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. 2025 Apr 12;16(4):457.
doi: 10.3390/mi16040457.

Accelerated Electro-Optic Switching in Liquid Crystal Devices via Ion Trapping by Dispersed Helical Carbon Nanotubes

Rajratan Basu  1 , Christian C Kehr  1
Affiliations

Accelerated Electro-Optic Switching in Liquid Crystal Devices via Ion Trapping by Dispersed Helical Carbon Nanotubes

Rajratan Basu et al. Micromachines (Basel). .

Abstract

Free ion impurities in liquid crystals significantly impact the dynamic electro-optic performance of liquid crystal displays, leading to slow switching times, short-term flickering, and long-term image sticking. These ionic contaminants originate from various sources, including LC cell fabrication, electrode degradation, and organic alignment layers. This study demonstrates that doping LCs with a small concentration of helical carbon nanotubes effectively reduces free ion concentrations by approximately 70%. The resulting reduction in ionic impurities lowers the rotational viscosity of the LC, facilitating faster electro-optic switching. Additionally, the purified LC exhibits enhanced dielectric anisotropy, further improving its performance in display applications. These findings suggest that helical carbon nanotubes doping offers a promising approach for mitigating ion-related issues in liquid crystals without the need for additional chemical treatments, paving the way for an efficient liquid crystal display technology.

Keywords: electro-optic effects; helical carbon nanotubes; ionic impurities; liquid crystals.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) An SEM image of hCNTs. (b) A schematic representation of the LC-CNT interaction: anchoring of a liquid crystal molecule on a carbon nanotube surface due to π–π electron stacking. The blue ellipsoid represents a generic liquid crystal molecule, while the black cylindrical honeycomb structure depicts the carbon nanotube surface. (c) Random distribution of free ions in a nematic phase. (d) hCNTs’ ion trapping process in a nematic phase.
Figure 2
Figure 2
Free ion concentration, ni, as a function of temperature for E7 and E7 + hCNTs samples listed in the legend. Typical error bars are shown. Inset: ion current, Iion as a function of time for E7, and E7 + hCNTs at 25 °C after the voltage is inverted across the cells. The peak represents the ion bump when positive and negative ions meet in the middle of the cell.
Figure 3
Figure 3
Rotational viscosity, γ1 as a function of temperature for E7 and E7 + hCNTs samples, listed in the legend. Typical error bars are shown. Inset: transient current, I(t) as a function of time for E7 and E7 + hCNTs at T = 25 °C.
Figure 4
Figure 4
(a) Dielectric constant, ε as a function of Vrms for E7 and E7 + hCNTs samples, listed in the legend at T = 25 °C. (b) Dielectric anisotropy, Δε as a function of temperature for E7 and E7 + hCNTs samples, listed in the legend. Typical error bars are shown.
Figure 5
Figure 5
(a) A schematic representation of the field-off bright state and field-on dark state for a nematic LC. The micrographs for E7 and E7 + hCNTs cells show the field-off bright state and the field-on dark state, respectively. (b) A schematic representation of the electro-optic experimental setup. (c) Dynamic electro-optic response in E7 and E7 + hCNTs filled test cells. The driving modulated square wave voltage profile at f = 20 Hz is indicated on the right-hand y-axis. The left-hand y-axis shows the normalized transmitted intensity over time as V is turned off (at t = 0) and then turned on (at t = 25 ms), for the two test cells, as identified in the legend at T = 25 °C.
Figure 6
Figure 6
(a) A micrograph for the E7 + hCNTs-2 cell under a cross-polarized microscope. Small black dots are hCNT aggregates. Schematic representation of the presence of hCNTs in the LC when (b) the field is off and (c) the construction of hCNT wires bridging the two electrodes of the cell at a high field. (d) Dielectric constant, ε as a function of Vrms [voltage cycle up (red arrows) and down (blue arrows)] for E7 + hCNTs-2 at T = 25 °C.
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