Improved Sensitivity of Flexible Conductive Composites Throughout the Working Strain Range Based on Bioinspired Strain Redistribution

Abstract

Elastomer conductive composites (ECCs) are wonderful candidates for stretchable strain sensors. However, the sensitivity of ECC-based flexible strain sensors is limited in low-strain range, the main working range for human movements, due to the insignificant geometric change of the sample shape and weak tunneling effect of the conductive network. Herein, bioinspired heterogeneous thermoplastic polyurethane (TPU)/carbon black (CB) composites (TCs) are assembled by hot pressing two TCs with different Young’s moduli in series. The modulus of the TCs is controlled by the CB content, Young’s modulus of TPU, and plasticizer content. Experimental results and finite element analysis (FEA) confirm that the low Young’s modulus component undergoes higher strain compared with the high Young’s modulus component, resulting in a more serious change of the conductive network and higher gauge factor (GF) values. Compared with homogeneous TCs, the GF of heterogeneous TCs was improved by a factor of 20.7 and 9.6 in the low-strain (0–6%) and high-strain range, respectively. The relationship between modulus variety and GF is quantitatively described, and the GF values depend on the Young’s modulus of the individual components. Constructing a heterogeneous structure with different Young’s moduli is a valuable and facile way to increase the sensitivity of ECC-based flexible strain sensors.

Boosted mechanosensitivity of stretchable conductive composite strain sensors based on kirigami cut design

“…To address this critical issue related to the limited sensitivity of conventional CEC-based strain sensors, many attempts have been carried out to optimize the CEC sensory layers morphologically or structurally. [13][14][15][16][17][18]20,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] Mechanosensitivity of the CEC-based strain sensor could be easily modulated by controlling density of the conductive network in the sensory composite. [13][14][15]25,27,28 Particularly, sensor with a lower network density exhibited enhanced sensitivity, while correspondingly resulting in limited stretchability (i.e., workable strain range).…”

“…Meanwhile, the CEC sensory films have been structurally modified by introducing pores 34,35 or surface structures 36,37 into the composite upon stretching, to induce large deformations locally in specific regions of the conductive network within the composite. This led to rapid increase in the resistance (i.e., high sensitivity) of the sensor under strain, compared to that of the pristine composite.…”