Avdusntningsinducerad självhopsättning av cellulosananokristaller i vätskesuspensioner till kolesteriska fasta structurer

Biobased and renewable cellulose nanocrystals (CNC) can form hierarchically structured assemblies with impressive optical and mechanical properties. These rod-shaped nanoparticles, produced through acid hydrolysis of biomass, self-assemble in aqueous suspensions and form a liquid crystalline anisotropic volume fraction (AVF), the extent of which depends on the concentration. The anisotropic chiral nematic liquid crystalline phase can be preserved in the dry state through evaporation-induced self-assembly (EISA). This transition is not fully understood and requires more thorough inspection, in order to create large-scale defect-free structures for demanding applications, such as impact resistant materials. This work addresses this by studying the conditions during EISA for producing highly ordered CNC films. Solid CNC films display structural colour, whose intensity and uniformity reveal how well the chiral nematic order is preserved and defined within the film. UV-Vis spectroscopy, optical microscopy and scanning electron microscopy (SEM) provide information on the formation and distribution of the structural colour. In the first part of this work, the EISA drying temperature was varied (23, 28, 36, 41, 51 and 61°C). The results showed deteriorated helical order within solid films produced at higher drying temperatures. This conclusion was deduced from UV-Vis spectroscopy data that implied a larger distribution of structural colours in the films dried at elevated temperatures. In the second part, five different concentrations of the suspensions (3-7% w/w), and thereby AVFs, were used, while keeping the drying conditions the same. One set of samples was dried immediately after casting, while another set was equilibrated prior to drying. The characterization of the dry films by microscopy, UV-Vis and SEM showed that suspensions dried from a high AVF and an equilibrated state produced films with more homogeneous, long-range order, having larger chiral nematic domains. In contrast, films dried from AVF=0 lacked long-range order and did not benefit from equilibration.Biobaserade och förnybara cellulosananokristaller (CNC) kan bilda hierarkiskt strukturerade enheter med imponerande optiska och mekaniska egenskaper. Dessa stavformade nanopartiklar, som produceras genom syrahydrolys av biomassa, självhopsätter sig vätskesuspensioner och bildar en vätksekristallin anisotrop volymfraktion (AVF), vars storlek beror på koncentrationen. Den anisotropa kirala nematiska vätskekristallina fasen bevaras i fast form genom Avdusntningsinducerad självhopsättning (EISA). Denna övergång är inte fullständigt förstådd och kräver noggrannare inspektion för att man skall kunna skapa defektfria strukturer i större skala, för mer krävande tillämpningar, såsom slagfasta material. Detta arbete fokuserar på denna övergång genom att studera omständigheterna under EISA för att producera CNC filmer med en organiserad struktur. Torra CNC filmer uppvisar strukturell färg, vars intensitet och likformighet avslöjar hur väl den chirala nematiska ordningen är bevarad och organiserad. UV-Vis-spektroskopi, optisk mikroskopi och skanningselektronmikroskopi (SEM) avslöjar distributionen av den strukturella färgen. I den första delen av detta arbete varierades torkningstemperaturen (23, 28, 36, 41, 51 och 61 ° C) under EISA. Enligt resultaten var organiseringen av den önskvärda spriralstrukturen sämre i fasta filmer framställda vid högre torkningstemperaturer. Denna slutsats härleddes från UV-Vis-spektroskopi-data som vars data avslöjade en större fördelning av strukturella färger i filmer producerade i förhöjda temperaturer. I andra delen användes fem olika suspensionkoncentrationer (3–7% vikt/vikt) och därigenom AVF:er, medan torkningsomständigheterna var konstanta. En uppsättning prover torkades omedelbart efter placeringen i substratet, medan en annan sats jämviktades före torkningen. Karaktäriseringen av torrfilmerna med mikroskopi, UV-Vis och SEM visade att de suspensionerna torkade från en högre AVF och ett jämviktat tillstånd producerade filmer med en mer homogen långdistansordning och större kirala nematiska domäner. Filmer torkade från AVF = 0 och utan jämviktning saknade långdistansordning

SELENE: Self-Monitored Dependable Platform for High-Performance Safety-Critical Systems.

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.[Otros] xisting HW/SW platforms for safety-critical systems suffer from limited performance and/or from lack of flexibility due to building on specific proprietary components. This jeopardizes their wide deployment across domains. While some research has been done to overcome these limitations, they have had limited success owing to missing flexibility and extensibility. Flexibility and extensibility are the cornerstones of industry adoption: industries dealing in capital goods need technologies on which they can rely on during decades (e.g. avionics, space, automotive). SELENE aims at covering this gap by proposing a new family of safety-critical computing platforms, which builds upon open source components such as the RISC-V instruction set architecture, GNU/Linux, and the Jailhouse hypervisor. SELENE will develop an advanced computing platform that is able to: (1) adapt the system to the specific requirements of different application domains, to changing environmental conditions, and to internal conditions of the system itself; (2) allow the integration of applications of different criticalities and performance demands in the same platform, guaranteeing functional and temporal isolation properties; (3) achieve flexible diverse redundancy by exploiting the inherent redundant capabilities of the multicore; and (4) efficiently execute compute-intensive applications by means of specific accelerators.This work has received funding from the European Unions Horizon 2020 research and innovation programme under grant agreement no. 871467.Hernández Luz, C.; Flich Cardo, J.; Paredes Palacios, R.; Lefebvre, C.; Allende, I.; Abella, J.; Trilla, D.... (2020). SELENE: Self-Monitored Dependable Platform for High-Performance Safety-Critical Systems. IEEE. 370-377. https://doi.org/10.1109/DSD51259.2020.00066S37037

Long-range order in nanocellulose films and coatings for next generation materials

Aqueous dispersions of cellulose nanocrystals (CNCs) undergo a concentration-driven self-assembly which leads to chiral nematic (N*) structuring in dried coatings. The structural color provided by the N* order offer promise as a sustainable alternative to decorative iridescent, metallic, and shimmering effects. This dissertation studied the effects of the self-assembly on both structural and optical properties of dried films and coatings. The progress of the self-assembly in the dispersion state, altered through equilibration at different concentrations, was found to significantly impact the resulting dried coating, in terms of the sizes and distribution of the regions of N* order. The internal mechanical stresses that build up during the drying of CNC dispersions were quantified during coating formation and after ageing. A desirable stress reduction was achieved by mixing non-interacting plasticizing additives into the dispersion prior to coating formation. Of interest particularly in decorative applications, are the gradients in structural color at the edges of coated areas, known as coffee rings, which were examined in non-circular coatings. Lastly, an infiltration setup was investigated by introducing highly interacting compounds into CNC films, including proteins, which interfere with the self-assembly when mixed into the dispersion prior to drying. The findings of this dissertation are of interest to both technological and decorative implementations of structured cellulose nanocrystal coatings, and in the development of biocolloidal coatings

Drying stresses to tune strength and long-range order in nanocellulosic materials

| openaire: EC/H2020/788489/EU//BioELCell Funding Information: We acknowledge funding support by the European research council under the advanced grant 788489 BioElCell. BLT is the recipient of the Khalifa University of Science and Technology (KUST) Faculty Startup Project (Project code: 84741140-FSU-2022-021). Publisher Copyright: © 2023, The Author(s), under exclusive licence to Springer Nature B.V.A vast range of extraction processes, chemistries, and wet processing methods have been explored to improve the opto-mechanical properties of nanocellulosic materials. However, the stresses that arise during drying have been scarcely examined, in particular for their impact on performance. As with papermaking, drying is a critical step that significantly impacts the properties of nanocellulosic materials. The nano- and micro-scaled dimensions of nanocelluloses provide opportunities beyond those achievable in paper science, as the associated drying stresses are several orders of magnitude higher than those at the macroscale. Drying may be utilized towards the generation of assemblies with functional structures and enhanced properties. Herein, we highlight recent examples where such drying stresses are tethered to the structure of nanocellulosic materials. Using cellulose nanocrystals (CNCs), we investigate how the stresses that develop upon consolidation, and that remain thereafter (i.e., residual stresses), correlate with the mechanical performance of the obtained materials. We extend this analysis through results that highlight the impact of the “history” of drying of CNCs on the dynamics of the residual stresses. We also briefly discuss how inhomogeneous concentration gradients in drying suspensions may play an important role in the formation of superstructures across a range of nanocellulosic materials. Overall, by highlighting the importance of drying, we expect a more closely scrutinized science of drying to improve the properties of structures based on nanocellulose.Peer reviewe

Effect of Anisotropy of Cellulose Nanocrystal Suspensions on Stratification, Domain Structure Formation, and Structural Colors

| openaire: EC/H2020/788489/EU//BioELCellOutstanding optical and mechanical properties can be obtained from hierarchical assemblies of nanoparticles. Herein, the formation of helically ordered, chiral nematic films obtained from aqueous suspensions of cellulose nanocrystals (CNCs) were studied as a function of the initial suspension state. Specifically, nanoparticle organization and the structural colors displayed by the resultant dry films were investigated as a function of the anisotropic volume fraction (AVF), which depended on the initial CNC concentration and equilibration time. The development of structural color and the extent of macroscopic stratification were studied by optical and scanning electron microscopy as well as UV–vis spectroscopy. Overall, suspensions above the critical threshold required for formation of liquid crystals resulted in CNC films assembled with longer ranged order, more homogeneous pitches along the cross sections, and narrower specific absorption bands. This effect was more pronounced for the suspensions that were closer to equilibrium prior to drying. Thus, we show that high AVF and more extensive phase separation in CNC suspensions resulted in large, long-range ordered chiral nematic domains in dried films. Additionally, the average CNC aspect ratio and size distribution in the two separated phases were measured and correlated to the formation of structured domains in the dried assemblies.Peer reviewe

Drying stresses in cellulose nanocrystal coatings: Impact of molecular and macromolecular additives

| openaire: EC/H2020/788489/EU//BioELCell Funding Information: We acknowledge funding support by the European Research Council under the advanced grant 788489 BioElCell. Luiz G. Greca & Karl Mihhels acknowledge funding from Aalto University School of Chemical Engineering and Konrad W. Klockars acknowledges funding from the Walter Ahlström Foundation . We acknowledge the support by Aalto University at OtaNano — Nanomicroscopy Center (Aalto-NMC). The authors are also grateful for the support of the Academy of Finland through its Centres of Excellence Programme (2014–2019) under Project 264677 “Molecular Engineering of Biosynthetic Hybrid Materials Research” (HYBER). We thank Prof. Olli Ikkala for his insightful comments. BLT is the recipient of the Khalifa University of Science and Technology (KUST) Faculty Startup Project (Project code: 84741140-FSU-2022-021 ). Publisher Copyright: © 2022The industrial implementation of cellulose nanocrystals (CNCs) in films and coatings requires thorough evaluation of the internal stresses post-consolidation, as they cause fracturing and peeling. Characterizing the impact of plasticizing additives on stress is therefore critical. Herein, we use the deflection of thin glass substrates to measure drying stresses in consolidating CNC films, and benchmark the impact of five additives (glucose, glycerol, poly(ethylene glycol) (PEG), poly(vinyl alcohol) (PVA) and bovine serum albumin). Glycerol and PEG reduced drying stresses effectively, while PEG of increased molecular weight (from 0.2 to 10 kDa), PVA, and BSA were less effective. We analyzed the temporal aspects of the process, where stress relaxation of up to 30 % was observed 2 years after coating formation. Finally, we provide a framework to evaluate the impact of CNC morphology on residual stresses. The introduced approach is expected to fast-track the optimization and implementation of coatings based on biocolloids.Peer reviewe

Infiltration of Proteins in Cholesteric Cellulose Structures

| openaire: EC/H2020/788489/EU//BioELCell The authors received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement no. 722842 (ITN Plant-inspired Materials and Surfaces—PlaMatSu), the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement no. 788489), the FinnCERES bioeconomy flagship funded by the Academy of Finland, and the Canada Excellence Research Chair initiative and the Canada Foundation for Innovation (CFI). This work moreover benefitted from support from the Swiss National Science Foundation through the National Center of Competence in Research Bio-Inspired Materials. L.G.G. acknowledges funding by the Aalto University School of Chemical Engineering doctoral program. L.K.B. and N.B. would like to thank Alexandre Redondo and Chris Rader for lab assistance. The authors also thank Sara Roldan Velasquez for all scientific discussions on mechanical properties andDr. Bodo Wilts for proofreading the manuscript and giving scientific advice and having constructive discussions.Cellulose nanocrystals (CNCs) can spontaneously self-assemble into chiral nematic (cn) structures, similar to natural cholesteric organizations. The latter display highly dissipative fracture propagation mechanisms given their "brick" (particles) and "mortar" (soft matrix) architecture. Unfortunately, CNCs in liquid media have strong supramolecular interactions with most macromolecules, leading to aggregated suspensions. Herein, we describe a method to prepare nanocomposite materials from chiral nematic CNCs (cn-CNCs) with strongly interacting secondary components. Films of cn-CNCs were infiltrated at various loadings with strongly interacting silk proteins and bovine serum albumin. For comparison and to determine the molecular weight range of macromolecules that can infiltrate cn-CNC films, they were also infiltrated with a range of poly(ethylene glycol) polymers that do not interact strongly with CNCs. The extent and impact of infiltration were evaluated by studying the optical reflection properties of the resulting hybrid materials (UV-vis spectroscopy), while fracture dissipation mechanisms were observed via electron microscopy. We propose that infiltration of cn-CNCs enables the introduction of virtually any secondary phase for nanocomposite formation that is otherwise not possible using simple mixing or other conventional approaches.Peer reviewe

Tessellation of Chiral-Nematic Cellulose Nanocrystal Films by Microtemplating

| openaire: EC/H2020/788489/EU//BioELCellIn biological architectures, material properties are optimized by the hierarchical structuring of components with a multiscaled order, from the nano- to the macroscales. Such designs enable, for instance, programmed yield points that maximize toughness. However, research efforts in biomimetic materials have focused on the assembly of nano- or macrostructures individually. In this study, high strength cellulose nanocrystals (CNCs), assembled into chiral-nematically ordered structures, are tiled into a higher level, macro-sized, architecture by topographical templating. As templates, two meshed architectures with distinct feature sizes are evaluated, and the optomechanical properties of the resulting films are compared to featureless, flat, CNC films. Controlling capillary stresses arising during CNC assembly is shown to enable control over the orientation of the chiral-nematic director across the topography of the template. Tuning the specific reflections and multiscaled fracture propagation is demonstrated for the microtemplated CNC films. The latter phenomenon contributed to enhancing the toughness of the material through a high tortuosity of fracture propagation in all (x, y, z) directions. The presented findings are expected to pave the way towards the incorporation of current research in cellular metamaterials with the research focusing on the generation of nanoscaled biomimetic constructs.Peer reviewe