Characterization of Microemulsions Formed in a Water/ABA Block Copolymer [Poly(hydroxystearic acid)−Poly(ethylene oxide)−Poly(hydroxystearic acid)]/1,2-Hexanediol/Isopropyl Myristate System

• Published in: Langmuir 2002-07, Vol.18 (15), p.5673-5680
• Main Authors: Plaza, M, Tadros, Th. F, Solans, C, Pons, R
• Format: Article
• Language: English
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la011597e

Microemulsions formed with water, isopropyl myristate, PHS−PEO−PHS polymeric surfactant, and alkanediol have been investigated using small-angle X-ray scattering (SAXS) and conductivity at 25 °C. Isopropyl myristate has a low solubility in water; however, this molecule has some polar character because of its ester group. The conductivities of samples with some added NaCl (used here to increase the conductivity sensitivity) are low, but compared to the conductivity of water/alkanediol mixtures, the values are high for most of the samples. The X-ray scattering curves show a correlation peak if the water content is high enough. A two-phase model for the invariant calculation fits the experimental results reasonably well provided that the partition of the oil between the polar and nonpolar phases is taken into account. This partition can be obtained from the ternary water/isopropyl myristate/alkanediol system, which has some mutual-solubility regions. A hard-sphere model can be fitted to the SAXS scattering data. The volume fractions fitted from this model deviate from the volume fractions of the low-polarity phase, indicating that the structure of most of the samples is of the bicontinuous type.