Chiang Mai Journal of Science

Rheological behavior and physical stability data of caffeine loaded water-in-oil (w/o) nanoemulsions have not been investigated. Therefore, the rheological behavior and physical stability of caffeine loaded w/o nanoemulsions were investigated in the present study. W/O nanoemulsions of caffeine were prepared by oil phase titration method and investigated for their rheological behavior. Optimized nanoemulsion was subjected to physical stability studies at 4 and 25 °C for the period of 3 months. The viscosity of prepared nanoemulsions was determined at different rate of shear using Cone and Plate Viscometer. The graph was plotted between shear stress Vs rate of shear and viscosity Vs rate of shear. The rheogram of prepared nanoemulsions (C1-C12) was observed as linear. The viscosity of all formulations was not changed by increasing the rate of shear which indicated Newtonian flow of prepared nanoemulsions. The droplet size, polydispersity index (PDI), viscosity and refractive index (RI) were determined for the period of three months. The droplet size was recorded in the range of 21.62-22.64 nm and 22.43-23.22 nm at 4 and 25 °C, respectively. No significant changes were recorded in droplet size, PDI, viscosity and RI of optimized nanoemulsions for the period of 3 months at both temperatures (P > 0.05). Results of these studies indicated that all the prepared nanoemulsions followed Newtonian behavior of flow and nanoemulsions can be used to enhance the stability of caffeine.