Bending electrostriction in polyurethane using in situ ultraviolet and visible spectroscopies

We measured the ultraviolet and visible spectra of polyurethane films while a high electric field (2 MV/m) was applied to the films in order to investigate the detailed mechanism of the bending electrostriction. The polyurethane films were composed of segmented polyester polyurethane to which a small amount of sodium acetate (∼10−4 mol/kg) was added. The films had ∼9-nm-thick gold electrodes on both surfaces. The obtained spectra showed reversible absorption that appeared during the application of the electric field and disappeared with its removal. The response of the absorption to the field application was very similar to that of the film’s bending due to the bending electrostriction. This suggests that the reversible absorption is directly related to the mechanism of the bending electrostriction. We also demonstrated that the absorption was attributed to the moiety “Ph–NH–COO” on the polyurethane, suggesting that this moiety is a trap site of injected charges that can be considered the cause of the bending electrostriction.