Impact of Viscosity and Refractive Index on Droplet Size and Zeta Potential of Model O/W and W/O Nanoemulsion

Abstract

This study was aimed to evaluate the impact of viscosity and refractive index on the magnitude of droplet size and zeta potential of model indomethacin loaded oil-in-water (o/w) nanoemulsion and 5-fluorouracil (5-FU) loaded water-in-oil (w/o) nanoemulsion. Droplet size and zeta potential of model nanoemulsions were determined using Brookhaven 90 plus/zeta plus particle size/zeta potential analyzer. Objective was achieved by adopting two control approaches. For studying the effects of viscosity, the refractive index was kept constant while changing the viscosity and in case of refractive index, magnitude of viscosity was held constant and changing the refractive index. The droplet size of model o/w or w/o nanoemulsions was found to vary nonlinearly by increasing or decreasing the viscosity. The droplet size and polydispersity index were also found to be changed significantly when refractive index of medium was changed from 1.29 to 1.43. The zeta potential of model nanoemulsions was not found to be measurable by increasing or decreasing the refractive index. These results indicate that care must be taken while performing such type of measurements especially in case of emulsion-based formulation, because small changes in setting parameters can significantly change the results of analysis.