Advances in Science and Technology Vol. 77

Abstract: For the direct measurement of chemical concentrations of substances in process liquids, sensors need to be fast and reliable. We investigated the usability of hydrogels as sensitive coating materials for piezo-electric thickness shear mode resonators. Hydrogels are cross-linked polymer networks that show well-defined shifts of their degree of swelling upon changes of environmental parameters such as ionic concentrations, concentrations of organic solvents or temperature. These changes of gel properties are then transferred into an electrical signal. The novel sensor solution exhibits response times of only few seconds and matches the reliability of innovative process measuring technology. A method for its application specific adaption is presented. It is based on optimizing the interrelation of the sensor structure, the manufacturing technology for the hydrogel layer, and the processing of the measured data. The performance of the method is illustrated with the example of a PVA/PAAhydrogel coated sensor which monitors the concentration of a cleaner used in surface technology. The developed measurement device for this application was approved with a measurement error of less than 5 %.

Abstract: Selectivity of new thioamide derivatives was assessed using those ligands as sensor materials in ion-selective membrane electrodes and tested towards Pb2+ - selectivity. The influence of the nature of the thioamide function (linear, branched or cyclic substituents) on their ionophoric properties was investigated. Electrodes based on cyclic thioamide moieties are promising analytical tools for monitoring Pb2+ concentration in natural and drinking waters.

Abstract: We prepared poly(vinylidene fluoride)/multiwalled carbon nanotube (MWCNT) nanocomposites using electrospinning process and investigated its effect on the polymorphic behavior and electroactive properties. The remanant polarization and piezoelectric response increased with the the amount of MWCNT and piezoelectric -phase crystal. Interfacial interaction between MWCNT and PVDF caused high degree of -phase derived from external stretching.

Abstract: Adaptive damping systems based on magnetorheological (MR) fluids allow the continuous control of vibration damping forces depending on the current conditions. In magnetorheological dampers known so far, the magnetic field for the control of the MR fluid is generated by the coil of an electromagnet. Two novel concepts for the magnetic circuit in magnetorheological dampers have been proven where hybrid magnetic circuits consisting of at least one permanent or hard magnet and an electromagnet are used. In the first concept, the electromagnet is combined with two permanent magnets, whose magnetization cannot be modified even by strong magnetic fields of the electromagnet. The main advantage of this configuration is the improved fail-safe behaviour of the damper in case of a power failure. In the second approach, the electromagnet is combined with a hard magnet, whose magnetization can be modified by the electromagnet. This configuration leads to high energy efficiency, because electric power is only required in short pulses for the switching of the hard magnet. Magnetic circuits with the combination of different magnetic field sources were designed supported by simulations of the magnetic flux distribution. Demonstration models for magnetorheological dampers with the distinguished magnetic circuits were constructed and their performances were tested. The results of the investigations are described in this contribution.

Abstract: The paper describes an experimental/theoretical activity that involves a magnetorheological fluid brake (MRFB). The variability affecting the plant parameters suggests the employment of a model reference adaptive control finalized to regulate the braking torque. This feedback control method is able to minimize the tracking error in presence of a plant characterized by a known dynamics and uncertain parameters. Numerical simulations have been carried out and the obtained results confirm the goodness of the proposed approach.

Abstract: A new rheological model is applied to the analysis of the behavior of electrorheological (ER) fluids. A comparison of the model’s predictions with experimental data shows that the proposed model correctly predicts the shear stress behavior both quantitatively and qualitatively. The shear stress data for the aligned particles’ structure reformation can be fitted as a function of shear rate with the new model. The yield stress was found to be almost linearly dependent on the field strength, different from the predictions of the polarization model.

Abstract: Chromogenic materials and devices allow the construction of glazings whose throughput of visible light and solar energy can be varied depending on the application of an electrical voltage or temperature. These glazings are of much interest for energy efficient buildings and are able to create energy efficiency along with indoor comfort. This paper outlines the basics of electrochromic and thermochromic technologies with foci on functional principles, materials, device and manufacturing technology, and selected results from research and development.

Abstract: C3-symmetrical tristriazolotriazines substituted with phenylene rings carrying lateral flexible alkoxy side chains were prepared via condensation/ring transformation of cyanuric chloride and tetrazoles. These star-shaped, planar compounds can form broad thermotropic mesophases. Due to the extensive π-conjugation, these compounds are highly emissive and the octupolar donor-acceptor electronic structure results in non-linear optical properties like solvatochromism. Brønstedt acids provoke halochromism of the absorption and of the fluorescence.

Abstract: Thermotropic materials offer an immense potential in adaptive solar control. They combine specific optical properties like absorbance and reflection, and high stability against solar radiation and heat with technology compatible processing capacities. Therefore, they represent perfect energy efficient materials. In detail, polymer blends, polymer-based hydrogels, casting resins, and thermoplastic films with a reversible temperature-dependent switching behavior have been investigated. Here a comparative evaluation of the different concepts with a view to their application in adaptive solar control is presented. Own current results exploit the well-known phase change materials and describe its use for adaptive solar control with extruded films or highly stable casting resins with thermotropic properties. Therewith, the status has changed from diffuse sunblind systems to intrinsic solar energy reflecting materials and a first smart window system based on phase change materials has now commercialized [1]. In summary: It is amazing that the solar energy itself is used as a promoter against solar heat.

Abstract: A series of new coordination polymers based on p-tert-butylcalix[4]arene- tetracarboxylic acid with Eu3+ (1a), Tb3+ (1b) and Tm3+ (1c) were prepared by hydro and solvothermal methods. The obtained solid compounds were characterized by infrared and luminescence spectroscopy, powder X-ray diffraction, scanning electron microscopy and thermogravimetric analysis. The infrared curves and the x-ray diffraction patterns indicate that the same crystalline structure was obtained for all lanthanides.