Pushing detectability and sensitivity for subtle force to new limits with shrinkable nanochannel structured aerogel

Abstract

There is an urgent need for developing electromechanical sensor with both ultralow detection limits and ultrahigh sensitivity to promote the progress of intelligent technology. Here we propose a strategy for fabricating a soft polysiloxane crosslinked MXene aerogel with multilevel nanochannels inside its cellular walls for ultrasensitive pressure detection. The easily shrinkable nanochannels and optimized material synergism endow the piezoresistive aerogel with an ultralow Young’s modulus (140 Pa), numerous variable conductive pathways, and mechanical robustness. This aerogel can detect extremely subtle pressure signals of 0.0063 Pa, deliver a high pressure sensitivity over 1900 kPa−1, and exhibit extraordinarily sensing robustness. These sensing properties make the MXene aerogel feasible for monitoring ultra-weak force signals arising from a human’s deep-lying internal jugular venous pulses in a non-invasive manner, detecting the dynamic impacts associated with the landing and take-off of a mosquito, and performing static pressure mapping of a hair.

Morphological Engineering of Sensing Materials for Flexible Pressure Sensors and Artificial Intelligence Applications

“…Commonly used sensing materials for piezoresistive sensors are conductive carbon material (e.g., carbon nanotubes (CNTs) [ 50 , 131 ], graphene [ 132 ], MXene [ 62 ], carbon black (CB) [ 133 ], carbonized silk [ 134 ] carbonized wood [ 61 ], and carbonized crepe paper [ 110 ]), conductive polymer (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) [ 37 ], polypyrrole (PPy) [ 82 ], polyaniline (PANI) [ 111 ]), metal nanowire (NW) [ 135 – 138 ], nanoparticle (NP) [ 139 ] and film [ 140 ] (e.g., AuNW [ 136 , 138 ], Ag NW [ 141 ], Cu NW [ 142 ], Pd NPs [ 139 ], Pt film [ 140 ]), metal-oxide (Fe 2 O 3 [ 78 ], ZnO [ 74 ], SnO 2 [ 143 ], In 2 O 3 [ 143 ], NiO [ 143 ]), liquid metal [ 144 , 145 ], and metal–organic frameworks (MOFs) [ 146 ]. The internal microstructure of the sensing material [ 102 ] and the electrode [ 89 , 147 ] includes cracks [ 98 , 99 ], micro-rough structures [ 93 , 102 , 103 , 148 ], porous hierarchical structures [ 104 , 106 , 149 ], and multiscale hierarchical structures [ 74 , 82 , 107 – 110 ]. These structures improve the sensing performance by increasing the space of contact change and delaying contact saturation.…”

“…Some nanometer-scale pressure sensors utilizing band energy [ 94 , 196 ], variable layer spacing [ 95 – 97 ], and cracks [ 98 , 197 ] have been developed in recent years. And the commonly used microstructures include microroughness [ 93 , 102 , 103 ], porous hierarchical structure [ 32 , 34 , 37 , 61 , 104 – 106 ], and multiscale hierarchical structure [ 25 , 63 , 74 , 82 , 107 – 110 ]. In the following, we will discuss pressure sensors focused on these microstructures in detail.…”

“…Micrometer-scale pressure sensors are the most commonly used microstructure of pressure sensors for both electrode [ 89 , 90 , 93 , 147 ] and active layer [ 25 , 48 , 62 , 75 , 88 ]. Major structures include microrough structures [ 93 , 102 , 103 ], porous structures [ 32 , 34 , 37 , 61 , 104 – 106 ], and multiscale hierarchical structures [ 25 , 50 , 63 , 74 , 82 , 107 – 110 ]. These are discussed in detail below.…”

“…Considerable part of porous structure is actually kind of hierarchical structures and the pore usually has various multiscale structures. In addition, some pore wall of porous structure is also composed of active materials with microstructure, such as small pore structure [ 61 ], interlayer structure [ 104 ], wrinkle morphology [ 211 ], and network structure [ 212 ], so we locate the classical porous structure part in the hierarchical structure section. Sensors with porous structure are suitable for the fabrication of flexible and portable electronic devices [ 126 ].…”

“…Therefore, various sensing materials with well-suited morphological microstructures have been investigated to achieve large conductive contact changes [ 61 , 86 , 87 ], effective stress concentration [ 74 ], and signal conduction [ 83 ] in the sensing layer [ 25 , 48 , 62 , 75 , 88 ] and electrode [ 66 , 89 – 93 ]. These microstructures commonly occur at the nanometer and micrometer scale, including variable energy bands [ 94 ], and tunable layer spacing [ 95 – 97 ], cracks [ 98 – 101 ], microroughness [ 93 , 102 , 103 ], porous hierarchical structure [ 32 , 34 , 37 , 61 , 104 – 106 ], and multiscale hierarchical structure [ 25 , 63 , 74 , 82 , 107 – 110 ]. The microstructure is fabricated using (attractive [ 111 – 113 ] or repulsive [ 26 , 114 ]) self-assembly, (lithography [ 115 ], patterning [ 116 ], polymerization [ 117 ]) patterning, and (mechanical force [ 66 ], electronic field [ 118 ], magnetic field [ 119 ], gas-bubbling processing [ 64 , 120 ], template confinement [ 121 ]) auxiliary manufacturing technologies.…”