Microfluidic Channel-Based Soft Electrodes and Their Application in Capacitive Pressure Sensing

Summary

Flexible electrodes have a wide range of applications in soft robotics and wearable electronics. The present protocol demonstrates a new strategy to fabricate highly stretchable electrodes with high resolution via lithographically defined microfluidic channels, which paves the way for future high-performance soft pressure sensors.

Abstract

Flexible and stretchable electrodes are essential components in soft artificial sensory systems. Despite recent advances in flexible electronics, most electrodes are either restricted by the patterning resolution or the capability of inkjet printing with high-viscosity super-elastic materials. In this paper, we present a simple strategy to fabricate microchannel-based stretchable composite electrodes, which can be achieved by scraping elastic conductive polymer composites (ECPCs) into lithographically embossed microfluidic channels. The ECPCs were prepared by a volatile solvent evaporation method, which achieves a uniform dispersion of carbon nanotubes (CNTs) in a polydimethylsiloxane (PDMS) matrix. Compared to conventional fabrication methods, the proposed technique can facilitate the rapid fabrication of well-defined stretchable electrodes with high-viscosity slurry. Since the electrodes in this work were made up of all-elastomeric materials, strong interlinks can be formed between the ECPCs-based electrodes and the PDMS-based substrate at the interfaces of the microchannel walls, which allows the electrodes to exhibit mechanical robustness under high tensile strains. In addition, the mechanical-electric response of the electrodes was also systematically studied. Finally, a soft pressure sensor was developed by combining a dielectric silicone foam and an interdigitated electrodes (IDE) layer, and this demonstrated great potential for pressure sensors in soft robotic tactile sensing applications.

Introduction

Soft pressure sensors have been widely explored in applications such as pneumatic robotic grippers¹, wearable electronics², human-machine interface systems³, etc. In such applications, the sensory system requires flexibility and stretchability to ensure conformal contact with arbitrary curvilinear surfaces. Therefore, it requires all the essential components, including the substrate, the transducing element, and the electrode, to provide consistent functionality under extreme deformation conditions⁴. Moreover, to maintain high sensing performance, it is essential to keep th....

Protocol

1. Synthesis of the ECPCs slurry

1. Disperse the CNTs into a toluene solvent at a weight ratio of 1:30 and dilute the PDMS base with toluene at a weight ratio of 1:1.
   NOTE: The whole experimental procedure, which is shown in Figure 1, should be carried out in a well-ventilated fume hood.
2. Magnetically stir the CNTs/toluene suspension and the PDMS/toluene solution at room temperature for 1 h.
   NOTE: This step allows the CNTs to be well-dispersed.......

Discussion

In this protocol, we have demonstrated a novel microfluidic channel-based printing method for stretchable electrodes. The conductive material of the electrode, the ECPCs slurry, can be prepared by the solvent evaporation method, which allows the CNTs to be well-dispersed into the PDMS matrix, thus forming a conductive polymer that exhibits a stretchability as high as the PDMS substrate.

In the scraping process, the ECPCs slurry is rapidly filled into the PDMS microfluidic channel with the help.......

Materials

Name	Company	Catalog Number	Comments
Camera	OPLENIC DIGITAL CAMERA
Carbon nanotubes (CNTs)	Nanjing Xianfeng Nano-technology		Diameter:10-20 nm,Length:10-30 μm
Hotplate Stirrer	Thermo Scientific	Super-Nuova+	Stirring and Heating Equipment
LCR meter	Keysight	E4980AL	Capacitance Measurment Equipment
Microscope	SDPTOP
Multimeter	Fluke		Resistance measurment Equipment
Oven	Yamoto	DX412C	Heating equipment
Photo mask	Shenzhen Weina Electronic Technology
Photoresist	Microchem	SU-8 3050
Polydimethylsiloxane (PDMS)	Dow Corning	Sylgard 184	Silicone Elastomer
Silicone Foam	Smooth on	Soma Foama 25	Two-component Platinum Silicone Flexible Foam
Silicone wafer	Suzhou Crystal Silicon Electronic & Technology		Diameter:2inch
Stirrer	IKA	Color Squid	Stirring Equipment
Toluene	Sinopharm Chemical Reagent		Solvent for the Preparation of ECPCs
Triethoxysilane	Macklin