Bitziou Eleni, Rudd Nicola C, Edwards Martin A, Unwin Patrick R
Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK.
Anal Chem. 2006 Mar 1;78(5):1435-43. doi: 10.1021/ac051692i.
The use of fluorescence confocal laser scanning microscopy (CLSM) for flow visualization is described, with a focus on elucidating the pattern of flow in the microjet electrode (MJE). The MJE employs a nozzle, formed from a fine glass capillary, with an inner diameter of approximately 100 microm, to direct solution at an electrode surface, using high velocity but at moderate volume flow rates. For CLSM visualization, the jetted solution contains a fluorescent probe, fluorescein at high pH, which flows into a solution buffered at low pH, where the fluorescence is extinguished, thereby highlighting the flow field of the impinging microjet. The morphology of the microjet and the hydrodynamic boundary layer are shown to be highly sensitive to the volume flow rate, with a collimated jet and thin boundary layer formed at the faster flow rates (approximately 1 cm(3) min(-1)). In contrast, at lower flow rates and for relatively large substrates, an unusual recirculation zone is observed experimentally for the first time. This effect can be eliminated by employing small substrates. The experimental observations have been quantified through numerical solution of the Navier-Stokes equations of continuity and momentum balance. The new insights provided by CLSM imaging demonstrate that flow in the MJE, and impinging jets in general, are more complex than predicted by classical models but are well-defined and quantifiable.
描述了使用荧光共聚焦激光扫描显微镜（CLSM）进行流动可视化，重点是阐明微喷射电极（MJE）中的流动模式。MJE采用由内径约为100微米的细玻璃毛细管制成的喷嘴，以高速但中等体积流速将溶液引导至电极表面。为了进行CLSM可视化，喷射的溶液含有荧光探针，即高pH值下的荧光素，它流入低pH值缓冲的溶液中，在那里荧光熄灭，从而突出撞击微喷射的流场。结果表明，微喷射的形态和流体动力边界层对体积流速高度敏感，在较快流速（约1 cm³ min⁻¹）下形成准直喷射和薄边界层。相比之下，在较低流速和相对较大的基底情况下，首次通过实验观察到一个异常的再循环区域。通过使用小基底可以消除这种影响。通过对连续性和动量平衡的Navier-Stokes方程进行数值求解，对实验观察结果进行了量化。CLSM成像提供的新见解表明，MJE中的流动以及一般的撞击射流比经典模型预测的更为复杂，但却是明确且可量化的。
