Nanoscale Res Lett (2010) 5:224–230 An increase in soybean lecithin concentration from 2.5 to 7.5% (w/w) resulted in a decrease in particle size (mean droplet size of F1-F3 were from 309 to 240 nm, mean droplet size of F4-F5 were from 238 to 182 nm, mean droplet size of F7-F9 were from 163 to 113 nm and the mean droplet size of F10-F12 were from 92 to 68 nm) at an increasing glycerol concentration except at glycerol concentration of 100% (w/w), which pronounced an increase in droplet size (from 58 to 75 nm) at a lecithin concentration of 7.5% (w/w). The viscosity of LNE was shown in Table 2, and the viscosity of LNE increased with the increase in glycerol concentration and lecithin content. When the glycerol concentration was less than 75%, the viscosity was below 200 mPa s. However, when the glyc- erol concentration was 100%, the viscosity signiﬁ- cantly increased, and the maximum viscosity reached 1,574.8 mPa s (F15). A possible explanation of the droplet size reduction after an increased soybean lecithin concen- tration and an increased glycerol content is that soybean lecithin freely moved and was able to absorb around the snake oil droplet, thereby resulting in an increased surface to volume ratio of the droplet. Moreover, soybean lecithin, localized to the surface of the emulsion particles, reduced interfacial free energy and provided a mechanical barrier to coalescence [23], while glycerol in the continuous aqueous phase reduced the water’s surface tension. At a glycerol concentration of 100%, an increased soybean lecithin concentration resulted in a sharp increase in the viscosity of the continuous aqueous phase, especially at a soybean 227 lecithin concentration of 7.5%. This high viscosity gener- ated difﬁculty in lecithin movement and a rapid covering of the oil droplet during the preparation procedure to prevent any coalescence. Interestingly, apart from the size and viscosity, the effect of glycerol on the emulsion appearance was also observed. When the formulation was composed of 0 and 25% (w/w) glycerol in the aqueous phase (F1-F6), the nanoemulsion appeared as a milky solution. When the formulation was composed of 50% glycerol in the aqueous phase (F7-F9), the nanoemulsion appeared as a semitransparent solution. Fur- thermore, when the glycerol concentration was increased to 75 and 100% in the aqueous phase (F10-F15), the nano- emulsion appeared as a transparent solution. Possibly, glycerol behaved as a continuous phase solvent, whereby it not only affected the appearance of the nanoemulsion but also increased the viscosity of the continuous phase so as to decrease the droplet collision frequency [24, 25]. Morphology of LNE FF-TEM has emerged as an artifact-free method for observing diverse systems such as surfactant aggregates, polymer and polymer–surfactant solutions, and micro- emulsions, as well as biological and biomedical systems. These methods provide the ability to observe microstruc- tures by rapid vitriﬁcation of the solution containing the aggregates [26–28]. The morphology of the LNE was observed with FF-TEM, but only micrographs of Fig. 1 TEM micrograph of different LNEs. The images represent the LNE F2 (a), the LNE F5 (b), the LNE F8 (c), the LNE F11 (d) and the LNE F14 (e) 123