Characterizing Homogeneous Chemistry Using Well-Mixed Microeddies

Abstract

Well-mixed reaction volumes are often sought in engineered microchemical devices and can be an important feature of naturally occurring physicochemical processes such as pitting corrosion. Steady streaming eddies can serve as well-mixed, easily controlled microliter chemical reactors for characterizing homogeneous chemical reactions. Here, steady streaming eddies are produced by oscillating a liquid-filled cuvette around a stationary cylindrical electrode (radius 406 microm, length 1.6 cm) at audible frequencies (75 Hz). Oxidant (ferricyanide) electrochemically dosed at small rates (<or=30 nmol/s) from the cylindrical electrode accumulates to millimolar concentrations within the closed streamlines of each eddy, where it mixes and reacts with an antioxidant (vitamin C) present in the bulk solution. The composition in the eddy is controlled by varying the oxidant dosing rate and the bulk antioxidant concentration (<or=10 mM), as well as the cuvette oscillation amplitude. A simple algebraic mole balance is combined with Raman spectroscopy measurements of oxidant concentration in the eddy and bulk to determine the reaction rate law and homogeneous rate constant (45 +/- 9 M(-1) s(-1)) for the antioxidant properties of vitamin C against ferricyanide. Numerical solutions to the full Navier-Stokes equations and species continuity equations illustrate the distribution of species during the reaction and general limitations to the assumption of a well-mixed eddy.

Dumbbell Fluidic Tweezers for Dynamical Trapping and Selective Transport of Microobjects

“…Since the plane of rotation now coincides with the observing plane of the microscope, fluid streamlines nearby the rotating DB as well as the trajectory of the trapped microbead can be examined. As the right panel of Figure shows, a microvortex is formed above the rotating DB, whose streamlines resemble that of a “streaming cell” reported in experiments of steady streaming . Under low or moderate rotation frequencies, the trapped microbead follows the fluid trajectory and orbits the microvortex center with self‐spinning motion.…”

“…They have their own limitations though, the major one being providing only static trapping on fixed positions (one exception was recently made by Ndukaife et al, who achieved a long‐range vortex using hybrid electrothermoplasmonic nanotweezer to transport objects to specific plasmonic nanoantennas). To our interest, another noncontact approach, hydrodynamic tweezers (HT), achieves particle trapping through frequency‐dependent steady streaming induced by fluid oscillation near microfabricated geometries such as cylindrical obstructions, and wall protrusions or cavities . In comparison with the conventional OT, MT, and DEP techniques, HT and some other similar techniques provide a noninvasive means to manipulate cells or microorganisms in low Reynolds number flow utilizing gentle but robust microeddies .…”

Steady streaming viscometry of Newtonian liquids in microfluidic devices

“…The magnitude of the characteristic streaming velocity scales as U s ∼ sω, where = s/a is the dimensionless amplitude and ω = 2πf is the angular frequency. At small scales, these rectified flows have been shown to be useful in non-contact manipulation [4], trapping [5][6][7][8], and sorting [9,10] of particles and cells as well as in enhancing pumping [11] and mixing [12][13][14] at low Reynolds numbers. There are opportunities to use steady streaming for the rheology of liquids as well [15].…”

Measuring gene expression in single bacterial cells: recent advances in methods and micro-devices

“…It relies on flow stagnation or microeddies (Lutz et al, 2006a;Tanyeri & Schroeder, 2013). Cells are trapped at steady streaming eddies generated by hydrodynamic forces (Lutz et al, 2006b). Compared to eukaryotic cells, applying hydrodynamic traps to small bacterial cells poses significant challenges since hydrodynamic forces are typically proportional to the surface areas of cells.…”