Fig. 1 and Table 1 summarize the rotational rheologic characteristics
of the SPI and SPI-MMT filmogenic dispersions. The
experimental values for shear stress as a function of the shear
rate conformed satisfactorily to the model of Ostwald de Waele
(Eq. (1)), thus yielding correlation coefficients greater than 0.999
in all instances. All the dispersions of SPI and SPI-MMT exhibited a
pseudoplastic flow behavior (K40, 0ono1, τ0¼0, with τ0 being
the yield stress; Table 1) and as such manifested decreasing
apparent-viscosity values upon increases in the deformationvelocity
gradient (Table 1 and Fig. 1). The pseudoplastic behavior
of the dispersions became progressively pronounced with
increases in the clay content of the formulation since those
increments produced a decline in the flow-behavior index (n)
along with a concomitant increase in the viscosity of the dispersions
(i.e., indicated by higher values of K and of the measured
apparent viscosity). Although this latter elevation was seen over
the entire range of shear rates analyzed, the increment in viscosity
in parallel with the increasing content of clay was more pronounced
at low shear-rate values.