Fig. 2: Experimental setup and results.
From: Formation mechanism of thermally controlled pH gradients
a Experimental setup. The thin thermal reaction chamber is continuously supplied with a premixed solution containing varying concentrations of formic acid and sodium hydroxide. The outflux is split into three parts (top 12%, middle 76% and bottom 12%) and the pH value of each fraction is measured (green circles). For experimental details see Methods. b These pH values are depicted for 75 mM formic acid and varying concentrations of NaOH (mNa) for the inlet (bulk) and the different outlets. While the bottom fraction qualitatively follows the bulk, especially the top fraction displays a complex, concentration-dependent behavior both for its value and for the resulting pH gradient \({\left(\Delta {{{{{{{\rm{pH}}}}}}}}\right)}_{{{{{{{{\rm{vert}}}}}}}}}\) between top and bottom of the heat flux cell (measurements for other formic acid concentrations shown in Supplementary Fig. 2). c When plotting the pH values of the different fractions (black circle: bulk, brown inverted triangle: top, green box: middle, pink triangle: bottom), a positive gradient (pHtop > pHbot, red) for low concentrations of NaOH is observed which is inverted (blue) at higher concentrations of NaOH and increases massively when mNa > mHCOOH. Error bars are shown as discussed in Methods. d In the absence of a temperature gradient, no pH gradient forms (mHCOOH = 75 mM).
