Flexoelectricity giant

J. Harden, B. Mbanga, N. Eber, K. Eodor-Csorba, S. Sprunt, J.T. Gleeson and A. Jakli, Giant flexoelectricity of bent-core nematic liquid crystals, Phys. Rev. Lett. 97(15), 157802/1-4, (2006). doi 10.1103/PhysRevLett.97.157802... 

Giant flexoelectricity of bent-core nematics studied by the flexing... 

Giant Flexoelectric Effect in Liquid Crystalline Elastomers. 89... 

We note here that, though the substrate curvature due to the converse giant flexoelectric effect could be observed, detection of the converse flexoelectric effect of calamitic nematics using the same geometry cannot be... 

A possible clue for resolving the problem of giant versus normal flexoelectricity of BC nematics may lie in recent observations of converse giant flexoelectricity. As flexoelectricity is a linear phenomenon, the deformation of the substrates is expected to be proportional to the applied voltage. In this experiment, however, no flexing was detected below a critical voltage corresponding to a critical electric field of IV/itm. This may be interpreted that the cluster contribution to flexoelectricity requires a threshold... 

Summarizing, experimental observations suggest that the giant (direct or converse) flexoelectricity of bent-core nematics is related to the polar smectic clusters occurring in them. In order to explore the exact mechanism for how clusters contribute to the flexoelectric response, further experimental and theoretical studies are needed. 

Finally, it is worth mentioning that a phenomenon analogous to the difference between the normal and giant flexoelectricity of calamitic and bent-core nematics, respectively, exists in crystals, ceramics and polymers too. The flexoelectric response (defined in Eq. (3.1)) of perovskite-type ferroelectrics, " of relaxor ferroelectric ceramics and polyvinylidene fluoride (PVDF) films are four orders of magnitude larger than the flexoelectricity of dielectric crystals. In those sohd ferroelectric materials the polarization induced by flexing is evidently of piezoelectric origin. 

The need for sohd substrates may be lifted by using self-supporting liquid crystalline elastomers (LCEs). It has been foimd that conventional LCEs can be soaked in BC nematics producing a swollen elastomer, which also shows giant flexoelectricity. 

J. Harden, M. Chambers, R. Verduzco, P. Luchette, J. Gleeson and S. Sprunt, Giant flexoelectricity in bent-core nematic liquid crystal elastomers, Appl. Phys. Lett. 96(10), 102907/1-3, (2010). doi 10.1063/1.3358391... 

Harden, J. Mbanga, B. Eber, N. Fodor-Csorba, K. Sprunt, S. Gleeson, J. T Jakli, A. Giant flexoelectricity of bent-core nematic hquid crystals. Phys. Rev. Lett. 2006, 97, 157802. 

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