Controlling the emulsion stability of cosmetics through shear mixing process
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Controlling the emulsion stability of cosmetics through shear mixing process Kwang-Mo Kim1, Hee Muk Oh1 and Jun Hyup Lee2,* Cosmax R&I Center, Cosmax, Seongnam 13486, Republic of Korea 2 Department of Chemical Engineering, Soongsil University, Seoul 06978, Republic of Korea (Received May 2, 2020; accepted July 17, 2020) 1
The manipulation of emulsion stability for kinetically sustainable cosmetic emulsions is an important technology in cosmetic industry, however the relationship between emulsifying process and long-term emulsion stability has not been elucidated. Herein, the effect of shear mixing process on the stability of oil-in-water cosmetic emulsions is investigated by varying the shear mixing rate, emulsification time, and water phase temperature. The analysis on droplet size distribution and shear viscosity revealed that the strong viscous forces at optimal shear mixing rate of 4000 rpm afforded the fine and uniform droplets for cosmetic emulsions, leading to the improvement of long-term emulsion stability. Moreover, since the prolonged shear mixing induced the destabilization of emulsion droplets through droplet coalescence, optimal shear mixing time of 3 min could improve the kinetic stability of cosmetic emulsions. The dependence of long-term emulsion stability on emulsification temperature was relatively low. The theoretical analysis using the Derjaguin-Landau-Verwey-Overbeek theory demonstrated that the shear mixing rate played a major role in sustaining fine and uniform cosmetic emulsions with long-term stability. The present study can greatly contribute to the fabrication of functional cosmetic emulsions with long-term stability by controlling the shear mixing parameters in simple emulsification process. Keywords: cosmetics, emulsions, long-term stability, shear mixing process, viscosity
1. Introduction Emulsions with dynamic inhomogeneous structures have received much attention due to a wide range of potential applications in cosmetics, foods, paints, pharmaceuticals, ink coatings, and adhesives (Goodarzi and Zendehboudi, 2019). The emulsion system is normally composed of two or more immiscible liquid phases, where one of the liquids is dispersed into small spherical droplets in another continuous fluid. The key to forming a homogeneous emulsion is to distribute the uniform and stable droplets in the continuous phase. However, since liquid phases have different surface tensions, common emulsions are inherently thermodynamically unstable and are easily separated through flocculation, creaming, coagulation, coalescence, phase inversion, and Oswald ripening when simply mixed without any surface active agents (Tcholakova et al., 2006; Dukhin et al., 2001; Kong et al., 2003; Kumar et al., 1996; Shields et al., 2001; Nii et al., 2009; Dyab, 2012; Tadros, 1994). To overcome this problem, the most common approach is to reduce the difference in surface tension between different phases and thus stabilize emulsions by enhancing their kinetic stability using emulsifiers involving surfa
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