Real-Time Observation of Hydrogen Peroxide Transport through the Oil Phase in a W/O/W Double Emulsion with Chemiluminescence Emission.

The evaluation of the transport rates of hydrophilic substances is important in agricultural and pharmaceutical chemistry and in the cosmetics and food-processing industries. Although there are some estimation methods focusing on the diffusion of the substances through the oil phase of the W/O/W core-shell double emulsions (oil microcapsules), all of them take several hours or days. This long-time measurement has a risk of rupture of the oil microcapsules, which causes significant errors. If it were possible to measure the transport rate of substances in the oil phase of the oil microcapsules in real time, the risk of rupture could be reduced. Here, we propose a new estimation method for the transport rates of hydrogen peroxide (HO) in the oil phase of an oil microcapsule for real-time estimation by means of chemiluminescence (CL) emission of the luminol reaction. We theoretically give the relationship among the CL emission intensity, diffusion coefficient, microcapsule size, and experimental time and successfully estimate the diffusion coefficient of HO in the oil phase of the oil microcapsule from the experimental data. Moreover, we discuss the dependence of the permeation of HO through the oil phase on the concentration of the oil-soluble surfactant; the difference in the permeation rate is likely to be attributed not to the diffusion coefficient but to the partition coefficient of HO in the oil microcapsule.