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 TiO 2 nanoparticles as active dispersed particles. Both the shear modulus and dielectric constant of the PU matrix can be adjusted by the molecular weight ( M n ) 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 TiO 2 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 M n of PDMS and the ERE containing PDMS with a lower M n of 2000 exhibited a higher dielectric constant. Rheological analyses showed that when the M n 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.