Synthesis,charge distribution,and dimerization behavior of lithium alkynylselenolates

The reactivity of alkynyl lithium compounds toward elemental gray selenium yields alkynylselenolates, which show significant interaction with the lithium counter ions, depending on solvent polarity and the electronic nature of the adjacent organic substituent. Likewise the dimerization behavior is different for alkyl‐ and aryl‐substituted alkynylselenolates. From the latter, unsymmetrical 1,3‐selenol is formed, the molecular structure of which was confirmed by X‐ray structure analysis. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:169–222, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20088     

Semiconducting properties of polypyrrole films in aqueous solution

The influence of the nature of the anions on the conductivity of polypyrrole films in aqueous solution was investigated by photocurrent spectroscopy combined with electrochemical impedance spectroscopy in dependence on the potential. As demonstrated, the conductivity of polypyrrole films at negative potentials can vary from a semiconducting to an ionic conducting state, depending on the size of the charge-compensating counter-anion incorporated during the electropolymerization. The reduced polypyrrole shows semiconducting properties when small anions are inserted, releasing the polymer matrix during the reduction process. The polymer can than be considered as a two-layer system, consisting of a semiconducting layer and a porous layer. Measurements at different thickness of polypyrrole films have shown that the position of the semiconducting layer is in the electrode/polymer interface. The ohmic resistance of the semiconducting layer is in the range 1–5 kΩ, the capacitance approaches a value of 100–500 nF and the flatband potential is −0.62 V_SCE. If large anions are incorporated, cation insertion takes place during reduction, the electrolyte content in the polymer then is relatively high and the polymer's behaviour is similar to that of an ionic conductor. The results are presented and discussed together with the example of methylsulfonate as a relatively small anion and polystyrenesulfonate as a large anion. Received: 28 July 1998 / Accepted: 22 February 1999     

Geometrically nonlinear composite shells with integrated piezoelectric layers

In order to show the significance of considering nonlinear deformations in piezoelectrical structures, a geometrical nonlinear shell element with integrated piezoelectric layers is introduced. The strain‐displacement relations are implemented using firstorder shear deformation theory with small strains but moderate rotations. The element has been tested on several benchmark problems and it can be concluded that the effect of geometrical nonlinearity is significant when the sensor properties of the piezoelectrical layers are predicted. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Environmental Stress Cracking of Polymers Monitored by Fatigue Crack Growth Experiments

This article describes fatigue crack growth experiments to investigate the degradation of the durability of polymers due to fluid environments. The degrading effect of media causing stress cracking can be observed on the fracture surfaces of tested samples by scanning electron microscopy. Strategies to improve environmental stress cracking like changes in molecular weight, orientation, toughening with rubber particles of different sizes are discussed. Fatigue crack growth experiments can be employed as a very fast and effective screening method.     

A numerical method for computing the response of composites with periodic microstructure

The stress‐strain response of a periodic structure due to an applied eigenstrain field is investigated. The periodic structure allows reduction of the problem to a representative volume element (RVE) problem. A review of Fourier series as a particular method of solving the set of differential equations is given, and an example problem is studied. Results of the latter method are compared to results obtained using discrete Fourier transforms in a different way.