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Carbon Nanotube-doped Liquid Crystal - Towards Faster LCDs

Written by: 
Rajratan Basu, US Naval Academy

Fig. 1: Schematic representation of LC (ellipsoids) + CNT (black rods) reorientation under an external electric field.

Liquid crystals (LCs) exhibit a phase of matter that has properties between those of a conventional liquid and those of a solid crystal. So, LCs can flow like a liquid, and at the same time the anisotropic LC-molecules maintain a long range crystalline order. Their unique combinations of liquid and solid-like properties allow liquid crystals to be used pervasively in the electro-optical display technology – known as liquid crystal display (LCD).

Prof. Basu, at the US Naval Academy, has recently shown that when a small amount of carbon nanotubes (CNTs) is doped in a nematic LC, the LC+CNT matrix shows a faster response to an electric field compared to that of the pure LC. This accelerated response could be used to develop faster LCDs.

The CNTs, embedded in the LC matrix, follow the LC reorientation, enhancing the overall dielectric anisotropy of the system, shown in Fig. 1. In general, liquid crystals contain a significant amount of free ions. The presence of ions would result in an increase in rotational viscosity, slowing down the director’s response to an external field. The CNTs in the media act as ion-catchers with a high ion-trapping coefficient. Thus, the CNTs, being suspended in the system, lower the free ion concentration, decreasing the rotational viscosity for the overall system, as illustrated in Fig. 2. With a lower rotation viscosity and enhanced dielectric anisotropy the hybrid system shows an accelerated response to the electric field.

Fig. 2: Schematic representation of ion (red spheres) trapping process of a CNT embedded in an LC (ellipsoids) mediated platform.

Reference: R. Basu, “Effect of carbon nanotubes on the field-induced nematic switching”, Applied Physics Letters 103, 241906 (2013).

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