J. Cosmet. Sci., 63, 333–344 (September/October 2012) 333 Preparation of emulsions by rotor–stator homogenizer and ultrasonic cavitation for the cosmeceutical industry NG SOOK HAN, MAHIRAN BASRI, MOHD. BASYARUDDIN ABD. RAHMAN, RAJA NOOR ZALIHA RAJA ABD. RAHMAN, ABU BAKAR SALLEH, and ZAHARIAH ISMAIL, Faculty of Science (N.S.H., M.B., M.B.A.R.), Institute of Bioscience (M.B., R.N.Z.R.A.R., A.B.S.), Faculty of Biotechnology and Biomolecular Sciences (R.N.Z.R.A.R., A.B.S.), Universiti Putra Malaysia, 43400 UPM Serdang, and Sime Darby Research Sdn Bhd, Carey Island, 42960 Pulau Carey (Z.I.), Selangor, Malaysia. Accepted for publication March 14, 2012. Synopsis Oil-in-water (O/W) nanoemulsions play an important key role in transporting bioactive compounds into a range of cosmeceutical products to the skin. Small droplet sizes have an inherent stability against creaming, sedimentation, fl occulation, and coalescence. O/W emulsions varying in manufacturing process were pre- pared. The preparation and characterization of O/W nanoemulsions with average diameters of as low as 62.99 nm from palm oil esters were carried out. This was achieved using rotor–stator homogenizer and ultrasonic cav itation. Ultrasonic cell was utilized for the emulsifi cation of palm oil esters and water in the presence of mixed surfactants, Tween 80 and Span 80 emulsions with a mean droplet size of 62.99 nm and zeta potential value at -37.8 mV. Results were comparable with emulsions prepared with rotor–stator homogenizer oper- ated at 6000 rpm for 5 min. The stability of the emulsions was evaluated through rheology measurement properties. This included non-Newtonian viscosity, elastic modulus G′, and loss modulus G″. A highly stable emulsion was prepared using ultrasonic cavitation comprising a very small particle size with higher zeta potential value and G′ G″ demonstrating gel-like behavior. INTRODUCTION An emulsion system consists of two immiscible liquids dispersed in one another and is thermodynamically unstable (1). An emulsion can be kinetically stable (long-term stability) with the presence of surfactant in the system by creating an energy barrier to fl occulation and coalescence (2) and existing in a metastable state (3). Most emul- sions fall into one of the two different classes: oil-in-water (O/W) and water-in-oil (W/O). The two types of emulsions are readily distinguished in principle, depending upon which kind of liquid forms the continuous phase (4). In O/W, tiny oil droplets Address all correspondence to Mahiran Basri at mahiran@science.upm.edu.my. Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia