Synergistic Effects of Nanoparticles and Surface Anchoring on Fine-Tuning the Photonic Bandgap in Blue Phase Liquid Crystals.

Precise control over the photonic bandgap in Blue Phase Liquid Crystals (BPLCs) remains challenging due to the inherent limitations of existing tuning methods. Here, we present a 2-fold approach that synergistically combines internal and external effectors to enable controlled, fine modulation of the photonic bandgap across a wide spectral range of 200 nm. Internally, nanoparticles (NPs) embedded within the BPLC lattice enhance the thermal stability of the blue phase and reduce the cubic unit cell size, thereby shifting the reflection bandgap toward shorter wavelengths. Externally, the chemical structure of homogeneous alignment layers (ALs) affects the spectral position of the Bragg reflection. By systematically varying four ALs and three NP doping levels (0, 0.5, and 2 wt %), a cooperative influence of both effectors on spectral tuning is observed. These interactions are qualitatively explained by contact-angle measurements and chemical interactions at the LC-AL and LC-NP interfaces. Kossel diagram analysis, together with a factor based on the total tuning range and associated statistical descriptors, is used to confirm and quantify Bragg wavelength shifts. The results demonstrate that combined internal and external control provides an effective strategy for adjusting the optical response and thermal behavior of BPLCs, supporting their application in photonic devices.