Dispersed phase concentration

If the dispersed phase concentration is not too high, and the species are very small, light-scattering can yield size information. The theory underlying the determination of size distribution for a colloidal dispersion is quite involved [13,75,76], When a beam of light enters a suspension some light is absorbed, some is scattered, and some is transmitted. Many dilute, fine emulsions and suspensions show a noticeable turbidity given by,... 

Sedimentation, or creaming, results from a density difference between the dispersed and continuous phases. This is not yet a destabilization of the dispersion, but produces two separate layers of dispersion that have different dispersed phase concentrations. One of the layers will contain an enhanced concentration of dispersed phase, which may promote aggregation. (The term creaming comes from the familiar separation of cream from raw milk.)... 

C = dispersed phase concentration (usually volume fraction). 

Loss of volatile solvent from a dispersion, causing the dispersed phase concentration to increase. 

The values of AE and AS (Table 1) suggest that the probe motion in frozen water and solutions of silica is the slipping by the rigid lattice, but in other cases this is the motion in viscous medium of surface water layers [12]. A kind of compensation effect reveals at that with rising the disperse phase concentration. That means a symbate increase of AE and AS, which is characteristic of the spin label motility in water-protein matrix [12]. 

These two expressions are valid only in the range of not very high disperse phase concentrations (cp 0.35). Some approaches to describe the dependence of viscosity on concentration in the range of high disperse phase contents are based on Taylor s well-known formula describing the dependence of viscosity on concentration for emulsions [59] ... 

An expression of the same form was obtained by Felderhof [61] when he analysed the flow perturbation caused by a single particle in terms of the force multipoles theory. Bedeaux [49] pointed out that when the disperse phase concentration approaches the maximum value (correlation interaction between... 

Drop size distribution in dilute suspensions of electrical conducting liquids may be determined using the Coulter principle but the need to add what may be undesirable conductive materials limits its applicability [213-215]. The use of chemical means to measure interfacial area has been used extensively for gas-liquid dispersions. Chemical reaction methods for determining the interfacial area of liquid-liquid systems involve a reaction of a relatively unchanging dispersed-phase concentration diffusing to the continuous phase. The disadvantage of this approach is that the mass transfer can affect the interfacial tension, and hence the interfacial area [216-218]. 

Figure 7 shows the rheograms (shear stress versus shear rate plots) of a typical emulsion system at different values of dispersed-phase concentration. The volume-surface mean diameter of the oil droplets for the system shown is 10 xm. For a given concentration, the variation of log t against log 7 is linear, a result indicating that the emulsions follow a power law (eq 2). 

A comparison of these expressions is given in Table I. This table shows the increase in the mixture resistance due to the presence of nonconducting particles or droplets, - Rj, divided by the fluid resistance as a function of the dispersed-phase concentration. R and Rj are the mixture and fluid resistances, respectively. Maxwell s (68) and Bruggeman s (74) relations give... 

Conductivity Probe for Local Solids Concentration Measurements. On the basis of the preceding discussion, local solids concentration can be determined by measuring the mixture conductivity, then using a calibration curve, for example, equation 20. However, using this method to measure solids concentration or dispersed-phase concentration is not an easy task. In the following sections, the development a new conductivity probe will be summarized (24). Also, various problems encountered with conductivity methods will be discussed. 

Intrinsic Viscosity For emulsions, the limit, as the dispersed-phase concentration approaches inflnite dilution, of the specific increase in viscosity, at low shear rate, divided by the dispersed phase concentration [i ] = lim o lim - >o flsp/C). 

Reduced Viscosity For emulsions, the specific increase in viscosity divided by the dispersed-phase concentration (r/Red =... 

The utility of the model to predict the effects of interdroplet mixing on extent of reaction was demonstrated for the case of a solute diffusing from the dispersed phase and undergoing second-order reaction in the continuous phase. For this comparison the normalized volumetric dispersed-phase concentration distribution is deflned as fv(y) dy equal to the fraction of the total volume of the dispersed phase with dimensionless concentration in the range y to y -i- dy, where y = c/cq and... 

Fig. 17. Comparison of volumetric dispersed-phase concentration distribution for various levels of droplet mixing for second-order reaction in the continuous phase, = 0.006 [after Zeitlin and Tavlarides (Z3)].

Effect of Dispersed Phase Concentration. In any application of these microemulsion systems to polyn rization processes, it would be desirable to maximize polymer yield. This can be accomplished by maximizing the acrylamide ratio at constant surfactant loading or, of course, the acrylamide ratio (as well as the water ratio) to the surfactant can be fixed and the total amount of surfactant in the system increased. Therefore, the effect of total dispersed phase concentration on the phase behavior was investigated. The dispersed phase concentration was defined as a volume fraction equalling the total volume of surfactants + acrylamide -l- water divided by the total volume. 

Coalescence, dispersion, and settling are all affected by dispersed phase concentration or volume fraction, 0. Liquid-liquid systems can be categorized with respect to 4> as follows ... 

In lyophilic colloidal systems, e.g. in polymer solutions, the disperse phase concentration may be sufficiently high, and the osmotic pressure reaches values that can be reliably measured. In this case osmotic pressure measurements, along with the application of osmosis-related phenomena, such as cryoscopy and ebullioscopy, provide methods for the study of such systems. For example, these methods allow one to determine the molecular weights of polymers. 

Abbreviations C is the solute or dispersed-phase concentration and ti0 is the viscosity of the pure solvent or dispersion medium. 

Inherent Viscosity (r jnh) In solutions and colloidal dispersions, the natural logarithm of the relative viscosity (rj/rjQ), all divided by the solute or dispersed-phase concentration (C). r/jnh = C l In(ri/ri0). In the limit of vanishing concentration, it reduces to the intrinsic viscosity. Also termed the logarithmic viscosity number. 

Intrinsic Viscosity The specific increase in viscosity, r SP, divided by the dispersed-phase concentration in the limits of both the dispersed-phase concentration approaching infinite dilution, and of shear rate, 7, approaching zero ... 

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