No abstract

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.

When homogeneous solutions that feature two-phase separation properties, such as a non-ionic surfactant aqueous solution, are fed into an open-tubular capillary tube, the solvent molecules are radially distributed into the tube, generating inner and outer phases. This is called "tube radial distribution phenomenon" (TRDP). In this study, a novel microflow-extraction system was proposed using double capillary tubes having different inner diameters in the TRDP. The tubes were fused-silica capillary tubes with a 75 and 250 m inner diameter; the smaller tube was inserted into the larger one through a T-type joint. A homogeneous aqueous solution containing 12 wt% Triton X-100 as a non-ionic surfactant and 2.4 M potassium chloride was fed into the larger tube at a flow rate of 20 L min -1 , where the tube was maintained at a temperature of 34°C. The homogeneous aqueous solution changed to a heterogeneous solution with two phases in the tube; the surfactant-rich phase was generated in the middle of the tube as an inner phase, while the aqueous phase containing a little of the surfactant was formed near the tube wall as an outer phase. In the TRDP Rhodamine B dissolved in the homogeneous solution was distributed into the inner surfactant-rich phase.The distributed Rhodamine B (red color) was observed with a bright-field microscope-CCD camera system.In the present microflow-extraction system, taking advantage of the TRDP, the inner phase containing Rhodamine B flowed inside the smaller tube, while the outer phase flowed outside the tip of the smaller tube into the larger tube, which was made using double capillary tubes having different inner diameters.This observation showed that Rhodamine B dissolved in the homogeneous solution was separated or extracted into the inner surfactant-rich phase through the double capillary tubes based on the specific microfluidic behavior of the TRDP.

An open-tubular capillary chromatography system has been developed using a ternary mixed solvent mixture, i.e., water–hydrophilic/hydrophobic organic solvent mixture as a carrier solution. In this study, the influence of adding surfactants to an analyte solution on separation performance was examined in a chromatographic system using a fused-silica capillary tube (75 µm inner diameter and 100 cm effective length) and a ternary mixture of water–acetonitrile–ethyl acetate (3:8:4 volume ratio) carrier solution. Sodium dodecyl sulfate (anionic), ethylhexadecyldimethylammonium bromide (cationic), and Triton X-100 (nonionic) were used as surfactants. Model analytes, 1-naphthol and 2,6-naphthalenedisulfonic acid, were separated in this order by adding the anionic and nonionic surfactants. These surfactants in the analyte solution greatly improved the separation performance (theoretical plate numbers for 2,6-naphthalenedisulfonic acid; &gt;10000) compared with the same separation performed in the absence of surfactants. On the other hand, the analytes were not separated at all using a cationic surfactant.

A new type of tube radial distribution phenomenon was observed in an aqueous micellar solution of non ionic surfactant that was fed into a microspace. A homogeneous aqueous solution containing 2 wt % Triton X 100 and 2.0 M sodium chloride was fed into a microchannel (40 µm in depth and 200 µm in width) in a microchip at a flow rate of 4.0 µL/min, where the microchip was maintained at a temperature of 34°C. The homogeneous aqueous solution changed to a heterogeneous solution with two phases in the microchan nel; the surfactant rich phase was generated around the middle of the channel, while the aqueous phase con taining little surfactant was formed near the wall. The radial distribution of the surfactant was observed through Rhodamine B dissolved in the aqueous micellar solution with a bright field microscope -CCD camera system. An open tubular capillary chromatographic system was also tried to develop using the fused silica capillary tube (75 µm inner diameter and 120 cm length) as a separation column and the aqueous micel lar solution as a carrier.