Stretchable kirigami-inspired conductive polymers for strain sensors applications

Kirigami metamaterials can be exploited in stretchable electronics owing to their architecture, which can be leveraged to amplify stretchability, bendability and deformability. Herein, we report a stretchable kirigami-structured poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/polydimethylsiloxane (PDMS) polymer composite. The electromechanical response and mechanical behavior of kirigami PEDOT:PSS-coated PDMS and polymer composite specimens were investigated and compared with their non-kirigami counterparts. The kirigami structure exhibited improved electromechanical properties owing to its characteristic architecture. This study illustrates the application of a kirigami polymer composite as a strain sensor for human motion detection.

A multi-axial mechanical tester (Mach-1 model v500csst, Biomomentum, Canada) was used to characterize the mechanical properties of the specimens (dimensions:45 mm × 15 mm and 1 mm thickness). The applied force was measured during the tests using a 70 N load cell. The mechanical tests were performed according to ASTM D882. The Young’s modulus (E) of each specimen was obtained from the slope of the force-displacement curve in the elastic region along the loading path. The elongation at break of the specimens was calculated to determine their stretchability. The equations used to calculate Young’s modulus and elongation at break are provided in the supplementary data. Each test was repeated three times to calculate the average values and standard deviations of the Young’s modulus and elongation at break.

The viscoelastic behavior of the samples was studied using cyclic and dynamic mechanical tests at room temperature. Cyclic tests were performed by applying pre-strain values (25%, 35%, 45%, and 55%) at a constant axial strain rate of 1 mm s-1. In addition, cyclic loading/unloading tests were conducted at 25% strain for 500 cycles, which is sufficiently high to stabilize the specimen response. At a 25% strain, the kirigami specimens opened entirely. The dynamic tests were performed by applying an axially sinusoidal strain on the samples at a frequency of 0.5 Hz, a speed rate of 1 mm s-1 at room temperature.

The electromechanical properties were measured using a customized uniaxial translational manipulator coupled with an electrical source measure unit (Agilent B2902A) in constant voltage mode. The electromechanical responses of the samples subjected to the given strains were recorded until they broke. The electrical durability of the non-kirigami and kirigami specimens was investigated under 1000 and 5000 loading/unloading cycles, respectively, at 25% strain. The lower number of cycles for the non-kirigami specimens was due to sample damage.