Organization of Amphiphiles, Part IX: Effect of Molecular Structure of Cosurfactants and Oils on the Phase Behavior of Tween-80: Alkanol-Oil-Water Systems

Abstract

In Tween-80:alkanol-oil-water pseudoternary system the area of the subregions are found to depend upon the molecular volume and structural hierarchy of oil and cosurfactants used. The threshold weight fraction of 0.35 for cosurfactant in emulsifier, required to get maximum area of bicontinuous region is attributed to difference in solubility of the emulsifier in oil and water. The measurement of different physicochemical parameters conforms to the phase transition from w/o to o/w through bicontinuous region.

The phase behavior of Tween-80:alkanol-oil-water systems have been studied at 30°C by varying the composition of the emulsifier. The areas of both isotropic and anisotropic regions are found to depend on the type of alcohols and oil used. The results have been attributed to the constraints in packing at the interface due to difference in molar volume as well as structural hierarchy in three-dimensional space. The percolation transition is evident from conductivity studies. The determination of area of the sub-regions as a function of surfactant:cosurfactant ratio reveals the existence of a maximum value for bicontinuous region at 0.35 weight fraction of cosurfactant in the emulsifier. This threshold weight fraction has been attributed to the difference in limiting solubility of emulsifier in water and oil. The phase inversion leading to drastic structural changes has been suggested from physicochemical properties measurements.

Keywords:

• Bicontinuous region
• molar volume
• percolation transition
• phase inversion
• W/O and O/W microemulsion
• water solubilization
• Winsor IV region

The authors thank the University Grants Commission, New Delhi for financial support to HPM (Teacher Fellowship) and project fellowship to SP (UGC sanction order no. F. 12–17/2003(SR) dated 31.03.2003). Support of the UGC (DRS) and the FIST (DST) to the department are also gratefully acknowledged.

Notes

N.B: The values in parentheses represent the area in square centimeter.

N.B: The values in parentheses represent the area in square centimeter.

N.B: The values in parentheses represent the area in square centimeter.

N.B: The values in parentheses represent the area in square centimeter.

N.B: The values in parentheses represent the area in square centimeter.

N.B: The values in parentheses represent the area in square centimeter.