Denis V. Anokhin

Unprecedented Route to Ordered Polyaniline: Direct Synthesis of Highly Crystalline Fibrillar Films with Strong π-π Stacking Alignment.

Films of polyaniline (PANI) featuring about 80% crystallinity and characterised with strong π-π stacking alignment parallel to the film surface have been obtained directly after the original synthesis upon simple drying of the aqueous PANI suspension. A strong anisotropy in the growth of the nano-sized crystals produced during the synthesis results in the formation of micrometer-length fibrils perpendicular to the film surface in the course of water evaporation. The regular intercalation of water molecules between the PANI chains seems to be crucial for their ordering throughout the synthesis and film formation.

Multiblock copolymer behaviour of α-CD/PEO-based polyrotaxanes: towards nano-cylinder self-organization of α-CDs

The present work demonstrates that α-cyclodextrin/poly(ethylene oxide) (α-CD/PEO)-based polyrotaxanes (PRs) behave as multiblock copolymers. One block type consists of a rod-like tube made of 6 to 7 weakly stacked α-CDs threaded along the PEO chain. The other one is made of a naked PEO segment, i.e. the PR part that is not covered by α-CDs. This multiblock behaviour induces the self-organization of PRs in concentrated solution in dimethyl sulfoxide (DMSO) at room temperature leading to the formation of nano-cylinders. These nano-cylinders consist of assemblies of roughly 60 α-CD rod-like tubes through hydrogen bonding. Moreover, crystallites of naked PEO segments are formed since PEO is in poor solvent conditions (DMSO) at room temperature. Furthermore, the formation of α-CD nano-cylinders as well as of naked PEO segment crystallites leads to physical gelation of PRs in DMSO.

A supramolecular structure with an alternating arrangement of donors and acceptors constructed by a trans-di-C60-substituted Zn porphyrin derivative in the solid state

When a molecule is constructed from geometrically isotropic [such as [60]fullerene (C60)] and anisotropic (such as porphyrin) units, as in the case of a trans-di-C60-substituted Zn porphyrin derivative (diZnCPD), great interest lies in the understanding of their individual contributions to structural formations and phase transitions. For this purpose, the compound, diZnCPD, was designed and synthesized. Its phase behavior was investigated viadifferential scanning calorimetry (DSC) and polarized light optical microscopy (POM) and its supramolecular structure was elucidated viawide-angle X-ray diffraction (WAXD) and selective area electron diffraction (SAED) in transmission electron microscopy (TEM). The diZnCPD possesses a polymorphism in its ordered structures. When cooled from the isotropic (I) phase with experimentally accessible rates, instead of transferring into its ultimate stable phase, this compound formed a less ordered, metastable phase with a layered structure at 152 °C. Annealing this metastable phase enabled a further transformation into a stable phase with a higher transition temperature. As such, this metastable phase is monotropic. The formation of the stable phase was thus thermodynamically favorable, but kinetically more difficult (with a higher barrier for the transformation). Direct formation of this stable phase from the I state was unsuccessful even after prolonged isothermal experiments over several days above 152 °C, indicating that the formation barrier of this stable phase is extremely high. The thermally stable phase possessed a supramolecular structure with a triclinic unit cell of a = 3.34 nm, b = 2.01 nm, c = 1.88 nm, α = 89°, β = 98°, and γ = 90°. Detailed structural analysis revealed that this is a donor–acceptor separated structure of C60s and porphyrins nearly along the [01] direction within which the zig-zag shaped C60 channels are along the [001] direction of the unit cell. We believe this is the first example of generating a donor–acceptor separated structure of C60s and porphyrins in the bulk through a thermal annealing process. This structure provides promising potential for the use of this material to fabricate supramolecular electronic devices without utilizing a solvent process.

Microstructure of Banded Polymer Spherulites: Studies with Micro-Focus X-ray Diffraction

Micro-beam X-ray diffraction has been used to investigate the texture of banded spherulites of melt-crystallized poly(trimethylene terephthalate), PTT, formed in films of approximately 30 to 50 μm thickness. The WAXS micro-diffraction patterns show that at the local scale, the PTT texture is close to that of a single crystal. In agreement with previous studies using selected-area electron diffraction, it is shown that the crystal growth direction is parallel to the a-axis of the unit cell. When plotted as a function of the distance to the spherulite center, the intensity of different diffraction peaks reveals the same periodicity. This means that the lamellar twist is strictly uniform. The latter observation is more compatible with the model explaining the twist as a result of unbalanced surface stresses than that of isochiral giant screw dislocations. The main features of the experimental diffractograms can be understood using the numerical approach, which is developed in the approximation of a purely geometric broadening of X-ray reflections. In particular, the simulation can predict the sequence of appearance of different diffraction peaks and their shape on the 2D micro-diffraction patterns.

Theory of X-ray reflection broadening for textures with double-axis averaging: from semicrystalline polymers exhibiting twisted lamellar growth to discotic liquid crystals

It is shown that textures with double-axis averaging similar to the a-texture, or Keller–Machin Type I texture, are not specific to semicrystalline polymers exhibiting twisted lamellar growth. In this work, such texture is observed in extruded fibers of a typical discotic molecule, trans-diC60-Zn porphyrin. Experimentally, these textures can be detected from the characteristic `comma-like azimuthal profiles of the non-equatorial diffraction peaks in two-dimensional X-ray patterns. Analytical expressions for the azimuthal intensity distribution are developed, which are in good agreement with the experiment. In the proposed generalized coordinates, the diffraction peak shape becomes universal. This provides a simple means of checking the closeness of the sample morphology to the a-texture from just one two-dimensional pattern, without constructing the whole X-ray pole figure.

Self‐Assembly of a Low‐Symmetry Monodendron Containing Two Asymmetrically Linked Molecular Wedges

Herein, we describe the synthesis of a low-symmetry monodendron, 3,4-bis(dodecyloxy)-5-[3,4,5-tris(dodecyloxy)benzyloxy]benzoic acid, following a simple route which starts from gallic acid ethyl ester and does not require any protecting groups. The self-assembled structures formed by the compound in 3D and 2D were investigated by synchrotron X-ray scattering and scanning force microscopy (SFM). In 3D, the compound forms a stable crystalline phase with an orthorhombic lattice in which the alkyl chains connected to different benzene rings form crystalline and amorphous domains. Upon cooling from the isotropic melt the compound exhibits a monotropic smectic mesophase. In 100-nm-thick films on a neutral substrate the structure loses its biaxiality, adopting a hexagonal columnar structure with the columns oriented parallel to the substrate. By contrast, in ultrathin films on graphite the SFM likely reveals two crystal orientations, which can develop due to the epitaxial adsorption on the substrate of the alkyl chains pertinent to different benzene rings.

Exploring the structure of inter-platelet galleries in organically modified montmorillonite using the small-angle X-ray scattering interface distribution function approach

Small-angle X-ray scattering interface distribution function (IDF) analysis is successfully applied to evaluate the two- and three-phase inter-platelet gallery structure in synthetic montmorillonite (MMT) modified with a mixture of chemically grafted and physically adsorbed chains of a typical organic modifier, octadecyl trimethyl ammonium bromide. Two distinctly different states of adsorbed chains in the inter-platelet galleries are identified. The first one corresponds to a fully cation-exchanged structure with an inter-platelet distance of about 21u2005A. In this case the organic modifier is in a liquid-like state, and the system does not exhibit any structural or thermal transitions between ambient temperature and 433u2005K. When the number of adsorbed chains exceeds the cation-exchange capacity of the MMT platelets the inter-platelet spacing is increased to 43u2005A. In this case, the variable-temperature IDFs reveal partially crystalline order in the inter-platelet galleries, which vanishes at the melting point of the alkyl tails confined in the galleries.