The promoting effect of Tween 60 on the formation of Kolliphor RH40 bicontinuous microemulsions

The formation of bicontinuous microemulsions requires large amounts of surfactants, limiting their applications. This study aims to explore the regulatory effect of composite surfactants on the transition of microemulsion systems from the W/O phase to the bicontinuous phase. Through ternary phase diagram analysis, viscosity measurement, conductivity test, dynamic light scattering analysis, rheological analysis and surface tension test, it investigates the regulatory effects of composite surfactant systems formed by PEG-100 stearate, Tween 60, and Span 60 each with Kolliphor RH40 on the transition. Ternary phase diagrams show that Tween 60, compared with Kolliphor RH40 alone, raises the maximum dilution line from L82 to L64, reducing surfactant use and broadening the range; PEG-100 stearate shows no improvement, while Span 60 lowers the line. Viscosity, conductivity and dynamic light scattering results indicate that Tween 60 reduces the water content required for transition from 40% to 35%, aiding the formation of the bicontinuous region. Rheological tests show that Tween 60 reduces the loss modulus and improves interfacial film integrity; surface tension tests confirm the further lowering of surface tension to promote the transition. Antibacterial tests show that the MIC and MBC of the Kolliphor RH40/Tween 60 system are 5.3 μg/mL and 7.8 μg/mL, lower than those of Kolliphor RH40 alone. It exhibits excellent stability under infinite dilution and in extreme environments. In conclusion, Kolliphor RH40/Tween 60 effectively regulates bicontinuous microemulsion formation, improves performance, and provides practical application ideas.