Han Tao: Controlling self-assembly of cellulose nanocrystals for multiphase colloids and chiral photonics

Abstract: 

The assembly of complex superstructures using biosourced nanoscale building blocks has broad implications in sustainable material development with property enhancement and structural synergy. However, achieving controlled self-assembly in bio-based nanoparticle systems remains challenging in terms of coordinating composition, interfacial organization, and morphology across multiple length scales. This thesis mitigates these challenges using cellulose nanoparticle as a model system, establishing generalizable strategies to program their self-assembly across different material states and hierarchical levels.

This thesis introduces the aqueous two-phase system as a powerful medium for programming the self-assembly of cellulose nanocrystals (CNCs). Such water-water interface confinement reveals how polymer partitioning, depletion forces, and interfacial permeability collectively govern cholesteric ordering, offering new physical insight into liquid-liquid templating of anisotropic nanoparticles. Beyond CNCs, this framework can be extended to other rod-like colloids, suggesting a universal route to control phase behaviour and structural organization in multicomponent soft-matter systems. The findings also emphasize the broader significance of colloid-polymer interactions in constructing dynamic, bioinspired architectures that may bridge synthetic control with biological complexity.

Moreover, this thesis lies the advent of using the intrinsic birefringence of natural, plant-based structures in the design of chiroptical materials. This approach delivers a sustainable, scalable route to create hierarchical photonic materials, paving the way for multifunctional optical platforms that unite sustainability, biocompatibility, and advanced photonic performance.

Key words: Nanocellulose, Cholesteric liquid crystal, Multiphase colloids, Chiral plasmonic metasurface

Opponent: Prof. Bruno Frka-Petešić, University of Cambridge, UK

Custos: Prof. Eero Kontturi, Aalto University School of Chemical Engineering

Link to electronic thesis: Thesis available for public display 7 days prior to the defence at Aaltodoc.