Preparation of Nano-Emulsions

Two methods may be applied for the preparation of nano-emulsions (covering the droplet radius size range 50-200 nm). Use of high-pressure homogenisers (aided by appropriate choice of surfactants and cosurfactants) or application of the phase inversion temperature (PIT) concept. 

---

FIGURE 21.8 Phase diagram in the pseudoternary system water/SDS hexanol (1 1.76)/dodecane. Emulsification paths for the preparation of nano-emulsions at a final water content of 98 wt%. 

Use of Nano-emulsions as Templates for the Preparation of Polymeric Nanoparticles 167... 

Izquierdo, P., Esquena, J., Tadros, T.F., Dederen, C., Garcia, M.J., Azemar, N. and Solans, C. (2002) Formation and stability of nano-emulsions prepared using the phase inversion temperature method. Langmuir, 18 (1), 26-30. 

Sole, I., Maestro, A., Gonzalez, C., Solans, C. and Gutierrez, J.M. (2006) Optimization of nano-emulsion preparation by low-energy methods in an ionic surfactant system. Langmuir, 22 (20), 8326-8332. 

P. Izquierdo, J. Esquena, T.F. Tadros, J.C. Dederen, M.J. Garcia, N. Azemar, and C. Solans Formation and Stability of Nano-Emulsions Prepared Using the Phase Inversion Method. Langmuir 18, 26 (2002). 

Emulsion polymerization was successfully employed for the preparation of nano-scale MIPs by synthesizing core-shell latexes with an imprinted shell. The use of a template with surfactant properties led to enhanced surface imprinting. Magnetic cores were synthesized to render MIPs which could be manipulated by magnetic fields in suspension, thereby facilitating the separation of the colloidal solid phase from the suspending solution. 

Thus, droplets prepared close to the PIT will be smaller than those prepared at lower temperatures. These droplets are relatively unstable towards coalescence near the PIT, although by rapid cooling of the emulsion the smaller size can be retained. This procedure may be applied to prepare mini (nano) emulsions. 

For the preparation of nano- and microgels, reactive monomers and macro-monomers are loaded into nano- and microreactors, which are usually emulsion droplets [23] or cavities generated by soft lithography [24]. After cross-linking the macromonomers inside of these nano- and microtemplates... 

Formation and stability of nano-emulsions prepared using the phase inversion temperature method, Langmuir 18, 26-30 (2002). 

Nano-emulsions are defined as a class of emulsions with uniform and extremely small droplet size (typically in the range 20-500 nm). The formation of kinetically stable liquid/hquid dispersions of such small sizes is of great interest from fundamental and applied viewpoints. In this review, nanoemulsion formation, with special emphasis on low-energy emulsification methods, is first discussed. This is followed by a description of nano-emulsion properties, focusing on their kinetic stability. Finally, relevant industrial applications of nano-emulsions in the preparation of latex particles, in personal-care formulations, and as drug dehvery systems are reported. 

Caldero, G., Garcfa-Celma, M.J. and Solans, C. (2011) Formation of polymeric nano-emulsions by a low-energy method and their use for nanoparticle preparation. Journal of Colloid and Interface Science, 353, 406-411. 

Spemarth, L. and Magdassi, S. (2007) Preparation of ethylcellulose nanoparticles from nano-emulsion obtained hy inversion at constant temperature. Micro el Nano Letters, 2, 90-95. 

Many commercially important polymers are produced via emulsion polymerization. This is also one of the most common methods to produce dye-doped beads. A dye is added to the mixture of monomers prior to initiating the polymerization and is either noncovalently entrapped or is copolymerized. The second method ensures that no leaching will occur from the particle but requires modification of the dye (typically by providing it with a double bond). This method is most common for preparation of pH-sensitive beads where a pH indicator is entrapped inside cross-linked polyacrylamide particles. The size of the beads can be tuned over a wide range so that preparation of both nano- and microbeads is possible. Despite thorough washing the surfactants are rather difficult to remove completely and their traces can influence the performance of some biological systems. 

N. Uson, MJ. Garcia, and C. Solans Formation of Water-in-Oil (W/O) Nano-Emulsions in a Water/Mixed Non-Ionic Surfactant/Oil Systems Prepared by a Low-Energy Emulsification Method. Colloid and Surfaces A Physicochem. Eng. Aspects 250, 415 (2004). 

---