This article describes a study of fumed silica particle layers adsorbed at the air-water interface. We have performed surface pressure, ellipsometry, and Brewster angle microscopy measurements. These determinations were complemented by surface viscoelasticity studies, using capillary waves to measure the compression moduli and an oscillating disc to measure the shear moduli. Our results show a strong influence of the particle hydrophobicity and surface density on the properties of the layers. Under compression-expansion, the particle layers rearrange quasi-instantaneously, and at high density, they buckle and/or collapse. Shear measurements show a transition from viscous to elastic behavior for particles with contact angles close to 90 degrees. The surface compression moduli are quite small and most likely not related to the stability of the foams made with these particles, in contrast to the case of more common surfactant foams.

† These authors contributed equally to this work. ‡ These authors contributed equally to this work.To maintain cell membrane homeostasis, lipids must be dynamically redistributed during the formation of transport intermediates, but the mechanisms driving lipid sorting are not yet fully understood. Lowering sphingolipid concentration can reduce the bending energy of a membrane, and this effect could account for sphingolipid depletion along the retrograde pathway. However, sphingolipids and cholesterol are enriched along the anterograde pathway, implying that other lipid sorting mechanisms, such as protein-mediated sorting, can dominate. To characterize the influence of protein binding on the lipid composition of highly curved membranes, we studied the interactions of the B-subunit of Shiga toxin (STxB) with giant unilamellar vesicles containing its glycosphingolipid receptor [globotriaosylceramide (Gb3)]. STxB binding induced the formation of tubular membrane invaginations, and fluorescence microscopy images of these highly curved membranes were consistent with co-enrichment of Gb3 and sphingolipids. In agreement with theory, sorting was stronger for membrane compositions close to demixing. These results strongly support the hypothesis that proteins can indirectly mediate the sorting of lipids into highly curved transport intermediates via interactions between lipids and the membrane receptor of the protein.