Agglomeration reverse addition

The above discussion of the potential negative effects from reverse addition (oiling out, poor crystal form, agglomeration) is necessarily qualitative, since this procedure, more so than many others, is strongly system dependent. The results could be satisfactory or unacceptable, depending on process requirements. Scale-up of reverse addition is particularly difficult because of the large deviations from equilibrium that are implicit in its implementation. 

Figure 9-18 Microscopic photo of crystals for Example 9.4, Option 2 (reverse addition). The cube-like crystals range in size from 20 to 40 pim. with significant agglomeration.

Figure 9-21 PSD of crystals for Example 9.4, Option 4 (forward vs reverse addition). Crystals formed under reverse addition shows a higher degree of agglomeration, as evidenced by the shoulder of the PSD.

An additional study revealed similar agglomeration behavior when the batch in DMF was charged into the antisoivent IP AC solvent (reverse addition). As shown in Fig. 9-21, PSD data revealed distinct shoulders from 10 to 100 pm for reverse addition operation. Again, this result corroborated the criticality of local mixing for the reverse addition operation. Oil droplets were also observed during this mode of addition. 

Reversible Electrodeposition of a silver iodide complex from a solution of 0.3 M Agl and KI or Rbl, and Ij in DMSO or diethyl malonate is an example for the third class of wet non-emissive electro-optic displays . As long as the silver content of the solution is high enough the solvent did not deteriorate when pulses of 50 V were passed through. The addition of AljOj, for preventing TiOj from agglomeration, and the use of RbAg4lj in DMSO as the solid ion-conductor established a cell which survive more than 10 cycles when operated at <2V drive, the realized response times were < 10 ms. 

As discussed in the review by Li et al. (2010), if the addition of a small fraction of nanofiller leads to an increase in breakdown strength then, beyond a certain point, this trend is reversed, presumably, as a consequence of increased nanofiller aggregation, which dominates any other factors. Then, the agglomerated nanoparticles behave, effectively, as micron-sized inclusions, the presence of which leads to a reduction in breakdown strength (Roy et al. 2005 Vaughan et al. 2006). This result is consistent with studies in which inclusion of various types were added to polymers (Morshuis et al. 1988), which showed empirically that the presence of sizeable particles degrades breakdown performance. 

---