Chirality inversion in colloidal self-assembly

Informazioni relative al progetto

CINCOS

ID dell’accordo di sovvenzione: 101154876

DOI

10.3030/101154876

Progetto chiuso

Data della firma CE 16 Aprile 2024

Data di avvio 1 Maggio 2024

Data di completamento 30 Aprile 2026

Finanziato da

• Marie Skłodowska-Curie Actions (MSCA)

Costo totale

Nessun dato

Contributo UE

€ 173 847,36

Coordinato da

MAX-PLANCK-GESELLSCHAFT ZUR FORDERUNG DER WISSENSCHAFTEN EV
Germany

Periodic Reporting for period 1 - CINCOS (Chirality inversion in colloidal self-assembly)

Periodo di rendicontazione: 2024-05-01 al 2026-04-30

Sintesi del contesto e degli obiettivi generali del progetto

Structurally-coloured films made from cellulose, the world’s most abundant biopolymer, show great promise as a sustainable alternative to conventional effect pigments and glitter. This colouration arises from the colloidal self-assembly of rod-like cellulose nanocrystals (CNCs), which spontaneously form a cholesteric liquid crystal phase with a helical periodic structure. In this system, control over colloidal chirality is crucial, because the handedness of the self-assembled structure determines the optical response and thus the colour and polarisation properties of the resulting films. Although cellulose can form both left- and right-handed helicoidal structures in nature, naturally-derived colloidal cellulose only forms a left-handed cholesteric phase, limiting the optical performance of CNC-based colourants. The CINCOS fellowship therefore explored how the morphology of CNCs could be tuned to control their self-assembly and enable structurally coloured films with inverted chirality, opening a route to more efficient and sustainable photonic materials for colours, pigments, and glitter replacements.

Lavoro eseguito dall’inizio del progetto fino alla fine del periodo coperto dalla relazione e principali risultati finora ottenuti

The fellowship has advanced the understanding of how particle morphology governs chiral self-assembly in nanocellulose systems, and demonstrated the fabrication of photonic laminates with a broad palette of colours and visual appearances. First, the project identified a new route to produce CNC-based chiral enhancers: centrifugation at high ionic strength induced partial lateral aggregation of CNCs, which occurred preferentially along their hydrophobic crystal faces, and the resulting particles enhanced the chiral interactions in cholesteric suspensions. The morphology of CNC bundles and aggregates was elucidated using in-depth, high-throughput characterisation via TEM, dynamic light scattering, cryo-electron tomography and 4D-STEM, as well as investigation of CNC self-assembly in suspension and in helicoidal photonic films. Second, by sequential deposition of cholesteric and aligned CNC layers, photonic laminates were fabricated with intense reflection of left- and/or right-circularly polarised light of specific colours, including extra-spectral colours not usually possible with helicoidal structures, as well as a diversity of visual textures, including matte, pearlescent and metallic appearances.

Progressi oltre lo stato dell’arte e potenziale impatto previsto (incluso l’impatto socioeconomico e le implicazioni sociali più ampie del progetto fino ad ora)

Before the fellowship, it was widely assumed that the morphology of CNCs was essentially determined by the original cellulose source and the hydrolysis conditions. It is now clear that the purification steps used after lab-scale CNC hydrolysis significantly affect the prevalence of partially aggregated “bundles” that promote cholesteric assembly, distinct from random aggregates that disrupt assembly. This deeper understanding of the origins of CNC bundles is of particular interest when transferring from lab-scale to industrial-scale production of CNCs, where ultrafiltration is often used instead of centrifugation. As CNCs continue to be utilised for various commercial applications, the insights from this fellowship will prove invaluable for elucidating the structure-function relationships for this sustainable material. Furthermore, the sequential deposition of CNCs to create photonic laminates greatly expands the regions of the colour gamut accessible in cellulose-only films to include intense reflection of secondary colours (e.g. magenta, cyan), as well as a highly customisable polarisation response. This approach is also compatible with large-scale fabrication, making it highly applicable to various commercial use cases of CNC-based films and effects pigments such as cosmetics and textiles.