Johannes S. Haataja | Searcharxiv

arXiv2022

Chiral Self-Assembly of Cellulose Nanocrystals is Driven by Crystallite Bundles

The transfer of chirality across length-scales is an intriguing and universal natural phenomenon. However, connecting the properties of individual building blocks to the emergent features of their resulting large-scale structure remains a challenge. In this work, we investigate the origins of mesophase chirality in cellulose nanocrystal suspensions, whose self-assembly into chiral photonic films has attracted significant interest. By correlating the ensemble behaviour in suspensions and films with a quantitative morphological analysis of the individual nanoparticles, we reveal an inverse relationship between the cholesteric pitch and the abundance of laterally-bound composite particles. These bundles thus act as colloidal chiral dopants, analogous to those used in molecular liquid crystals, providing the missing link in the hierarchical transfer of chirality from the molecular to the colloidal scale.

cond-mat.soft↗

arXiv2021

Topological invariance in whiteness optimisation

Increasing the light scattering efficiency of nanostructured materials is becoming an active field of research both in fundamental science and commercial applications. In this context, the challenge is to use inexpensive organic materials that come with a lower refractive index than currently used mineral nanoparticles, which are under increased scrutiny for their toxicity. Although several recent investigations have reported different disordered systems to optimise light scattering by morphological design, no systematic studies comparing and explaining how different topological features contribute to optical properties have been reported yet. Using in silico synthesis and numerical simulations, we demonstrate that the reflectance is primarily determined by second order statistics. While remaining differences are explained by surface area and integrated mean curvature, an equal reflectance can be obtained by further tuning the structural anisotropy. Our results suggest a topological invariance for light scattering, demonstrating that any disordered system can be optimised for whiteness.

physics.optics↗