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Herein we report the synthesis of cellulose nanocrystals (CNCs) grafted with poly(acrylic acid) (PAA) chains of different lengths using Cu-mediated surface initiated-controlled radical polymerization (SI-CRP). First, poly(tert-butylacrylate) (PtBA) brushes were synthesized; then, subsequent acid hydrolysis was used to furnish PAA brushes tethered onto the CNC surfaces. The CNCs were chemically modified to create initiator moieties on the CNC surfaces using chemical vapor deposition (CVD) and continued in solvent phase in DMF. A density of initiator groups of 4.6 bromine ester groups/nm(2) on the CNC surface was reached, suggesting a dense functionalization and a promising starting point for the controlled/living radical polymerization. The SI-CRP of tert-butylacrylate proceeded in a well-controlled manner with the aid of added sacrificial initiator, yielding polymer brushes with polydispersity values typically well below 1.12. We calculated the polymer brush grafting density to almost 0.3 chains/nm(2), corresponding to high grafting densities and dense polymer brush formation on the nanocrystals. Successful rapid acid hydrolysis to remove the tert-butyl groups yielded pH-responsive PAA-polyelectrolyte brushes bound to the CNC surface. Individually dispersed rod-like nanoparticles with brushes of PtBA or PAA were clearly visualized by AFM and TEM imaging.

This review considers the most recent developments in supramolecular and supraparticle structures obtained from natural, renewable biopolymers as well as their disassembly and reassembly into engineered materials. We introduce the main interactions that control bottom-up synthesis and top-down design at different length scales, highlighting the promise of natural biopolymers and associated building blocks. The latter have become main actors in the recent surge of the scientific and patent literature related to the subject. Such developments make prominent use of multicomponent and hierarchical polymeric assemblies and structures that contain polysaccharides (cellulose, chitin, and others), polyphenols (lignins, tannins), and proteins (soy, whey, silk, and other proteins). We offer a comprehensive discussion about the interactions that exist in their native architectures (including multicomponent and composite forms), the chemical modification of polysaccharides and their deconstruction into high axial aspect nanofibers and nanorods. We reflect on the availability and suitability of the latter types of building blocks to enable superstructures and colloidal associations. As far as processing, we describe the most relevant transitions, from the solution to the gel state and the routes that can be used to arrive to consolidated materials with prescribed properties. We highlight the implementation of supramolecular and superstructures in different technological fields that exploit the synergies exhibited by renewable polymers and biocolloids integrated in structured materials.

Nanocelluloses with native crystalline internal structures have attracted considerable interest due to their plant-based origin, high mechanical properties, modifiability, and chiral liquid crystallinity, which suggest novel functional sustainable materials. [1−27] In particular, cellulose nanocrystals (CNCs) are colloidal rods, having a typical lateral dimension of 5−10 nm and length of 50−300 nm. Above a critical aqueous concentration, they exhibit lefthanded chiral nematic (cholesteric) liquid crystallinity (LC) and optical iridescence, [4][5][6] which is preserved in dried films [4,28] . It allows templating for photonic materials using inorganics, nanoparticles, polymers, and pyrolyzed carbonized matter. [10,12,16,25,26] On the other hand, the CNCs have been suggested to possess a right-handed twist along their nanorod axis to explain the left-handed twist in their chiral LC. [6] Recently, the right-handed twist of individual CNCs and nanocelluloses of three different origins was observed by cryo-electron tomography (cryo-ET), and electron and atomic force microscopy [27,29] supported by molecular dynamics simulations [30−32] .Exploiting the twisting shape along the individual CNC nanorods could allow new optical functions in the nano/colloidal scale in dilute aqueous dispersions, i.e. not limited to the chiral LC based on the inter-rod assembly involving a larger length scale. Surprisingly, such optical findings have not been reported so far.Surface plasmons, i.e. collective oscillations of the conduction electrons on metal surfaces, allow physics and applications ranging from photonic devices, sensing, and solar cells to pharmacology. [33−37] In nanoparticles (NPs) the oscillations become coupled to allow a chiral plasmonic response, provided that they are sufficiently closely positioned and assembled in a chiral manner. This manifests in circular dichroism (CD) spectroscopy, which describes the difference in absorption between left-and right-handed circularly polarized light. The chiral coupling of surface plasmons induces a bisignated CD signal with a zerocrossing at the characteristic localized surface plasmon resonance wavelength of the isolated NPs. Such a Cotton effect is either dip−peak or peak−dip, depending on the handedness of chirality. [38−42] In chiral biological molecules, such as DNA, proteins and polypeptides, the CD signal is at ultraviolet wavelengths, whereas the CD signal of helical metal nanoparticle assemblies is at the visible wavelengths. This extends the applications to e.g. in biosensing. [37] Chiral nanoparticle assemblies have been shown using helical polymers, supramolecular fibers, and DNA-based constructs as templates. [40−42] In particular, a chiral plasmonic signal is obtained using DNA-origami to organize the nanoparticles in well-defined helices with tunable pitch, separation, and handedness. [40,41] Even if the above approaches are promising allowing in-depth tunable chiral plasmonic response, introducing rapid, scalable, and economic ways for producing chiral plas...

Cellulose nanocrystals (CNCs) are high aspect ratio colloidal rods with nanoscale dimensions, attracting considerable interest recently due to their high mechanical properties, chirality, sustainability, and availability. In order to exploit them for advanced functions in new materials, novel supracolloidal concepts are needed to manipulate their self-assemblies. We report on exploring multivalent interactions to CNC surface and show that dendronized polymers (DenPols) with maltose-based sugar groups on the periphery of lysine dendrons and poly(ethylene-alt-maleimide) polymer backbone interact with CNCs. The interactions can be manipulated by the dendron generation suggesting multivalent interactions. The complexation of the third generation DenPol (G3) with CNCs allows aqueous colloidal stability and shows wrapping around CNCs, as directly visualized by cryo high-resolution transmission electron microscopy and electron tomography. More generally, as the dimensions of G3 are in the colloidal range due to their ~6 nm lateral size and mesoscale length, the concept also suggests supracolloidal multivalent interactions between other colloidal objects mediated by sugar-functionalized dendrons giving rise to novel colloidal level assemblies.

Tosylation and acylation of cellulose were performed under mild reaction conditions using imidazolium based ionic liquids (ILs) as solvents. The non-degradative nature, lower viscosity, as well as higher solubility of cellulose in [amim]Cl encouraged us to carry out the reactions in this media. The reactions described here were optimised for this particular solvent in order to obtain different cellulose derivatives with high yields, homogeneity and degree of substitution (DS). Two reagents employed for the in situ activation of carboxylic acids were N,N 0 -carbonyldiimidazole (CDI) and 1-ethyl-3-(3 0 -dimethylaminopropyl)carbodiimide hydrochloride (EDCI). Final products were characterised by solution and solid-state NMR techniques.

The complex nature of typical colloids and corresponding interparticle interactions pose a challenge in understanding their self-assembly. This specially applies to biological nanoparticles, such as those obtained from chitin, which typically are hierarchical and multidimensional. In this study, we obtain chitin nanocrystals by one-step heterogeneous acid hydrolysis of never-dried crab residues. Partial deacetylation facilitates control over the balance of electrostatic charges (zeta potential in the range between +58 and +75 mV), and therefore

The iridescence displayed by films made from cellulose nanocrystals (CNCs) has long been the subject of fundamental research. This has expanded our understanding of colloidal self-assembly towards the development of advanced materials. However, the application of such findings is less reported for visual designs that exploit structural color. Aesthetic outputs are already in reach, but requires input from trend setters in the design and art industries. In this realm, the CNCbased iridescence uniquely offers broadband, multicolored reflections through the ''coffee ring'' effect, which arises upon evaporation-induced self-assembly (EISA). Although this effect has been thoroughly studied in the context of axisymmetric patterns, complex geometries remain to be evaluated for large-scale implementation. This is central to the present efforts, where EISA of CNC suspensions occurred onto noncircular surfaces. We used orientation-dependent contact angle measurements, profilometry and fixed-light source photography to unveil the effect of asymmetric drying fluxes at sharp angles, between 30°and 90°, on CNC particle deposition and resulting color patterns. We also demonstrate the causality between increased capillary fluxes and deposition with the help of modelling via energy minimization of the suspension volume onto a given surface and using the diffusion equation to obtain the local concentration of water vapor during EISA. Lastly, we study the effect of background reflections as well as light and temperature resistance of CNC-based reflectors, both important for any deployment. The results from this multidisciplinary effort, involving applied design, art and colloid chemistry, point to the excellent prospects of CNC films for the development of structured and chromatic patterns.