Volume 17, Issue 6

A newly designed and constructed sliding plate rheometer is used to measure the high frequency (210 Hz) linear viscoelastic properties of two model polymers: polybutene (PB) and polydimethylsiloxane (PDMS). Using well-known rheological models, extrapolations of the viscoelastic measurements obtained on a rotational parallel plate rheometer to a frequency of 210 Hz are used to assess the performance of the high frequency sliding plate rheometer. Good agreement between the extrapolated and measured data demonstrates the ability of the sliding plate rheometer to measure the high frequency rheological properties of both Newtonian and shear-thinning materials.

The dynamic viscoelastic properties of liquid crystalline polymer (LCP) and polyethylene terephthalate (PET) blends were studied at two different temperatures: 265°C at which LCP was in solid state and 285°C at which LCP was in molten state. The PET was in molten state at both the temperatures. The storage modulus, G’ , loss modulus, G’’ , dynamic viscosity, h ’ , of blends with different compositions were evaluated and compared. The morphology of these samples was studied using scanning electron microscope, which exhibited composition dependency. A maxima was observed in the viscosity versus composition plot corresponding to 90/10 LCP/PET blend at 285°C. The G’ versus G’’ plots demonstrated the composition dependency of LCP/PET blends.

The assumptions implicit in the simplified expressions used to convert the torque-rotational speed data of parallel-disk viscometry into rim shear rate and rim shear stress are identified. The rim shear stress generated by the simplified expression is compared against the actual rim shear stress. The error involved is quantified for two standard rheological models and for a set of laboratory data. Under normal operation conditions of parallel-disk viscometers this error was found to be within the acceptable limit. However, for highly shear thinning fluids and for fluids exhibiting yield stress this error can become very large. The suitability of the approximate rim shear stress in wall slip determination is then briefly discussed.

We apply the Landmark Paper Index (LPI), calculate and analyze indices for all papers published in rheological journals (‘ η -journals’) between 1991 and 2007. We discuss the effect of formal criteria on the LPI.

Genetic Programming (GP) is used to estimate the functions that describe the torque and the force acting on the external sphere due to steady state motion of viscoelastic fluid between two eccentric spheres. The GP has been running based on experimental data of the torque at different eccentricities to produce torque for each target eccentricity. The angular velocity of the inner sphere and the eccentricity of the two spheres have been used as input variables to find the discovered functions. The experimental, calculated and predicted torque and forces are compared. The discovered function shows a good match to the experimental data. We find that the GP technique is a good new mechanism of determination of the force and torque of fluid in eccentric sphere model.