Practical Examples of Nano-Emulsions

The HLB temperature was determined using conductivity measurements, whereby 10 mol dm NaCl was added to the aqueous phase (to increase the 

The HLB temperature decreases with increasing surfactant concentration - this could be due to the excess nonionic surfactant remaining in the continuous phase. 

Nano-emulsions were prepared by rapidly cooling the system to 25 °C. The droplet diameter was determined using photon correlation spectroscopy (PCS). The results are summarised in Table 9.1, which shows the exact composition of the emulsions, HLB temperature, z-average radius and polydispersity index. 

O/W nano-emulsions with droplet radii in the range 26-66 nm could be obtained at surfactant concentrations between 4 and 8%. The nano-emulsion droplet size and polydispersity index decreases with increasing surfactant concentration. 

The decrease in droplet size with increase in surfactant concentration is due to the increasing surfactant interfacial area and decrease in interfacial tension, y. As mentioned above, y reaches a minimum at the HLB temperature. Therefore, the minimum in interfacial tension occurs at lower temperature as the surfactant concentration increases. This temperature becomes closer to the cooling temperature as the surfactant concentration increases, resulting in smaller droplet sizes. 

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