Reconstruction by fluorescence imaging of the spatio-temporal evolution of the viscosity field in Hele-Shaw flows

Abstract

We study the spatio-temporal evolution of the viscosity field during stable and unstable radial flows of glycerol-water solutions in a horizontal Hele-Shaw cell where a localized temperature gradient is imposed. The viscosity field is reconstructed from the measurement of the fluorescence emitted by a viscosity-sensitive molecular probe (Auramine O). For an immiscible flow, the viscosity and temperature fields are obtained accurately. For miscible displacements, we show how the interplay between the viscosity changes of both fluids and the variation of the fluid thickness in the gap prevents obtaining strict quantitative reconstruction of the viscosity field. We explain how the reconstructed viscosity field can nevertheless be interpreted to obtain information about the fluid thickness and the local viscosity and temperature.

Influence of microscopic precipitate structures on macroscopic pattern formation in reactive flows in a confined geometry

“…The concentration field is influenced both by the flow and by the concentration changes due to the precipitation reaction. 19,20 Furthermore, the shadowgraph optics is able to image precipitate membranes which may appear transparent in the direct camera records. 3 Results and discussion…”

Experimental demonstration of the suppression of viscous fingering in a partially miscible system

“…In fully miscible systems, these effects have often been reported along with observation of the shade of the dye. [62][63][64][65][66] Conversely, the effects are rarely discussed in immiscible systems, wherein almost no dye shading is observed. Similarly, in the present pattern with suppressed VF, no significant dye shading is observed.…”

Molecular Rotors for In Situ Local Viscosity Mapping in Microfluidic Chips

“…16,17 However, their use for quantitative characterization in other contexts remains scarce. 18,19 lifetime imaging (of FMRs and other fluorophores) have been proved to be powerful tools for mapping the viscosity in complex three-dimensional flows 20−23 but they were performed with a sophisticated lifetime measurement setup operating directly in time domain, which requires a pulsed laser source, and are thus difficult to be applied by nonspecialists.…”

“…FMRs have been acknowledged as excellent local viscosity probes with real-time response and high spatial resolution − and are, for instance, used as contrast agents in cell bioimaging. , However, their use for quantitative characterization in other contexts remains scarce. , More particularly, in microfluidic context, regular and confocal fluorescence lifetime imaging (of FMRs and other fluorophores) have been proved to be powerful tools for mapping the viscosity in complex three-dimensional flows − but they were performed with a sophisticated lifetime measurement setup operating directly in time domain, which requires a pulsed laser source, and are thus difficult to be applied by nonspecialists.…”