Publications (4)0 Total impact
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ABSTRACT: Self-organization leads to nanoscale polymeric structures based on competing interactions [1,2] and incorporation of sev-eral schemes of self-organization gives rise to hierarchical structures. [1,3±6] Previously we have introduced a concept where amphiphilic molecules are physically bonded selec-tively to one block of a block-copolymer to form specific re-ceptor±substrate supramolecules (supramolecules are defined elsewhere [7,8]) and they self-organize to form structure-within-structures. [5,6,9] In this communication we show how the scheme allows the preparation of mesoporous materials. The starting material is the diblock copolymer polystyrene-block-poly(4-vinyl pyridine), PS-block-P4VP, with a stoichiometric amount of pentadecyl phenol, PDP, hydrogen bonded to the latter block. The block lengths have been selected to give a lamellar-within-cylindrical morphology, where the P4VP/ PDP-blocks form cylinders within the rigid glassy PS-medium and where the P4VP/PDP-complexes, being of a comb-like architecture, self-organize as lamellae [10] within the cylinders. In addition to such a local order, we accomplish overall orien-tation by applying an oscillatory shear flow to align the cylin-ders. The orientation is verified using small-angle X-ray scat-tering (SAXS). Hollow cylinders with P4VP brushes on the interior walls are achieved in a straightforward way by dis-solving the PDP molecules away from the cylinders, as shown by SAXS and FTIR. Such ªhairy tubesº open possibilities for controllable mesoporous membranes as the conformation of the brushes depends on the solvent. In addition, P4VP further allows chemical modification to tailor the membranes. Biochemical systems allow several examples of functional membranes, such as the cell walls with their transport pro-teins, and numerous biomimetic concepts have thus been pur-sued. Synthetic functional membranes have major technologi-cal applications, such as in purification. Potential concepts have been demonstrated based on mesoporous materials due to organic/inorganic assemblies, [11±13] cross-linked structures of amphiphiles containing crown ethers, [14,15] mesotubes based on degradable polymer fibers as templates, [16] polymerized tubes with polyacrylic acid brushes obtained by degradation process, [17,18] self-organization of rod-coil copolymers, [19] and nanoporous carbon membranes, [20] to mention a few. In this communication we describe a simple method for constructing mesoporous materials, based on physically matching molecules as templates. Comb coil diblock copoly-mers form a specific architecture of self-organizing block copolymers, [2,21,22] in which a dense set of repulsive side chains is covalently connected to the backbone. Even carefully matched physical bonds suffice to bond the side chains to allow self-organization. [23,24] For example, in P4VP the pyri-dine groups are hydrogen-bonding acceptors that form suffi-ciently strong hydrogen bonds with stoichiometric amounts of alkyl phenols, such as PDP, to form lamellar order. [25] If such a receptor±substrate supramolecule is selected to be one block of a diblock copolymer, a comb coil supramolecule PS-block-P4VP(PDP) 1.0 is formed, capable of hierarchical self-organi-zation [5,6,9] (Scheme 1). Scheme 1.
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Riikka Mäki-Ontto
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ABSTRACT: Structures, which are significantly smaller than e.g. in the present day microelectronics, are pursued in nanotechnology. Structures near molecular level can be constructed for example by imitating biological systems where self-organization and molecular recognition are used to form supramolecules. In this work hierarchically self-organized supramolecular nanostructured materials are constructed with peculiar conductivity behavior. The structures are, as such, not macroscopically aligned and therefore the conductivity is isotropic throughout the macroscopic sample. Two types of supramolecular materials are studied under an oscillatory shear flow in order to find routes towards macroscopically oriented hierarchical structures. The first type consists of 20 - 50 Å lamellar structure due to self-organization of comb-shaped supramolecules. The second structure is a hierarchically self-organized, i.e. lamellar-within-lamellar structure, where there are structures at two length scales, i.e. at 20 - 50 Å and 200 - 1000 Å. Shear flow conditions allowing optimal macroscopic order were identified. Finally, macroscopically aligned protonically conducting material is presented, which shows globally tridirectional conductivity with anisotropic hopping conductivity. Asymmetric structures i.e. lamellae-within-cylinders are also briefly studied and a method is found to achieve mesoporous materials with polymer brushes at the walls of emptied cylinders. The brushes can be used to tailor the functionalities of the pores. The results of this work show that materials, which are relatively simple to produce, allow tailored macroscopic properties due to their aligned self-organized nanoscale structures.
951-22-5733-5.
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ABSTRACT: In this work we present the orientational behavior of comb copolymer-like supramolecules P4VP(PDP)1.0, obtained by hydrogen bonding between poly(4-vinylpyridine) and pentadecylphenol, during large-amplitude oscillatory shear flow experiments over a broad range of frequencies (0.001-10 Hz). The alignment diagram, presenting the macroscopic alignment in T/TODT vs ω/ωc, contains three regions of parallel alignment separated by a region of perpendicular alignment. For our material, the order-disorder temperature TODT = 67 °C and ωc, the frequency above which the distortion of the chain conformation dominates the materials’ viscoelasticity, is around 0.1 Hz at 61 °C. For the first time flipping from a pure transverse alignment via biaxial transverse/perpendicular alignment to a perpendicular alignment as a function of the strain amplitude was found.
