Investigating the effect of dipropylene glycol and mixed-surfactant concentrations on perfume release

Abstract

HypothesisThe solubilization and release of perfume from aqueous micellar solutions are to a large extent dependent on the geometric, surface and electrostatic properties of the micelle. These properties are influenced by the molecular structure of the surfactant, the solvent properties, and additives (hydrotropes). Both surfactant and co-solvent are expected to affect solvent polarity, hence addition of a co-solvent of lower polarity than water should reduce the size of micelles, whereas addition of surfactant should increase the size of micelles. ExperimentThe effect of dipropylene glycol and surfactant concentration on micelle size and perfume release were systematically studied on (a) branched-chain sodium trideceth-2 sulfate (ST2S)/cocamidopropyl betaine (CAPB), and (b) linear-chain sodium laureth-1 sulfate (SLE1S)/CAPB mixed-surfactant systems. Combined small-angle neutron scattering (SANS) and GC-MS studies were conducted to elucidate the impact of co-solvent and surfactant on fractional charge/size of micelle and perfume release from formulations. Principal component analysis (PCA) was done to determine if the 12-PRM perfume accord could be simplified into smaller groups of PRMs. Statistical analysis was performed to determine if perfume release was significantly correlated to any aspects of the colloidal domain as a function of DPG or surfactant concentration. FindingsThe micelles shrank, aggregation numbers decreased, and fractional charges increased with increasing DPG concentration, whereas the opposite occurred with increasing surfactant concentrations. These trends were largely consistent for both mixed-micelle systems. GC-MS headspace concentration results further demonstrated that although the perfume headspace concentrations typically follow certain trends, performance is largely dependent on surfactant and DPG concentration. PCA showed that the 12-PRM accord could be treated as two components of perfume molecules, with florol strongly contributing to the second component. Statistical analysis showed that the first component significantly correlated to the micelle size and volume fraction as a function of DPG and surfactant concentration in both mixed-surfactant systems. This is the first time the release of a multi-component perfume accord was systematically studied as a function of DPG and surfactant concentration, and how DPG and surfactant variation affect the colloidal domain in the presence of a multi-component perfume accord.