Ka. Newman et Kd. Stolzenbach, KINETICS OF AGGREGATION AND DISAGGREGATION OF TITANIUM-DIOXIDE PARTICLES AND GLASS-BEADS IN A SHEARED FLUID SUSPENSION, Colloids and surfaces. A, Physicochemical and engineering aspects, 107, 1996, pp. 189-203
Colloidal (0.2 mu m) titanium dioxide (rutile) particles aggregated wi
th and disaggregated from much larger (26 mu M) glass beads in a conti
nuously sheared suspension with constant pH and ionic strength chosen
to yield relatively slow (hours to days) kinetics. Measured rates of a
ggregation and disaggregation varied in response to systematic perturb
ations in the fluid shear and in the concentration of titanium oxide p
articles in suspension. The observed kinetics indicate that aggregatio
n and disaggregation occurred simultaneously, the net direction of exc
hange being determined by the relative rates of attachment and detachm
ent. Aggregated TiO2 particles were either weakly attached and exchang
ed relatively rapidly or strongly attached and exchanged relatively sl
owly, probably reflecting the influence of TiO2 particle clusters and
the geometric and electrostatic heterogeneity of the glass bead surfac
e. The rate of fluid shear did not appear to affect significantly the
kinetics of attachment and detachment, and the associated steady-state
partitioning of TiO2 between the free and attached states. However, T
iO2 particles that were effectively strongly attached under weak shear
were observed to detach when the shear increased. Collisions between
the glass beads had little effect on the aggregation and disaggregatio
n rates.