Measurement of pH field of chemically reacting flow in microfluidic devices by laser-induced fluorescence

Abstract

The interaction between chemical reactions and the flow field in microfluidic devices is investigated by a laser-induced fluorescence technique refined for use at microscopic spatial resolution. The pH distribution of chemically reacting flow at a Y-junction in a neutralization reaction in a microfluidic device is successfully visualized at a spatial resolution of 0.89 µm × 0.89 µm.

Spatially dependent diffusion coefficient as a model for pH sensitive microgel particles in microchannels

“…The MG swelling (deswelling) or "lag" time, s s , is typically in the range 10 À3 -10 À1 s. 50,51 A swelling theory based on a stress balance on the solid network predicts s s s B , 50 which indicates that the reversible swelling-deswelling transition can take place on a time scale less than the time it takes the model particle to diffuse a distance equal to its diameter, which justifies the imposition of sharp diffusion coefficient boundaries in the present computer model. Typical microfluidic channel widths are from a few to hundreds lm across, [44][45][46]52 which correspond to from several to hundreds of particle diameters, or approximately the same number of s B to diffuse across the system channel. The simulations were carried out for the same order of magnitude number of s B as experiment, which is sufficient time for the particles to come to equilibrium in one stripe, cross between stripes ("residence time"), and explore the whole system.…”

“…For example, a constant pH gradient across a microchannel can be established during laminar flow in Y-type microchannels. 44,45 Also the sharpness of the interface can be varied by design, and more complex pH-fields can be achieved by varying the size, shape, and the structure of the confining walls or introducing special constrictions (so called "mixers") into the device. [46][47][48] Therefore, a dispersion of stimuli-active microgel particles in a microchannel with inhomogeneous solvent composition is a practical realization of particle Brownian motion with a varying diameter and position-dependent diffusion in a confined space.…”

Measurement of fluid motion and temperature changes in the real model of the heat exchanger using pLIF

“…The measurement was based on a well-defined relationship between the intensity of the fluorescence and the temperature, while other experimental parameters were constant. [14] The fluorescence physically corresponds to an atomic deexcitation process with emission of a photon of lower energy than the one which caused the excitation. In principle the fluorescent dye emits the light on different wavelength then that it is required for their excitation.…”

Fluid velocity and LIF temperature measurement in a real model of heat exchanger

“…Today we can use the non-invasive, simultaneous, very accurate measurement technique, which gives us detailed information about the flow variations in time. The Planar Laser Induced Fluorescent technique (PLIF) (Distelhoff et al,1997) has a lot of various markers mostly based on the reaction principles (Shinohara et al, 2004) for tracing the temperature field as well as concentration changes or pH values monitoring. [1 -3] Here we used a classical Rhodamine B to investigate the temperature field changes.…”