An embedded printed flexible strain resistance sensor via micro-structure design on graphene-filled conductive silicon rubber

Abstract

Flexible sensors with multifunction are tremendously attractive with the assistance of materials design, novel manufacturing, as well as microstructure fabrication. In this study, graphene was efficiently dispersed in a solvent and filled into silicon rubber (SR), which was forward embedded-printed as a flexible strain resistance sensor (FSRS) with functional macrostructure and modified microstructure. Comprehensively considering the environmental protection of dispersion solvent and the cost of surfactants, a stable dispersion of graphene was established in an ultrasound-aided ball milling process, where absolute ethanol was selected as the solvent and sodium dodecyl sulfonate (SDS) as the surfactant. The printed pattern of graphene-filled conductive silicon rubber (CSR) was optimized and embedded-printed as the conductive sensitive material (CSM), in which the FSRS with a spiral-patterned CSM was chosen for its high sensitivity. Micropores with an optimized interspacing of 10 mm were further introduced into the spiral CSM to significantly improve the sensitivity (GF=51±4) of the fabricated FSRS at a considerable working strain (20~30%) and long-life working duration (>104 cycles). The FRSR was sensitive enough to capture various motions of single and multi-joints and identify the rhythm of played music, which exhibited its potential application as a wearable flexible sensor.

Graphene in rubber formulations: a comprehensive review and performance optimization insights

“…Mechanical grinding is the method of mechanically crushing or mixing graphene using grinding balls, a pestle, or sand. The grinding balls are made up of materials such as zirconia 31,[76][77][78] and stainless steel. 79 When the balls are moving rapidly in a ball miller, the collision between the balls generates shear force which results in a smaller graphene particle size.…”

“…79 When the balls are moving rapidly in a ball miller, the collision between the balls generates shear force which results in a smaller graphene particle size. Surfactants, 31,[77][78][79] ionic liquids, 80 or other exfoliating agents 76 are essential to assist in graphene functionalization and exfoliation during the grinding process.…”

“…79 Similarly, graphene is dissolved in ethanol and ground with sodium dodecyl sulfonate at 200 rpm for 6 hours in the ratio of solvent : graphene = 80 : 1 and ball : material = 3 : 2 for fabrication of graphene in flexible sensor application. 77 Melamine is a kind of common surfactant that is capable of exfoliating graphene into defect-free few-layer graphene, 31,78 while Darvan is generally used to stabilize graphene dispersion during the grinding process. 31,81 It is worth reporting that curcumin, a type of polyphenol, acts as an exfoliating agent for graphene.…”

“…For instance, silicone rubber is selected as the matrix for strain sensors due to its excellent thermal stability that is attributed to the higher bond energy of Si-O, low cytotoxicity, biocompatibility, and excellent elasticity. 77,89,119 The silicone rubber latex also acts as the "elastic balloon" to support the destruction and reconstruction of the graphene network under strain. This contributes to the improvement of overall sensitivity, workable range, and stability of flexible strain sensors.…”

“…The sensor with a spiral-line discloses the highest sensitivity at 25 gauge factor and good stability under the strain load for >10 4 cycles compared to straight-line, poly-line, and square-line patterns due to the directionless structure. 77 The vacuum-filtered rGO/ SWCNTs hybrid filler is transfer printed on the pre-stretch polydimethylsiloxane rubber to form a flexible strain sensor that possesses the synergistic effect from the hybrid filler. The distinctive wrinkled, cracked, and bridged hybrid rGO/ SWCNTs networks on the coated rubber substrate allow the storage of stress which contributes to the high sensitivity and prompt alteration in the conductive pathway when strain is applied.…”