Abstract
Micro-fluid mechanics is an important area of research in modern fluid mechanics because of its many potential industrial and biological applications. However, the field is not fully understood yet. In previous work, when passing ultrapure water (UPW) in which air was dissolved (UPW*) through micro-orifices, we found that the flow velocity decreased and stopped over time, and membranes were frequently formed in the orifice when the flow stopped. The membrane came from the dissolved air in UPW*, and membrane formation was closely related to electric charges generated in orifices by the flow. In the present paper, we clarified the components of the membrane and suggested a mechanism for membrane formation. We examined the effect of contaminants on the membrane formation and confirmed our previous results. We identified the chemical components of the membrane and those present in the UPW* itself by using an electron probe microanalyzer and found that the proportion of each element differed between the membrane and UPW*. Raman and infrared (IR) spectroscopy showed that the membrane consisted of organic substances such as carotenoids, amides, esters, and sugars. We irradiated UPW* with ultraviolet light to cut organic chains that may be left in UPW* as contaminants. We found a similar membrane and organic compounds as in nonirradiated UPW*. Furthermore, although the UPW that was kept from contact with air after it was supplied from the UPW maker (UPW0) and bubbled with Ar gas (UPW0 bubbled with Ar) formed no membrane, the UPW0 bubbled with CO2 formed thin membranes, and Raman and IR analysis showed that this membrane contained carboxylic acid salts, carotenoids, or a mixture of both. We found that electric grounding of the orifice reduces the probability of membrane formation and that the jets issuing from an aperture bear negative charges, and we assumed that the micro-orifices possess positive charges generated by flows. Consequently, we suggest that organic compounds are synthesized from nonorganic matter in air or CO2 dissolved in water by the action of hydroxyl radicals generated by flows through micro-orifices.
Highlights
Micro-fluid mechanics is an important area of research in modern fluid mechanics because of its many potential applications in biology, medical science, engineering, and industry
In a previous study [13], we measured the velocity (V ) of ultrapure water (UPW, hereafter used as having the general meaning of ultrapure water) through a 20-μm orifice under a constant applied pressure (Pt) of between 50 and 1000 Pa for several types of UPW: UPW in which air was dissolved (UPW*), which was stored in a beaker after it was supplied by the UPW maker and exposed to air for more than 1 day; UPW* from which air was extracted by vacuum; UPW that was kept from contact with air after it was obtained from the UPW maker (UPW0); and UPW0 that was bubbled with Ar gas (UPW0 bubbled with Ar)
We examined the components by using an electron probe microanalyzer (EPMA; EPMA-1610, Shimadzu Corp., Japan) and the compounds by observing Raman and infrared (IR) spectra for membranes formed in UPW*, UPW* irradiated with ultraviolet (UV) light (UV-irradiated UPW*), and UPW0 with dissolved CO2
Summary
Micro-fluid mechanics is an important area of research in modern fluid mechanics because of its many potential applications in biology, medical science, engineering, and industry. Flows through micro-orifices or short microtubes have been explored solely in relation to the flow properties [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]. We found that V decreased for all types of water tested with elapsed time, and the flow stopped. We removed the orifice in which the flow stopped from the experimental apparatus, observed it by using phase contrast microscope (PCM; Wraymer Inc., USA) and scanning electron microscopy (SEM; EPMA-1610, Shimadzu Corp., Japan), and found that a membrane frequently existed in the orifice. Membrane formation was found to decrease in an orifice that was electrically grounded, which means that electric charges are closely related to membrane formation. The detailed results have been published elsewhere [13]
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