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Shear-induced particle migration in binary colloidal suspensions
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Image of FIG. 1.
FIG. 1.

(a) Schematic of the experimental setup near the entrance of the rectangular-cross-section capillary tube. The suspension has a uniform concentration at the entrance because the flow is from a Teflon tube that has a much larger cross section. (b) Glass rectangular-cross-section flow chamber showing the relative position of the microscope and the corresponding image slices. The capillary tube length is (along ) and is not shown to scale.

Image of FIG. 2.
FIG. 2.

2D slices of a binary suspension of 3.0 and diameter particles taken along the vertical axis of the channel at a distance far downstream of the channel inlet (, where is half of the channel width). The slices are at the bottom wall, the center, and the top wall. Particle migration to the center is clearly visible by eye. Some segregation of the large and small particles is evident: the slices closest to the walls clearly have a lower concentration of large particles than that of small particles, and vice versa for the center slice. At the channel entrance, the suspension is . The scale bar is in length.

Image of FIG. 3.
FIG. 3.

Cross-stream concentration profiles showing downstream enrichment of the channel center by large and small particles of a flowing binary suspension. (a) Center enrichment by the large particles at for . (b) Center enrichment by the small particles for suspension at . (c) Comparison of the small particles in binary suspension (0.10,0.10) with monodisperse suspension (0.0,0.10) at . (d) Comparison of the large particles in binary suspension (0.10,0.25) with monodisperse suspension (0.10,0.0) at .

Image of FIG. 4.
FIG. 4.

Plots of the (a) unnormalized and (b) normalized evolution parameters for large particle suspensions (0.10,0) and (0.15,0). Entrance lengths are and .

Image of FIG. 5.
FIG. 5.

Plots of the cross-stream concentration profile of both the small and large particles for binary suspension (0.10,0.10). The downstream evolution of the profile is evident with increasing values of , as is indicated; is the half-width of the channel. The axis is as defined in Fig. 1. For this experimental run, the large particle entrance length is .

Image of FIG. 6.
FIG. 6.

(a) Plot of entrance length vs volume fraction for monodisperse suspensions of the large (radius ) and small (radius ) particles. The plots were derived from the computations outlined by Semwogerere et al. (Ref. 11). (b) Phase space for particle enrichment for the binary suspension of small particles and large particles. The solid line represents an estimate, using Eq. (1), of the line of equal entrance lengths of monodisperse suspensions of the two particle species; see text for details. The dot-dashed line is obtained from the computations of part (a). Above each line, and thus the large particles are predicted to enrich the center, while below each line, the converse is true. The three crosses are the positions in phase space for the three different binary suspensions used (see Table I).

Image of FIG. 7.
FIG. 7.

Plots that compare the evolution of a single particle species in a binary suspension to that of its monodisperse counterpart, along with comparison of downstream concentration profiles. The open symbols represent the monodisperse suspension, and the closed symbols represent the same species in the binary suspension. The dashed lines are exponential fits to the experimental data. (a) Downstream growth of the normalized evolution parameter for large particles in binary suspension (0.10,0.10) and monodisperse suspension (0.10,0.0). The corresponding entrance lengths are in the binary suspension and in the monodisperse suspension. (b) Their downstream concentration profiles at . (c) Downstream evolution of the small particles in binary suspension (0.10,0.25) and monodisperse suspension (0.0,0.25). Their entrance lengths are and . (d) Their downstream concentration profiles at for the monodisperse suspension and for the binary suspension.


Generic image for table
Table I.

Characteristics of the nine samples studied, which are organized into matched sets of 3. The samples are named using the convention . The entrance lengths and for the large and small particles, respectively, are given in terms of the half-width of the channel, . For the binary samples, the entrance lengths noted correspond to the individual species (large or small). The uncertainties in are the standard deviations obtained from the three experimental runs performed on each suspension. The dashes in the table indicate a species not present in a given sample, for which the entrance length is thus not defined.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Shear-induced particle migration in binary colloidal suspensions