2 research outputs found

    A pH-Sensitive Laser-Induced Fluorescence Technique To Monitor Mass Transfer in Multiphase Flows in Microfluidic Devices

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    We present a pH-sensitive laser-induced fluorescence (LIF) technique to investigate mass transfer in reactive flows. As a fluorescent dye, we used 5-(and-6)-carboxy SNARF-1, which, when excited with a pulsed Nd:YAG laser at 532 nm, provides good sensitivity in the range 4 ≤ pH ≤ 12. For validation, we first applied the dye to single-phase reactive flows by investigating the neutralization of sodium hydroxide with hydrochloric acid. Comparison to the classical passive mixing case showed that this dye was able to capture the reaction progress and to quantify the mass transport. Next, we investigated the absorption of CO<sub>2</sub> in an alkaline solution using gas–liquid flow and found that the LIF technique is able to quantify the local mass-transfer rate in microfluidic systems. Results for different microchannel geometries highlight the strong connection between local mass transfer and secondary flow structures in gas–liquid Taylor flow

    Size-Controlled Flow Synthesis of Gold Nanoparticles Using a Segmented Flow Microfluidic Platform

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    Segmented flow is often used in the synthesis of nanomaterials to achieve narrow particle size distribution. The narrowness of the distribution is commonly attributed to the reduced dispersion associated with segmented flows. On the basis of the analysis of flow fields and the resulting particle size distribution, we demonstrate that it is the slip velocity between the two fluids and internal mixing in the continuous-phase slugs that govern the nature of the particle size distribution. The reduction in the axial dispersion has less impact on particle growth and hence on the particle size distribution. Synthesis of gold nanoparticles from HAuCl<sub>4</sub> with rapid reduction by NaBH<sub>4</sub> serves as a model system. Rapid reduction yields gold nuclei, which grow by agglomeration, and it is controlled by the interaction of the nuclei with local flow. Thus, the difference in the physical properties of the two phases and the inlet flow rates ultimately control the particle growth. Hence, a careful choice of continuous and dispersed phases is necessary to control the nanoparticle size and size distribution