## 4 Conclusions  
The development of a fast and low cost de-electroadhesion mechanism remains a challenging topic in EA research. EA pads with exposed electrodes have been shown to have a faster de-electroadhesion speed for certain materials. In this work, a comprehensive study was conducted on the de-electroadhesion speed of EA designs with exposed electrodes by comparing eight different flexible and lightweight object materials and six different base materials. Experimental results showed that the de-electroadhesion speed was strongly dependent on the object material properties. Plastic materials demonstrated the longest release time, while cellulose-based materials showed the shortest release time. The following factors were found to affect the de-electroadhesion speed of an object: dielectric constant; mass-specific density of the object; compliance; molecular weight; and surface roughness. Comparison of the six base materials indicated that for fast de-electroadhesion of various types of objects, silicone film could be one of the best candidates for base material selections in EA grippers with exposed electrodes. However, for certain objects (such as paper tissue and silicone film in this study), acrylic could be a better option. The de-electroadhesion speed was also found to be related to the charging period, and a shorter charging period could speed up the de-electroadhesion. These findings will enable the design of cost-effective EA-based robotic end effectors with rapid release capabilities. EA grippers with quicker de-adhesion ability could significantly improve the overall throughput of assembly lines where material pick-and-place tasks are involved. In addition, more efficient and faster locomotion speeds could be achieved for crawling or climbing robots where EA is employed in their active adhesion and de-adhesion feet.  
The following are available online at [[http://www.mdpi.com/2076-3417/9/14/2796/s1](http://www.mdpi.com/2076-3417/9/14/2796/s1)]([http://www.mdpi.com/2076-3417/9/14/2796/s1](http://www.mdpi.com/2076-3417/9/14/2796/s1)), Table S1: Parameters of tested substrate materials, Table S2: Raw data of release period of all tested EA base substrates on all tested substrates, Table S3: Raw data of the release period against different charging period. Silicone base substrate and Mylar object are used in this comparison, Video S1: Demonstration of de-adhesion process.  
Conceptualization, C.C., X.G. and J.G.; methodology, C.C., X.G. and J.G.; software, C.C. and X.G.; validation, C.C., X.G. and J.G.; formal analysis, C.C., X.G. and J.G.; investigation, C.C., X.G., J.G. and A.C.; resources, C.C., X.G., J.G. and A.C.; data curation, C.C., X.G., J.G. and A.C.; writing--original draft preparation, C.C., X.G., J.G. and A.C.; writing--review and editing, C.C., X.G., J.G. and A.C.; visualization, C.C., X.G., J.G. and A.C.; supervision, A.C.; project administration, A.C.; funding acquisition, A.C.  
This research was funded by EPSRC grant EP/P025846/1. [PERSON] was funded by the EPSRC Centre for Doctoral Training in Future Autonomous and Robotic Systems (FARSCOPE) at the Bristol Robotics Laboratory. [PERSON] thanks the support from EP/M020460/1.  
The authors declare no conflict of interest.