Wednesday, 23 January 2019

Conductivity switching in a carbon nanotube/liquid crystal composite

S. Krishna Prasad, M. Vijay Kumar, C .V. Yelamaggad, Carbon, 59, 512 −517 (2013)

Blends of conducting materials in insulating hosts have been extensively investigated owing to their obvious importance from both fundamental and technological points of view. In fact, reorientation of the nematic director (average orientation direction of the LC  molecules) from the equilibrium direction to that dictated by the field, and the concomitant change in the parameters such as electrical conductivity caused by the presence of CNTs, have been well demonstrated. The drawback in these systems, however, is that the return to the equilibrium value, achieved by switching the external field off, is controlled by the viscosity of the medium and thus quite slow. Here we demonstrate that the current through the sample can be field-driven between the two anisotropic values (170:1) by simply changing the frequency of the applied voltage, and exhibiting at least a millisecond response. The conductivity not only increases by two orders of magnitude with respect to that for the host liquid crystal, but achieves negligible temperature dependence. We also explain the frequency dependence of the ac conductivity by the extended pair approximation model.

Posted by S. Krishna Prasad