Silica agglomerates

A model has been developed to describe the penetration of polydimethylsi-loxane (PDMS) into silica agglomerates [120]. The kinetics of this process depend on agglomerate size and porosity, together with fluid viscosity. Shearing experiments demonstrated that rupture and erosion break-up mechanisms occurred, and that agglomerates which were penetrated by polymer were less readily dispersed than dry clusters. This was attributed to the formation of a network between sihca aggregates and penetrated PDMS, which could deform prior to rupture, thereby inhibiting dispersion. 

To elucidate some of these effects, PCS (photon correlations spectroscopy) measurements of the protein/A-300 systems were performed.4 The Oef(pH) graphs have a maximum close to pH(IEP) of the proteins (Figure 6). However, at pH far from pH(IEP) of the proteins, the PSDs of protein/A-300 are similar to those for pure silica suspensions, but Def is smaller pure silica due to decomposition of silica agglomerates and aggregates from the action of proteins. This effect is independent of protein type, since the interaction of protein molecules with silica particles can be stronger than between silica... 

Particle Size Distribution of Fumed Silica Agglomerates at Low Shear Stress... 

The direct comparison of the results from optical methods with those from aerodynamic methods requires knowledge of the density of the particles to convert the aerodynamic diameter into the geometric diameter. Because of the unknown porosity of the silica agglomerates, no valid conversion was known. Experiments using a direct optical method to measure fractions of aerodynamic classified silica agglomerates [1] led to an effective particle density of a silica agglomerate of about 0.075 g/cm. ... 

This combination of LD and sample feeding allows high reproducibility at close to technical handling conditions (Fig. 5). This method is nondestructive, i.e., silica agglomerates are mostly preserved and the aerosol concentration is sufficiently high. 

TEM revealed that the unmodified silica agglomerated in polyisoprene better dispersion was observed in both thermal- and radiation-induced admicellar polymerization. The silica prepared in both thermal- and radiation-induced admicellar polymerization using the 3 types of surfactants are smaller than 100 nm. 

R. Wengeler, A. Teleki, M. Vetter, S.E. Pratsinis, H. Nirschl, High-pressure liquid dispersion and fragmentation of flame-made silica agglomerates. Langmuir 22(11), 4928 935 (2006). doi 10. 1021/la053283n... 

In addition, although the TEM observations indicate that the nano-silica agglomerates can deform and be pulled apart in PP matrix, it is still unknown whether voiding and... 

Silica particles are polar and porous (Section 1.4.6). The silica particles show not only significant interparticle van der Waals forces, but also strong polar and dipole bonds. This results in much higher viscosities than in carbon black compounds (Eq. 8.3) and more complex rheological properties generally. Silica compounds are hard to process and silica agglomerates are difficult to disperse in rubber matrices [ 12]. The surface of silica is hydrophilic, which is incompatible with oleophilic rubber matrices. There has been much research on breakup of silica agglomerates [13 to 20]. 

Kim, K.-J. and J.L. White, Silica surface modification using different aliphatic chain length silane coupling agents and their effects on silica agglomerate size and processability. Composite Interfaces, 2002. 9(6) 541-556. 

---