Bare particles electrolyte concentrations

PVA and TaM -for the 88%-hydrolyzed PVA. The same dependence was found for the adsorbed layer thickness measured by viscosity and photon correlation spectroscopy. Extension of the adsorption isotherms to higher concentrations gave a second rise in surface concentration, which was attributed to multilayer adsorption and incipient phase separation at the interface. The latex particle size had no effect on the adsorption density however, the thickness of the adsorbed layer increased with increasing particle size, which was attributed to changes in the configuration of the adsorbed polymer molecules. The electrolyte stability of the bare and PVA-covered particles showed that the bare particles coagulated in the primary minimum and the PVA-covered particles flocculated in the secondary minimum and the larger particles were less stable than the smaller particles. 

It is interesting to compare these results with the electrophoretic measurements made under identical electrolyte concentrations. Figure 8 shows that the variation of electrophoretic mobility with sodium chloride concentration is different for the bare and the PVA-covered particles. For the bare particles, the mobility remains constant up to a certain salt concentration, then increases to a maximum and decreases sharply, finally approaching zero. The maximum in electrophoretic mobility-electrolyte concentration curve with bare particles has been explained earlier (21) by postulating the adsorption of chloride ions on hydrophobic polystyrene particles. In contrast, for the PVA-covered particles, the mobility decreases with increasing electrolyte concentration until it approaches zero at high salt concentration. 

Figure 7. W versus electrolyte concentration (NaCl) for different-size particles (o) 190nm particles ( ) 400nm particles open points for bare particles and closed points for particles covered withVinol 107 at saturation.

FIGURE 13.3 Fractal dimensions for bare particles aggregating at different electrolyte concentrations. Inset Time evolution of the scattered light intensity as a function of a concentration of 0.250 M of KCl. The fractal... 

FIGURE 13.4 X parameter as a function of the electrolyte concentration for bare particles. This parameter was obtained from the slopes of the long-time evolution of the nnmber-average mean clnster size. 

For the bare particles at high electrolyte concentration, the structural coefficient ko is very close to unity and the surface-to-surface distance between the particles contained in the aggregates is approximately zero. The expected result is in good agreement with other experiments [30,56] and simulations [57]. The obtained value is, however, significantly smaller than the values reported in [58] for carbonaceous soot aggregates formed in laminar diffusion flames. This is not surprising... 

FIGURE 13.12 Average diffusion coefficient normalized by Dq for bare (0%) and coated particles (50%) aggregating at pH 4.8 and two different electrolyte concentrations. The solid lines show the best fits using the kernel given by Equation 13.15. 

Structural and Kinetic Parameters for Bare (0%) and Functionalized Particles (50%) at Different Electrolyte Concentrations... 

The investigations include the effect of (i) PVA molecular weight, particularly at higher concentrations which give different adsorption isotherms (ii) latex particle size over the range 190-llOOnm using a low-molecular-weight fully-hydrolyzed PVA (iii) electrolyte on bare and PVA-covered particles of different sizes. 

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