Porous Polydimethylsiloxane–Silver Nanowire Devices for Wearable Pressure Sensors

Abstract

We demonstrate a simple, nonlithographic method for fabricating piezoresistive pressure sensors with a broad range of working pressures and low detection limit. Our wearable pressure sensor is fabricated by using two metallized, porous polymer layers which undergo a change in resistance as a function of pressure. This sensor has a sandwich structure composed of top and bottom sheets of porous polydimethylsiloxane (PDMS) fabricated by using a simple templating method. The inner face of each of these layers is coated with a layer of conductive silver nanowires (AgNWs). The AgNW layers are initially in light contact, and the device undergoes a change in resistance when pressure is applied perpendicular to the plane of the sheets. In these devices, the size of the pores is an important determinant of the device sensitivity and range. Powder templates of KCl, NaCl, and sugar are used to create different sized pores (60–90, 200–275, and 400–550 μm, respectively) in the elastomeric PDMS layers, which in turn affects the mechanical deformability of the devices. The sensors fabricated with KCl porous layers (which had the smallest pores) demonstrate the best performance, with a sensitivity of 14.1 kPa–1 (up to 3.5 kPa), 4.8 kPa–1 (up to 10 kPa), and 1.84 kPa–1 (up to 40 kPa) and good stability over 1000 loading and unloading cycles. Pressure sensors are also fabricated by decreasing the ratio of PDMS base to curing agent from the standard 10:1 formulation, which increases the stiffness of the viscoelastic PDMS layer and thus shortens the response time. The stiffest formulation (5:1 (base:curing agent)) sample gives the shortest response time of ∼47 ms. Wearable electronic applications of these devices, including pulse measurement, facial movements, and sound tracking, are demonstrated in this work.

Flexible and Stretchable Temperature Sensors Fabricated Using Solution‐Processable Conductive Polymer Composites

“…[1][2][3] Accurate measurement of localized temperature on biological tissues-even while undergoing resistance, capacitance) upon exposure to the stimulus of interest. [24][25][26][27][28] In these composites systems, conducting nanoparticles (e.g., carbon-based materials or metal particles) impart electrical conductivity to the composite, while the polymer matrix (which is typically insulating) provides mechanical stability. [29][30][31] At low concentration the composite may be non-conductive, however when the loading of nanomaterials is increased beyond a certain threshold the resistance may drop abruptly.…”

Wearable Sensors for Monitoring Human Motion: A Review on Mechanisms, Materials, and Challenges

“…Another sandwich structure of the AgNW-coated porous PDMS structure was also recently reported with a broad range of working pressure and the capability of adjusting the sensitivity by changing the pore size. 51…”

Recent Advances on Nanocomposite Resists With Design Functionality for Lithographic Microfabrication

“…In addition, conductive networks based on metallic NWs may function as heating elements, dissipating heat via Joule effect (Huang et al, 2015;Martínez et al, 2018a;Martínez et al, 2018b). Also, the high sensitivity of the resistivity to the percolation status of the NCPRs provides interesting possibilities in the development of strain gauge sensors (Lee et al, 2012;Kim et al, 2015;Martinez et al, 2015) and pressure sensors (Cho et al, 2017;Dan et al, 2019). Upon mechanical deformation, the structure of the percolating network is disrupted and a change in the electrical resistance is easily detected.…”