Relevant Shear Rates Research Articles

Rheology control of organic coatings with new hydrophobic silicas

The rheological effects of hydrophobic pyrogenic silicas were examined using binder systems designed, in particular, for automobile top coats. Rheological measurements to characterize the flow behaviour, especially with regard to sagging, in the relevant shear rate and shear stress were carried out in addition to practical tests. By means of a shear strain jump experiment the rheological conditions during and directly after paint application were simulated using a rheometer. Based on the results obtained and additional measurement of viscoelastic parameters a new approach to understanding the mechanism of rheology control with pyrogenic silicas in coating systems was developed.

Shear stress-facilitated calcium ion transport across lipid bilayers

Small unilamellar liposomes were used in this study of shear stress effects on the trans-bilayer flux of calcium ions (Ca 2+). Liposome suspensions were prepared from 99% egg phosphatidylcholine by a microporous filter extrusion technique. The inner aqueous phase of the unilamellar liposomes contained indo-1 5−, a fluorescent indicator of free Ca 2+. The external aqueous phase was composed of Hepes-buffered saline containing normal physiological levels of common ionic species. Calcium ion levels were set at 100 nM and 1 mM in the inner and outer aqueous phases, respectively. Liposome suspensions were exposed to graded levels of uniform shear stress in an optically modified rotational viscometer. Intraliposome Ca 2+ concentration was estimated from continuous measurement of indo-1 5− fluorescence. Electronically measured particle size distribution was used to determine liposome surface area for estimation of trans-bilayer Ca 2+ flux. Trans-bilayer Ca 2+ flux increased linearly with applied shear rate from 27 s −1 to 2700 s −1. Diffusional resistance of the lipid bilayer, not the convective resistance of the surrounding fluid, was the limiting step in the transport of Ca 2+. Liposome permeability to Ca 2+ increased by nearly two orders of magnitude over the physiologically relevant shear rate range studied. Solute transport in injectable liposome preparations may be dramatically influenced by cardiovascular fluid stress. Solute delivery rates determined in liposomes exposed to static conditions may not accurately predict in vivo, cardiovascular solute transport.

Melt Flow Behaviour of Liquid Crystalline Polymer

Abstract The method proposed earlier to estimate complete flow curves depicting the variation of melt viscosity over industrially relevant shear rate and temperature through the melt flow index has been extended to liquid crystalline polymer melts. The present work considers the study of the thermotropic system of the copolymer of poly(ethylene terephthalate) and p-hydorxybenzoic acid with different ratio of the components. A master curve is shown to exist for the system when modified viscosity function is plotted against modified shear rate. A new rheological model has been suggested to fit the master curve adequately as the curve is different from the conventional form.