Uwe Beginn

Thermotropic columnar mesophases from N-H...O, and N...H-O hydrogen bond supramolecular mesogenes

Abstract The structures of supramolecular columnar mesophases that depend on the presence of either N–H⋯O, or N⋯H–O– hydrogen bonds (subsumed under the term ‘N|H|O-bonds’) are reviewed. The thesis is supported that supramolecular mesogenes bridge different fields of liquid crystal research, offering the opportunity to create a unified picture of thermotropic, and lyotropic mesomorphism. With the examples of N|H|O hydrogen bond mesogenes the molecular structures of the respective mesogenes are presented, and general principles to rationally construct such molecules are discussed. A connection is drawn to systems from isolated columns as found in low molecular weight organogels. Perspectives, and outlooks for possible applications of N|H|O hydrogen bonded columnar phases are given.

Preparation of Isophorone Diisocyanate Terminated Star Polyethers

Reactive star shaped isocyanate prepolymers have been prepared by endcapping hydroxy functionalized poly(alkylene oxide)s with isophorone diisocyanate. Selective reaction conditions have been worked out to reduce the amount of chain extension and crosslinking due to reaction of both isocyanate groups of the IPDI moieties. By combining 1 H and 13 C NMR spectroscopy with size exclusion chromatography (SEC), the fractions of the monourethane isomers, and the extent of diurethane formation was determined. The effect of catalysis, of the excess of isocyanate, and of the type of poly(alkylene-oxide) on the product structure and composition were investigated.

Field-cycling NMR relaxometry of polymers confined to artificial tubes: verification of the exponent 3/4 in the spin–lattice relaxation dispersion predicted by the reptation model

Abstract 2 H field-cycling NMR relaxometry was applied to deuterated linear polyethyleneoxide (PEO) of different chain lengths confined in a porous matrix of cross-linked polyhydroxyethylmethacrylate (PHEMA). The PHEMA pore diameter was of the order of 10 nm, i.e. smaller than or similar to the dimension which the PEO coils would have in the unconfined melt. The frequency and molecular weight dependences of the spin–lattice relaxation time predicted by de Gennes as T 1 ∝ M 0 ω 3/4 on a timescale short compared with the Rouse relaxation time are well reproduced experimentally.

Synthesis and Characterization of Tris-Methacrylated 3,4,5-Tris[(alkoxy)benzyloxy]benzoate Derivatives

The synthesis of liquid crystalline 3,4,5-tris(11-methacryloylundecyl-1-oxybenzyloxy)benzoic acid, 2-methyl-(1,4,7,10,13-pentaoxacyclopentadecane)-3,4,5-tris[4-(11-methacryloylundecyl-1-oxy)benzyloxy] benzoate and its 1:1 complex with sodium triflate is described. The observed mesophases were identified, by polarized optical microscopy and contact preparation techniques, to be of hexagonal columnar disordered structure. The amphiphiles form lyotropic columnar phases in concentrated methacrylate solvents, while at low solute contents supramolecular organogels emerge.

Liquid Crystalline Primary Benzamides

Abstract Several alkoxybenzamides are synthesized and characterized by spectroscopic and chromatographic methods. 3,4,5-Tris(alkoxy)benzamides have been found to exhibit a mesophase of a columnar or stack-like type.

Self-organization of 3,4,5-tris(octyloxy)benzamide in solution and embedding of the aggregates into methacrylate resins

The physical gelation of organic solutions of 3,4,5-tris(octyloxy)benzamide at ambient temperature, subsequent to shock-freezing in liquid nitrogen is reported. Microscopic investigations of the morphology of these supramolecular organogels suggests the occurrence of networks of rod-like crystals with diameters tetween 0.1 - 1 μm. The fine structure of the gel was shown to depend on the solvent used. Takinqg monomer/crosslinker mixtures as solvents, the gel structures could be permanently fixed by low-temperature curing. Comparing the morphology of the dried liquid gels and the polymerized gels, no change due to the hardening of the matrix have been found. The supramolecular aggregates of the benzamide seem t o contain considerable amounts of monomers, because the observed melting temperature depression can not be explained by the finite-size of the crystals.

Thermotropic columnar mesophases of wedge‐shaped benzenesulfonic acid mesogens

The synthesis and characterisation are reported of two groups of new amphiphilic sulfonate compounds, 2,3,4‐tris(dodecyloxy)benzenesulfonates, 2,3,4‐tris(dodecyloxy)benzenesulfonamide and the isomeric 3,4,5‐tris(dodecyloxy)benzenesulfonates. As revealed by a combination of thermo‐optical microscopy, differential scanning calorimetry and X‐ray scattering techniques, the occurrence of mesophases is controlled by the radius of the cation and the symmetry of the molecule. The sulfonates exhibited a rich phase behaviour involving cubic, ordered and disordered columnar mesophases, depending on the counter ion and the type of substitution. It is proposed that the term ‘cunitic’ molecules should be introduced as a class descriptor for wedge‐shaped molecules and their columnar phases.

New carbohydrate amphiphiles, 2 Gel formation and gel morphologies

The physical gelation of 3,4,5-trialkoxy-N-( 1-deoxysorbitol- 1-yl)benzamides and 3,4,5-trialkoxy-N-(2-deoxyglucos-2-yl)benzamides in organic solvents and monomeric methacrylates at ambient temperature is reported. UV polymerization of the methacrylate solvent yielded interpenetrating networks of the crosslinked polymethacrylate and the aggregated solute. The embedded gels exhibit two different morphologies depending on the solvent. Either white/turbid gels containing a percolating network of globular aggregates (o = 1-10 μm) or clear, transparent gels consisting of rod-like crystals (o = 4-100 nm) were found. The sphere morphology consists of small rod-shaped crystallites assembled to spherical objects and is assumed to be caused by a liquid-liquid demixing process prior to gelation.

NEW CARBOHYDRATE AMPHIPHILES : I. SYNTHESIS

The synthesis and characterization of two groups of new amphiphilic carbohydrates, 3,4,5-tris(alkoxy)- N -(1-deoxysorbitol-1-yl)benzamide and 3,4,5-tris(alkoxy)- N -(2-deoxyglucos2-yl)benzamide are described. The phase behaviour was investigated by differential scanning calorimetry and thermo-optical analysis. All the investigated compounds exhibit thermotropic mesophases. Depending on the length of the alkyl chains, hexagonal columnar and cubic mesophases are obtained.

Fabrication and fluorescence properties of perylene bisimide dye aggregates bound to gold surfaces and nanopatterns

Perylene bisimide dyes with two different imide substituents have been synthesized by sequential imidization reactions to give the disulfide 8 bearing two perylene bisimide dyes. Aggregation properties of this bis-perylene dye were studied by UV/Vis absorption and steady-state polarization-dependent as well as time-resolved fluorescence spectroscopy and the results were compared to those of the symmetrical perylene bisimide dye 4. In both cases, aggregation is expressed in a strong bathochromic shift of the excitation and the emission spectra and increasing concentration results in an increase in lifetime from 5 to 8 ns. By means of the thiol linker, self-assembly of 8 on gold surfaces was accomplished leading to surface-bound dye aggregates. Intense fluorescence from these dye aggregates was observed on surfaces decorated with hexagonal gold patterns, whereas the fluorescence is only weak on plain gold substrates.