Elasticity of Gold nanorod/nematic composites

P Lakshmi Madhuri, S Krishna Prasad, Pravin Shinde and B L V Prasad,
J. Phys. D: Appl. Phys. 49, 425304 (2016)

The elastic behaviour of a composite comprising a nematic liquid crystal (NLC) doped with a small concentration of sterically stabilized gold nanorods (AuNR). The composite exhibits not only a large reduction in the magnitude of the threshold voltage for switching (Vth by 20%), the splay (K11, 40%) and bend (K33, 40%) elastic constants, but presents an unprecedented feature: Substantial diminution in the temperature dependence of these parameters, almost to the point of becoming thermally invariant. This observation achieves significance since the electro-optic switching of liquid crystal devices is largely controlled by K11 and K33. Electrical conductivity measurements also show interesting behaviour upon the inclusion of nanorods. Whereas the intrinsic Arrhenius behaviour governing the temperature dependence is enhanced, the frequency dependence depicts qualitative features of Jonscher’s universal model, albeit with a higher exponent. Further, photoisomerization of an azobenzene guest component provides an additional influence on the elastic constants. The results are discussed in terms of (a) the effect of the order parameter dependence seen from the viewpoint of an extended mean-field model, and (b) local order.

Posted by S. Krishna Prasad