Organization of Amphiphiles, Part VII: Effect of Variation of Composition and Salt on the Phase Behavior of Some Ethoxylated Surfactants

Abstract

The effect of variation in composition of the emulsifier and presence of salt on the phase and clouding behavior of a pseudo‐ternary system of the type H₂O‐oil‐emulsifier has been investigated at 300±1 K. The emulsifier constitutes polyoxyethylated alkyl phenol/polyoxyethylated alkyl ethers and isobutanol in different mole ratios. Large numbers of domains are observed when composition of surfactant and cosurfactant in emulsifier is varied. Appearance of these domains in the phase diagram has been attributed to the formation of different type of organized assemblies. The electrical conductivity of BL‐9‐isobutanol(1∶1)‐hexane‐2% brine versus various compositions of the emulsifier is found to increase slowly with the addition of water, followed by rapid increase to a plateau leading to a sigmoidal plot. This significant change in electrical conductivity for small change in weight fraction of water is attributed to the percolation transition. The three arms of the electrical conductivity plot are suggested due to W/O to O/W microemulsion transition through bicontinuous structure, and the bicontinuous phase area is delineated. The ordering of water molecule around surfactant molecules has been arrived at through electrical conductivity and cloud point measurements.

Keywords:

• Polyoxyethylated nonionic surfactants
• phase behavior of pseudoternary systems
• electrical conductivity
• cloud point
• gel

Acknowledgments

The authors thank UGC and DST for funding through DRS and FIST to the department. The authors also thank UGC for the award of a project fellowship to one of the authors (SP).