Effect of Toluene and Hexane Sorption on the Rheology and Interfacial Properties of Lecithin-Based Emulsion Gels

A novel sorbent material consisting of a gel made from canola oil and water, emulsified with lecithin, was used to remove two model solvents from water. Sorption capacity was quantified through small-scale batch experiments. The structure and the mechanical properties of the gel were compared with and without added solvent to assess their cohesiveness upon removing contaminants from water. Confocal microscopy showed that the initial gel consisted of water droplets clustered in a canola oil continuous phase. The G' of the gels increased with solvent absorption to a maximum at 33% (v/v) hexane or 24% (v/v) toluene. Larger absorbed volumes led to decreases in G' of the gel. G' for solvent mixtures of 50% toluene and 50% hexane was intermediate between G' measured for the same volumes of pure solvents. Confocal microscopy suggests that the decrease of G' upon addition of large solvent volumes was due to a simple dilution effect. It is hypothesized that the initial increase in storage modulus was caused by changes in the structure of the lecithin films formed at the oil-water interfaces. This hypothesis was evaluated through measurements of interfacial tension, visualization of the interface with optical microscopy, force measurements of a single droplet under compression using a cantilevered-capillary force apparatus, compressional isotherm measurements conducted using a Langmuir trough. The cantilevered-capillary force apparatus and Langmuir trough experiments demonstrated that lecithin films at the canola oil-water interface were rigidified by toluene and hexane addition.