Diameter‐Dependence of the Morphology of PS‐b‐PMMA Nanorods Confined Within Ordered Porous Alumina Templates

Summary: Polystyrene‐block‐poly(methyl methacrylate) nanorods were prepared by wetting ordered porous alumina templates. We systematically investigated the diameter‐dependence of their morphologies by varying the pore diameters of the templates from 400 nm down to 25 nm. If the pore diameter exceeds the period of the block copolymer, the pores accommodate a non‐integer number of repeat periods. In case of smaller pores the occurrence of an ordered state could not be unambiguously verified.

TEM image of an ultra‐thin slice containing a cross‐section of a polystyrene‐block‐poly(methyl methacrylate) nanorod embedded in epoxy resin.     

Interfacial Properties of Asymmetric Polymer Mixtures

Using a Monte‐Carlo simulation of a continuous space Rod Bead Model the interface properties of systems of flexible polymer chains with different sizes of monomers are investigated. An immiscible polymer blend in the strong segregation state is modeled by a double sandwich system of chains differing by an factor of two in the size of the beads and the interfacial tension is calculated by a virial theorem method. The simulation data are compared to self‐consistent mean field and experimental data. The results show that the simulation data agree very satisfactory with mean‐field results. The interfacial tension decreases for asymmetric systems in comparison to symmetric systems with comparable volume contents of monomers and interaction strengths due to a decrease of the effective interaction. The parameters of the investigated systems are close to the properties of PS, PMMA and PI melts. A comparison with experimental results yields a very good agreement with data for PS/PMMA and less satisfactory for PS/PI. Additionally to the interfacial tension we have studied the interfacial width, the deformation of polymer chains near the interface, distributions of chain ends, monomer densities and distributions of centers of mass of chains.

Snapshot of a typical configuration for chains with different monomer sizes and equal number of monomers per chain.     

The effect of a cluster on a chemical reaction: a quasiclassical trajectory study

We have calculated product rotational state distributions for the D + H₂ reaction trapped in the center of icosahedral argon cluster at various cluster temperatures. All the degrees of freedom are treated classically in the present calculations. The rotational state distributions exhibit considerable dependence on the cluster environment and its temperature as compared with those obtained in the gas phase reaction.     

Effect of electron correlation on positronium formation in positron-helium scattering

A three-parameter correlated wave function for the helium ground state is used to study the scattering reaction , where Ps stands for positronium atom. An exact analytical expression is constructed for the first Born scattering amplitude for Ps formation from helium. Based on this numerical results are presented for both differential and total cross-sections. It is demonstrated that the inner electronic correlation of the target atom plays a crucial role in explaining the discrepency between theory and experiment. Received: 9 April 1998 / Revised: 29 September 1998 / Accepted: 19 October 1998     

Interfacial Properties of Flexible and Semiflexible Polymers

Using a continuous space rod‐bead model and an off‐lattice Monte Carlo technique we investigate interfacial properties between two incompatible polymers of different stiffnesses. The interfacial tension is determined by using virial theorem and analyzing the spectrum of capillary waves. Detailed interfacial profiles for segment and chain densities and orientations are obtained. The simulation results agree with mean field approaches for not too large stiffness disparities and show a marked tendency towards a plateau at higher stiffness disparities where the differences to mean field approaches increase.     

基于2,5-噻吩二甲酸的钙(Ⅱ)和钡(Ⅱ)配位聚合物的合成、晶体结构及性质

在溶剂热条件下,合成了2个碱土金属配位聚合物[Ca (tdc)(DMF)₂]_n(1)和[Ba (tdc)]_n(2)(H₂tdc=2,5-噻吩二甲酸),分别用元素分析、红外光谱、X射线单晶衍射、粉末衍射、热重分析和荧光光谱对它们进行了表征。结构分析表明,配合物1具有4,4连接的二维层状结构,拓扑符号为(4⁴·6²),而配合物2呈现三维网络结构。固体荧光测试表明配合物1比配合物2具有更显著的荧光性能。     

Reaction kinetics of hydrated electrons in a quaternary micro emulsion system: A pulse radiolysis study

The pulse-radiolysis technique has been employed to produce and study the kinetics of hydrated electrons (e_aq⁻) in a quaternary micro emulsion (Sodium Lauryl Sulfate (NaLS)/water/cyclohexane/1-pentanol) system. Two orders of magnitude higher life time (20 μs) of the e_aq⁻ has been obtained as compared to that in reverse micelles reported earlier. Several probes including a biomolecule have been used to determine the water pool concentrations and quenching constants (k_q). The observed yield and half life (t_1/2) of the hydrated electrons vary smoothly as the water droplet sizes are changed. The bimolecular rate constants for the reaction of e_aq⁻ with different solutes have been determined. It has been observed that the measured bimolecular rate constants for the reaction of hydrated electrons with different solutes are indicative of the solubilization sites, the water core sizes, and the surrounding environment. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 699–705, 1998     

Structure and Conformation of Individual Molecules upon Adsorption of a Mixture of Benzoporphyrins on Ag(111), Cu(111), and Cu(110) Surfaces

The front cover artwork is provided by the groups of Prof. Dr. Hans-Peter Steinrück and Prof. Dr. Norbert Jux at the Friedrich-Alexander-Universität (FAU) Erlangen-Nürnberg. The image shows a mixture of six 2H-tetrakis-(3, 5-di-tert-butyl-phenyl)(x)benzoporphyrins (2H-diTTBP(x)BPs, x = 0, 1, 2-cis, 2-trans, 3, or 4) molecules forming a porous square structure on Ag(111) as observed in scanning tunneling microscopy (STM) at room temperature. Read the full text of the Research Article at 10.1002/cphc.202300355 .     

Introduction of Ferrocene as a Facilitator for the Construction of Supramolecular Polymers

Proper monomer design is the key to enhancing the strength of noncovalent interactions between the molecules toward the efficient formation of supramolecular polymers (SPs). We have designed and synthesized 1,n′-disubstituted ferrocene-azobenzene-long alkyl chains, Fc(CONH-Azo-TDP)₂, to afford SPs with a high probability. The design exploits the ‘‘molecular ball-bearing’’ property of the ferrocene core, which allows two azobenzene arms to rotate in the planes of cyclopentadienyl rings, generating the most suitable molecular conformation required for SP formation. This ferrocene monomer formed a supergel consisting of SPs supported by strong intermolecular (H-bonding and π-π stacking) interactions and higher enthalpy gain than the reference molecules, where the central ferrocene core was replaced by flexible aliphatic as well as rigid benzene linkers. The molecular conformation involved in SPs, the strength of noncovalent interactions, and the process of supramolecular polymerization were investigated through NMR, UV-Vis, XRD and TEM studies. The results demonstrate that ferrocene may act as a good modulator for constructing efficient SPs.     

Nanostructured Composites with Layered Morphology: Structure and Properties

Using different microscopic techniques, we investigate the morphology and the micro-deformation processes in two entirely different classes of polymer based composites: natural biocomposites and synthetic polymer composites. The emphasis has been put on the comparison of the micromechanical properties of those composite materials. In the natural layered composites exemplified by human cortical bone, analogous to the synthetic glassy polymers, craze-like deformation zones were formed. A strong dependence of deformation mechanisms (such as transition from formation of single crazes to multiple crazing behaviour) on the layer dimension was observed in the layered composites made up of different amorphous polymers.