Preparation nanoemulsions

The formation of ethylcellulose nanoemulsions by a low-energy method for nanoparticle preparation was reported recently. The nanoemulsions were obtained in a water-polyoxyethylene 4 sorbitan monolaurate-ethylcellulose solution system by the PIC method at 25 °C [54]. The solvent chosen for the preparation of the ethylcellulose solution was ethyl acetate, which is classed as a solvent with low toxic potential (Class 3) by ICH Guidelines [78]. Oil/water (O/W) nanoemulsions were formed at oil/ surfactant (O/S) ratios between 30 70 and 70 30 and water contents above 40 wt% (Figure 6.1). Compared with other nanoemulsions prepared by the same method, the O/S ratios at which they are formed are high, that is, the amount of surfactant needed for nanoemulsion preparation is rather low [14]. For further studies, compositions with volatile organic compound (VOC) contents below 7 wt% and surfactant concentrations between 3 and 5 wt% were chosen, that is, nanoemulsions with a constant water content of 90% and O/S ratios from 50 50 to 70 30. 

Phase inversion along the dilution path (by addition of water to the oil/surfactant mixture) followed for nanoemulsion preparation was confirmed by conductivity measurements, and was found to be essential for obtaining finely dispersed systems, as transparent dispersions were not obtained if the order of addition of the components was changed following an experimental path with no phase inversion (Figure 6.2). 

Yang, H.J., Cho, W.G. and Park, S.N. (2009) Stability of oil-in-water nanoemulsions prepared using the phase inversion composition method. Journal of Industrial and Engineering Chemistry,... 

Yuan, Y., Gao, Y., Zhao, J., Mao, L. (2008). Characterization and stability evaluation of p-carotene nanoemulsions prepared by high pressure homogenization under various emulsifying conditions. Food Research International, 41, 61-68. 

Figure 14.11 r versus time at 25 °C for nanoemulsions prepared using the system water-C,2E04-hexadecane. 

The stability of nanoemulsions prepared using isohexadecane was assessed by following the droplet size as a function of time. Plots of versus time for four... 

As expected, the nanoemulsions prepared using high-pressure homogenisation showed a lower Ostwald ripening rate when compared to systems prepared using the PIT method. This is illustrated in Figure 14.18, which shows plots of versus... 

Unfortunately, the droplet size distribution of a nanoemulsion prepared by the PIT process is relatively large. Due to the high Laplace pressure, Ostwald ripening takes place rapidly, limiting the lifetime of the nanoemulsions to a few minutes to a few days. The addition of a water-insoluble component can significantly reduce the breakdown kinetics however, long-term stability is rarely achieved with this process. 

For styrene nanoemulsions prepared with 10 2 M sodium lauryl sulfate and a 1 1 molar ratio of ionic surfactant fatty alcohol, the order of decreasing stability with fatty alcohols of different chain length is Ci6 > Qg > CM > Ci2 > C10. For sodium lauryl sulfate-Ci6 alcohol mixtures, the order of decreasing stability with different sodium lauryl sulfate fatty alcohol ratios is 1 3 > 1 2 > 1 1 > 1 6 > 1 0.5. The 1 3 and 1 2 ratios produce emulsions with stabilities > 1 month. The presence of rodlike liquid-crystalline structures at 1 1 to 1 3 ionic surfactant fatty alcohol ratios is believed to be essential for the preparation of a stable nanoemulsion. (El-Aaser, 1984). 

Wang, L., Mutch, K.J., Eastoe, J., Heenan, R.K., and Dong, J. 2008. Nanoemulsions prepared by a two-step low-energy process. Langmuir 24 6092-6099. 

Methods of nanoemulsion preparation have been described in detail. A schematic illustration of the overall process is depicted in Figure 12.2. Three different approaches can be used to incorporate the drug and/or the various components in the aqueous or oil phase. The most common approach is to dissolve the water-soluble ingredients in the aqueous phase and the oil-soluble ingredients in the oil phase. The second approach, which is used in fat emulsion preparations involves the dissolution of an aqueous-insoluble emulsifier in alcohol and then the dispersion of the alcohol solution in water followed by evaporation and total removal of the alcohol until a fine dispersion of the emulsifier in the aqueous phase is reached. The third approach, which is mainly used for hydrophobic drug... 

K. Nakabayashi,F. Amemiya, T. Fuchigami, K. Machida, S. Takeda, K. Tamamitsu, M. Atobe, Highly clear and transparent nanoemulsion preparation under surfactant-free conditions using tandem acoustic emulsification. Chem. Commun. 47, 5765-5767 (2011)... 

Further evidence for Ostwald ripening was obtained by using a more soluble oil, namely a branched hexadecane (Arlamol HD). The results are shown in Fig. 1.31 for nanoemulsions prepared using 4% surfactant. It can be seen that the more soluble oil (Arlamol HD) give a higher rate of Ostwald ripening when compared with a less soluble oil such as hexadecane. 

Rey, C.M., Maestro, A., Sole, L, Gonzalez, C., Solans, C., and Gutierrez, J.M., Optimization of nanoemulsions prepared by low-energy emnlsification methods at constant temperature using a factorial design study, Colloids Surf. A Physicocherrt Eng. Aspects, 2006, 288, 144-150. 

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