Re-agglomeration

The selection of an optimum surfactant, or combination of surfactants, was necessary primarily to prevent re-agglomeration of the dispersed sample while settling. In addition, it was demonstrated that the use of a blender (Waring) was an effective aid in dispersing these two components. The violent action of the blender did not cause a change in the concn of coarse particles in the dispersion with increasing blending times up to 17 minutes... 

We developed another dispersant presenting properties for a special application. In some cases when an ultra fine calcium carbonate slurry is spray dried, a re-agglomeration of the powder often occurs, due to high water adsorption. This powder aggregation is detrimental to the quality of the final product. 

The consequence is an inhomogeneous distribution of additives in the individual polymer phases and thermodynamic nonequilibrium after mixing. The latter effect may cause demixing and re agglomeration of additives. A well-known example in this regard is the flocculation or reagglomeration of silica in S-SBR compounds [3]. 

Fig. 6.11-10 Re-agglomeration (aggregation) of electrostatically dispersed Si02, Aerosil 0X50 (manufacturer Degussa) left) original sample ...

For milling solids in air by mecharrical grinding or by air-jet mills (used for microrrization ) a lower limit of about 2 pm is given by re-agglomeration counteracting the comminution. A further degree of comminution can be achieved only if the solid is suspended in a liquid wherein. 

Once a powder is dispersed, it sometimes helps to add a stabilizer (or admixture) to the sample, such as sodium hexametaphosphate. The stabilizer alters the charge on the surface of the particles, preventing re-agglomeration. 

The results presented above indicate that ultrasonication was effective in dispersing CNTs in DMPU. However, the nanotube bundles were found to re-agglomerate upon standing after sonication. As shown in Figme 4, the size distribution of CNT/ DMPU dispersion (without PANi) shows a considerable increase in hydrodynamic diameter when measured 60 minutes after sonication, compared with the sample measured immediately following sonication. 

Hi) separation and distribution of the resulting fragments in the polymer matrix, so that re-agglomeration will not occur. 

Although we focus in this paragraph on Li alloying with simple elements of the periodic table, very often amorphous carbon is added to the particular element under scrutiny, either to prevent re-agglomeration of nanostructures (when such nanostructures are of concern) or to improve the electrical conductivity of the anode... 

Despite these weak interactions between stabilizer and particle surface, longterm stability of the particle system was observed [21]. Re-agglomeration of the ITO particles is possible by the addition of an anti-solvent to the particle dispersion. To investigate the re-agglomeration of the particles and the thereby incurred processes on their surface in detail, the amount of the stabilizer on the surface which was detected by solid-state C-NMR is compared with TGA. ITO particles... 

The redispersion of the stabilized ITO nanoparticles leads to a decrease in stability of the nanoparticles, measured as decreased fraction of stable particles after the hrst redispersion cycle. This is due to the weak interactions between the stabilizer and the particle surface, as shown above by the ITC measurements. By precipitation and redispersion of the particles, some stabilizer molecules were detached from the surface because of the addition of the organic solvent. The detachment still small enough to achieve redispersion of the nanoparticles during the redispersion steps was verified by TGA and is plotted in Fig. 9 (right). In case of the first re-agglomeration step, the amount of bound stabilizer on the surface is still sufficient to achieve full redispersion of the nanoparticles. However, after three precipitation-redispersion cycles, the amount of coupled stabilizer molecules is so low that only 35 % of the particles are stable [20]. 

The size of the debris particles is an important piece of information. However, it is difficult to characterize the size after the test. The debris retained in the subcompartment is typically present as re-agglomerated particles. Therefore, it is difficult to characterize their size. Only the debris that is transported... 

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