posted on 2022-12-15, 19:11authored byQunmei Wei, Pengrong Lv, Yang Zhang, Jiwen Zhang, Zhuofan Qin, Laurens T. de Haan, Jiawen Chen, Ding Wang, Ben Bin Xu, Dirk J. Broer, Guofu Zhou, Liming Ding, Wei Zhao
Cholesteric liquid crystals (CLCs) are chiral photonic
materials
with selective reflection in terms of wavelength and polarization.
Helix engineering is often required in order to produce desired properties
for CLC materials to be employed for beam steering, light diffraction,
scattering, and adaptive or broadband reflection. Here, we demonstrate
a novel photopolymerization-enforced stratification (PES)-based strategy
to realize helix engineering in a chiral CLC system with initially
one handedness of molecular rotation throughout the layer. PES plays
a crucial role in driving the chiral dopant bundle consisting of two
chiral dopants of opposite handedness to spontaneously phase separate
and create a CLC bilayer structure that reflects left- and right-handed
circularly polarized light (CPL). The initially hidden chiral information
therefore becomes explicit, and hyper-reflectivity, i.e., reflecting
both left- and right-handed CPL, successfully emerges from the designed
CLC mixture. The PES mechanism can be applied to structure a wide
range of liquid crystal (LC) and polymer materials. Moreover, the
engineering strategy enables facile programming of the center wavelength
of hyper-reflection, patterning, and incorporating stimuli-responsiveness
in the optical device. Hence, the engineered hyper-reflective CLCs
offer great promise for future applications, such as digital displays,
lasing, optical storage, and smart windows.