Investigation of inner and outer phase formation in tube radial distribution phenomenon using various types of mixed solvent solutions.

When mixed solvent solutions, such as ternary water-hydrophilic/hydrophobic organic solvents, water-surfactant, water-ionic liquid, and fluorous-organic solvents are delivered into a microspace under laminar flow conditions, the solvent molecules are radially distributed in the microspace, generating inner and outer phases. This specific fluidic behavior is termed "tube radial distribution phenomenon" (TRDP). In this study, the factors influencing the formation of inner and outer phases in the TRDP using the above-mentioned mixed solvent solutions were investigated. We examined phase diagrams, viscosities of the two phases (upper and lower phases in a batch vessel), volume ratios of the phases, and bright-light or fluorescence photographs of the TRDP. When the difference in viscosities between the two phases was large (> approximately 0.73 mPa·s), the phase with the larger viscosity formed an inner phase regardless of the volume ratios, whereas when the difference was small (< approximately 0.42 mPa·s), the phase with the larger volume formed an inner phase. The TRDP using a water-surfactant mixed solution was also investigated in capillary chromatography based on TRDP.