Emulsion monodisperse multiple

For the successful preparation of emulsions, the wetting conditions on the membrane surface are crucial. It is necessary that the membrane surface is only wetted by the liquid that forms the continuous phase. The droplet size correlates with the membrane pore size by a simple relation, Dd = /Dm where / is a value typically between 2 and 8 (35). Droplets can be produced with diameters in the pm-, as well as in the sub-micrometre range. This technique has been successfully applied to produce monodisperse emulsions and multiple emulsions, as well as to carry out polymerizations leading to polymer particle in the pm size range with narrow size distributions (36, 37). Further advantages (38) are as follows the droplet size is controllable and generally a quite narrow DSD can be achieved, the method is reproducible and the scale-up is easy just by increasing the number of membrane modules, the characteristic features are independent of scale-up, batch as well as continuous operations modes are possible, the continuous phase is exposed to a lower stress. 

Vladisavljevic, G.T., Shimizu, M., and Nakashima, T., Preparation of monodisperse multiple emulsions at high production rates by multi-stage premix membrane emulsification, J. Membr. Set, 244 (1-2), 97-106, 2004. 

In this chapter, we describe the new technologies that can produce various double emulsions of controlled sizes, structures and compositions. We also explain the emerging new applications of the monodisperse double emulsions prepared using those technologies. Section 21.2 describes the use of porous materials for emulsification membranes. Section 21.3 describes the use of a channel array or through-holes fabricated on a silicon substrate. Section 21.4 describes the use of microfiuidic channels on a planar substrate. Section 21.5 explains coaxial microcapillary devices. Section 21.6 describes the applications of monodisperse multiple emulsions to a new class of functional materials. 

Chu LY, Utada AS, Shah RK, et al Controllable monodisperse multiple emulsions, Angew Chem Int Ed 46 8970-8974, 2007. 

Deng NN, Wang W, Ju XJ, et al Wetting-induced formation of controllable monodisperse multiple emulsions in microfluidics, Lab Chip 13 4047-4052, 2013b. 

Emulsions are metastable colloids made out of two immiscible fluids, one being dispersed in the other, in the presence of surface active agents. The droplet volume fiaction may vary from zero to almost one dense emulsions are sometimes called biliquid foams since their structure is very similar to the cellular structure of air-liquid foams for which the continuous phase is very minor. From dilute to highly concentrated, emulsions exhibit very different internal dynamics and mechanical properties. When diluted, droplets are agitated by Brownian motion and behave as viscous Newtonian fluids, whereas when more concentrated, namely above the random close packing volume fraction which is 64% for monodisperse droplets, the internal dynamics are severely restricted and they behave as viscoelastic solids. Simple direct emulsions are composed of oil droplets dispersed in water while inverse emulsions are composed of water droplets dispersed in an oil continuous phase. In fact, emulsions are in principle made out of two immiscible phases for which the interfacial tension is therefore non-zero, and may involve other hydrophilic-like or lipophilic-like fluids in the presence of suitable surface active species, each phase being possibly comprised of numerous components. Sometimes, simple emulsions may also contain smaller droplets of the continuous phase dispersed within each droplet of the dispersed phase. Such systems are called double emulsions or multiple emulsions. ... 

The control that can be exerted over the flow of immiscible fluids in micro-fluidic devices to formation of monodisperse droplets and bubbles can be extended to formation of more complicated objects and architectures of the droplets, such as multiple emulsions [27-32], Janus particles [33, 34] and other morphologies of liquid droplets, solidified particles and capsules [35-39], Figure 13 presents micrographs of the droplets, particles and capsules produced in exemplary techniques. 

T. Nisisako, S. Okushima, and T. Torii, Controlled formulation of monodisperse double emulsions in a multiple-phase microfluidic system, Soft Matter, 1, 23-27, (2005). 

FIGURE 20.13 Examples of multiple emulsions formed in microfluidic systems (a) multiple shells-multiple cores configurations of monodisperse triple emulsions made with cascaded microcapillary devices results. (Reproduced with permission from Utada, A.S. et al.. Bull. MRS, 32(09), 702, 2007.), (b) composite emulsion formed by droplets of different composition and different volumes. (Reproduced with permission from Hashimoto, M. et al.. Small, 3(10), 1792, 2007.), and (c) examples of anisotropic particles formed by either polymerization (spheres and disks, rods) of droplets of monomer or thermal setting of droplets. (Reproduced with permission from Xu, S. et al., Angew. Chem. Int. Ed. Engl, 44(5), 724, 2005.)... 

Multiple emulsions are much more stable, with smaller globule size and smaller inner droplet size, more monodispersed and more viscous compare to multiple emulsions stabilized with monomeric surfactant. Today s multiple emulsions can retain the solute for longer periods of time on the shelf. 

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