arXiv subjects

Bruno Frka-Petesic

Publications and source records attributed to Bruno Frka-Petesic.

5 recordsLinked to original sources

arXiv2025

Tailoring the Morphology of Cellulose Nanocrystals via Controlled Aggregation

Cellulose nanocrystals (CNCs) are elongated nanoparticles derived from natural cellulose, with potential applications ranging from rheological modifiers and emulsion stabilizers to photonic pigments and sensors. For most applications, precise control over CNC morphology and surface chemistry is essential, but the relationship between process parameters, CNC characteristics, and their resulting behavior is poorly understood. Here, we investigate the impact of centrifugation and ionic strength on CNC morphology after dialysis using transmission electron microscopy, small-angle X-ray scattering and scanning electron diffraction. We find that the centrifugation step commonly applied during CNC purification promotes the formation of compact composite nanoparticles made of aligned crystallites, referred to as 'bundles', that are associated preferentially along their hydrophobic faces. In stark contrast, transient exposure to high ionic strength leads to fractal-like, irregular composite nanoparticles. We then examine the consequence of these morphological differences on the cholesteric self-organization of the CNCs: aligned bundles reduce the cholesteric pitch in suspension, causing a blue-shift in the color of dish-cast photonic films, while misaligned particles promote gelation, producing colorless films. This study reveals the importance of sample history, in particular, the often-disregarded purification steps, on CNC characteristics and their ensemble behavior, thereby unlocking new routes for tailoring this promising nanomaterial.

cond-mat.soft↗

arXiv2025

Tuning the morphology of aerosolised cellulose nanocrystals via controlled aggregation

Cellulose nanocrystals (CNCs) are polycrystalline, rod-shaped nanoparticles isolated from cellulose, which have attracted increasing attention for a wide variety of applications. While there has been significant research into CNCs in suspensions, hydrogels and films, there have been remarkably few studies that investigated their properties during and after aerosolisation. Here, we studied how aerosolisation impacts the size and morphology of different CNCs suspensions with different surface functionalities. By building a new experimental setup, we observed that colloidally-metastable aqueous CNC suspensions, achieved by carboxylation of the surface hydroxy groups or by exposure to high intensity ultrasonication, yield large particulates upon aerosolisation under ambient temperatures. In contrast, aqueous suspensions of unfunctionalised CNCs tend to produce, upon aerosolisation, smaller particulates, despite suffering from poor colloidal stability in liquid suspension. Our results demonstrate that both the aerosolisation process itself and the properties of the CNC suspension play a crucial role in determining the final particle size and morphology of CNC-based particles, highlighting the need to consider colloidal stability and surface functionality when designing CNC-based materials for applications involving aerosol delivery or spray drying.

cond-mat.soft↗

arXiv2022

Cellulose Photonic Pigments

When pursuing sustainable approaches to fabricate photonic structures, nature can be used as a source of inspiration for both the nanoarchitecture and the constituent materials. Although several biomaterials have been promised as suitable candidates for photonic materials and pigments, their fabrication processes have been limited to the small to medium-scale production of films. Here, by employing a substrate-free process, structurally coloured microparticles are produced via the confined self-assembly of a cholesteric cellulose nanocrystal (CNC) suspension within emulsified microdroplets. Upon drying, the droplets undergo multiple buckling events, which allow for greater contraction of the nanostructure than predicted for a spherical geometry. This buckling, combined with a solvent or thermal post-treatment, enables the production of dispersions of vibrant red, green, and blue cellulose photonic pigments. The hierarchical structure of these pigments enables the deposition of coatings with angular independent colour, offering a consistent visual appearance across a wide range of viewing angles.

cond-mat.soft↗

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↗

arXiv2018

Incorporation of magnetic nanoparticles into lamellar polystyrene-b-poly(n-butyl methacrylate) diblock copolymer films: influence of the chain end-groups on nanostructuration

In this article, we present new samples of lamellar magnetic nanocomposites based on the self-assembly of a polystyrene-b-poly(n-butyl methacrylate) diblock copolymer synthesized by atom transfer radical polymerization. The polymer films were loaded with magnetic iron oxide nanoparticles covered with polystyrene chains grown by surface initiated-ATRP. The nanostructuration of the pure and magnetically loaded copolymer films on silicon was studied by atomic force microscopy, ellipsometry, neutron reflectivity and contact angle measurement. The present study highlights the strong influence of the copolymer extremity - driven itself by the choice of the ATRP chemical route - on the order of the repetition sequences of the blocks in the multi-lamellar films. In addition, a narrower distribution of the nanoparticles' sizes was examined as a control parameter of the SI-ATRP reaction.

cond-mat.mtrl-sci↗