The electrorheology of suspensions of Na-fluorohectorite clay in silicone oil
Microscopy picture of ER chains obtained from applying a 1 kV/mm electric field to a suspension of Na-Fh clay crystallite aggregates in a silicone oil. The red bands seen in the upper and lower parts of the image are copper electrodes, and the distance between them is 1 mm.
Viscosity of the Na-Fh suspensions as a function of the volume fraction , for . The viscosity values have been obtained from linear fits (shown as plain lines) onto the flow curves (shown as symbols) in the inset.
(a) Flow curves of Na-Fh suspensions with , for different strengths of the applied electric field; experimental measurements are plotted as symbols, while corresponding fits of the CCJ model [Eq. (3)] are drawn using solid lines. (b) Corresponding evolution of the viscosity as a function of shear rate.
Scaling of the data of Fig. 3(a) using Eq. (1) with , for a particle fraction . The plain line represents the asymptotic Bingham model. is a reference electric field value.
(a) Flow curves of Na-Fh suspension for two different values at . (b) Viscosity curves for the same suspensions.
Log-log plot of the static yield stress as a function of the strength of the applied dc electric field for different volume fractions of the Na-Fh particles.
Log-log plot of the scaled static yield stress versus particle volume fraction. The dashed line (power law with an exponent of 1.70) represents the behavior of our previously reported laponite suspensions (Parmar et al., 2008).
Bifurcation in the rheology of a Na-Fh suspension of volume fraction , under applied electric field strengths of (a) 530 and (b) .
Bifurcation yield stress as a function of the applied electric field, for three different particle volume fractions. The fitted power-law exponents are , , and , respectively. This decrease of the exponent with volume fraction is attributed to the growing discrepancy between the measured and applied voltages.
Evolution of the current density as a function of the electric field strength, for particle fractions and ; the data, reproduced from Rozynek et al., 2010, are rescaled by , so as to make the values at coincide.
Critical stresses (in pascal) measured for various electric field strengths and particle fractions. Leak currents prevent accurate measurement for the two larger electric fields and particle fractions . See also Fig. 9, in which these values are plotted as a function of .
Exponents and , as defined by Eq. (1), obtained for ER laponite suspensions (results taken from Parmar et al., 2008) and Na-Fh ER suspensions (this study) from our three yield stress estimates: dynamic, static, and bifurcation yield stress (y.s.). For an explanation of and comparison between the various exponent values, see the discussions in Secs. IV D, V A, and V B.
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