Relation Of Dynamic Lamellar Structure And Shear Stress Of Pm-er Fluids

There are many experimental [1-2] and theoretical [3] studies on the lamellar structure under electric and shear fields for dielectric ER fluids. It was found that the number of particle rings of the lamellar structure increases with electric field, and decreases with rotation speed [1], and the rotatOing directions of the particle rings are opposite for the adjacent rings [2]. However, there are only few quantitative comparisons between the ER effect and the parameters of lamellar structure such as band number density, band width and gap width of different ER materials at different electric field, angular velocity. Analysis of such comparison would reveal the nature why the ER effect degrades under high shear rate.To realize such comparison, one needs to build an electrorheoscope which can record images of particle patterns while, at the same time, measuring shear stress of the material at different electric field and different rotation speed. An electrorheoscope has been established based on a Haake Mars electrorheometer. When recording the images of the structure patterns, the electrorheoscope can measure shear stress of the material using parallel plate electrodes. The images cover circular patterns with diameters as large as 35 mm at resolution of 50μm, or with diameters as small as 100μm at a resolution of 1μm.The parameters of lamellar structure of different PMER fluids such as particle ring number density, ring width and gap width verses radius at different electric field, rotation speed and solid phase volume fraction are measured and analyzed using scaling process. It is found that the data collapse when certain scaling function is properly chosen. Certain critical behavior is revealed from such scaling process. This result is compared with the lamellar structure of dielectric ER fluids.The Onsager principle claims that the Onsager action fractional which is the summation of time derivative of free energy and energy dissipation function, is minimum for dynamic systems at a state not too far from equilibrium [4]. Using the Onsager principle, we tried to understand the mechanism of the formation of such lamellar structure. The historical efforts of understanding of above behaviors will be reviewed, and the current study will be presented and discussed.