel even at -20 °C. The wearable PVA/EG hydrogel as a flexible sensor possessed desirable sensing performances with a competitive GF value of 0.725 and fatigue resistance (50 cycles) when used to monitor various human motions and physiological signals. Overall, this hydrogel sensor shows strong potential for application in the fields of human motion monitoring, written information sensing, and information encryption and transmission.

Sensitivity-enhanced optical pressure sensor based on MoS2

A sensitivity-enhanced optical pressure sensor based on molybdenum disulfide (MoS₂) is proposed. The sensing principle is that the pressure causes the deformation of the polydimethylsiloxane (PDMS) pressure structure above the MoS₂ film, leading to the change of the ambient refractive index, so that a measurable light propagation difference in the waveguide under the film is created to reflect the micro changes of the pressure. The pressure is finally numerically converted to the wavelength shift of the interference peak of the obtained spectrum. The process is simulated and analyzed using MoS₂ dielectric film, in contrast with that using graphene dielectric film. It turns out that under same conditions, the MoS₂ film has a more distinct modulation effect on light than that of the graphene film. Experiments using the real sensor prototype are carried out and the results show that the pressure measuring sensitivity is improved to 96.02 nm/kPa in the pressure range of 0-0.6 kPa, which is much higher than the typical optical pressure sensors. The proposed optical pressure sensor based on MoS₂ is of high potential to support ultra-sensitive pressure detection in many applications.