Oscillatory Shear Flow-Induced Alignment of Lamellar Melts of Hydrogen-Bonded Comb Copolymer Supramolecules

Reversal of Handedness of Ionic liquid based Chiral Block Copolymers via Self-Assembly in Solution and Bulk Phase

Polymerized ionic liquid (PIL) based ionic chiral block copolymers (BCPs*) were synthesized by functionalization of poly(4-vinyl pyridine) segment in poly(styrene)-block-poly(4-vinyl pyridine) (PS-b-P4VP) block copolymer. Owing to the ease of ion...

Towards Monodomains of Self-Organized Comb-Shaped Polymeric Supramolecules

We have previously shown that hierarchical self-organization is achieved upon physically bonding amphiphilic molecules to diblock copolymers. Here we discuss the effect of imposed shear flow to achieve overall alignment of the locally self-organized structures. We will first present shear aligned polystyrene-block-poly(4-vinyl pyridine) diblock copolymers (PS-b-P4VP), where pentadecyl phenol (PDP) has been hydrogen bonded to the pyridines. Depending on the selected molecular weights, eg. hexagonal arrangement of PS cylinders in the lamellar matrix of P4VP(PDP) can be obtained with high overall order of both structures. This is a template to obtain discrete PS nanorods, which have P4VP corona once the PDP molecules have been cleaved off by a solvent treatment. Selecting a relatively high molecular weight PS block and a short P4VP block leads to mesoporous materials with emptied cylinders with P4VP brushes at the walls. The glassy state of the PS matrix prevents the pores from collapsing. The pyridine groups of PS-b-P4VP can be protonated using eg. toluene sulphonic acid and the resulting polymeric salt has been complexed using PDP. The weight fractions have been selected so that the polyelectrolyte/amphiphile complex self-organizes into cylindrical domains with hexagonal packing. Shear alignment leads to high overall order. SAXS in combination with structural models suggests that within the cylinders there are parallel self-organized layers. The conductivity is anisotropic. We will also discuss dielectric reflectors based on self-organized block polyelectrolytes consisting PS-b-P4VP where DBSA has been complexed to P4VP. In this case, plasticization due to the oligomeric side chains promotes a facile structure formation at long periodicities in comparison to concepts based on eg. blends of high molecular weight polymers and block copolymers. Finally, plasticized comb-shaped supramolecules based on rigid conjugated poly(p-pyridine) are discussed. Even gentle shearing leads to highly aligned lamellar structures, which show efficient polarized photoluminescence.

A rheo-optical apparatus for real time kinetic studies on shear-induced alignment of self-assembled soft matter with small sample volumes

In soft materials, self-assembled nanoscale structures can allow new functionalities but a general problem is to align such local structures aiming at monodomain overall order. In order to achieve shear alignment in a controlled manner, a novel type of rheo-optical apparatus has here been developed that allows small sample volumes and in situ monitoring of the alignment process during the shear. Both the amplitude and orientation angles of low level linear birefringence and dichroism are measured while the sample is subjected to large amplitude oscillatory shear flow. The apparatus is based on a commercial rheometer where we have constructed a flow cell that consists of two quartz teeth. The lower tooth can be set in oscillatory motion whereas the upper one is connected to the force transducers of the rheometer. A custom made cylindrical oven allows the operation of the flow cell at elevated temperatures up to 200 degrees C. Only a small sample volume is needed (from 9 to 25 mm(3)), which makes the apparatus suitable especially for studying new materials which are usually obtainable only in small quantities. Using this apparatus the flow alignment kinetics of a lamellar polystyrene-b-polyisoprene diblock copolymer is studied during shear under two different conditions which lead to parallel and perpendicular alignment of the lamellae. The open device geometry allows even combined optical/x-ray in situ characterization of the alignment process by combining small-angle x-ray scattering using concepts shown by Polushkin et al. [Macromolecules 36, 1421 (2003)].

Alpha-helical-within-discotic columnar structures of a complex between poly(ethylene oxide)-block-poly(l-lysine) and a hexa-peri-hexabenzocoronene

Poly(ethylene oxide)-block-poly(l-lysine) (PEO-PLL) was complexed with an amphiphilic hexa-peri-hexabenzocoronene (HBC). This produced a thermotropic liquid crystalline material (PEO-PLL-HBC), which was investigated by FTIR spectroscopy and differential scanning calorimetry as well as by wide- and small-angle X-ray scattering. It was found that the poly(l-lysine) blocks form an alpha-helical secondary structure. Each helix is surrounded symmetrically by six discotic columns of HBC, which gives an alpha-helical-within-discotic column structural entity. The dense packing of these entities produces hexagonal sublattices (formed by the columns) in the frame of a two-dimensional hexagonal lattice (formed by the helices). An order-order transition from a columnar structure Col1 to Col2 was found at 54 degrees C. The unit cell constants are 5.75 nm (Col1) and 6.60 nm (Col2). The larger unit cell size of Col2 was explained by a higher intracolumnar order of the latter in which the packing distance of the disklike HBC cores is well-defined (0.353 nm). PEO-PLL-HBC combines essential features of liquid crystals with a basic structural element of proteins into a single material.