Silanization has rendered spherical (75 ± 5 μm diameter) glass particles to be weakly (sample A, ϑ = 55°), moderately (sample B, ϑ = 72°), and highly (sample C, ϑ = 90°) hydrophobic. Nonequilibrium surface pressure (Π) vs surface area (A) isotherms have been determined for monoparticulate layers which were prepared from samples A, B, and C at water−air interfaces in a Langmuir film balance. The effect of hydrophobicity on the particle−particle interaction and on the energy (E r) which is necessary for the removal of a particle from the water−air interface (particle−subphase interaction) has been elucidated. Contact cross-sectional areas (CCSA), surface coverages (SC), and collapse energies (E c), evaluated from Π vs A isotherms, provided semiquantitative information on the structural strength. Monoparticulate layers which were formed from the most hydrophobic glass spheres (sample C) had a structural strength which was almost 5 times greater than that of those which were formed from the least hydrophobic sample (sample A), as revealed by the E c values which were elucidated for these systems. Long-term stability, determined by time-dependent surface-pressure measurements, was only found for sample C. The energy of a particle−particle contact was calculated, for the strongly cohesive layer of sample C, to be (1.2−1.4) × 10-10 J. The weakly cohesive layer, prepared from sample A, had a 490-nm interparticle distance at the secondary energy minimum and a total repulsive interaction energy in the range of (0.5−1.3) × 10-13 J between two beads at an interparticle distance of 1−200 nm. Values for adhesion work (W r) were calculated from in situ contact-angle measurements and compared to corresponding E r values which were obtained experimentally by the isotherms. The significant discrepancies between the W r and E r values which were found for sample A or sample B were rationalized in terms of contact-angle hysteresis, dynamic wetting, and distortion of the electric double layer around the interfacial beads.

Stöber silica particles having diameters of ca. 100 and ca. 200 nm were prepared and silylated using trimethylsilyl N,N-dimethylcarbamate, achieving a range of surface coverage by trimethylsilyl groups by varying the amounts of silylating agent used. The efficacy of silylation was characterized in terms of hydrophobicity of the particles which was assessed by film balance investigations at water−air interfaces and additionally by imaging the long- and short-range structures of silica particulate layers at water−air interfaces and on mica supports by using Brewster-angle and atomic force microscopies.

Self-division is one of the most common phenomena in living systems and one of the most important properties of life driven by internal mechanisms of cells. Design and engineering of synthetic cells from abiotic components can recreate a life-like function thus contributing to the understanding of the origin of life. Existing methods to induce the self-division of vesicles require external and non-autonomous triggers (temperature change and the addition of membrane precursors). Here we show that pHresponsive giant unilamellar vesicles on the micrometer scale can undergo self-division triggered by an internal autonomous chemical stimulus driven by an enzymatic (urea-urease) reaction coupled to a cross-membrane transport of the substrate, urea. The bilayer of the artificial cells is composed of a mixture of phospholipids (POPC, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine) and oleic acid molecules. The enzymatic reaction increases the pH in the lumen of the vesicles, which concomitantly changes the protonation state of the oleic acid in the inner leaflet of the bilayer causing the removal of the membrane building blocks into the lumen of the vesicles thus decreasing the inner membrane area with respect to the outer one. This process coupled to the osmotic stress (responsible for the volume loss of the vesicles) leads to the division of a mother vesicle into two smaller daughter vesicles. These two processes must act in synergy; none of them alone can induce the division. Overall, our self-dividing system represents a step forward in the design and engineering of a complex autonomous model of synthetic cells. † Electronic supplementary information (ESI) available: Description of the chemical model for the conned urea-urease enzymatic reaction. Descriptions of molecular dynamics simulations and lm balance experiments. Description of videos (Videos S1-S3). Supporting Tables S1, S2 and Fig. S1-S8. See