The flexoelectricity1 providing linear coupling is a phenomenon that takes place in liquid crystal systems. If the nematic liquid crystals (NLCs) molecules are slightly pear shaped and exhibit a longitudinal permanent dipole, like the cyanobiphenyls, an applied field not only orients the nematic director along the field direction but also causes a slight splay distortion of the director field. The most important aspect of this effect is that positive and negative voltages cause opposite splays, creating a first harmonic electro-optic response2,3. The flexoelectric effects in NLCs-based composites have not been investigated systematically.
In this work, the flexoelectricity in planar thin films of NLCs pentylcyanobiphenyl (5CB) nanostructured by inclusion of gold nanoparticles (AuNPs) were studied. Polymer-coated nanospheres of AuNPs with a mean diameter of 20 nm were dispersed in 5CB at a concentration of 0.5 wt% 4. AuNPs/5CB nanocomposite films with a thickness of 25 μm were characterized by polarizing microscopy and flexo-electro-optic spectroscopy. The flexoelectric origin of the first harmonic spectra in AuNPs/5CB nanocomposite nematic system was discussed.
Acknowledgments: This work was supported by the National Science Fund (NSF) of Bulgaria contract № KP-06-N58/6 from 19.11.2021, “Liquid crystal nanocomposite for applications in photonics, sensorics and biomedicine”.
1. A. Buka and N. Eber, Flexoelectricity in liquid crystals, (London, Imperial College Press, 2013), 290 pp.
2. A.G. Petrov et al., Liq. Cryst 19, 169 (1995).
3. A.G. Petrov et al., JOAM 9, 420 (2007).
4 G.B. Hadjichristov et al., J. Appl. Phys. 115, 083107 (2014).