Structural study of six cycloalkylammonium cinnamate salt structures featuring one‐dimensional columns and two‐dimensional hydrogen‐bonded networks

Six ammonium carboxylate salts, namely cyclopentylammonium cinnamate, C₅H₁₂N⁺·C₉H₇O₂⁻, (I), cyclohexylammonium cinnamate, C₆H₁₄N⁺·C₉H₇O₂⁻, (II), cycloheptylammonium cinnamate form I, C₇H₁₆N⁺·C₉H₇O₂⁻, (IIIa), and form II, (IIIb), cyclooctylammonium cinnamate, C₈H₁₈N⁺·C₉H₇O₂⁻, (IV), and cyclododecylammonium cinnamate, C₁₂H₂₆N⁺·C₉H₇O₂⁻, (V), are reported. Salts (II)–(V) all have a 1:1 ratio of cation to anion and feature three N⁺—H...O⁻ hydrogen bonds forming one‐dimensional hydrogen‐bonded columns consisting of repeating R₄³(10) rings, while salt (I) has a two‐dimensional network made up of alternating R₄⁴(12) and R⁶₈(20) rings. Salt (III) consists of two polymorphic forms, viz. form I having Z′ = 1 and form II with Z′ = 2. The latter polymorph has disorder of the cycloheptane rings in the two cations, as well as whole‐molecule disorder of one of the cinnamate anions. A similar, but ordered, Z′ = 2 structure is seen in salt (IV).     

Rietveld refinement of the cocrystal 2,4‐dihydroxybenzoic acid–N′‐(propan‐2‐ylidene)nicotinohydrazide (1/1)

A further example of using a covalent‐bond‐forming reaction to alter supramolecular assembly by modification of hydrogen‐bonding possibilities is presented. This concept was introduced by Lemmerer, Bernstein & Kahlenberg [CrystEngComm (2011), 13 , 55–59]. The title structure, C₉H₁₁N₃O·C₇H₆O₄, which consists of a reacted niazid molecule, viz.N′‐(propan‐2‐ylidene)nicotinohydrazide, and 2,4‐dihydroxybenzoic acid, was solved from powder diffraction data using simulated annealing. The results further demonstrate the relevance and utility of powder diffraction as an analytical tool in the study of cocrystals and their hydrogen‐bond interactions.     

Shear modulus determination in model hydrogels by means of elongated magnetic nanoprobes

The mechanical characterization of complex soft matter by quasi-static magnetometry using nanoscopic magnetic probes is demonstrated for model hydrogels doped with two types of elongated magnetic nanoparticles. Chemically crosslinked poly(acrylamide) (PAAm) hydrogels serve as the matrix in which nickel nanorods or weakly magnetized hematite (α-Fe₂O₃) ellipsoids are embedded as local probes. We investigated the swelling behavior of the ferrogels in order to verify that their equilibrium swelling degree in water is not influenced by the probes, shows a good correlation with the Frenkel–Flory–Rehner model. The proposed magnetomechanical method relies on a correlation between the shear modulus of the PAAm hydrogel matrix and the coercive fields of the corresponding isotropic ferrogels. By extending the Stoner–Wohlfarth model for single-domain blocked magnetic particles by a term for particle rotation in an elastic matrix, information on the shear modulus of the matrix can be obtained. Comparison of the results with the expected relation from rubber elasticity theory illustrates both the general potential as well as the limits of the approach. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Sol–gel synthesis of sodium and lithium based materials

Sodium and lithium cobaltates are important materials for thermoelectric and battery applications due to their large thermoelectric power and ability to (de-) intercalate the alkali metal. For these applications, phase pure materials with controlled microstructure are required. We report on the sol?Cgel synthesis of sodium- and lithium-based materials by using acetate precursors. The produced Na_2/3CoO₂, Li(Ni_1/3Mn_1/3Co_1/3)O₂, and Li(Ni_1/2Co_1/2)O₂ powders are phase pure with grain sizes below 1???m. X-ray diffraction and energy-dispersive spectral analyses show that the cation stoichiometry is preserved in the lithium-based compounds. Despite the low temperatures, the sodium content is reduced by 1/3 as compared to the initial value. Chemical phases of the investigated powders are formed in the sol?Cgel route at temperatures typically 100?C200?K lower than those used in the conventional solid-state synthesis of these materials. The suggested sol?Cgel synthesis is a low temperature process suited for production of phase pure and homogeneous materials with volatile cations.     

The interaction of cationic polymers with human hair

We present a combination of electrochemical methods, i.e. polyelectrolyte titration and streaming potential measurement, and AFM to characterise the adsorption and desorption behaviour and the morphology of a set of polyquaternium polymers on human hair. Specific charge density and molar mass are correlated to the amount of adsorbed polymer and the ease of desorption. Results are in line with a simple model of coulombic interaction between hair and polymer and are interpreted on this basis.     

Phase Behavior and Mesophase Structures of 1,3,5‐Benzene‐ and 1,3,5‐Cyclohexanetricarboxamides: Towards an Understanding of the Losing Order at the Transition into the Isotropic Phase

One of the simplest and most‐versatile motifs in supramolecular chemistry is based on 1,3,5‐benzenetricarboxamides. Variation of the core structure and subtle changes in the structures of the lateral substituents govern the self‐assembly and determine the phase behavior. Herein, we provide a comprehensive comparison between the phase behavior and mesophase structure of a series of 1,3,5‐benzene‐ and 1,3,5‐cyclohexanetricarboxamides that contain linear and branched alkyl substituents. Depending on the substituent, different crystalline, plastic crystalline, and liquid crystalline phases were formed. The relatively rare columnar nematic (N_C) phase was only observed in cyclohexane‐based trisamides that contained linear alkyl substituents. Of fundamental interest in liquid crystalline supramolecular systems is the transition from the mesomorphic state into the isotropic state and, in particular, the question of how the order decreases. Temperature‐dependent IR spectroscopy and XRD measurements revealed that columnar H‐bonded aggregates were still present in the isotropic phase. At the clearing transition, mainly the lateral order was lost, whilst shorter columnar aggregates still remained. A thorough understanding of the phase behavior and the mesophase structure is relevant for selecting processing conditions that use supramolecular structures in devices or as fibrillar nanomaterials.     

Does a Photocatalytic Synergy in an Anatase–Rutile TiO2 Composite Thin‐Film Exist?

It has often been suggested that anatase–rutile mixtures/composites synergistically enhance photocatalysis. However, in the case of dense thin‐films containing an intimate mix of both anatase and rutile phases, such an effect has not been observed. In synthesising combinatorial films with graded film thickness and phase, and applying established photocatalytic mapping methods, we were able to assess how dense thin‐films of intimately mixed anatase–rutile mixtures affect photocatalytic performance. We found that no photocatalytic synergy between anatase–rutile composites (29≤rutile %≤83) within such dense thin‐film systems exists. In fact, an increased presence of rutile caused the photocatalytic activity to fall. This was explained by the unfavourable energetics in the multiple electron transfers required between several neighbouring rutile and anatase sites for the photo‐generated electron to reach the material’s surface; encouraging the trapping of electrons within the bulk and increasing the likelihood of charge recombination. The decrease in photocatalytic activity was found to vary linearly with rutile component.     

Charge carrier mobility,photovoltaic, and electroluminescent properties of anthracene‐based conjugated polymers bearing randomly distributed side chains

This article reports on the synthesis, characterization, and properties of various anthracene‐containing poly (p‐phenylene‐ethynylene)‐alt‐poly(p‐phenylene‐vinylene) (PPE‐PPV) polymers (AnE‐PVs) bearing statistical distributions of various side chains. Primarily, the ratio of linear octyloxy and branched 2‐ethylhexyloxy side chains at the poly(p‐phenylene vinylene) (PPV) parts was varied, leading to the polymers stat, stat1, and stat2. Furthermore, polymers also containing asymmetric substituted PPV and poly(p‐phenylene ethynylene) units (bearing methoxy and 2‐ethylhexyloxy side chains) were prepared yielding stat3, stat4, and stat5. These materials exhibit a broad variation in their photovoltaic properties. It is once more shown that side chains and their distribution can crucially affect the photovoltaic device performance. The introduction of units with asymmetric substitution into these systems seems to be harmful for their utilization in photovoltaic applications. Organic field‐effect transistors were fabricated to investigate hole mobilities in these new materials. Large variance was observed, falling in the range of almost two orders of magnitude, indicating rather different π–π stacking behavior of the polymer backbones owing to side‐chain modifications. Moreover, a selection of the new polymeric systems was investigated regarding their potential for light‐emitting diode (LED) applications. Polymer LEDs using the polymers AnE‐PVstat, ‐stat3, ‐stat4, and ‐stat5, as the active layer showed turn‐on voltage of ～2 V and exhibited red light emission. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012