Interfacial behavior and supramolecular aggregates in fluorinated surfactant-free oil-in-water (O/W) microemulsions

Luis Rafael Chen

Key information

Authors:

Supervisors:

Pedro Jorge Rodrigues Morgado (Pedro Jorge Rodrigues Morgado); Eduardo Jorge Morilla Filipe (Eduardo Jorge Morilla Filipe)

Published in

December 18, 2025

Abstract

Surfactant-free systems have recently gained significant attention in the scientific community, as they challenge the traditional assumption in colloid and interface science that surfactants are essential to stabilize microemulsions. The spontaneous formation of surfactant-free microemulsions (SFMEs) in certain systems composed of water, oil, and a hydrotrope capable of promoting the solubilization of the hydrophobic component opens new possibilities for greener and more sustainable formulations, leading to simpler, more biodegradable, and less toxic systems with applications in fields such as healthcare and cosmetics. This work aims to deepen the understanding of the 1H,1H-perfluoroheptan-1-ol/water/ethanol ternary system, with particular focus on defining the limits of the pre-Ouzo region. Solutions with increasing perfluoroheptanol concentrations were prepared for three solvents containing ethanol/water volumetric ratios of 2.831, 1.985, and 1.490. Liquid–vapour surface tension measurements were performed at 298.15 K, allowing the determination of the Critical Aggregate Concentration (CAC), which was found to increase with the ethanol fraction in the solvent. Complementarily, molecular dynamics simulations were carried out for each solvent composition, at concentrations below, near, and above the experimentally estimated CAC. The simulations revealed a clear transition from monomer-dominated systems to stable aggregates. Overall, the results demonstrate that increasing the ethanol content delays aggregation to higher perfluoroheptanol concentrations, confirming the role of ethanol as a hydrotropic stabilizer in fluorinated surfactant-free systems.