Water quality stewardship (e.g., for flowback analysis) and/or site mapping may be accomplished in real-time and at the point of sampling through the use of a microfluidic platform that is sensitive to composition.  A microfluidic device is an efficient tool for analysis in that it is portable, uses small volumes of material under well-characterized and controllable conditions, and also allows for both discrete and continuous measurement.  In this work, a microfluidic surface tensiometer was developed to measure concentration variations of aqueous samples as a function of the fluid's surface tension�a property that is influenced by composition.  Fabricated devices employ two channels�each with its own inlet and outlet�that are separated by a membrane with an array of pores (or gaps) of increasing width.  Air and aqueous solution streams are separately introduced into the device at known flow rates and pass through the parallel channels.  If the pressure of the air stream exceeds the resistive surface tension forces of the aqueous fluid within a gap, the air will penetrate into the aqueous channel at and beyond this gap, which is easily detected through visual means.  The behavior follows what is predicted by the Young-Laplace equation, with the air penetrating into the water stream at smaller gap widths when the pressure differential is higher and when the surface tension of the aqueous stream is reduced by a dissolved contaminant.  In the latter case, a compositional change may be detected if the critical gap of penetration moves from its desired (i.e., clean) position, thereby permitting a composition to be calibrated to a particular gap width.  Experiments with water-only and ethanol-water mixtures demonstrate the predicted trends and compositional dependence, with additional studies planned to further characterize and fine-tune the device design and operation.

Microfluidic surface tensiometer for compositional analysis

247th National Meeting (2014)

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