Suspensions dynamic mobility

The Smoluchowski formula, which is used in the AcoustoSizer from the measured dynamic mobility, is valid for a disperse suspension of spherical particles according to Eq. 1. 

The amount of Si ions dissolution is found to be dependent on surface modification, which was confirmed by induchvely coupled plasma-atomic emission spectrometer (ICP-AES) analysis. Table 2.2 shows the dissolution amount of Si ions with and without surface modification of fumed silica slurry. Without surface modification, the amount of Si dissoluhon was 1.370 0.002 mol/L, whereas surfaces modified with poly(vinylpyrrolidone) (PVP) polymer yielded a dissoluhon of 0.070 0.001 mol/L, almost 20 hmes less than the unmodified surface. Figure 2.6 represents the electro-kinetic behavior of silica characterized by electrosonic amplitude (ESA) with and without surface modification. When PVP polymer modified the silica surface, d5mamic mobility of silica particles showed a reduchon from -9 to -7 mobility units (10 m /Vxs). Dynamic mobility of silica particles lacking this passivation layer shows that silica suspensions exhibit negative surface potentials at pH values above 3.5, and reach a maximum potential at pH 9.0. However, beyond pH 9.0, the electrokinetic potential decreases with an increasing suspension pH. This effect is attributed to a compression of the electrical double layer due to the dissolution of Si ions, which resulted in an increase of ionic silicate species in solution and the presence of alkali ionic species. When the silica surface was modified by... 

O Brien has shown (10) that for a dilute suspension of spherical particles (less than about 4% by volume, say) wifli thin double layers, the dynamic mobility is related to the particle properties as follows ... 

One immediate effect of increasing the particle concentration in the emulsion is that the acoustic impedance, Zg, can no longer be approximated as equal to that of the dispersion medium. Since Eq. (1) remains valid at all concentrations commonly encountered, it is important that the correct value of Zg is used, so that the correct value of the dynamic mobility is obtained from the measured ESA signal. In principle, the value of Zg for the emulsion could be a complex function of the frequency and the properties of the suspension, but the exact behavior is of little consequence for measurements with the AcoustoSizer, since it measures the value at each frequency before calculating from ESA signal. 

Dukhin et al. [83-85] have performed the direct calculation of the CVI in the situation of concentrated systems. In fact, it must be mentioned here that one of the most promising potential applicabilities of these methods is their usefiilness with concentrated systems (high volume fractions of solids, 4>) because the effect to be measured is also in this case a collective one. The first generalizations of the dynamic mobility theory to concentrated suspensions made use of the Levine and Neale cell model [86,87] to account for particle-particle interactions. An alternative method estimated the first-order volume fraction corrections to the mobility by detailed consideration of pair interactions between particles at all possible different orientations [88-90]. A comparison between these approaches and calculations based on the cell model of Zharkikh and Shilov [91] has been carried out in Refs. [92,93],... 

Arroyo, F.J., Carrique, F., Ahualli, S., and Delgado, A.V., Dynamic mobility of concentrated suspensions comparison between different calculations, Phys. Chem. Chem. Phys., 6, 1446, 2004. 

R. J. Hunter, Recent developments in the electroacoustic charactiaisation of colloidal suspensions and emulsions. Colloids Surf. A 141(1), 37-65 (1998). doi 10.1016/S0927-7757(98)00202-7 C. Knosche, Mdglichkeiten und Grenzen der elektroakustischen Spektroskopie zur Gewinnung von Partikelgrofieninformationen. PhD thesis, Technische Universitiit Dresden, 2001 M. Loewenberg, R.W. O Brien, The dynamic mobility of nonspherical particles. J. Colloid Interface Sci. 150(1), 158-168 (1992). doi 10.1016/0021-9797(92)90276-R R.W. O Brien, Electro-acoustic effects in a dilute suspension of spherical particles. J. Fluid Mech. 

Selected suspensions were studied in detail regarding sedimentation behavior (LUMiSizer, L.U.M. GmbH) and dynamic mobility of the primary particles (Zetasizer, Malvern Instruments) to get a detailed information about the effect of changed suspension formulation on suspension properties. 

Besides the determined suspension properties like solid content, dynamic mobility, or viscosity, obviously the primary particle shape has a decisive influence on the... 

The increase of suspension temperature leads to defined reduction of the pH value, the viscosity is significantly increased. Furthermore, the dynamic mobility is strongly influenced — from negative values at room temperature, positive values were measured at 50 °C. 

The piimaiy particles within a suspension containing 40 wt% of AI2O3 fine particles and a polyvinyl alcohol binder Mowiol 4-88 were dispersed using an electrosteric sodium polyacrylate dispersant with a chain length of 8000 g/mol NaPA 8000. The dispersant addition leads to a slight reduction of the viscosity of the suspension. The pH value is slightly increased at constant suspension density. As already described in literature [26], the additirm of the dispersant results in an increased dynamic mobility of the primary particles. The sedimentation speed is reduced. 

The variation of additives showed no defined impact on the determined suspension densities or pH values. Opposite to that, the varied additive types showed an effect on the resulting suspension sedimentation speed, viscosity, and dynamic mobility of the primary particles (Table 11.17). 

From these results, it became clear that the known correlations between suspension viscosity, sedimentation velocity, and dynamic mobility, valid for simple suspensions consisting of a disperse phase (particles), a liquid medium and eventually a dispersing agent, are not applicable, if a further (polymeric) phase is added. 

For the investigation of the changed suspensitm properties because of varied additive amount, suspensions of comparable solid content (40 wt%), primary particle size, and additive type polyvinyl alcohol Mowiol 4-88 were compared (Table 11.19). The stepwise increase of the additive amount leads to a slightly decreasing pH value. The viscosity increases while the sedimentation speed decreases. This is confirmed by the determined decreasing dynamic mobility values. An explanation can be found in the increasing amount of polymer molecules... 

From the studied variations of suspension formulation it became clear that for suspensions containing a liquid medium (water), a disperse phase (particles), and eventually a dispersing agent the known correlations between dynamic mobility, sedimentation speed, and viscosity are valid. An increased viscosity is a result of reduced dynamic mobility. Parallel the sedimentation speed is increased. This leads to the formation of granules with higher sheU thickness, the amotmt of homogeneous granules increases. 

Different from acoustic attenuation spectroscopy, in electroacoustic spectral analysis, sound waves are generated by an applied high frequency electric field across a colloidal suspension and subsequently detected. This is called the electrokinetic sonic amplitude effect (ESA) [38]. These sound waves arise because the alternating electric field pushes the suspended particle forwards and backwards. By measuring the magnitude and phase angle of the sound waves at multiple frequencies (typically from 1-10 MHz), the particle dynamic mobility, Pd, can be determined, provided the concentration and the density of the... 

Turning again to the problem of bidisperse suspensions, we will show below that the presence of even minute amounts of tiny particles can greatly affect the dynamic mobility of large latex particles. Comparison between experimental data and theoretical approaches to the calculation of m in the... 

DYNAMIC MOBILITY OF BIMODAL SUSPENSIONS 5.3.1 General Behavior and Effect of Particle Size... 

FIGURE 5.9 Real (a) and imaginary (b) parts of the dynamic mobility of suspensions of spherical particles in 0.5 mM KCl, with ( )= 1%, = -100mV and the particle radii indicated. (Reprinted from Jimenez, M.L. et al. 2007. Croat. Chem. Acta 80 453-459. With permission from the Croatian Chemical Society.)... 

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