Highly stretchable and transparent dielectric gels for high sensitivity tactile sensors

Soft tactile sensors have been widely used in wearable electronics and soft robotics. Among different sensing technologies, soft capacitive sensors receive much attention due to good signal repeatability, temperature insensitivity, relative simplicity of fabrication and adaptability of configuration. Many methods such as adding nano-fillers have been developed to increase the sensitivity of capacitive sensors. However, the existing methods usually sacrifice the transparency and reduces the flexibility. In this work, we propose to use dielectric gels to fabricate capacitive sensors for the first time. We synthesize dielectric gels by using ethylene carbonate and propylene carbonate as solvents and 2-Ethylhexyl acrylate and acryloyl morpholine as polymer networks. The synthesized dielectric gels are extremely soft, highly stretchable, and fully transparent to visible lights. The relative permittivity is as high as 30. We demonstrate that the sensitivity of the capacitive sensor made of the new dielectric gel increases about 6 times compared to the sensors made of VHB, PDMS, or Ecoflex. We design a touch sensor with the dielectric gel to control the LED, and also demonstrate the use of the dielectric gels as the transparent cover layer of a cell phone which may displace the traditional protective layer made of glass in future wearable electronics.