Figure 3.

Microscopic description of the contiguous droplet-bilayer system. (A) Microscopic contributions to the free energy density of a monolayer and of a bilayer. For the monolayer: the surface tension of the bare water/oil interface (${\gamma }_{o/w}$), the interaction of the PL tails with the oil phase $(f_{\text{mo}}={\epsilon }_{\text{mo}}{\rho }_m)$, the lateral interaction between PLs ($f_{\text{int}}$), and the interaction of the PL headgroups with water ($f_{\text{hyd}}$). For the bilayer: the unfavorable interactions of the PL tails with water ($f_{\text{phob}}={\gamma }_{\text{phob}}$), the trans interaction between PL tails ($f_{\text{mm}}={\epsilon }_{\text{mm}}({\rho }_{be}+{\rho }_{bi})$) of the apposed leaflet, the lateral interaction between PLs ($f_{\text{int}}$), and the interaction of the PL headgroups with water ($f_{\text{hyd}}$). (B) Lateral pressure as a function of PL density at the triolein-water interface deduced from a compression isotherm obtained from a pending droplet experiment (see Fig. S2A and B). (C) Chemical potential of a bilayer and a monolayer as a function of PL density. The two chemical potentials vary identically but are shifted by the amount ${\epsilon }_{\text{mm}}-{\epsilon }_{\text{mo}}$. At equilibrium, a monolayer in contact with a bilayer has the same chemical potential (${\mu }_b={\mu }_m$) and therefore has different PL densities, whose values are directly affected by the ${\epsilon }_{\text{mm}}-{\epsilon }_{\text{mo}}$ gap. (D) Molecular structure of the different oils used to probe the effect of oil composition on monolayer-bilayer surface tension diagram. (E) Monolayer-bilayer surface tension diagram of DOPC DEVs made with different oil composition: sterol ester-triolein (1:3) (red circles), triolein (black circles), and squalene (blue circles). DEVs were selected with a droplet symmetrically positioned with respect to the bilayer. Black dot represents the average monolayer tension of osmotically deflated triolein DEVs (bilayer tension <0.03mN/m; n = 17). Blue dot represents the average monolayer tension of osmotically deflated squalene DEVs (bilayer tension <0.09mN/m; n = 9). See Fig. S2C for monolayer-bilayer tension diagram of squalene and sterol ester-triolein (1:3) DEVs with asymmetric positions of the droplet.