Hierarchical Self-Assembly of Halogen-Bonded Block Copolymer Complexes into Upright Cylindrical Domains

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 nanofabricatio

Supramolecular amplification of amyloid self-assembly by iodination

Amyloid supramolecular assemblies have found widespread exploitation as ordered nanomaterials in a range of applications from materials science to biotechnology. New strategies are, however, required for understanding and promoting mature fibril formation from simple monomer motifs through easy and scalable processes. Noncovalent interactions are key to forming and holding the amyloid structure together. On the other hand, the halogen bond has never been used purposefully to achieve control over amyloid self-assembly. Here we show that single atom replacement of hydrogen with iodine, a halogen-bond donor, in the human calcitonin-derived amyloidogenic fragment DFNKF results in a super-gelator peptide, which forms a strong and shape-persistent hydrogel at 30-fold lower concentration than the wild-type pentapeptide. This is remarkable for such a modest perturbation in structure. Iodination of aromatic amino acids may thus develop as a general strategy for the design of new hydrogels from unprotected peptides and without using organic solvents

Gas phase synthesis of non-bundled, small diameter single-walled carbon nanotubes with near-armchair chiralities

We present a floating catalyst synthesis route for individual, i.e., non-bundled, small diameter single-walled carbon nanotubes (SWCNTs) with a narrow chiral angle distribution peaking at high chiralities near the armchair species. An ex situ spark discharge generator was used to form iron particles with geometric number mean diameters of 3–4 nm and fed into a laminar flow chemical vapour deposition reactor for the continuous synthesis of long and high-quality SWCNTs from ambient pressure carbon monoxide. The intensity ratio of G/D peaks in Raman spectra up to 48 and mean tube lengths up to 4 μm were observed. The chiral distributions, as directly determined by electron diffraction in the transmission electron microscope, clustered around the (n,m) indices (7,6), (8,6), (8,7), and (9,6), with up to 70% of tubes having chiral angles over 20°. The mean diameter of SWCNTs was reduced from 1.10 to 1.04 nm by decreasing the growth temperature from 880 to 750 °C, which simultaneously increased the fraction of semiconducting tubes from 67% to 80%. Limiting the nanotube gas phase number concentration to ∼10 exp 5 cm exp −3 prevented nanotube bundle formation that is due to collisions induced by Brownian diffusion. Up to 80% of 500 as-deposited tubes observed by atomic force and transmission electron microscopy were individual. Transparent conducting films deposited from these SWCNTs exhibited record low sheet resistances of 63 Ω/□ at 90% transparency for 550 nm light.Peer reviewe

Polymersomes with asymmetric membranes and self-assembled superstructures using pentablock quintopolymers resolved by electron tomography

| openaire: EC/FP7/291364/EU//MIMEFUNPolystyrene-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.Peer reviewe

Iodoperfluoroalkanes as structure-directing agents for polymer self-assembly

Supramolecular polymers are formed by self-assembly of tailored building blocks through noncovalent interactions. The choice of strong unidirectional interactions can lead to shape-persistent nanostructures with a high degree of internal order and new functionalities respect to similar covalent polymers. Recently, halogen bonding (XB) has proven to be one of the most effective way to assemble halogenated organic compounds and polymers with suitable electron-donor groups into stable macromolecular structures. Fluorination of the molecular backbone of certain halogenated building blocks enhances their ability to work as halogen bonding donors, giving rise to particularly strong interactions. Herein, we show that XB strength and directionality, coupled with the segregation tendency of perfluoroalkyl and alkyl chains, might open the way to several new possibilities for structure control and molecular imprinting of polymeric materials, as well as for the tuning of their functional properties. Moreover, fluorinated XB-donors can be highly effective also for light-induced surface patterning applications, showing potential for numerous applications in photonics and nanotechnology

HALOGENATION OF AMYLOIDOGENIC PEPTIDES PROMOTES EFFICIENT FIBRILS AND HYDROGELS FORMATION

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Anisotropic ionic conductivity in fluorinated ionic liquid crystals suitable for optoelectronic applications

In this work, we report a library of thirteen fluorinated ionic liquids consisting of iodide salts of 1-alkyl-3-polyfluoroalkyl-imidazolium cations. By changing the length of the alkyl and polyfluoroalkyl pendants, we discovered that particular combinations of these result in compounds showing a mesophase. The nature and the molecular arrangement of the mesophase are characterised by polarised optical microscopy and powder X-ray diffraction analysis, among others. We demonstrate that, after the addition of I2 to generate the I-/I3- redox couple, anisotropic ionic conductivity takes place along preferential pathways in the lamellar structure of the mesophase. Notably, the addition of I2 does not suppress the mesophase temperature range, contrary to previously reported systems. Furthermore, the tendency of these materials to supercool allows the molecular arrangement in the mesophase to be retained in a solid film at ambient temperatures. Finally, we demonstrate their applicability as a quasi-solid electrolyte by preparing dye-sensitised solar cells with power conversion efficiencies comparable to the previous reports. © 2013 The Royal Society of Chemistry