Polydimethylsiloxane-Based Polyurethane as the Matrix of Electrorheological Elastomers with an Adjustable Dielectric Constant and Improved Field-Active Efficiency

The matrix of electrorheological elastomers (EREs) requires a low modulus, a low dielectric constant, and a high strength. Commonly used silicone rubber (polydimethylsiloxane, PDMS) has a low modulus and a low dielectric constant but insufficient strength to bear loads. Compared with PDMS, polyurethane (PU) exhibits a higher strength but also a higher modulus and dielectric constant. In this study, PDMS-based PU elastomers were synthesized to form the matrix of EREs and ionic liquid-modified TiO2 nanoparticles as active dispersed particles. Both the shear modulus and dielectric constant of the PU matrix can be adjusted by the molecular weight (Mn) of the PDMS which was used as the soft segment of PU. The PU matrix demonstrated a distinct semicrystalline and microphase separation structure, and the addition of TiO2 nanoparticles reduced the crystallization ability and microphase separation of PU. The dielectric analysis showed that the dielectric constant of the EREs was significantly affected by the Mn of PDMS and the ERE containing PDMS with a lower Mn of 2000 exhibited a higher dielectric constant. Rheological analyses showed that when the Mn of PDMS was 2000, the storage modulus and electrorheological efficiency of the ERE could reach 0.9 MPa and 251% under an electric field strength of 3.0 kV/mm. Such performance shown by the PU–PDMS EREs is difficult to achieve in PDMS EREs without adding plasticizers.