X. Li, T. Pawale, J. Swain, M. Anwasi, S. Kaluarachchi, Y. Wang, Y. Yang, D. A. Czaplewski, R. Divan, G. Tierra
University of North Texas,
United States
Keywords: directed self-assembly, chiral liquid crystals, Bouligand structure, hierarchical helix
Summary:
The naturally occurring Bouligand structure, renowned for its unique helicoidal arrangement and enhanced mechanical properties, has become a research focus due to the remarkable strength exhibited by these intrinsically soft materials. Biomimicking this structure has often centered on fibrous structure in bulk materials translating this architecture into the thin-film regime for miniaturized, wearable devices with programmable functions remains challenging. Here, we directed the self-assembly of the cholesteric phase, adapting the pattern’s period to a ~290 nm pitch, into hierarchical helical structures, addressing mechanical limitations in soft systems. Alternating homeotropic and planar anchoring regions align uniform lying-down helices at the nanoscale, guiding a secondary microscale helical structure exhibiting both left- and right-handed twists. The resulting rope-like texture degenerates when the pattern period deviates from the pitch yet effectively occupies 3D space, enabling scalable, precise, position-based structures in thin film. A temperature-sensitive chiral dopant allows optical modulation, while nanoscale dynamic mechanical analysis based on atomic force microscopy reveals enhanced mechanical response. Simulations replicating the Bouligand configuration, rotating LC layers 45° in either direction, validate helical structure formation as the system transitions to a lower-energy state. This research paves the way for designing and manufacturing miniaturized or wearable devices with nanometer-scale precision in regulating optical and mechanical properties.