Subject Shear stability

Ye and co-workers exploited the shear stability of highly branched, high molecular weight polyethylenes (PEs) as lubricant viscosity index improvers [252, 253]. Viscosity index of a lubricant is a critical parameter which defines its quality and application temperature range. They synthesized PEs with controllable chain topologies ranging from linear to a hyperbranched dendritic structure by chain walking polymerization [254]. The PE samples were blended into a base paraffinic oil (density 0.8659 g mL at 15 °C, kinematic viscosity 30.06 cST at 40 °C) to form lubricants. The lubricants were subjected to the Kurt Orbahn (KO) test to measure the shear stability index, which is expressed by... 

Latexes should be stable under zero-shear conditions at room temperature. However, when latex is pumped from the reactor to a tank, or from tank to tank, it is subjected to shear forces that can cause shear-induced coagulation of the latex particles. Additional surfactant, called a post-stabiliser (296), is often added to latexes to improve shear stability. Also, in cold climates, latexes may be exposed to extreme temperatures that cause the aqueous phase to begin to freeze, thereby compressing the latex particles together, and causing coagulation (358). Poststabilisers are also added to improve freeze-thaw stability and electrolyte tolerance. 

Second, sensors are often intended for a single use, or for usage over periods of one week or less, and enzymes are capable of excellent performance over these time scales, provided that they are maintained in a nfild environment at moderate temperature and with minimal physical stress. Stabilization of enzymes on conducting surfaces over longer periods of time presents a considerable challenge, since enzymes may be subject to denaturation or inactivation. In addition, the need to feed reactants to the biofuel cell means that convection and therefore viscous shear are often present in working fuel cells. Application of shear to a soft material such as a protein-based film can lead to accelerated degradation due to shear stress [Binyamin and Heller, 1999]. However, enzymes on surfaces have been demonstrated to be stable for several months (see below). 

From a technical standpoint, it is also important to note that colloids display a wide range of rheological behavior. Charged dispersions (even at very low volume fractions) and sterically stabilized colloids show elastic behavior like solids. When the interparticle interactions are not important, they behave like ordinary liquids (i.e., they flow easily when subjected to even small shear forces) this is known as viscous behavior. Very often, the behavior falls somewhere between these two extremes the dispersion is then said to be viscoelastic. Therefore, it becomes important to understand how the interaction forces and fluid mechanics of the dispersions affect the flow behavior of dispersions. 

The residual monomer content will by external plasticization cause a considerable lowering of the polymer glass transition temperature. A correlation between stability and softness of the polymer particles may exist. The hydrophobic part of the emulsifier molecules may partly penetrate the particle surface and thus be anchored to the surface to some extent. The resistance to deformation of such a stabilizing layer, when subjected to mechanical shear, is assumed to be dependent on the polymer particle softness. With soft particles polymer chain entanglement may also occur on particle-to-particle contact, making redispersion of agglomerates more unlikely. 

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