On the sign of flexoelectric coefficients in nematic liouid crystals

Abstract

We measure the distortion of a nematic liquid crystal placed in a quadrupolar field distribution. This allows the measurement of (e₁+e₃)/K, where e₁ and e₃ are the flexoelectric coefficients and K a bend curvature elastic constant. For MBBA, e₁+e₃ is found negative, contrary to previous estimates. For 80CB, e₁+e₃ is found positive. This confirms the conformational origin of flexoelectricity in this later compound.