Extended Data Fig. 4: Measurement of transport of solutes and solvent between droplets in 1D droplet arrays.

Plots of droplet volume versus time from 1D droplet arrays in which alternating droplets contain a high and low concentration of solute. Solutes formaldehyde (C1), glycolaldehyde (C2), glyceraldehyde (C3), threose (C4), xylose (C5), sucrose (C12) and methanol (MeOH) were analyzed. For each condition, the volume of a representative single droplet and the mean volume of its two nearest neighbors is shown. Data for all droplets and center-to-center droplet separations of 40 µm, 30 µm, 20 µm, 14 µm and 8 µm are shown in Supplementary Fig. 2 and confirm the dependence of osmotically driven volume changes on inter-droplet distance found in the model (Extended Data Fig. 3d). a, Solute concentrations of 0.8M (red dots) and 0.08M solute (blue dots) for C1 to C12 and 15% (red dots) and 0% (blue dots) for MeOH, with 20 µm inter-droplet spacing. Meaningful volume changes were only detected for C3, C4, C5 and C12, indicating that \({P}_{{C}_{3-12}}/{P}_{{H}_{2}O}\,\le 0.01\) (as in the model similar volume changes are only observed for \({P}_{{C}_{1}}/{P}_{{H}_{2}O}\,\le 0.01\), see Extended Data Fig. 3a, and different molar volumes of solutes has only a minor effect, see Extended Data Fig. 3c). Indeed, the absence of meaningful volume change for C2 implies that \({P}_{{C}_{3-12}}/{P}_{{C}_{2}}\le 0.01\) (as no meaningful volume change is observed in the model with \({P}_{{C}_{1}}/{P}_{{H}_{2}O}=1.0\), see Extended Data Fig. 3a). b, Solute concentrations of 8M (red dots) and 0.8M solute (blue dots) for C1 with 20 µm inter-droplet spacing and C2 with inter-droplet distances of 40 µm, 30 µm, 20 µm, 14 µm and 8 µm. No meaningful volume change was observed for C1, indicating that \({P}_{{C}_{1}}\ge {P}_{{H}_{2}O}\) (as no meaningful droplet volume changes are observed with the model when \({P}_{{C}_{1}}/{P}_{{H}_{2}O}\ge 1.0\), see Extended Data Fig. 3b). However, important volume change was observed for C2, and the curves show the best fit for \({P}_{{H}_{2}O}\) and \({P}_{{C}_{2}}\) using the transport model. c-d, \({P}_{{H}_{2}O}\), and \({P}_{{C}_{2}}\) by fitting experimental data for droplets containing C2 to the transport model (see panel b). c, \({P}_{{H}_{2}O}\) as a function of the inter-droplet distance, \(L\) (left panel) and \({P}_{{H}_{2}O}L\) as a function of \(L\) (right panel). d, \({P}_{{C}_{2}}\) as a function of the inter-droplet distance, \(L\) (left panel) and \({P}_{{C}_{2}}L\) as a function of \(L\) (right panel). In panels c and d each small blue point corresponds to data from a single droplet and the mean volume of its two nearest neighbours and the large black point is the mean value for all data points. The values of \({P}_{{H}_{2}O}\) and \({P}_{{C}_{2}}\) are inversely proportional to \(L\), and \({P}_{{H}_{2}O}L\) and \({P}_{{C}_{2}}L\) are independent of \(L\). The mean \({P}_{{H}_{2}O}L\) is 532±148 mol min⁻¹ µm⁻¹ (SD, n = 43) and the mean \({P}_{{C}_{2}}L\) is 32±5 mol min⁻¹ µm⁻¹ (SD, n = 43). The mean value of \({P}_{{C}_{2}}/{P}_{{H}_{2}O}\) is 0.063±0.013 (SD, n = 43). Assuming \({P}_{{C}_{3-12}}/{P}_{{C}_{2}}\le 0.01\) (see above) this implies that \({P}_{{C}_{3-12}}/{P}_{{H}_{2}O}\,\le 0.0006\). See also Source Data.

Source data