Quantitative comparison of thermal and solutal transport in a T-mixer by FLIM and CFD

Abstract

The development and adoption of lab-on-a-chip and micro-TAS (total analysis system) techniques requires not only the solving of design and manufacturing issues, but also the introduction of reliable and quantitative methods of analysis. In this work, two complementary tools are applied to the study of thermal and solutal transport in liquids. The experimental determination of the concentration of water in a water-methanol mixture and of the temperature of water in a microfluidic T-mixer are achieved by means of fluorescence lifetime imaging microscopy (FLIM). The results are compared to those of finite volume simulations based on tabulated properties and well-established correlations for the fluid properties. The good correlation between experimental and modelled results demonstrate without ambiguity that (1) the T-mixer is an adiabatic system within the conditions, fluids and flow rates used in this study, (2) buoyancy effects influence the mixing of liquids of different densities at moderate flow rates (Reynolds number Re ( 10 -2 ), and (3) the combination of FLIM and computational fluid dynamics has the potential to be used to measure the thermal and solutal diffusion coefficients of fluids for a range of temperatures and concentrations in one single experiment. As such, it represents a first step towards the full-field monitoring of both the extent and the kinetics of a chemical reaction.

Unravelling the effect of temperature on viscosity-sensitive fluorescent molecular rotors

“…The lifetime of 2 , which was previously used as both a temperature and a viscosity marker, 9,15–17 shows pronounced viscosity dependence (Fig. 2).…”

Optically trapped microsensors for microfluidic temperature measurement by fluorescence lifetime imaging microscopy

“…The dependence of <> on temperature is shown graphically in Figure 3, together with the corresponding curve for KR in bulk water. The lifetime-temperature response of the microdroplets resembles that of the bulk solution, 13 confirming that containment of KR in the microdroplet does not inhibit its conformational freedom. The small decrease in lifetime of KR in the microdroplets compared with bulk aqueous solution may be accounted for by the effect of the local environment (presence of NaCl and surfactants and the proximity of an oil/water interface) on the non-radiative decay rate and the effect of increased refractive index, which increases the radiative rate.…”

Fluorescence lifetime imaging (FLIM): Basic concepts and some recent developments

“…While FLIM of rhodamine B in methanol was used to map the temperature in a glass microchip from 10 • C to about 95 • C with a ±3 • C accuracy (Benninger et al, 2006), and FLIM of Kiton red, a watersoluble rhodamine B derivative, was used to map thermal and solution transport processes in a microfluidic T-mixer (Mendels et al, 2008), these dyes have a limited sensitivity to temperature. They may cover a large dynamic range from 10 • C to 100 • C, but they are not very sensitive to temperature variations around 37 • C.…”

“…However, applications in diverse areas such as forensic science (Bird et al, 2007), combustion research (Ehn et al, 2011;Ni and Melton, 1996), luminescence lifetime mapping in diamond (Liaugaudas et al, 2009(Liaugaudas et al, , 2012, microfluidic systems (Benninger et al, 2005a(Benninger et al, , 2006Elder et al, 2006;Graham et al, 2010;Magennis et al, 2005;Robinson et al, 2008), art conservation (Comelli et al, 2004(Comelli et al, , 2005, remote sensing (Esposito, 2012;Ge et al, 2012;Lin et al, 2012), lipid order problems in physical chemistry (Togashi et al, 2005), the spatial distribution of dopants in perovskite oxides (Rodenbücher et al, 2013) and temperature sensing (Bennet et al, 2011;Benninger et al, 2006;Graham et al, 2010;Mendels et al, 2008;Okabe et al, 2012) have also been reported. FLIM has been carried out from the UV (Li et al, 2004;Schüttpelz et al, 2006) to the near infrared (Becker and Shcheslavskiy, 2013) and it is not surprising that fluorescence lifetime-based imaging is widely used in the biomedical sciences, and that this trend shows no signs of abating.…”