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Sensors 2015, 15(5), 11587-11600;

Mapping the Salinity Gradient in a Microfluidic Device with Schlieren Imaging

Department of Mechanical Engineering, National Taiwan University, 1 Roosevelt Road Section 4, Taipei 10617, Taiwan
These authors contributed equally to this work.
Author to whom correspondence should be addressed.
Academic Editor: Stefano Mariani
Received: 3 March 2015 / Revised: 12 May 2015 / Accepted: 18 May 2015 / Published: 20 May 2015
(This article belongs to the Special Issue Modeling, Testing and Reliability Issues in MEMS Engineering 2013)
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This work presents the use of the schlieren imaging to quantify the salinity gradients in a microfluidic device. By partially blocking the back focal plane of the objective lens, the schlieren microscope produces an image with patterns that correspond to spatial derivative of refractive index in the specimen. Since salinity variation leads to change in refractive index, the fluid mixing of an aqueous salt solution of a known concentration and water in a T-microchannel is used to establish the relation between salinity gradients and grayscale readouts. This relation is then employed to map the salinity gradients in the target microfluidic device from the grayscale readouts of the corresponding micro-schlieren image. For saline solution with salinity close to that of the seawater, the grayscale readouts vary linearly with the salinity gradient, and the regression line is independent of the flow condition and the salinity of the injected solution. It is shown that the schlieren technique is well suited to quantify the salinity gradients in microfluidic devices, for it provides a spatially resolved, non-invasive, full-field measurement. View Full-Text
Keywords: salinity gradient; microscale schlieren technique; microfluidic; quantitative analysis salinity gradient; microscale schlieren technique; microfluidic; quantitative analysis

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Sun, C.-L.; Chen, S.-T.; Hsiao, P.-J. Mapping the Salinity Gradient in a Microfluidic Device with Schlieren Imaging. Sensors 2015, 15, 11587-11600.

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