The instability of nanoemulsions were mainly due to Ostwald ripening. The droplet charge was influenced by the stability of nanoemulsions significantly. In this work, the properties of the shea butter oil-loaded nanoemulsions were investigated in detail with the addition of cationic surfactants (cetyl trimethyl ammonium chloride, 1631; octadecyl trimethyl ammonium chloride, 1831), anionic surfactants (alcohol ethoxysulfate, AES; dodecyl phosphate ester sodium salt, MAP), and zwitterionic surfactants (cocoamidopropyl betaine, CAB; dodecyl hydroxysulfobetaine, 20HD). By increasing the concentration of cationic surfactants, the positively charged nanoemulsions were prepared and the smallest droplets were being formed with 0.05% 1831. Upon the addition of anionic surfactants, a more negative value was obtained and the smallest droplets were being formed with 0.1% AES. The ionic surfactants by increasing the electrostatic interactions between droplets and incorporation into the oil phase improved the stability of the nanoemulsions via lowering the Ostwald ripening rate, and especially improved the high temperature stability. By increasing the concentration of zwitterionic surfactants, a less negative zeta potential was observed and the stability of the nanoemulsions did not improve. The results proved that the electrosteric repulsion had an appreciable impact on the stability of the nanoemulsions. GRAPHICAL ABSTRACT

Three types of multiple emulsions were prepared with lecithin. The morphology, stability, and rheological properties of the three types of W/O/W multiple emulsions were evaluated. The formulation factors, including salts and aliphatic alcohol, were further examined. The three types of multiple emulsions were formed by different emulsifiers. An excellent multiple emulsion occurred with 2 wt% lecithin concentration, stabilized by 0.05 wt% NaCl. All multiple emulsions showed shear-thinning behavior, i.e., the apparent viscosity decreased with the increase of the shear rate. With the high concentration of lecithin, the multiple emulsions exhibited the highest viscosity at low shear rate and had higher storage modulus (G′) and the loss modulus (G″). This study was conducted to reveal that different types of multiple emulsions can be formed with lecithin, and that the stability and rheological properties were different with different types of multiple emulsions.

Three series of solid lipid are formulated in nanostructured lipid carriers (NLC) system, which encapsulated with sun filter to evaluate the effect on the physicochemical properties of the nanocarriers. Production is performed by ultrasonication–homogenisation, analysis by particle size, zeta potential (ZP), transmission electron microscope, Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD). Moreover, the encapsulation efficiency, ultraviolet performance and in vitro release are also investigated. The particle sizes of NLCs are between 185 and 225 nm and the polydispersity index is lower than 0.4, ZP from −56.4 to −78.6 mV, and the particles are spherical and in homogenous shading. All prepared NCLs encapsulated the sun filter and the EE are higher than 73%. DSC analysis revealed α- to β-polymorphic modification existed in the system of fatty alcohol and fatty acid. However, α, β and β′-polymorphic modifications are exist in the system of cetyl palmitate (PC). Compared with conventional emulsion, all NLCs displayed perfect photo-protective property, especially for the alcohol system. The photo-stability studies showed that the all NLCs have the ability to improve the photo-stability of sunscreens. The in vitro release study suggested all three NLCs displayed sustained release profile and they were fit well with Higuchi equation.