Bioinspired Gradient Poly(ionic liquid) Ionogels for Ionic Skins with an Ultrawide Pressure Detection Range

Abstract

Recently, with the increasing demand for artificial skins and human bodily motion/physical signals monitoring, flexible pressure sensors with a wide detection range are urgently needed. Transparent and stretchable gels with ionic conductivities are considered to be ideal candidates for flexible pressure sensors. However, the gel-based pressure sensors usually show a relatively narrow detection range, which significantly limits their practical applications. Herein, we report an unprecedented bioinspired highly flexible modulus/conductivity-dual-gradient poly(ionic liquid) (PIL) ionogel, which is achieved by constructing three layers of PIL ionogels with different monomer concentrations via a layer-by-layer gelation method. The flexible pressure sensor based on the gradient PIL ionogel exhibits an ultrabroad detection range of 10 Pa−1 MPa. This wearable pressure sensor is highly stable in environments and able to monitor both the tiny pressures as low as 10−100 Pa and the high pressures up to 0.1−1 MPa during human body movements. This work provides a powerful strategy for the preparation of flexible gradient materials that are promising for wearable electronics with a wide pressure detection range.

Ionic Flexible Mechanical Sensors: Mechanisms, Structural Engineering, Applications, and Challenges

“…Reproduced with permission. [149] Copyright 2022, American Chemical Society. network structure, biocompatibility, and high ionic conductivity make them good candidates for IFMS devices.…”

“…[23] In 2014, Suo's group developed a new sensory sheet based on ionic conductors, and named it "ionic skin" for the first time. [22] Subsequently, ion transport layers using ions as signal carriers, including ionic liquids, [24][25][26][27] electrolyte solution-nanofluidic membranes, [28][29][30] ionic gels, [19,[31][32][33] polyionic liquids, [34][35][36] and hydrogels, [37][38][39] are widely used in the development of IFMS.…”

An ultra-tough and ultra-sensitive ionogel pressure/temperature sensor enabled by hierarchical design of both materials and devices

“…Inspired by this, man-made hierarchical materials and devices have been extensively developed in the past decades. 28 It has been well demonstrated that the elegant incorporation of orthogonal dynamic bonds with different bond strengths and bond dynamics into a single network can greatly improve the mechanical properties while maintaining the reversible properties of polymers. 29,30 Moreover, delicate design of the microstructures and interfaces across multiple levels of hierarchy has been demonstrated to be effective to improve the comprehensive performances of exible sensors.…”

Anisotropic Hydrogels with Multiscale Hierarchy Based on Ionic Conductivity for Flexible Sensors

“…However, most traditional conductive hydrogels have simple structures and poor mechanical properties. So there are many efforts between the structure designs and hydrogel properties, such as single-network hydrogels, , double-network hydrogels, , and cross-linking hydrogels. , Many attempts have been made in the conductivity of hydrogels, such as introducing conductive polymers, ions, ionic liquids, and nanoconductive fillers (graphene, MXenes, and carbon nanotubes). − …”

“…So there are many efforts between the structure designs and hydrogel properties, such as single-network hydrogels, 10,11 double-network hydrogels, 12,13 and cross-linking hydrogels. 14,15 Many attempts have been made in the conductivity of hydrogels, such as introducing conductive polymers, 16 ions, 17 ionic liquids, 18 and nanoconductive fillers (graphene, MXenes, and carbon nanotubes). 19−21 Despite this, conductive hydrogels' structure, properties, and biocompatibility are certainly different from human tissues and muscles.…”