This paper deals with the influence of the nature and number of solid interfaces on the alignment of the columns in a semiconducting discotic liquid crystal. The solid substrates have been characterized in terms of their roughness and surface energy. The alignment of the discotic liquid crystal columns on these substrates has been determined by optical microscopy under crossed polarizers and by tapping-mode atomic force microscopy. The nature of the substrates has negligible influence on the alignment. The key parameter is the confinement imposed to the film. These surprising observations are explained by the antagonist alignment role of gas and solid interfaces.

A joint theoretical and experimental study of the electronic and structural properties of liquid crystalline metal-free phthalocyanines bearing a strong potential for charge and exciton transport has been performed. The synthesis of such compounds has been triggered by quantum chemical calculations showing that: (i) hole transport is favored in metal-free phthalocyanines by their extremely low reorganization energy (0.045 eV) and large electronic splittings; and (ii) the efficiency of energy transfer along the one-dimensional discotic stacks is weakly affected by rotational disorder due to the two-dimensional character of the molecules. We have synthesized two metal-free phthalocyanines with different branched aliphatic chains on the gram scale to allow for a full characterization of their solid-state properties. The two compounds self-organize in liquid crystalline mesophases, as evidenced by optical microscopy, differential scanning calorimetry, X-ray powder diffraction, and molecular dynamics simulations. They exhibit a columnar rectangular mesophase at room temperature and a columnar hexagonal mesophase at elevated temperature.

Well-defined π-conjugated oligomers play an important role in the field of organic electronics, because their precise chemical structure and conjugation length give rise to welldefined functional properties and facilitate control over their supramolecular organization. In this review, we present different complementary approaches for the control of molecular assembly into well-defined structures on the nanoscale, applied to oligothiophenes as a typical conjugated system. We consider self-assembly in solution, sublimation of individual molecules in the vapor phase, and aggregation in thin deposits from compounds molecularly dispersed in a solution. We demonstrate that the development of substituted, soluble π-conjugated materials allows not only a control of their organization in the solid state but also the possibility of determining the degree of order in solution. During these self-assembly processes, the interplay between the conjugated molecules, the solvent, and the substrate surface is of primary importance. Depending on the interactions between the molecules and the substrate, one-dimensional (nanowires) or two-dimensional (platelets) objects can be generated. The self-organization of conjugated building blocks in solution or on surfaces, leading to the construction of nanoscopic and mesoscopic architectures, represents a starting point for the construction of molecular electronics or even circuits, through surface patterning with nanometer-sized objects.

We study the effect of the cyclization of a linear poly(styrene-b-isoprene) PS-PI copolymer on the morphology of the micelles formed in heptane (a selective solvent for PI). The linear and the cyclic copolymers have exactly the same degree of polymerization, i.e. 290 for PS and 110 for PI, i.e., volume fraction Φ PS ) 0.78. We use dynamic light scattering (DLS) and atomic force microscopy (AFM) techniques to characterize the micellar morphology made from copolymer molecules, focusing on the effect of cyclization. We also report the concentration effect on the micelle size and shape made from the linear and cyclic copolymers. Our results show that the micelles made from linear PS-PI adopt a "classical" spherical shape and keep the same morphology parameters over the range of investigated concentrations. In contrast, the micelles arising from cyclic copolymer chains adopt a giant wormlike shape. In this later case, both the size and the shape evolve when the concentration is increased, starting from small individual "sunflower-like" micelles, at low concentrations, to giant wormlike micelles at higher concentrations. Our results suggest also that these giant wormlike micelles made from cyclic copolymer chains result from the self-assembly of "sunflower-like" elementary micelles.

We have studied the effect of polystyrene (PS) homopolymer addition on the morphology of self-assembled block copolymer micelles made from linear or cyclic poly(styrene-b-isoprene), PS-b-PI, in a selective solvent for the PI block (heptane). Both copolymers have the same composition: the degree of polymerization is 290 for the PS block, and 110 for the PI block, and we focused on the influence of the addition of small amounts of PS homopolymer on the micellar morphology. For the copolymer concentrations considered, the linear copolymer self-organizes into spherical micelles while the cyclic copolymer forms cylindrical micelles. PS and PI chains constitute the core and the corona of these micelles, respectively, due to the different affinity of the blocks for heptane. Consequently, the PS homopolymer added is "solubilized" into the micellar core. Dynamic light scattering (DLS) data combined with atomic force microscopy (AFM) results show that the addition of PS homopolymer induces a drastic change in the micellar organization. Indeed, a morphological transition, from spheres to cylinders for the linear copolymer, and from cylinders to vesicles for the cyclic copolymer, is observed. These results highlight the fact that a small incorporation of PS homopolymer is clearly sufficient to modify the morphology (size and shape) of the micelles. This approach could be a key parameter for the design/control of micelles for specific applications in nanotechnology.

New water-soluble amphipatic hyperbranched organic polymers composed of a hydrophobic polystyrene core and a hydrophilic shell have been synthesized and characterized. An arborescent polystyrene core is first synthesized by the “graft-on-graft” technique based on the iterative grafting of end-functional polystyryllithium chains onto reactive poly(chloroethyl vinyl) ether backbones. Chain-extension of the external branches of the hyperbranched polystyrene is then achieved by living cationic polymerization of protected hydrophilic vinyl ethers. This yields polystyrene dendrigrafts surrounded by a dense poly(vinyl ether) shell that is made hydrophilic by deprotection of hydroxyl functions of vinyl ether units. The obtained nanometer-sized macromolecular structures are fully soluble in aqueous media and present unimodal and narrow size distribution with an average diameter of about 100 nm. The dimensions and shape of the individual macromolecules before and after the deprotection step were further investigated in solution by dynamic light scattering (DLS) and as isolated unimolecular deposits using atomic force microscopy and cryomicroscopy.The results obtained using both imaging techniques are in agreement with those obtained by DLS and provide additional information on the internal structure of the amphipatic dendrigrafts. Both the protected and the deprotected amphipatic polymers exhibit a complex internal organization constituted by distinct subdomains. These peculiar morphologies result from the internal segregation of chemically distinct macromolecular blocks that constitute the dendrigraft branches and associate with neighboring blocks to form separate phases.

A convenient method to induce face-on orientation of an alkoxy phtalocyanine discotic mesogen is described. The alignment is imposed by the confinement of the discotic thin films with a top sacrificial polymer layer that is easily removed by washing with a selective solvent, after thermal annealing. Thin films have been characterized by optical and atomic force microscopy, UV-Vis absorption spectroscopy, and grazing incidence wide angle X-ray scattering. The data converge in showing the central role of the sacrificial layer in promoting alignment with the planar molecules orienting parallel to the substrate in an essentially homeotropic arrangement over large lateral length scales and the persistence of this desirable alignment after removal of the layer.

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