PIT tuning effects of hydrophobic co-surfactants and drugs

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The formation of O/W nanoemulsions by the phase inversion temperature (PIT) method has been studied in water/Miglyol 812 systems. The effects of a hydrophobic co-surfactant (Igepal) and a hydrophobic drug (α-tocopherol) on tuning and optimising the PIT, which is essential for industrial processes, were studied. The hydrophilic poly-oxyethylated surfactant used was Kolliphor HS15. For these systems temperature induced phase inversion was not feasible in the presence of the hydrophilic surfactant alone. The addition of the hydrophobic co-surfactant was necessary to induce phase inversion and formation of stable O/W emulsions. Increasing the concentration of either the hydrophobic surfactant or of the hydrophobic drug, led to the formation of smaller drops, to the decrease of the PIT and the decrease of the transitional phase inversion zone. The effects of the hydrophobic/hydrophilic surfactant ratio, and of the hydrophobic drug concentration on tuning and optimising the PIT and the drop diameter were studied. Nanoemulsions with mean drop diameter ranging from 80nm to 196nm were produced for Kolliphor/Igepal systems and from 50nm to 100nm for Kolliphor/α-tocopherol systems. The polydispersity index was smaller than 0.2. α-Tocopherol acted as a co-surfactant. It could replace the hydrophobic co-surfactant, Igepal, and led to the decrease of the PIT by 10–15°C. Temperature cycling did not have any significant effect on the PIT, nor on the drop sizes. However, it had a significant effect on the phase inversion process by changing the phase inversion path.