Measurement of the Converse Flexoelectric Effect of a Bent-Core Nematic Liquid Crystal

Flexoelectricity is a linear coupling between bend or splay distortions and electric polarization$^{1}$. It is a unique property of orientationally ordered materials of which liquid crystals are the best known example. It has been shown that the bend flexoelectric coefficient in ``banana'' bent-core liquid crystals is three orders of magnitude higher than the effect found in calamitic liquid crystals$^{2}$. Using a Mirau interferometer attached to the objective port of a microscope, we were able to measure the converse effect. This polarity dependent flexing of a thin cell yielded displacements of 100nm when 100V DC was applied to a 1cm x 2cm x 25$\mu $m cell filled with the bent-core nematic liquid crystal 4-chloro-1,3-phenylene bis 4-[4'-(9-decenyloxy) benzoyloxy] benzoate (ClPbis10BB). The substrates were 100$\mu $m thick Mylar with ITO as a conducting layer. These preliminary experiments show the promise of new types of soft actuators or beam steering devices. References: $^{1}$Meyer R.B. (1969). \underline {Physical Review Letters} \textbf{22}(18): 918-921. $^{2}$Harden, J., B. Mbanga, et al. (2006). \underline {Physical Review Letters} \textbf{97}(15). Acknowledgement: NSF DMR-0606160 and NSF REU-0649017