Effect of ionic liquids on structure and electromechanical properties of plasticized polyvinyl chloride (PVC) gels

Polyvinyl chloride (PVC) gels, as electroactive polymers, have various applications in the fields of soft actuators and sensors. The relationship between the structure and electromechanical properties of PVC gels, however, has not been fully understood so far. In this work, the effect of different alkyl chain length of 1-allyl- imidazolium cations of tetrafluoroborate (BF4)-based ionic liquid (IL) on structure, mechanical and dielectric properties, bending actuation, sensing and electroadhesion properties of plasticized polyvinyl chloride/dibutyl adipate (PVC/DBA) gel were investigated. The interaction between DBA and ILs in PVC/DBA/IL gels leads to the disruption of interactions between inter-DBA molecules and subsequent formation of DBA-rich phases with DBA/ IL complexes. The number of DBA-rich phases in PVC/DBA/IL gels increases as the alkyl chain length of the cation in IL increases, due to an enhanced interaction between DBA and ILs with an increase in the alkyl chain length of the cation in IL. The Young's modulus of the PVC/DBA gel was slightly reduced, while the dielectric constant significantly increased when IL was added. Additionally, the bending actuation properties and capacitance pressure sensing sensitivity of the PVC/DBA/IL gel increased with an increase in the alkyl chain length of the cation of IL. However, there was an opposite trend observed for electroadhesion peel strength. Among the studied PVC/DBA/IL gels, the bending displacement, pressure sensing sensitivity, and electroadhesion peel strength of PVC/DBA/IL gel with 3.2 wt% of 1-allyl-3-butylimidazolium tetrafluoroborate ([ABIM]BF4) increased by 2.6 times, 7.5 times, and 1.7 times compared to PVC/DBA gel, respectively. These results provide new insights into understanding the relationship between structure and electromechanical properties of PVC gels for their application in actuation, sensing, and electroadhesion integrated soft grippers.