On the Relationships between the Hydrophilic–Lipophilic Balance and the Nanoarchitecture of Nonionic Surfactant Systems

Abstract

AbstractBuilding links between established parameters for the characterization of surfactant systems is useful not only for the understanding of the underlying phenomena but also for the judicious formulation of products. Herein, we review comprehensively the literature data to find correlations between the hydrophilic–lipophilic balance (HLB) and the molecular packing parameter (CPP) for a variety of nonionic surfactants in water. The interfacial area per surfactant molecule, a fundamental variable to calculate CPP, follows a power law as a function of the number of ethylene oxide (EO) groups in the surfactant. The exponent ranges from 0.3 to 0.7, which may reflect changes in the conformation of the EO chain depending on the nature of the hydrophobic group; there is also apparently a transition toward a collapsed conformation of the EO chains at high surfactant concentrations. CPP is found to change linearly with HLB in the range of data studied, although the parameters of the linear fitting depend on the nature of both hydrophobic and hydrophilic moieties of the surfactant; this would also imply a linear relationship between CPP and the HLB temperature (i.e., Phase Inversion Temperature) according to the Kunieda–Shinoda equation. Analysis of the liquid crystal regions of the surfactant phase diagram at constant temperature indicates that the HLB values required for the morphological phase transitions defined by CPP increase with surfactant concentration. The present report may serve as a contribution to the programmed design of nanoarchitectures in surfactant systems.