A facile method for preparing an easy processing, repeatable and flexible pressure sensor was presented via the synthesis of modified multi-walled carbon nanotubes (m-MWNTs) and polyurethane (PU) films. The surface modification of multi-walled carbon nanotubes (MWNTs) simultaneously used a silane coupling agent (KH550) and sodium dodecyl benzene sulfonate (SDBS) to improve the dispersibility and compatibility of the MWNTs in a polymer matrix. The electrical property and piezoresistive behavior of the m-MWNT/PU composites were compared with raw multi-walled carbon nanotube (raw MWNT)/PU composites. Under linear uniaxial pressure, the m-MWNT/PU composite exhibited 4.282%kPa⁻¹ sensitivity within the pressure of 1 kPa. The nonlinear error, hysteresis error and repeatability error of the piezoresistivity of m-MWNT/PU decreased 9%, 16.72% and 54.95% relative to raw MWNT/PU respectively. Therefore, the piezoresistive response of m-MWNT/PU had better stability than that of raw MWNT/PU composites. The m-MWNT/PU sensors could be utilized in wearable devices for body movement detection, monitoring of respiration and pressure detection in garments.

Strain sensors based on silver nanowires (AgNWs) have attracted much attention due to their wide application of electronic skin, smart textiles, and health monitoring. In this work, we report a flexible strain sensor based on an Ecoflex flexible substrate. AgNWs and Multi-walled carbon nanotubes (MWCNTs) doped as a conductive material. The excellent ductility and elongation at break in Ecoflex, as well as excellent heat resistance and impact resistance, can increase the test range and increase the sensing range of the sensor. AgNWs-based sensors enhance the sensitivity of the sensor to 118.19 while improving linearity and stability and reducing hysteresis. In addition, strain sensors can be utilized to monitor body movements such as finger flexion, leg movements, and so on. In this work, smart gloves are used to monitor finger movements using flexible strain sensors, which show its great potential for wearable electronics applications.

A wearable, low-cost, highly repeatable piezoresistive sensor was fabricated by the synthesis of modified-graphite and polyurethane (PU) composites and polydimethylsiloxane (PDMS). Graphite sheets functionalized by using a silane coupling agent (KH550) were distributed in PU/N,N-dimethylformamide (DMF) solution, which were then molded to modified-graphite/PU (MG/PU) composite films. Experimental results show that with increasing modified-graphite content, the tensile strength of the MG/PU films first increased and then decreased, and the elongation at break of the composite films showed a decreasing trend. The electrical conductivity of the composite films can be influenced by filler modification and concentration, and the percolation threshold of MG/PU was 28.03 wt %. Under liner uniaxial compression, the 30 wt % MG/PU composite films exhibited 0.274 kPa⁻¹ piezoresistive sensitivity within the range of low pressure, and possessed better stability and hysteresis. The flexible MG/PU composite piezoresistive sensors have great potential for body motion, wearable devices for human healthcare, and garment pressure testing.

Ionic flexible force sensors based on materials of different ionic electrolyte layers and flexible electrodes and their applications.

In recent years, flexible sensors have been reported in numerous applications; however, they still face challenges such as single response to stimulus signals and low sensitivity. We report a flexible sensor based on structurally adjustable nano-through-hole array films that have high responses to pressure, temperature, and humidity. Polypyrrole/polyurethane single-walled carbon nanotube films with different sizes of nano-through-hole array films are prepared using anodic aluminum oxide templates, and the relationship between their pore diameter and pore depth and the three sensing properties is discussed in depth using finite element simulation and other methods. The experimental results show that the nano-through-hole array film with a pore diameter of 440 nm and a pore depth of 6.9 μm has a higher specific surface area and stress–strain response speed. The pressure sensitivity of the sensor reaches up to 102.99 kPa⁻¹ within 0.004–10 kPa; the temperature sensitivity reaches up to 0.72% °C⁻¹ within 20–80 °C; the humidity sensitivity reaches up to 3.51% RH⁻¹ within 20–80% RH; and the crosstalk between the three response signals is less than 5%. The sensor shows great potential in the application of human physiological signal monitoring.