Enhanced electric field-induced strain in non-percolative carbon nanopowder/polyurethane composites

This study deals with the improvement of electric field-induced thickness strain of polyurethane (PU) elastomer films by carbon black ( C) nanopowder incorporation in the polymer matrix. Different carbon volume concentrations -0.5, 0.7, 1 and 1.5%-have been tested. Weak-field dielectric and resistivity measurements revealed that a percolative effect is not induced by carbon filling up to 1.5 vol%. Thickness strain measurements showed that both pure PU and C/PU composite films exhibit similar strain variations which are not governed only by electrostatic forces (Maxwell stress) and/or electrostriction forces. The highest strain amplitude value observed was obtained for 1% C composite thin film (S-a=-7.4% at E=17.8 kV mm(-1)). In comparison the highest S-a for pure PU thin film was -6.7% at E=37.5 kV mm(-1)). In the case of thick samples, the thickness strain was not enhanced by C loading, which strongly suggests interfacial space charge effects in pure PU film, confirmed by the frequency dependence of strain level.