Graphene-based printable conductors for cyclable strain sensors on elastomeric substrates

Abstract

Printable stretchable devices, which can be used in a wide range of environments, are required for a range of flexible or stretchable electronics applications. Here we present an ink containing liquid exfoliated graphene and natural rubber, which can be printed onto a variety of elastomeric substrates and recover conductance after multiple strains of up to 15%. In addition, the printed composite acts as a strain sensor with a gauge factor of around 7. The robust character of these composites allows for operation at temperatures up to 150ºC. The combination of the effectiveness of the device, along with comparable performance at elevated temperatures while being relatively cheap makes this ideal for integration with automotive components. For applications that require superior conductivity, silver nanowires can be added. The enhanced conductivity composite cannot withstand higher temperatures due to the breakdown of the nanowires. However, at room temperature the material shows similar recovery of conductivity after cycling leading to a highly conductive, room temperature, printable, stretchable composite.

A Simple Model Relating Gauge Factor to Filler Loading in Nanocomposite Strain Sensors

“…5,13 These nanocomposites contain conductive nanoparticles dispersed within an insulating matrix, typically a polymer. While nanocomposites utilising fillers such as Graphene [14][15][16][17][18] and CNTs [19][20][21] have been widely investigated, piezoresistive behaviour has been observed with a host of other nanofillers such as conductive polymers, 22 carbon black 23,24 , silver nanowires 25 , carbon fibres 26 and semiconducting materials. 27,28 The electrical properties of conductive composites are understood in great detail, with much experimental and theoretical work (e.g.…”

“…Extensive research has underlined the versatility of polymer nanocomposites where materials can be tailored to display a range of desired properties such as excellent conductivity, mechanical reinforcement, electromagnetic interference shielding, enhanced thermal stability, and polymer self-healing. − Piezoresistive nanocomposites have proved particularly promising in the area of strain sensing as they display impressive and tunable sensitivities which far surpass current commercially available strain sensors. , These nanocomposites contain conductive nanoparticles dispersed within an insulating matrix, typically a polymer. While nanocomposites utilizing fillers such as graphene − and CNTs − have been widely investigated, piezoresistive behavior has been observed with a host of other nanofillers such as conductive polymers, carbon black, , silver nanowires, carbon fibers, and semiconducting materials. , …”

Fluid‐Dynamics‐Processed Highly Stretchable, Conductive, and Printable Graphene Inks for Real‐Time Monitoring Sweat during Stretching Exercise

“…Stretchable and printable graphene inks can be prepared by incorporating graphene flakes into soft polymer matrices such as polyurethane, Ecoflex, polydimethylsiloxane, and butadiene rubber. [ 55–58 ] The graphene filler serves as an electrical conductor, while the polymer matrix provides flexibility and stretchability to the composite structure. The ink components, that is, the graphene filler, viscoelastic polymer, and solvent, are generally formulated in various mixing reactors, such as mortars, ball‐mills, sonication baths, and high‐speed mixers, to form stable and printable inks.…”

Printed Stretchable Graphene Conductors for Wearable Technology

“…For studying the dynamic behavior of the resistance during cycling, the dynamic gauge factor (DGF) would be more appropriate. 45 Here, , where ΔR i = R max, i – R min, i and ϵ i is the effective strain during cycle i . An analysis of the DGF is included in section 11.4 of the Supporting Information .…”

“…Lately, graphene-based strain sensors have been manufactured through screen printing. − In addition, stretchable supercapacitors were printed from inks composed of a conductive polymeric binder (PEDOT:PSS) to which some graphene was added to enhance the performance . Recently, printed stretchable sweat sensors were realized from an ink containing GNP and a thermoplastic polyurethane (TPU) binder in N -methyl-2-pyrrolidone (NMP), and strain sensors were produced by decorating cotton fabrics with a GNP-based ink followed by a polyurethane layer .…”