PPG-silica suspensions

In order to study the onset of the Saffman-Taylor instability for the PPG-silica suspensions, we estimated the imposed shear rate 2v/b at which the unstable finger for the first time appears. The 2v/b values are obtained as 72, 30, 17, and 11 s for the 2.5, 5.0, 7.5, and 10.0 wt% PPG-silica suspensions, respectively and they are independent of the injection pressure. Moreover, these values are close to the critical shear rates of the corresponding PPG-silica... 

The relative finger width A is well known related to the dimensionless parameter 7/5=12 rfeffv/y) (W/bf (75,79), where yis the surface tension of the displaced fluid. At the present time the surface tensions of the silica suspensions are not available and the values of A are plotted as a function of 7/5 12 (rjeffVt) (W/bf in Figure 7. The A value of PPG gradually decreases and tends to approach to a plateau value of ca. 0.5 at higher l/B value. The A values of the 2.5 and 5.0 wt % PPG-silica suspensions also decrease with an increase with 7/5 and they are smaller than that of PPG at the higher 7/5... 

An HPMC sample kindly supplied by Shin-Estu Chemical Co. was purified by the method described previously (5) and its molecular weight was determined to be 250x10 by the intrinsic viscosity measurement. PPG with the molecular weight of 725 was purchased from the Aldrich Chemical Co. and it was used without further purification. Silica suspensions were prepared by mechanically... 

Figure 4, Double-logarithmic plots of steady-state shear viscosities as a function of shear rate for PPG (circular) as well as 2.5 (filled circular), 5.0 (filledsquare), 7.5 (filled triangle), and 10.0 (filleddiamond) wt % silica suspensions in dispersed in PPG.

Figure 5. Typical fingering patterns for PPG as well as the 2.5 and 7.5 wt % silica suspensions dispersed in PPG at the injection pressure of 6.0 kPa from...

Moreover, the A values of the 7.5 and 10.0 wt % silica suspensions at the lower value of 1/B are larger than that of PPG. The presence of the larger value of A qualitatively agrees with the theoretical prediction of Ben TVmar and Poire (20) for shear thickening fluids. 

Figure 8. Plots of v for PPG as well as 2,5, 5,0, 7,5, and 10,0 wt% silica suspensions in dispersed in PPG as a function of (b /12t]e Vp, The dashed straight line has a slope of one. Symbols are the same as in Figure 7.

A similar scaling behavior was also found in three kinds of silica (PPG Fli-Sil 132, 135 an 233) /silicone oil suspensions at particle weight fraction 9 wt%, electric field strength range 0-0.5 kV/mm, and shear rate range 0.028-0.28 s" [451- q/q, vs. Mn/AT for those three suspensions at Ml=. 5 is shown in Figure 2. These results seem to indicate there is a transition happening in ER systems from the viscous controlled state to the polarization controlled state, which is the phase transition indeed and will be addressed in the next section... 

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