We have studied the influence of geometric confinement imposed on the supramolecular architecture of a discotic model compound confined to self-ordered nanoporous alumina. We systematically varied the pore diameter and the chemical nature of the pore walls and studied the systems thus obtained by means of wide angle X-ray diffraction and differential scanning calorimetry. A dominant planar core phase was found for high-energy pore walls consisting of alumina, whereas no apparent texture was present in the case of pore walls coated with non-polar poly(p-xylylene). Inside pores of 35 and 180 nm in diameter, pronounced geometric confinement effects and interfacial effects influence the structure formation. Additionally, we performed molecular dynamics simulations using a coarsegrained discotic potential.
We have evaluated the effect of slit‐like nanoconfinements imposed on columnar discotic phases within a discotic block copolymer displaying a lamellar microphase. Findings are that the columns are oriented uniformly along the lamellar normal within the plane of thin films, that a rectangular rather than a hexagonal columnar phase is formed within the discotic regions, that the thermodynamic stability of the columnar phase is strongly reduced relative to the low molar mass model compounds and finally, that the isotropic phase can be unusually strongly supercooled with respect to the columnar phase formation. Slit‐like nanoconfinements allow thus to induce novel types of the intrinsic order and columnar orientations.magnified image
The viscoelastic properties of a binary mixture of a mesogenic side-chain block copolymer in a low molecular weight nematic liquid crystal are studied for mass concentrations ranging from the diluted regime up to a liquid crystalline gel state at about 3%. In the gel state, the system does not flow, exhibits a polydomain structure on a microscopic level, and strongly scatters light. Below the gelation point, the system is homogeneous and behaves like a usual nematic, so the continuum theory of liquid crystals can be applied for interpreting the experimental data. Using the dynamic Fréedericksz transition technique, the dependence of the splay elastic constant and the rotational viscosity on the polymer concentration have been obtained. Comparing the dynamic behavior of block copolymer solutions with the respective homopolymer solutions reveals that, above a mass concentration of 1%, self-assembling of the block copolymer chain segments in clusters occurred, resulting in a gel state at higher concentrations. The effective cluster size is estimated as a function of the concentration, and a scaling-law behavior near the sol-gel transition is confirmed. This technique may serve as an alternative method for determining the gelation point.
We present a combinatorial approach to the synthesis of block copolymer series by anionic polymerization, utilizing a specially designed reactor setup. The setup features one main reactor and three secondary reactors to carry out anionic polymerizations on laboratory-scale quantities at low temperatures. The implementation was demonstrated with three series of ABand ABC-block copolymers with identical A-and AB-blocks, respectively. The B-block in AB-diblock copolymers and the C-block in ABC-triblock copolymers can be varied with respect to block length or chemical constitution. Well-defined series of block copolymers are useful for advanced optimization of functional block copolymers in nanotechnology applications.
Cover: A special reactor setup was developed for the combinatorial anionic polymerization of block copolymers. This is an efficient and reliable approach for the synthesis of block copolymer series with well‐defined compositions, enabling detailed comparative studies and tailoring of block copolymer properties. Further details can be found in the article by R. Pettau, C. Erdelen, and H.‐W. Schmidt* .
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