Emulsions polydispersity

Figure 1.20. Effect of the viscosity ratio p on the emulsion polydispersity P. The dashed line represents the limit between polydisperse and monodisperse emulsions. (Adapted from [149]).

Polydispersity coefficient ko (1.22) is one more important magnitude characterizing resulted emulsions. For monodisperse systems - kn = 1 and for polydisperse kn < 1, and the lesser the ko parameter value, the bigger the dispersal of particles by their sizes. The ratio Ls/dd practically doesn t influence on resulted emulsions polydispersity as in the case of dispersions formation with surface-volumetric diameter d32 (Fig. 3.33). Particles dispersal is increased when dd/dc ratio is raised and sufficiently homogeneous emulsions are formed in divergent-convergent canal of tubular apparatus with dd / d = 1,6. In particular for Ls / dd = 2-3 the value of ko at dd / dc = 1,6 is 0,72-0,75, where as at da / d = 2 and 3 kn is decreased down to 0,63 and 0,41 accordingly. 

In that specific case, DSC measurements allowed us to study quite easily the influence of agitation on the emulsion polydispersity while other classical techniques were not ap-... 

Emulsion polymeriza tion of ABS (241) gives a mbber-phase particle morphology which is mostly deterrnined by the mbbet-seed latex. Since the mbber particle size, polydispersity, and cross-linking ate estabhshed before the preparation, the main variables relate to grafting, molecular weight... 

For acrylic polymers produced via emulsion polymerization, a set of two or more 30-cm-long columns with 10-ju,m or less packing material will usually ensure that the observed polydispersities are minimally influenced by column band broadening. 

V. Mishra, S. M. Kresta, J. H. Masliyah 1998, (Self-preservation of the drop size distribution function and variation in the stability ratio for rapid coalescence of a polydisperse emulsion in a simple shear field), J. Colloid Interface Sci. 197, 57. 

The emulsions are characterized by the mean diameter d and the polydispersity P, defined by ... 

The observations of model systems made of monodisperse dilute emulsions can be generalized to polydisperse and concentrated emulsions. 

The previous experiments were all performed on dilute emulsions for which the dispersed phase represents 2.5 wt% of the emulsion. The results obtained for a concentrated emulsion with oil mass fraction equal to 75% sheared at 500 s and 3000 s are reported in Fig. 1.16 [156]. The primary emulsion was polydisperse with d = 57 am. The two previously described regimes still exist. The first regime is particularly efficient in reducing the diameter because one drop breaks into 160 droplets through the Rayleigh instability for an applied shear rate of 500 s (di( = 10.5 am) and into 6200 droplets for an applied shear rate of 3000 s ... 

Figure 1.15. Fragmentation kinetics of a polydisperse emulsion. (Adapted from [156].)...

J. Bibette, F. Leal-Calderon, and P. Gorria Polydisperse Double Emulsion, Corresponding Monodisperse Double Emulsion and Process to Fabricate the Monodisperse Emulsion. Patent WOO 121297 (1999). 

The first observation of depletion flocculation by surfactant micelles was reported by Aronson [3]. Bibette et al. [4] have studied the behavior of silicone-in-water emulsions stabilized by sodium dodecyl sulfate (SDS). They have exploited the attractive depletion interaction to size fractionate a crude polydisperse emulsion [5]. Because the surfactant volume fraction necessary to induce flocculation is always lower than 5%, the micelle osmotic pressure can be taken to be the ideal-gas value ... 

Figure 3.2. Microscopic image of a polydisperse emulsion (a) and of the emulsion obtained after six fractionation steps (b). The droplet volume fraction in both pictures is around 60%. (Reproduced with permission from [5].)...

J. Bibette Depletion Interactions and Fractionated Crystallization for Polydisperse Emulsion Purification. J. Colloid Interface Sci. 147, 474 (1991). 

Figure 5.6. a) Experimental time evolution of the diameter Ds (B) and the polydispersity P ( , right scale) for an octane-in-water emulsion stabilized with SDS. b) Schematic representation for the evolution of Dj as a function of time. (Adapted from [42].)... 

---