Nanoemulsions: A review on low energy formulation methods, characterization, applications and optimization technique

Nanoemulsions are emulsions with droplet size in the order of 100 nm and are kinetically stabilized dispersions formulated by combination and stabilization of two immiscible phases using a surfactant. They exhibit useful properties due to small droplet size leading to high surface area per unit volume, higher stability, optically transparent appearance, flexible fluidity and increased bioavailability of lipophilic components. Recently, interdisciplinary applications of nanoemulsions in consumer products, i.e. pharmaceuticals, pesticides, cosmetics, food, paint and environmental applications have attracted interest in its research. Various authors have focussed on preparing nanoemulsions through different methods, including high-energy and low-energy. High energy methods mainly includes microfluidization, high pressure homogenization and ultrasonication whereas, low energy methods comprise of phase transition temperature, phase inversion composition, spontaneous emulsification, micro emulsion dilution and recently developed approach such as D phase emulsification (DPE). In this review article, we address the growing usefulness of low energy method due to ease in its scale-up, less consumption of energy and increased stability in formulation of nanoemulsions. It also includes review on characterization techniques, applications of nanoemulsions and optimization studies for industrial scale up.