Professor University of Toronto Toronto, Ontario, Canada
Abstract: When I started my graduate studies under their guidance, Professors Harwell and Sabatini asked me: could we formulate a microemulsion for chlorinated solvents (dense non-aqueous phase liquids or DNAPLs) that could have high solubilization capacity and maintain an interfacial tension (IFT) greater than 0.1 mN/m (to avoid DNAPL sinking in contaminated aquifers)? This question sparked the greater question, how can we connect formulation conditions (restrictions) with surfactant and additive selection and with formulation properties?... and with formulation performance? The answer to these questions led to the hydrophilic-lipophilic difference (HLD) + net-average curvature (NAC) model or HLD-NAC, which was later combined with more traditional chemical engineering models to predict formulation performance. This presentation summarizes the journey's highlights, mentioning the role of brilliant traveling companions. The objective of this presentation is not to review the details of the HLD-NAC but rather to provide a picture of the start and evolution of the HLD-NAC model as an equation of state for surfactant-oil-water (SOW) systems, pointing to key people and references to consult to get better acquainted with the details of the model and its more recent forms and applications. The original question of the Professors is also revisited with the latest form of the HLD-NAC, illustrating where the journey has taken us thus far and what seems to be peeking on the horizon for the HLD-NAC community.
