Monodispersed emulsions

The interaction between the dispersed-phase elements at high volume fractions has an impact on breakup and aggregation, which is not well understood. For example, Elemans et al. (1997) found that when closely spaced stationary threads break by the growth of capillary instabilities, the disturbances on adjacent threads are half a wavelength out of phase (Fig. 43), and the rate of growth of the instability is smaller. Such interaction effects may have practical applications, for example, in the formation of monodisperse emulsions (Mason and Bibette, 1996). 

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]).

C. MabiUe, V. Schmitt, P. Gorria, F. Leal Calderon, V. Faye, and B. Deminiere Rheological and Shearing Conditions for the Preparation of Monodisperse Emulsions. Langmuir 16, 422 (2000). 

P. Perrin Amphiphilic Copolymers A New Route to Prepare Ordered Monodisperse Emulsions. Langmuir 14, 5977 (1998). 

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). 

T.G. Mason, A.H. Krall, H. Gang, I. Bibette, and D.A. Weitz Monodisperse Emulsions Properties and uses. P. Becher (ed). Encyclopaedia of Emulsion Technology, Ch. 6, p. 299, Marcel Dekker, New York, Basel, Hong Kong (1996). 

T. Mason Rheology of Monodisperse Emulsions. Ph.D Thesis, Princeton University (1995). 

Recently, Bibette has described a procedure for the production of truly monodisperse emulsions and HIPEs this will be described in section 1.3.3. 

Chuah, A.M., Kuroiwa, T., Kobayashi, I., Nakajima, M. (2009). Effect of chitosan on the stability and properties of modified lecithin stabilized oil-in-water monodisperse emulsion prepared by microchannel emulsification. Food Hydrocolloids, 23, 600-610. 

Monodisperse emulsions, prepared by the double-jet method, have a narrow range of grain sizes of uniform shape. The grains can be either cubic or octahedral, depending on the conditions of preparation. 

This, however, is in conflict with results obtained when fine grain monodisperse emulsions were exposed under vacuum (Section IV.A). We found that several emulsions of this type showed no low-intensity reciprocity failure under the best vacuum conditions, and in some the highest sensitivity occurred in the region of lowest irradiance, in direct contradiction with the requirements of the supersaturation mechanism. 

The traditional methods of emulsion preparation, especially those involving stirring and shaking, tend to lead to uncontrolled and wide drop-size distributions. Several methods for the preparation of fairly monodisperse emulsions exist, of which the simplest is probably the extrusion of a dispersed phase through a pipette into a flowing continuous phase. Other, more involved methods are discussed by Mason [433],... 

For practical applications in the food industry, where large-volume production is conducted, it is especially important to obtain high disperse-phase flux. Abrahamse et al. [8] reported on the industrial-scale production of culinary cream. In this study they evaluated the required membrane area for different types of membranes an SPG membrane, an a-Al203 membrane and a microsieve filter. The requirements for culinary cream production were a droplet size between 1 and 3 pm and a production volume of 20 m3/h containing 30% disperse phase. They concluded that to produce large quantities of monodisperse emulsions the most suitable was a microsieve with an area requirement of around 1 m2. 

The volume is closed with a contribution by J. Bibette who describes and illustrates a simplified process of making monodisperse emulsions and emulsion based particles with predictable size and size distribution by a simple shearing device. I regard this very flexible route as important for the conception of many future particle-based systems, devices and procedures, and it is rather the rule than the exception that colloid chemistry nicely integrates mechanical and engineering procedures to access the nanoscale in a rational way. 

The process leading to monodisperse emulsions was initially described by Mason and Bibette [ 1,24,26-28]. For that purpose, they first prepare a crude mother emulsion obtained by progressively incorporating oil into the surfactant-water phase. In a second step, they apply a simple and well-controlled shear to this crude emulsion that becomes monodisperse after no more than a few seconds. Figure 1 shows microscope images before and after application of a shear under the same conditions used by Mason and Bibette. The shear has the effect of reducing both the average diameter and the distribution width of the mother emulsion. 

The aim of this first section is to describe the rupturing mechanisms and the mechanical conditions that have to be fulfilled to obtain monodisperse emulsions. A simple strategy consists of submitting monodisperse and dilute emulsions to a controlled shear step and of following the kinetic evolution of the droplet diameter. It will be demonstrated that the observed behavior can be generalized to more concentrated systems. The most relevant parameters that govern the final size will be listed. The final drop size is mainly determined by the amplitude of the applied stress and is only slightly affected by the viscosity ratio p. This last parameter influences the distribution width and appears to be relevant to control the final monodispersity. 

Fig. 10. Images of monodisperse emulsions obtained under different conditions a Ifralan 55%, y=8400 s-1, b Ifralan 45%, y=2600 s, c Ifralan 25%, y=4700 s 1,d Ifralan 15%, y=7350 s 1...

The binding capacity is essentially determined by the total specific surface of the magnetic droplets. Since this parameter must be controlled with great accuracy, monodisperse emulsions become necessary. 

In this article we have shown how a capillary instability may generate a well-defined characteristic size. The materials that derive are essentially emulsions made of liquid or crystallizable droplets. The monodispersity make it possible to obtain materials with perfectly controlled and reproducible properties, which certainly cannot be achieved in presence of polydisperse emulsions. This is why monodisperse emulsions are not only model systems for fundamental science but also materials with commercial applications. 

Bibette J, Leal Calderon F, Gorria P (1999) Polydisperse double emulsion, corresponding monodisperse double emulsion and process to fabricate the monodisperse emulsion WO0121297... 

The methods developed recently for formation of monodisperse emulsions by applying a fractionated crystallisation process on an initial crude emulsion and creating large capillary (disjoining) pressures in them using osmotic stress techniques [520] are particularly suitable for the comparison of the properties of free emulsion films and films in emulsions. 

Recently a new method for formation of monodisperse emulsions that creates high capillary pressures, involving osmotic stress technique, has been introduced [73]. It proves to be most reliable for the purpose. Preliminary calculations showed that the emulsion films in such monodisperse systems rupture in a narrow range of critical disjoining pressure. For example, NaDoS emulsion films rupture in the range from 1 to 1.3-105 Pa, which is analogous to foam films from the same surfactant solution. Unfortunately, the foam film type has not been considered. 

Industrial processes are at this moment predominantly based on the first class (using intense flow fields). The second class based on membranes or micro-channels seems to have large potential for making more complex products for example, monodisperse emulsions or double emulsions. The third class is used in the production of foods, but also in other industries where emulsions need to be made in which the dispersed phase has a high viscosity compared to the continuous phase. 

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