Wide temperature range of an electrically tunable selective reflection of light by oblique helicoidal cholesteric

ABSTRACT

Oblique helicoidal cholesteric liquid crystals (Ch_OH) offer an unprecedented opportunity to tune selective reflection of light in a broad spectral range from ultraviolet to infrared by an electric field. The major problem is that the temperature range of stable Ch_OH is typically above the room temperature and is relatively narrow, a few degrees. In this work, we demonstrate that by using a mixture of flexible dimeric and rod-like molecules, one can significantly expand the temperature range of intense Bragg reflection, from 16°C to 27°C. We demonstrate that the selective reflection peak, reflection intensity, bandwidth and threshold electric field are all temperature dependent and discuss the associated mechanisms. The results show that both the electric field and temperature can be used to tune the structural colour of oblique helicoidal cholesteric structures. The proposed material can be used in switchable optical devices based on liquid crystals, such as light modulators, indoor smart windows, and filters.

Graphical abstract

KEYWORDS:

• colour tuning
• chiral nematic
• oblique helicoid
• electrooptics
• twist-bend nematic

Acknowledgments

The work was supported by the NSF DMR grant 1410378. The visit of M.M. to the Liquid Crystal Institute, Kent State University, was supported by the Polish Ministry of Science and Higher Education under Mobilność Plus program (grant no. 1644/MOB/V/2017/0) and the Kosciuszko Foundation exchange program. The FFTEM image, Figure 1, was obtained at the (cryo) TEM facility at the Advanced Materials and Liquid Crystal Institute, Kent State University, supported by the Ohio Research Scholars Program “Research Cluster on Surfaces in Advanced Materials”. We thank Min Gao and his team for assistance in the experiment. The authors thank Timothy J. White, University of Colorado Boulder, and Mariacristina Rumi, Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, for the supply of CB7CB. We are grateful to Peter Palffy-Muhoray and Tianyi Guo for providing the equipment for capacitance measurements.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Science Foundation [1410378]; Kosciuszko Foundation [2017]; Ministerstwo Nauki i Szkolnictwa Wyższego [1644/MOB/V/2017/0].