Highly sensitive microfluidic strain sensors with low hysteresis using a binary mixture of ionic liquid and ethylene glycol

We present a simple liquid-type strain sensor using a binary mixture of ethylene glycol (EG) and ionic liquid (IL) in a linear microfluidic channel. The EG/IL-based strain sensor showed highly sensitive response to tensile strain in a polydimethylsiloxane (PDMS) microfluidic channel. In addition, the EG/IL-based strain sensor exhibited outstanding signal recovery and high sensitivity to applied strain (200%) in an Eco-Flex microfluidic channel. The EG/IL-based strain sensor exhibited 2.3 times higher gauge factor at 200% strain, compared to the microfluidic strain sensor using neat IL. Moreover, the EG/IL strain sensor showed clear signal responses with negligible hysteresis, even at high strain speed of 16.667 mm/s. Compared to other liquid-type strain sensors, the EG/IL-based strain sensor exhibited very high resistance variations, surpassing the elastic channel deformation effect. To explain this effect, the conducting behavior of ionic liquids in ethylene glycol was also investigated. This novel fabrication of EG/IL-based strain sensors shows potential for the development and practical application of liquid-type strain sensors.