Fig. 3: Comparison of analytically predicted and experimentally measured pH gradients.
From: Formation mechanism of thermally controlled pH gradients
a Heat maps of theoretically calculated pH differences are compared to measurements (circles) for varying concentrations of formic acid (mform) and sodium hydroxide (NaOH, mNa). Our model predicts a complex phase diagram with a positive (yellow), a weakly negative (green) and a strongly negative (blue) pH gradient. The inversion is shown by a black dashed line and corresponds to \({S}_{{{{{{{{\rm{H}}}}}}}}}^{{{{{{{{\rm{eff}}}}}}}},0}=0\), see Eq. (9). The experimental results are in very good agreement with the analytical model. b Theoretical (orange line) and experimental (blue circles) pH differences for 150 mM and 75 mM formic acid (white lines in a), showing again the good agreement between theory and experiment. The error bars include experimental standard deviations from replicate measurements as well as uncertainties accounting for concentration fluctuations from thermal gradient effects in the outflow channels (for more details see Methods).
