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Resonance phenomena are discussed in detail. The influence of significant parameters as the moment of inertia and the measuring constants are enlightened and verified with measurements. It is shown that resonance frequencies weekly depend upon the moment of inertia and strongly on the geometrical coefficient of the measuring system. Both parameters form the configuration constant. If a measuring system is replaced, the moment of inertia changes little but the configuration constant changes more. Thus resonance frequencies can be shifted some decades. The comparison between the developed formalism and measurements gives good results for different rheological measuring modes. Even at pronounced resonances measurements provide proper results. The formalism can be used for the simulation of measuring values. However, deformation oscillations along the rotating axis generate resonances of higher order at higher frequencies. These phenomena contribute systematically errors and should be avoided.

Transmission electron microspray (TEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), X-ray scattering, rheological measurements, and dynamic light scattering (DLS) were used to investigate the temperature-dependent self-assembly of the single-chain bolaamphiphile dotriacontan-1,1'-diyl-bis[2-(trimethylammino)ethyl phosphate] (PC-C32-PC). A feature of the self-assembly process is that it is driven solely by hydrophobic interactions of the long alkyl chains.

A new magneto-rheology device (MRD) was constructed, which can be used in combination with a Physica MCR roational rheometer form Anton Paar. The MRD is build around a parallel-plate measuring geometry. Maximum magnetic flux densities of up to 1 Tesla in the air gap between the two plates are possible. The distribution of the magnetic flux density in the measuring gap has been evaluated with the help of a three-dimensional Hall sensor. The MRD system allows simultaneous software controlled setting of the magnetic field strength and the use of all possible rheological test modes of the rheometer. In the past mostly flow curves based on purely rotational measurements have been used to investigate the rheological behavior of MRFs giving only limited information. A measuring method is introduced, which is based on oscillatory measurements and thus allowing an exact determination of a substance's visco-elastic properties as a function of the magnetic field strength. In addition to structure investigations at various magnetic field strength with standard oscillatory strains sweeps an oscillation measurement with constant amplitude and constant frequency was performed while changing the magnetic field strength in a logarithmic ramp (magneto-sweep). On a typical MRF significant transition points are observed which distinguish different regions. These transitions can directly be correlated to corresponding changes in the material's structure resulting from the increase in the magnetic flux density. [ABSTRACT FROM AUTHOR]

The temperature-dependent self-assembly of the single-chain bolaamphiphile dotriacontan-1,1'-diyl-bis[2-(trimethylammonio)ethyl phosphate] (PC--C32--PC) was investigated by transmission electron microscopy (TEM), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), X-ray scattering, rheological measurements, and dynamic light scattering (DLS). At room temperature this compound, in which two phosphocholine headgroups are connected by a C32 alkyl chain, proved to be capable of gelling water very efficiently by forming a dense network of nanofibers (Köhier et al. Angew. Chem., Int. Ed. 2004, 43, 245). A specific feature of this self-assembly process is that it is not driven by hydrogen bonds but solely by hydrophobic interactions of the long alkyl chains. The nanofibers have a thickness of roughly the molecular length and show a helical superstructure. A model for the molecular structure of the fibrils which considers the extreme constitution of the bolaamphiphile is proposed. Upon heating the suspensions three different phase transitions can be detected. Above 49 °C, the temperature of the main transition where the alkyl chains become "fluid", a clear low-viscosity solution is obtained due to a breakdown of the fibrils into smaller aggregates. Through mechanical stress the gel structure can be destroyed as well, indicating a low stability of these fibers. The gel formation is reversible, but as a drastic rearrangement of the molecules takes place, metastable states occur. [ABSTRACT FROM AUTHOR]