**Ultra-Sensitive Piezo-Resistive Sensors Constructed with Reduced Graphene Oxide**/**Polyolefin Elastomer (RGO**/**POE) Nanofiber Aerogels**

**Weibing Zhong <sup>1</sup> , Haiqing Jiang <sup>2</sup> , Liyan Yang <sup>2</sup> , Ashish Yadav <sup>2</sup> , Xincheng Ding <sup>2</sup> , Yuanli Chen <sup>2</sup> , Mufang Li <sup>2</sup> , Gang Sun 1,3 and Dong Wang 1,2,\***


Received: 2 November 2019; Accepted: 12 November 2019; Published: 14 November 2019

**Abstract:** Flexible wearable pressure sensors have received extensive attention in recent years because of the promising application potentials in health management, humanoid robots, and human machine interfaces. Among the many sensory performances, the high sensitivity is an essential requirement for the practical use of flexible sensors. Therefore, numerous research studies are devoted to improving the sensitivity of the flexible pressure sensors. The fiber assemblies are recognized as an ideal substrate for a highly sensitive piezoresistive sensor because its three-dimensional porous structure can be easily compressed and can provide high interconnection possibilities of the conductive component. Moreover, it is expected to achieve high sensitivity by raising the porosity of the fiber assemblies. In this paper, the three-dimensional reduced graphene oxide/polyolefin elastomer (RGO/POE) nanofiber composite aerogels were prepared by chemical reducing the graphene oxide (GO)/POE nanofiber composite aerogels, which were obtained by freeze drying the mixture of the GO aqueous solution and the POE nanofiber suspension. It was found that the volumetric shrinkage of thermoplastic POE nanofibers during the reduction process enhanced the compression mechanical strength of the composite aerogel, while decreasing its sensitivity. Therefore, the composite aerogels with varying POE nanofiber usage were prepared to balance the sensitivity and working pressure range. The results indicated that the composite aerogel with POE nanofiber/RGO proportion of 3:3 was the optimal sample, which exhibits high sensitivity (ca. 223 kPa−<sup>1</sup> ) and working pressure ranging from 0 to 17.7 kPa. In addition, the composite aerogel showed strong stability when it is either compressed with different frequencies or reversibly compressed and released 5000 times.

**Keywords:** wearable pressure sensor; piezoresistive sensor; fiber assembly; nanofiber aerogel; reduced graphene oxide
