Surfactants are a unique category of amphiphilic molecules present all around us, in industrial and commercial products, as well as in the biological world. Surfactant molecules reside at the interface to reduce the free energy of the system; which consequentially reduces the surface tension (SFT) or interfacial tension (IFT). Despite surfactant formulations being ubiquitous in many areas, there still lacks a fundamental understanding of how these surfactant molecules and their interactions affect the macroscopic solution properties.

A critical review on the use of microfluidics for interfacial tensiometry is conducted; the literature spanning approximately two decades is collated and categorised into eleven unique categories. The measurement principal for each category is described, and a comprehensive comparison of the categories given. The bulk behaviour of surfactant solutions is explored using SANS and rheology measurements; surfactant self-assembly is greatly influenced by environmental factors, such as surfactant concentration, the addition of any salt, and the temperature. The complete micellar phase map of sodium dodecyl sulphate (SDS) and sodium chloride (NaCl) is investigated at 25°C, and the low concentration SDS, high concentration NaCl region is further explored at higher temperatures up to 85°C to investigate the transition from elongated micelles to worm-like micelles. The mesoscopic micellar properties are then related to the macroscopic viscosity.

The molecular properties and interactions of surfactants and surfactant mixtures are then explored using the macroscopic surface property of SFT. The surface and micellar interaction parameters are determined for surfactant mixtures of SDS and dodecyl dimethyl amine oxide (DDAO) with differing ratios to find the mixture with the most synergy. Machine learning techniques are implemented in conjunction with the Szyszkowski isotherm and critical micelle concentration to predict the complete SFT isotherm for hydrocarbon surfactants; the most influential descriptors for the SFT isotherm prediction are discussed in greater detail.