Compression of dispersions to high stress under electric fields: effects of concentration and dispersing oil.

Dispersions of various concentrations (15-35%) were prepared in silicone oils of vastly different viscosities (40, 1000, 10,000, and 30,000 mPa s) and compressed to high values of stress while under an electric field of 2 kV/mm. A purpose of this study was to observe the effect of compression and E field simultaneously on these dispersions and assess predictions of most common and relevant theories. As shown, static stresses of over 1000 kPa could readily be obtained although the data presented here were held below 300 kPa to protect the load cell and equipment. The results are compared to and discussed in terms of a power law fit for stress vs gap since most theories predict such a dependence. The PL exponents fall around 3 ranges: (-2), (-3), and much less than (-3). The PL coefficients however reflect in systematic way the viscosities of the dispersing oils. The compressive stress vs strain behavior is studied with regard to particle concentration and dispersing oil viscosity.

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