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The arrangements of metal nanoparticles into spatially ordered structures is still challenging, but DNA-based nanostructures have proven to be feasible building blocks in directing the higher-ordered arrangements of nanoparticles. However, an additional DNA functionalization of the particles is often required to link them to the DNA frames. Herein, we show that ordered 3D metal nanoparticle superlattices could be formed also by plainly employing electrostatic interactions between particles and DNA nanostructures. By utilizing the negatively charged DNA origami surface, we were able to assemble 6-helix bundle DNA origami and cationic gold nanoparticles (AuNPs) into well-ordered 3D tetragonal superlattices. Further, the results reveal that shape and charge complementarity between the building blocks are crucial parameters for lattice formation. Our method is not limited to only AuNPs and the origami shapes presented here, and could therefore be used in construction of a variety of functional materials.

openaire: EC/H2020/742829/EU//DRIVEN We synthesized permethylated maltoheptaose oligosaccharides, whose both ends, untrivially, have been functionalized with supramolecular binders 2-ureido-4[1H]-pyrimidinones (UPy) after single ring-opening of β-cyclodextrin counterpart. In 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), they show lyotropic liquid crystallinity. In the dried state they allow linear saccharide-based supramolecular polymers by UPy-dimerization.

Light-responsive supramolecular self-assemblies exhibit interplay between order and dynamics of the self-assembling motifs, through which the thermal isomerization rate of azobenzene chromophores can be tuned by orders of magnitude. By using supramolecular complexes of 4-(4-alkylphenylazo)phenols hydrogen-bonded to poly(4-vinylpyridine) as model systems, we demonstrate that the thermal isomerization rate of the hydroxyazobenzene derivatives increases 5700-fold when the material undergoes a transformation from a disordered, low-azobenzene-concentration state to a high-concentration state exhibiting lamellar, smectic-like self-assembly. Drastically smaller thermal isomerization rates are observed in disordered structures. This allows us to attribute the change to a combination of increased number density of the hydroxyazobenzenes inducing plasticization, and cooperativity created by the chromophore-chromophore interactions through self-assembled molecular order and alignment. Our results pinpoint the importance of molecular self-assembly and intermolecular interactions in modifying the dynamics in supramolecular complexes in a controlled manner. We foresee this to be important in light-controlled dynamic materials. publishedVersion

The right-handed twist along aqueous dispersed cellulose nanocrystals allows right-handed chiral plasmonics upon electrostatic binding of gold nanoparticles in dilute environment, upon tuning the particle sizes and concentrations. Simulations using nanoparticle coordinates from cryo-electron tomography confirm the experimental results. The finding suggests generalization for other chiral and helical colloidal templates for nanoscale chiral plasmonics.

We fabricated, characterized, and tested novel fibrous aerogel membranes in direct contact membrane distillation (MD) to elucidate the effects of a model high-porosity membrane material on MD performance. Unsupported bacterial nanocellulose aerogels exhibit higher porosity, thinner fibers, and lower bulk thermal conductivity than any previously reported MD materials. Modeling and experiments demonstrate that these material properties confer significantly higher intrinsic membrane permeability and thermal efficiency than symmetric PVDF phase inversion membranes with lower porosity. Development of macroporous fibrous membranes with aerogel-like porosity and thermal conductivity (>98% and

Hybrid aerogels consisting of cellulose nanofibers (CNF) and modified few-walled carbon nanotubes (FWCNT) are investigated under cyclic mechanical compression to explore "electrical fatigue". For this purpose the FWCNTs were hydrophilized, thus promoting their aqueous dispersibility to allow FWCNT/CNF hybrid hydrogels, followed by freeze-drying to obtain hybrid aerogels. The optimized composition consisting of FWCNT/CNF 20/80 wt/wt showed conductivity of 10-5 S cm-1 as promoted due to double percolation, and showed only small changes in electrical and mechanical behaviour upon cycling 100 times. The electrical behaviour under cycled compression shows good stability and reversibility.

We report that star-shaped molecules with cholic acid cores asymmetrically grafted by low molecular weight polymers with hydrogen bonding end-groups undergo aggregation to nanofibers, which subsequently wrap into micrometer spherical aggregates with low density cores. Therein the facially amphiphilic cholic acid (CA) is functionalized by four flexible allyl glycidyl ether (AGE) side chains, which are terminated with hydrogen bonding 2-ureido-4[1H]pyrimidinone (UPy) end-groups as connected by hexyl spacers, denoted as CA(AGE6-C6H12-UPy)4. This wedge-shaped molecule is expected to allow the formation of a rich variety of solvent-dependent structures due to the complex interplay of interactions, enabled by its polar/nonpolar surface-active structure, the hydrophobicity of the CA in aqueous medium, and the possibility to control hydrogen bonding between UPy molecules by solvent selection. In DMSO, the surfactant-like CA(AGE6-C6H12-UPy)4 self-assembles into nanometer scale micelles, as expected due to its nonpolarCA apexes, solubilized AGE6-C6H12-UPy chains, and suppressed mutual hydrogen bonds between the UPys. Dialysis in water leads to nanofibers with lateral dimensions of 20-50 nm. This is explained by promoted aggregation as the hydrogen bonds between UPy molecules start to become activated, the reduced solvent dispersibility of the AGE-chains, and the hydrophobicity of CA. Finally, in pure water the nanofibers wrap into micrometer spheres having low density cores. In this case, strong complementary hydrogen bonds between UPy molecules of different molecules can form, thus promoting lateral interactions between the nanofibers, as allowed by the hydrophobic hexyl spacers. The wrapping is illustrated by transmission electron microscopy tomographic 3D reconstructions. More generally, we foresee hierarchically structured matter bridging the length scales from molecular to micrometer scale by sequentially triggering supramolecular interactions.

Upon surgery, local inflammatory reactions and postoperative infections cause complications, morbidity, and mortality. Delivery of human adipose mesenchymal stem cells (hASC) into the wounds is an efficient and safe means to reduce inflammation and promote wound healing. However, administration of stem cells by injection often results in low cell retention, and the cells deposit in other organs, reducing the efficiency of the therapy. Thus, it is essential to improve cell delivery to the target area using carriers to which the cells have a high affinity. Moreover, the application of hASC in surgery has typically relied on animal-origin components, which may induce immune reactions or even transmit infections due to pathogens. To solve these issues, we first show that native cellulose nanofibers (nanofibrillated cellulose, NFC) extracted from plants allow preparation of glutaraldehyde cross-linked threads (NFC-X) with high mechanical strength even under the wet cell culture or surgery conditions, characteristically challenging for cellulosic materials. Secondly, using a xenogeneic free protocol for isolation and maintenance of hASC, we demonstrate that cells adhere, migrate and proliferate on the NFC-X, even without surface modifiers. Cross-linked threads were not found to induce toxicity on the cells and, importantly, hASC attached on NFC-X maintained their undifferentiated state and preserved their bioactivity. After intradermal suturing with the hASC decorated NFC-X threads in an ex vivo experiment, cells remained attached to the multifilament sutures without displaying morphological changes or reducing their metabolic activity. Finally, as NFC-X optionally allows facile surface tailoring if needed, we anticipate that stem-cell-decorated NFC-X opens a versatile generic platform as a surgical bionanomaterial for fighting postoperative inflammation and chronic wound healing problems.

Macromolecular architecture plays an important role in the self-assembly process of block copolymer amphiphiles. Herein, two series of stimuli-responsive amphiphilic 3-miktoarm star hybrid terpolypeptides and their corresponding linear analogues were synthesized exhibiting the same overall composition and molecular weight but different macromolecular architecture. The macromolecular architecture was found to be a key parameter in defining the morphology of the nanostructures formed in aqueous solutions as well as to alter the self-assembly behavior of the polymers independently of their composition. In addition, it was found that the assemblies prepared from the star-shaped polymers showed superior tolerance against enzymatic degradation due to the increased corona block density on the outer surface of the nanoparticles. Encapsulation of the hydrophobic anticancer drug Everolimus resulted in the formation of intriguing non-spherical and non-symmetric pH-responsive nanostructures, such as "stomatocytes" and "multi-compartmentalized suprapolymersomes", while the pH-triggered release of the drug was also investigated. Owing to the similarities of the developed "stomatocytes" with red blood cells, in combination with their pH-responsiveness and superior stability over enzymatic degradation, they are expected to present advanced drug delivery properties and have the ability to bypass several extra- and intracellular barriers to reach and effectively treat cancer cells.

openaire: EC/H2020/742829/EU//DRIVEN There is an emerging quest for lightweight materials with excellent mechanical properties and economic production, while still being sustainable and functionalizable. They could form the basis of the future bioeconomy for energy and material efficiency. Cellulose has long been recognized as an abundant polymer. Modified celluloses were, in fact, among the first polymers used in technical applications; however, they were later replaced by petroleum-based synthetic polymers. Currently, there is a resurgence of interest to utilize renewable resources, where cellulose is foreseen to make again a major impact, this time in the development of advanced materials. This is because of its availability and properties, as well as economic and sustainable production. Among cellulose-based structures, cellulose nanofibrils and nanocrystals display nanoscale lateral dimensions and lengths ranging from nanometers to micrometers. Their excellent mechanical properties are, in part, due to their crystalline assembly via hydrogen bonds. Owing to their abundant surface hydroxyl groups, they can be easily modified with nanoparticles, (bio)polymers, inorganics, or nanocarbons to form functional fibers, films, bulk matter, and porous aerogels and foams. Here, some of the recent progress in the development of advanced materials within this rapidly growing field is reviewed.

The understanding of the interaction between light and complex, random structures is the key for designing and tailoring the optical appearance and performance of many materials that surround us, ranging from everyday consumer products, such as those for personal care, paints, and paper, to light diffusers used in the LED-lamps and solar cells. Here, it is demonstrated that the light transport in membranes of pure cellulose nanofibrils (CNFs) can be controlled to achieve bright whiteness in structures only a few micrometers thick. This is in contrast to other materials, such as paper, which require hundreds of micrometers to achieve a comparable appearance. The diffusion of light in the CNF membranes is shown to become anomalous by tuning the porosity and morphological features. Considering also their strong mechanical properties and biocompatibility, such white coatings are proposed as a new application for cellulose nanofibrils.

openaire: EC/FP7/291364/EU//MIMEFUN Polystyrene-block-poly(1,4-isoprene)-block-poly(dimethyl siloxane)-block-poly(tert-butyl methacrylate)-block-poly(2-vinyl pyridine), PS-b-PI-b-PDMS-b-PtBMA-b-P2VP, self-assembles in acetone into polymersomes with asymmetric (directional) PI-b-PDMS membranes. The polymersomes, in turn, self-assemble into superstructures. Analogically to supravesicular structures at a smaller length scale, we refer to them as suprapolymersome structures. Electron tomograms are shown to be invaluable in the structural assessment of such complex self-assemblies.

Photoisomerization of azobenzene derivatives is a versatile tool for devising light-responsive materials for a broad range of applications in photonics, robotics, microfabrication, and biomaterials science. Some applications rely on fast isomerization kinetics, while for others, bistable azobenzenes are preferred. However, solid-state materials where the isomerization kinetics depends on the environmental conditions have been largely overlooked. Herein, an approach to utilize the environmental sensitivity of isomerization kinetics is developed. It is demonstrated that thin polymer films containing hydroxyazobenzenes offer a conceptually novel platform for sensing hydrogen-bonding vapors in the environment. The concept is based on accelerating the thermal cis-trans isomerization rate through hydrogen-bond-catalyzed changes in the thermal isomerization pathway, which allows for devising a relative humidity sensor with high sensitivity and quick response to relative humidity changes. The approach is also applicable for detecting other hydrogen-bonding vapors such as methanol and ethanol. Employing isomerization kinetics of azobenzenes for vapor sensing opens new intriguing possibilities for using azobenzene molecules in the future. publishedVersion

Cyclophanes are macrocyclic supramolecular hosts famous for their ability to bind atomic or molecular guests via noncovalent interactions within their well-defined cavities. In a similar way, porous crystalline networks, such as metal–organic frameworks, can create microenvironments that enable controlled guest binding in the solid state. Both types of materials often consist of synthetic components, and they have been developed within separate research fields. Moreover, the use of biomolecules as their structural units has remained elusive. Here, we have synthesized a library of organic cyclophanes and studied their electrostatic self-assembly with biological metal-binding protein cages (ferritins) into ordered structures. We show that cationic pillar[5]arenes and ferritin cages form biohybrid cocrystals with an open protein network structure. Our cyclophane–protein cage frameworks bridge the gap between molecular frameworks and colloidal nanoparticle crystals and combine the versatility of synthetic supramolecular hosts with the highly selective recognition properties of biomolecules. Such host–guest materials are interesting for porous material applications, including water remediation and heterogeneous catalysis.

The construction of precise soft matter nanostructures in solution presents a challenge. A key focus remains on the rational design of functionalities to achieve the high morphological complexity typically found in biological systems. Advances in controlled polymerizations and self-assembly increasingly allow approaches toward complex hierarchical nanomaterials. By combining tailor-made cylindrical polymer brushes, block copolymers and interpolyelectrolyte complexation-driven self-assembly, we demonstrate a facile construction of uniformly compartmentalized and topographically structured polymeric nanowires in aqueous media. The approach offers a modular avenue in programming the internal morphology of polymer nanowires by varying the block copolymer composition and topology.

Nanocomposite materials made from cellulose show a great potential as future high-performance and sustainable materials. We show how high aspect ratio cellulose nanofibrils can be efficiently aligned in extrusion to fibers, leading to increased modulus of toughness (area under the stress-strain curve), Young’s modulus, and yield strength by increasing the extrusion capillary length, decreasing its diameter, and increasing the flow rate. The materials showed significant property combinations, manifesting as high modulus of toughness (~28–31 MJ/m3) vs. high stiffness (~19–20 GPa), and vs. high yield strength (~130–150 MPa). Wide angle X-ray scattering confirmed that the enhanced mechanical properties directly correlated with increased alignment. The achieved moduli of toughness are approximately double or more when compared to values reported in the literature for corresponding strength and stiffness. Our results highlight a possibly general pathway that can be integrated to gel-spinning process, suggesting the hypothesis that that high stiffness, strength and toughness can be achieved simultaneously, if the alignment is induced while the CNF are in the free-flowing state during the extrusion step by shear at relatively low concentration and in pure water, after which they can be coagulated.

The self-assembly of block copolymers in the bulk phase enables the formation of complex nanostructures with sub 100 nm periodicities and long-range order, both relevant for nanotechnology applications. Here, we map the bulk phase behavior of polystyrene-block-polybutadiene-block-poly(tert-butyl methacrylate) (SBT) triblock terpolymers on a series of narrowly distributed polymers with widely different block volume fractions, ϕS, ϕB and ϕT. In dependence of ϕ, we find the lamella–lamella, core-shell cylinder, cylinder-in-lamella and core-shell gyroid morphology, but also a rarely observed cylinder-in-lamella phase. The bulk morphologies are thoroughly characterized by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) and display unusually broad stability regions, i.e. morphologies are observed over a broad range of compositions. We attribute this phase behavior to the asymmetric distribution of block–block incompatibilities, along the SBT block sequence, which are relatively large for S/B and S/T interfaces, but small for B/T. The higher enthalpic penalties at the S/B and S/T interface cause B to preferentially spread on the T microdomain thereby adopting its geometry. The morphological behavior of SBT is thus dominated by the volume ratio of the end blocks, ϕS and ϕT, which reduces the number of potential morphologies to only a few, mostly the core-shell analogue of diblock copolymer morphologies. In general, a simplified terpolymer bulk behavior with large stability regions for morphologies offers straightforward synthetic targeting of specific morphologies that usually only appear in a small parameter space as demonstrated here on the core-shell gyroid.

One of the major, but often overlooked, challenges toward high end applications of nanocelluloses is to maintain their high mechanical properties under hydrated or even fully wet conditions. As such, permanent covalent cross-linking or surface hydrophobization are viable approaches, however, the former may hamper processability and the latter may have adverse effect on interfibrillar bonding and resulting material strength. Here we show a concept based on physical cross-linking of cellulose nanofibers (CNF, also denoted as microfibrillated cellulose, MFC, and, nanofibrillated cellulose, NFC) with chitosan for the aqueous preparation of films showing high mechanical strength in the wet state. Also, transparency (∼70–90% in the range 400–800 nm) is achieved by suppressing aggregation and carefully controlling the mixing conditions: Chitosan dissolves in aqueous medium at low pH and under these conditions the CNF/chitosan mixtures form easily processable hydrogels. A simple change in the environmental conditions(i.e., an increase of pH) reduces hydration of chitosan promoting multivalent physical interactions between CNF and chitosan over those with water, resulting effectively in cross-linking. Wet water-soaked films of CNF/chitosan 80/20 w/w show excellent mechanical properties, with an ultimate wet strength of 100 MPa (with corresponding maximum strain of 28%) and a tensile modulus of 4 and 14 GPa at low (0.5%) and large (16%) strains, respectively. More dry films of similar composition display strength of 200 MPa with maximum strain of 8% at 50% air relative humidity. We expect that the proposed, simple concept opens new pathways toward CNF-based material utilization in wet or humid conditions, which has still remained a challenge.

Compounds that can gelate aqueous solutions offer an intriguing toolbox to create functional hydrogel materials for biomedical applications. Amphiphilic Janus dendrimers with low molecular weights can readily form self-assembled fibers at very low mass proportion (0.2 wt?%) to create supramolecular hydrogels (G'»G'') with outstanding mechanical properties and storage modulus of G'>1000 Pa. The G' value and gel melting temperature can be tuned by modulating the position or number of hydrophobic alkyl chains in the dendrimer structure; thus enabling exquisite control over the mesoscale material properties in these molecular assemblies. The gels are formed within seconds by simple injection of ethanol-solvated dendrimers into an aqueous solution. Cryogenic TEM, small-angle X-ray scattering, and SEM were used to confirm the fibrous structure morphology of the gels. Furthermore, the gels can be efficiently loaded with different bioactive cargo, such as active enzymes, peptides, or small-molecule drugs, to be used for sustained release in drug delivery.

Cellulose is one of the most abundant, naturally occurring biopolymers on Earth with remarkable properties and thus “naturally” attractive for diverse applications. In recent years, nanocelluloses received renewed interest among cellulosic materials due to their nanosized dimension, high stiffness of crystalline domains, and—depending on source and processing conditions—liquid crystallinity, high aspect ratio, and high specific surface area. Given their broad range of physical appearance, nanocelluloses display a likewise broad range of applicability with the potential to replace plastics, serve as templates for chiral nematic photonics, support catalysts as high surface scaffold, and aid in tissue healing. Their specific surface chemistry further offers various ways for covalent and supramolecular modification. In many cases, such modification is even necessary to enhance compatibility with hydrophobic components and to ease processing. This article addresses both the extraction of nanocelluloses from plant cells and their use in material design utilizing supramolecular chemistry. These include supramolecular interactions with the nanocellulose surface, hydrogen bonding, metallosupramolecular and protein-mediated interactions, and supramolecular polymer–polymer entanglements of surface-grafted polymer brushes as well as combinations of the aforementioned.

Material properties depend critically on the packing and order of constituent units throughout length scales. Beyond classically explored molecular self-assembly, structure formation in the nanoparticle and colloidal length scales have recently been actively explored for new functions. Structure of colloidal assemblies depends strongly on the assembly process, and higher structural control can be reliably achieved only if the process is deterministic. Here we show that self-assembly of cationic spherical metal nanoparticles and anionic rod-like viruses yields well-defined binary superlattice wires. The superlattice structures are explained by a cooperative assembly pathway that proceeds in a zipper-like manner after nucleation. Curiously, the formed superstructure shows right-handed helical twisting due to the right-handed structure of the virus. This leads to structure-dependent chiral plasmonic function of the material. The work highlights the importance of well-defined colloidal units when pursuing unforeseen and complex assemblies., Colloidal self-assembly is a unique method to produce three-dimensional materials with well-defined hierarchical structures and functionalities. Liljeström et al. show controlled preparation of macroscopic chiral wires with helical plasmonic superlattice structure composed of metal nanoparticles and viruses.

We report sequential self-assembly of low molecular weight asymmetric star-like polymers from nanometric spherical micelles (core diameter 8–12 nm) to colloidal spherical superstructures (d > 500–1000 nm) in aqueous media, as directed by quadruple hydrogen bonding moieties activated by solvent exchanges. The molecules consist of a rigid asymmetric steroidal cholic acid (CA) core, whose hydroxyl groups are first grafted with four oligomeric allyl glycidyl ether (AGE) chains involving six repeat units. The allylic double bonds are thiol-clicked with cysteamine (HS-(CH2)2-NH2), and in the final step their amino end groups are conjugated with 2-ureido-4[1H]-pyrimidinone (UPy) via isocyanate chemistry using UPy-(CH2)6-NCO to obtain asymmetric star-like facially amphiphilic molecules denoted as CA[(AGE-NH2)6]4-(UPy)n. They self-assemble into spherical micelles in dimethyl sulfoxide (DMSO), which suppresses the dimerization of UPys. Solvent exchange from DMSO to water activates the inter-micellar hydrogen bonds via the peripheral UPy units, which triggers the formation of spherical submicron to micron scale superstructures. Based on three-dimensional (3D) reconstruction using transmission electron tomography (ET), we show that such structures are composed of densely packed micellar network. Our work shows that surfactant-like molecules, characteristically leading to micelles, can undergo complex and hierarchical self-assembly to microscale by equipping the solubilising chains with hydrogen bonding units that can be switched ON and OFF by sequential solvent exchanges.

Summary Self-assembly of block copolymers into well-defined, ordered arrangements of chemically distinct domains is a reliable strategy for preparing tailored nanostructures. Microphase separation results from the system, minimizing repulsive interactions between dissimilar blocks and maximizing attractive interactions between similar blocks. Supramolecular methods have also achieved this separation by introducing small-molecule additives binding specifically to one block by noncovalent interactions. Here, we use halogen bonding as a supramolecular tool that directs the hierarchical self-assembly of low-molecular-weight perfluorinated molecules and diblock copolymers. Microphase separation results in a lamellar-within-cylindrical arrangement and promotes upright cylindrical alignment in films upon rapid casting and without further annealing. Such cylindrical domains with internal lamellar self-assemblies can be cleaved by solvent treatment of bulk films, resulting in separated and segmented cylindrical micelles stabilized by halogen-bond-based supramolecular crosslinks. These features, alongside the reversible nature of halogen bonding, provide a robust modular approach for nanofabrication., Graphical Abstract, Highlights • Halogen bonding small molecules to block copolymers yields hierarchical self-assembly • Fluorinated additives increase block repulsion χ and enhance microphase separation • Upright cylinder structure alignment is favored by fluorocarbon low surface energy • Segmented cylindrical micelles can be obtained by solvent treatment of bulk films, The Bigger Picture Directed self-assembly (DSA) is probably the most promising strategy for high-volume cost-effective manufacturing at the nanoscale to support the ever-growing needs of the semiconductor market. DSA exploits the spontaneous self-assembly of block copolymers onto lithographically nanopatterned surfaces, resulting in large-area fabrication of periodic nanostructures on the scale of a few tens of nanometers. Tailoring the structure, periodicity, and orientation of the block copolymer is crucial and requires control over features such as block volume fraction, immiscibility, and surface energy. Here, we use fluorocarbon additives that specifically form halogen bonds with only one of the blocks, promoting microphase separation even upon rapid casting and without subsequent solvent annealing, which, along with the reversible nature of the halogen bond, could pave the way for new self-assembly routes toward the alignment and periodicity of block copolymers and nanostructures., Halogen bonding drives the hierarchical self-assembly of low-molecular-weight perfluorinated molecules and diblock copolymers. Specifically, binding of the ditopic halogen-bond donor 1,8-diiodoperfluorooctane to pyridine nitrogens of poly(styrene)-block-poly(4-vinylpyridine) results in lamellar-within-cylindrical self-assembly and promotes upright cylindrical alignment in films. This feature, along with the reversible nature of the halogen bond, provides a robust and modular approach for nanofabrication. Thanks to the robust halogen-bond-based crosslinks, separated segmented cylindrical micelles can be obtained by solvent treatment of bulk films.

Controlled surface-initiated atom transfer radical polymerization (SI-ATRP) has previously been described as a versatile method that allows grafting polymer brushes on purely cellulosic forms of nanocelluloses, i.e., cellulose nanocrystal (CNC) nanorods and bacterial cellulose (BC) networks. However, corresponding SI-ATRP on long and entangled cellulose nanofibers (CNFs), having typically more complex composition and partly disordered structure, has been only little reported due to practical and synthetic challenges, in spite of technical need. In this work, the feasibility of SI-ATRP on CNFs is exemplified on the polymerization of poly(n-butyl acrylate) and poly(2-(dimethyl amino)ethyl methacrylate) brushes, both of which showed first order polymerization kinetics up to a chain length of ca. 800 repeat units. By constructing high and low initiator densities on CNF surfaces, we also show that, surprisingly, a higher grafting density of polymer brushes around CNF causes noticeable degradation of the CNF na...

Amyloid peptides yield a plethora of interesting nanostructures though difficult to control. Here we report that depending on the number, position, and nature of the halogen atoms introduced at either one or both phenylalanine benzene rings of the amyloid [small beta] peptide-derived core-sequence KLVFF, four different architectures were obtained in a controlled manner. Our findings demonstrate halogenation may develop as a general strategy to engineer amyloidal peptide self-assembly and obtain new amyloidal nanostructures.

openaire: EC/FP7/291364/EU//MIMEFUN Nacre inspires researchers by combining stiffness with toughness by its unique microstructure of aligned aragonite platelets. This brick-and-mortar structure of reinforcing platelets separated with thin organic matrix has been replicated in numerous mimics that can be divided into two categories: microcomposites with aligned metal oxide microplatelets in polymer matrix, and nanocomposites with self-assembled nanoplatelets-usually clay or graphene oxide-and polymer. While microcomposites have shown exceptional fracture toughness, current fabrication methods have limited nacre-mimetic nanocomposites to thin films where fracture properties remained unexplored. Yet, fracture resistance is the defining property of nacre, therefore centrally important in any mimic. Furthermore, to make use of these properties in applications, bulk materials are required. Here, up to centimeter-thick nacre-mimetic clay/polymer nanocomposites are produced by the lamination of self-assembled films. The aligned clay nanoplatelets are separated by poly(vinyl alcohol) matrix, with 106-107 nanoplatelets on top of each other in the bulk plates. Fracture testing shows crack deflection and a fracture toughness of 3.4 MPa m1/2, not far from nacre. Flexural tests show high stiffness (25 GPa) and strength (220 MPa) that, despite the hydrophilic constituents, are not substantially affected by exposure to humidity.

We describe the synthesis and self-assembly of particularly high periodicity of diblock copolymers composed of poly(benzyl-l-hydroxyproline) (PBLHyP) and poly(γ-benzyl-l-glutamate) (PBLG), that is, two polypeptide blocks with dissimilar helical structures. The robust helicity of the PBLHyP block is driven by steric constraints of the repeat units, while PBLG forms α-helices driven by hydrogen bonding, allowing defects and deformations. Herein, high-molecular-weight diblock copolypeptides of PBLG-b-PBLHyP with three different volume fractions of the PBLHyP-blocks are discussed. For shorter PBLHyP blocks, hexagonal packing of PBLHyP helices is observed, while by increasing the length of the PBLHyP block, keeping at a similar PBLG block length, the packing is distorted. Zig-zag lamellar structures were obtained due to the mismatch in the packing periodicities of the PBLG and PBLHyP helices. The frustration that takes place at the interface leads the PBLHyP to tilt to match the PBLG periodicity. The zig-zag morphology is reported for the first time for high-molecular-weight helix-helix (rod-rod) copolypeptides, and the self-assembled periodicity is uncommonly large.

Nanocomposite hydrogels are prepared combining polymer brush-modified ‘hard’ cellulose nanocrystals (CNC) and ‘soft’ polymeric domains, and bound together by cucurbit[8]uril (CB[8]) supramolecular crosslinks, which allow dynamic host–guest interactions as well as selective and simultaneous binding of two guests, i.e., methyl viologen (the first guest) and naphthyl units (the second guest). CNCs are mechanically strong colloidal rods with nanometer-scale lateral dimensions, which are functionalized by surface-initiated atom transfer radical polymerization to yield a dense set of methacrylate polymer brushes bearing naphthyl units. They can then be non-covalently cross-linked through simple addition of poly(vinyl alcohol) polymers containing pendant viologen units as well as CB[8]s in aqueous media. The resulting supramolecular nanocomposite hydrogels combine three important criteria: high storage modulus (G′ > 10 kPa), rapid sol–gel transition (

Even though nanocomposites have provided a plethora of routes to increase stiffness and strength, achieving increased toughness with suppressed catastrophic crack growth has remained more challenging. Inspired by the concepts of mechanically excellent natural nanomaterials, one-component nanocomposites were fabricated involving reinforcing colloidal nanorod cores with polymeric grafts containing supramolecular binding units. The concept is based on mechanically strong native cellulose nanocrystals (CNC) grafted with glassy polymethacrylate polymers, with side chains that contain 2-ureido-4[1H]-pyrimidone (UPy) pendant groups. The interdigitation of the grafts and the ensuing UPy hydrogen bonds bind the nanocomposite network together. Under stress, UPy groups act as sacrificial bonds: simultaneously providing adhesion between the CNCs while allowing them to first orient and then gradually slide past each other, thus dissipating fracture energy. We propose that this architecture involving supramolecular binding units within side chains of polymer grafts attached to colloidal reinforcements opens generic approaches for tough nanocomposites.

Starch is a sustainable polysaccharide with many existing and foreseen applications. Even if a plethora of routes have been described to plasticize it, e.g. with glycerol, sorbitol, and polyols, there remain major challenges related to retrodegradation, stability, and plasticizer leaching. Here we describe plasticization of starch using star-shaped molecules to combine the seemingly conflicting requirements: efficient plasticization typically assigned to low molecular weight hydrogen bonding plasticizers and reduced leaching typical for high molecular weight molecules. Efficient plasticization is allowed by the short, flexible, and hydrogen bonding dangling side chains, which are connected to the core of the plasticizer, leaving crystalline starch domains to allow self-reinforcement. The star-shaped plasticizer, a cyclic phosphazene having six covalently bound aminoethoxy ethanol side groups, was synthesized via nucleophilic substitution, and a series of films using rice starch and different weight fractions of the plasticizer were prepared by drop casting. Incorporating ≥ca. 10 wt% of the plasticizer leads to transparent plasticized films. FTIR indicates that the samples having ≤ca. 60 wt% of the plasticizer involve both plasticized amorphous domains and reinforcing crystalline domains, suggesting self-reinforced nanocomposite structures. The composition with 20 wt% of the plasticizer shows a high tensile modulus of 1.12 GPa and a yield strength of 20.9 MPa, still showing a large strain of 8.8%. No retrodegradation is observed after two months and no clear tackiness is observed even during aging of one year, suggesting stability and suppressed plasticizer leaching. We suggest that the star-shaped hydrogen bonding plasticizers show promising potential to optimize starch-based materials for advanced applications.

Here, we present a new family of light-responsive, fluorinated supramolecular liquid crystals (LCs) showing efficient and reversible light-induced LC-to-isotropic phase transitions. Our materials design is based on fluorinated azobenzenes, where the fluorination serves to strengthen the noncovalent interaction with bond-accepting stilbazole molecules, and increase the lifetime of the cis-form of the azobenzene units. The halogen-bonded LCs were characterized by means of X-ray diffraction, hot-stage polarized optical microscopy, and differential scanning calorimetry. Simultaneous analysis of light-induced changes in birefringence, absorption, and optical scattering allowed us to estimate that

Metal nanoclusters (NCs) are being intensely pursued as prospective luminophores because of their tunable electronic and optical properties. Among the various fluorescent NCs, gold nanoclusters (GNCs) are attractive due to their biocompatibility and excellent photostability, even if so far, they have had limited application potential due to poor quantum yield (QY). In this context, a facile route is demonstrated to tune up the photophysical and photochemical activities of water‐borne luminescent GNCs through the formation of self‐assembled nanocluster superstructures. The approach involves the controlled introduction of Sn2+ ions, directing GNCs from individual particles into 3D spherical gold nanocluster colloidal frameworks (GNCFs). In these, the reduction in the nonemissive relaxation pathways leads to significant enhancement of luminescence signals (QY from ≈3.5% to ≈25%), likely owing to restricted movements of ligands. This approach paves ways for GNCFs as a potent agent for biomedical imaging and therapies, while their high photocatalytic activity is an added advantage

Several approaches have recently been shown for self-assembled biomimetic composite films, aiming at combinations of high toughness, strength, and stiffness. However, it remains challenging to achieve high toughness using simple processes especially for bulk materials. We demonstrate that ionically interacting cationic native nanofibrillated cellulose (C-NFC) and anionic nanoclay, i.e. montmorillonite (MTM), allow local self-assemblies by a simple centrifugation process to achieve 3D bulk materials. The composite with MTM/C-NFC of 63/37 w/w has a high compressive strain to failure of 37% with distinct plastic deformation behaviour, a high work to fracture of 23.1 MJ m−3, and a relatively high compression strength of 76 MPa. Unlike the conventionally used sequential deposition methods to achieve well-defined layers for the oppositely charged units as limited to films, the present one-step method allows quick formation of bulk materials and leads to local self-assemblies, however, having a considerable amount of nanovoids and defects between them. We suggest that the nanovoids and defects promote the plastic deformation and toughness. Considering the simple preparation method and bio-based origin of NFC, we expect that the present tough bulk nanocomposites in compression have potential in applications for sustainable and environmentally friendly materials in construction and transportation.

Nacre-mimetic bionanocomposites of high montmorillonite (MTM) clay content, prepared from hydrocolloidal suspensions, suffer from reduced strength and stiffness at high relative humidity. We address this problem by chemical modification of xyloglucan in (XG)/MTM nacre-mimetic nanocomposites, by subjecting the XG to regioselective periodate oxidation of side chains to enable it to form covalent cross-links to hydroxyl groups in neighboring XG chains or to the MTM surface. The resulting materials are analyzed by FTIR spectroscopy, thermogravimetric analysis, carbohydrate analysis, calorimetry, X-ray diffraction, scanning electron microscopy, tensile tests, and oxygen barrier properties. We compare the resulting mechanical properties at low and high relative humidity. The periodate oxidation leads to a strong increase in modulus and strength of the materials. A modulus of 30 GPa for cross-linked composite at 50% relative humidity compared with 13.7 GPa for neat XG/MTM demonstrates that periodate oxidation of the XG side chains leads to crucially improved stress transfer at the XG/MTM interface, possibly through covalent bond formation. This enhanced interfacial adhesion and internal cross-linking of the matrix moreover preserves the mechanical properties at high humidity condition and leads to a Young's modulus of 21 GPa at 90%RH.

Superhydrophobicity and self-cleaning require a combination of surface topography and low-energy surfaces, where mechanical damage of the topography or contamination with oils lead to loss of the nonwetting properties. We show that such vulnerability can be solved by superamphiphobic (i.e., both superhydrophobic and superoleophobic) surfactant-coated aerogel surfaces. Using silica aerogels as model materials, the self-similar network structure allows fresh re-entrant surface topographies even after removal of the uppermost layer upon mechanical abrasion, and superoleophobicity suppresses oil contamination. Given the recent progress toward mechanically strong aerogels, we foresee that the concept can open routes for robust self-cleaning coating technologies.

The classic nanocomposite approach aims at percolation of low fraction of exfoliated individual reinforcing nanoscale elements within a polymeric matrix. By contrast, many of the mechanically excellent biological nanocomposites involve self-assembled and space-filled structures of hard reinforcing and soft toughening domains, with high weight fraction of reinforcements. Here we inspect a new concept toward mimicking such structures by studying whether percolation of intercalated domains consisting of alternating rigid and reinforcing, and soft rubbery domains could allow a transition to a reinforced state. Toward that, we present the functionalization of rigid native cellulose nanocrystals (CNCs) by esterification with a dense hydrocarbon chain brush containing cross-linkable double bonds. Composite films with 0-80 wt % of such modified CNCs (mCNCs) within a poly(butadiene) (PBD) rubber matrix were prepared via cross-linking by UV-light initiated thiol-ene click reaction. Transmission electron microscopy showed structures at two length scales, where the mCNCs and PBD form domains having internal aligned self-assemblies of alternating hard mCNCs and soft PBD with periodicity of ca. 40 nm, and where additional PBD connects such domains. Increasing the weight fraction of mCNCs causes an uncommon abrupt transition from PBD-dominated soft materials to significantly reinforced mCNC-dominated mechanical properties, suggesting that the intercalated self-assembled mCNC/PBD domains percolate in PBD upon passing 30-35 wt % of mCNCs. Maximum stress of 16 MPa at mCNC fraction of 80 wt % was obtained. The mechanical properties of the composites show exceptional insensitivity to air humidity. The shown simple concept of percolative intercalated nanocomposites suggests searching for more general biomimetic compositions involving several deformation mechanisms for improved mechanical properties.

We report supracolloidal self-assembly of atomically precise and strictly monodisperse gold nanoclusters involving p-mercaptobenzoic acid ligands (Au102-pMBA44) under aqueous conditions into hexagonally packed monolayer-thick two-dimensional facetted colloidal crystals (thickness 2.7 nm) and their bending to closed shells leading to spherical capsids (d ca. 200 nm), as controlled by solvent conditions. The 2D colloidal assembly is driven in template-free manner by the spontaneous patchiness of the pMBA ligands around the Au102-pMBA44 nanoclusters preferably towards equatorial plane, thus promoting inter-nanocluster hydrogen bonds and high packing to planar sheets. More generally, the findings encourage to explore atomically precise nanoclusters towards highly controlled colloidal self-assemblies. peerReviewed

Block copolymers self-assemble into a variety of nanostructures that are relevant for science and technology. While the assembly of diblock copolymers is largely understood, predicting the solution assembly of triblock terpolymers remains challenging due to complex interplay of block/block and block/solvent interactions. Here we provide guidelines for the self-assembly of linear ABC triblock terpolymers into a large variety of multicompartment nanostructures with C corona and A/B cores. The ratio of block lengths NC/NA thereby controls micelle geometry to spheres, cylinders, bilayer sheets and vesicles. The insoluble blocks then microphase separate to core A and surface patch B, where NB controls the patch morphology to spherical, cylindrical, bicontinuous and lamellar. The independent control over both parameters allows constructing combinatorial libraries of unprecedented solution nanostructures, including spheres-on-cylinders/sheets/vesicles, cylinders-on-sheets/vesicles, and sheets/vesicles with bicontinuous or lamellar membrane morphology (patchy polymersomes). The derived parameters provide a logical toolbox towards complex self-assemblies for soft matter nanotechnologies., Self-assembly of diblock copolymers into useful nanostructures is well understood, unlike the solution self-assembly of triblock copolymers. Here, Müller and co-workers provide guidelines for the self-assembly of linear ABC triblock terpolymers into different multicompartment nanostructures.

The solution self-assembly of amphiphilic diblock copolymers into spheres, cylinders, and vesicles (polymersomes) has been intensely studied over the past two decades, and their morphological behavior is well understood. Linear ABC triblock terpolymers with two insoluble blocks A/B, on the other hand, display a richer and more complex morphological spectrum that has been recently explored by synthetic block length variations. Here, we describe facile postpolymerization routes to tailor ABC triblock terpolymer solution morphologies by altering block solubility (solvent mixtures), blending with homopolymers, and block-selective chemical reactions. The feasibility of these processes is demonstrated on polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM) that assembles to patchy spherical micelles, which can be modified to evolve into double and triple helices or patchy and striped vesicles. These results demonstrate that postpolymerization treatments give access to a broad range of morpholog...

The chiral nematic self-assembly of aqueous suspensions of cellulose nanocrystals is partially preserved on evaporation of water, but the ordering of the rod-like nanoparticles may become distorted by changes in volume, ionic strength and surface and convective forces during evaporation, thus affecting the morphology and optical properties of the dried film. Proposed applications for these solids with chiral nematic order require confirmation of their structure. A SEM examination of the fracture surface of a slowly-dried film showed a surprisingly regular fan-like pattern which is shown to be characteristic of cross-sections of the left-handed helicoidal arrangement of nanocrystals, where the helicoidal axis was almost perpendicular to the film surfaces. Superimposed on this pattern was what appeared to be a regular porosity, which is postulated to result from pull-out of the nanocrystals oriented orthogonal to the fracture surface.

Nanofibrillated cellulose (NFC) is a natural fibrillar material with exceptionally high mechanical properties. It has, however, been exceedingly difficult to achieve nanocomposites with drastically improved mechanical properties by dispersing NFC as random networks to polymer matrices, even using compatibilization. We show nanocomposites consisting of aligned assemblies of multilayered graphene and NFC with excellent tensile mechanical properties without any surface treatments. The optimum composition was found at 1.25 wt % graphene multilayers, giving a Young’s modulus of 16.9 GPa, ultimate strength of 351 MPa, strain of 12%, and work-of-fracture of 22.3 MJ m–3. This combines high strength with relatively high toughness and is obtained by direct exfoliation of graphite within aqueous hydrogels of NFC where an optimum sonication power is described. The results suggest the existence of an attractive interaction between multilayered graphene flakes and cellulose. Aligned assemblies are obtained by removal of water by filtration. The concept can be beneficial for applications because it results in high mechanical properties by a simple and environmentally green process.

Nature offers exciting examples for functional wetting properties based on superhydrophobicity, such as the self-cleaning surfaces on plant leaves and trapped air on immersed insect surfaces allowing underwater breathing. They inspire biomimetic approaches in science and technology. Superhydrophobicity relies on the Cassie wetting state where air is trapped within the surface topography. Pressure can trigger an irreversible transition from the Cassie state to the Wenzel state with no trapped air—this transition is usually detrimental for nonwetting functionality and is to be avoided. Here we present a new type of reversible, localized and instantaneous transition between two Cassie wetting states, enabled by two-level (dual-scale) topography of a superhydrophobic surface, that allows writing, erasing, rewriting and storing of optically displayed information in plastrons related to different length scales.

We show how the self-assembly of miktoarm star copolymers can be controlled by modifying the side chains of their polypeptide arms, using A2B and A2B2 type polymer/polypeptide hybrids (macromolecular chimeras). Initially synthesized PS2PBLL and PS2PBLL2 (PS, polystyrene; PBLL, poly(e-tert-butyloxycarbonyl-l-lysine)) miktoarms were first deprotected to PS2PLLHCl and PS2PLLHCl2 miktoarms (PLLHCl, poly(l-lysine hydrochloride)) and then complexed ionically with sodium dodecyl sulfonate (DS) to give the supramolecular complexes PS2PLL(DS) and PS2(PLL(DS))2. The solid-state self-assemblies of these six miktoarm systems were studied by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and small- and wide-angle X-ray scattering (SAXS, WAXS). The side chains of the polypeptide arms were observed to have a large effect on the solubility, polypeptide conformation, and self-assembly of the miktoarms. Three main categories were observed: (i) lamellar self-assemblies at the block c...

A generic approach for heterogeneous surface modification of cellulosic materials in aqueous medium, applicable for a wide range of functionalizations, is presented. In the first step, carboxymethyl cellulose (CMC) modified with azide or alkyne functionality, was adsorbed on a cellulosic substrate, thus, providing reactive sites for azide–alkyne cycloaddition click reactions. In the second step, functional units with complementary click units were reacted on the cellulose surface, coated by the click-modified CMC. Selected model functionalizations on diverse cellulosic substrates are shown to demonstrate the generality of the approach. The concept by sequentially combining the robust physical adsorption (“physical click”) and robust chemical reaction (“chemical click”) allows versatile, simple, and environmentally friendly modification of a cellulosic substrate with virtually any azide- or alkyne-modified molecule and even functionalization with several types of units.

El pdf del artículo es la versión post-print.-- et al., Strongly luminescent silver nanoclusters with tunable emission are directly synthesized in organic polar and apolar solvents. We show that an amphiphilic polystyrene-block-poly(methacrylic acid) block copolymer can be universally used as their support medium. A remarkable similarity in spectroscopic properties is observed between these clusters and charge-transfer organic dyes. This journal is © 2012 The Royal Society of Chemistry.

We show that in a hydrogen bonded LC side chain diblock copolymer with lamellar morphology on the block copolymer level, two distinct packing mechanisms of the side chain blocks are possible depending on the amount of hydrogen bonded side chains. We mixed a hydrogen bonding mesogen, cholesteryl hemisuccinate (CholHS), with poly(1,2-butadiene)-block-poly(2-vinylpyridine) (PBd-P2VP) and poly(styrene)-block-poly(4-vinylpyridine) (PS-P4VP), in which the poly(vinylpyridine) act as host blocks, and we varied the CholHS to pyridine repeat unit ratio (x). With all x, a lamellar morphology on the block copolymer level was achieved. However, at low binding of CholHS to the host block, the CholHS side chains microphase separated into a single layer inside the poly(pyridine) lamellae resulting in a novel microphase separated structure. This includes, for example, the PS-P4VP sample with x = 0.25 and all the PBd-P2VP based samples since hydrogen bonding of CholHS to P2VP was sterically limited as revealed by infrared ...

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.