Dielectric elastomers (DEs) as one class of electronic type of electroactive polymers (EAPs) can be deformed under electrical stimulation, and have important applications in the soft robots, wearable electronic devices, and medical rehabilitation machinery so on. In this work, the bending actuation mechanism, and electromechanical properties of nanostructured dielectric poly (styrene-b-(ethylene-co-butylene)-b-styrene)/white mineral oil (SEBS/WO) blend films were investigated under free electrodes condition. The morphology and mechanical properties of SEBS/WO films were adjusted by the content of WO, where the WO selectively swelled the poly (ethylene-co-butylene) (PEB) domains. The phase transition of lamellar (LAM) structure to hexagonal array packed cylinder (HEX) of SEBS/WO films was observed when added WO content larger than 17 wt%. The modulus and the polystyrene (PS) domain radius of SEBS/WO blend films with HEX structure were decreased as increase of WO weight fraction. The bending displacement of SEBS/WO films was almost linearly dependent on the applied electric voltages, and the single cantilever model based calculated bending force was almost linearly dependent on inverse of PS domain radius for SEBS/WO films with HEX morphology. The bending actuation mechanism of SEBS/WO films with HEX morphology was suggested that the bending actuation of SEBS/WO films was caused by electrostatic attraction force between inter-PS domains induced squeezing deformation of poly (ethylene-co-butylene) (PEB) domains. The SEBS/WO blend films with 50 wt% of WO content showed 6.54 mm

(corresponding to 23.56?) at 2 kV (50 V/mm of nominal electric field). Our results can provide new insight on development of nanostructured electroactive elastomers for applications in the soft actuator materials.