Figure 2. Time evolution of fluorescence intensity measured by experiment and fitted by theory.

(a) A representative fluorescence image of HPS aggregation in the microfluidic mixer (with subtraction of background fluorescence). White dashed lines indicate the outline of microfluidic mixer. (b) Kinetic profiles of HPS aggregation at various initial HPS concentrations (the solvent condition: DMSO mole fraction of 0.16). The solute–solvent surface tension (γ_sl) through theoretical fitting (solid lines) of experimental data (symbol points) are 20.9 (±0.6), 20.7 (±0.6), 20.5 (±0.6), and 20.3 (±0.6) cal mol⁻¹ Å⁻² at initial HPS concentration of 6, 4, 3 and 2 mM, respectively. (c) Kinetic profiles of HPS aggregation in various solvent conditions (initial HPS concentration of 6 mM). For clear illustrations, the relative fluorescence curves in part (b) corresponding to HPS concentrations of 3, 4 and 6 mM are shifted along y axis by 0.2, 0.4 and 0.6, respectively. Similarly, relative fluorescence curves in part (c) corresponding to DMSO mole fractions of 0.26 and 0.21 are shifted by 0.2 and 0.4, respectively. The solute–solvent surface tension (γ_sl) through theoretical fitting (solid lines) of experimental data (symbol points) are 19.5 (±0.6), 18.5 (±0.6) and 17.0 (±0.6) cal mol⁻¹ Å⁻² in the solvent condition with a DMSO mole fraction of 0.21, 0.26 and 0.32, respectively. The Pearson correlation coefficients for all fitted curves are larger than 0.98 (Supplementary Fig. 11).