Response surface modeling of self-assembled fatty amphiphiles for improved stability of o/w emulsions

This work aimed to study and elaborate the relationships existing between the most common composition factors of an oil-in-water emulsion. Mixed fatty alcohols with different chain lengths and surfactants pair with different HLBs in addition to paraffin oil were employed to study their influence in an oil/fatty amphiphiles/water system. Box–Behnken design planned the experiments and the hot, high shear homogenization techniques were used in the formulation step. For characterization, emulsions with droplets’ average diameters ranging from (2.1 to 7.6 µm) were successfully formulated, and extended from liquid-like lotions to stiff semisolid creams possessing a non-Newtonian shear thinning behavior. These systems showed adequate stability until the application of an external stress resulting in a creaming phenomenon. Therefore, highly significant (P-value <0.0001) quadratic models were built within the RSM that are valid for fixed experimental conditions and relate the independent variables with their rheological, structural and stability responses. The desirability approach was utilized, thereby a new model was developed expressing the desired Smix/FA ratio in the absence and throughout the oil content range; this model approximated a 0.41 ratio for a ternary system that validate the effectiveness of using surfactants pair against an individual surfactant, while 0.77 was the ratio for a higher internal phase that can be reached after an exponential transition portion between the two limits. Overall, the findings in this study could be very useful for topical cosmetic and pharmaceutical formulations and lengthen the knowledge on the fatty amphiphiles association and their contribution to the stability of emulsions.