Noise couette flow

Alternatively, one could use SLLOD equations to do direct simulations, such as shear a system under planar Couette flow and measure the shear stress. As we have already discussed, this approach has been used successfully to calculate a host of transport properties. It is important to remember, however, that direct simulation is often unable to simulate realistic materials at experimentally accessible shear rates. At low shear rates, the nonequilibrium response becomes small compared to the magnitude of the equilibrium fluctuations that naturally arise. The extremely small signal-to-noise ratio would demand prohibitively long simulations before any meaningful answers could be obtained. 

The results presented here illustrate the general feasibility of this technique. They relate primarily to the behavior of thermal and current noise in the glass transition (Tg) or melting (Tm) region of an amorphous (polystyrene) and a crystalline (HD-polyethylene (HDPE)) polymer rendered conductive by the addition of minor amounts of carbon black, and further they relate to the noise of aqueous solutions of certain polymers during Couette flow. Because of experimental diflBculties, noise measurements on solid polymers during deformation and flow have not yet produced useful results. 

The results obtained during the Couette flow of aqueous solutions of polyethylene oxide and other water-soluble polymers appear especially promising since they showed an appreciable increase in the current noise level with shear rate. The current noise level depended also on the viscosity (molecular weight) of the solution. A slight increase of thermal noise was recorded also. The pseudoplasticity exponent n in the Ostwald-de Waele power law formula and the exponent a in the l/f -frequency distribution of the current noise were interrelated. This relation appeared to be generally valid. 

Noise in Aqueous Solutions during Couette Flow. Using the cells shown in Figiure 5, thermal and current noise levels were determined for aqueous solutions of PEO of varying molecular weight. The significance of the results was corroborated by measurements on aqueous solutions of other polymers. 

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