We present a methodology that combines Mach-Zehnder interferometry, a custom relative humidity (RH) controlled chamber, and a confined two-dimensional droplet geometry to enable precise investigations of drying of complex fluids and the associated transport mechanisms. This approach is applied to a model binary mixture, water-glycerol, the concentration-dependent thermodynamic and transport properties of which are relatively well documented. High-resolution interferometric imaging ($6\mu \mathrm{m}{\mathrm{pixel}}^{-1}$, 1 $\mathrm{frame}{\mathrm{s}}^{-1}$) allows simultaneous measurement of drying kinetics and internal concentration fields with $\pm 0.5\%$ accuracy, characterized here over a wide range of RH (25–95%), and thus Péclet numbers. The experimental results closely match a quasisteady, isothermal model of vapor-diffusion-controlled evaporation coupled to diffusion within the droplet. These data enable extraction of both the concentration-dependent mutual diffusion coefficient $D\left(\phi \right)$ and the water chemical activity $a_w\left(\phi \right)$ over almost the entire range of glycerol volume fraction $\phi$, even from a single low-RH experiment. While $a_w\left(\phi \right)$ agrees well with literature values, our measurements yield a consistent fit for $D\left(\phi \right)$. Complementary experiments with fluorescence microscopy confirm that buoyancy-driven convection, although present, remains negligible, so that mass diffusion dominates solute transport in this confined geometry. The overall agreement validates the methodology, demonstrating its robustness as a quantitative framework for probing drying dynamics and transport in complex fluids, with broad applicability to controlled evaporation studies.

Close

PrevNext

View figure in article

• Diffusion
• Drop & bubble phenomena
• Evaporation
• Transport phenomena
• Binary fluids
• Complex fluids
• Drops & bubbles
• Hele-Shaw cell
• Interferometry