Electrostatic Interaction-Driven\nFabrication of Large-Area,\nFreestanding Nanoparticle Surfactant Membranes with Controllable Elastic\nProperties

Nanoparticle surfactants assembled at water–oil\ninterfaces\ncan significantly lower the interfacial tension and can be used to\nstabilize liquids. Understanding and actively tuning the mechanical\nproperties of the generated membranes, which comprise the nanoparticle\nsurfactants, are of significant fundamental interest for the interfacial\nbehavior of nanoparticles and of interest for water purification,\ndrug encapsulation, enhanced oil recovery, and innovative energy transduction\napplications. Here, we present electrostatic interaction-driven fabrication\nof freestanding and close-packed SiO<sub>2</sub> surfactant membranes\nwith diameters up to 0.10 mm. The membranes of 20–30 nm in\nthickness were spanned over holes with a diameter of 2 μm, exhibiting\na Young’s modulus ranging from 1.5 to 5.9 GPa. The controllable\nelastic properties of the fabricated nanoparticle surfactant membranes\nare found to be dictated by the strength of interactions between nanoparticles\nand ligands, between ligands and ligands, and between the nanoparticle\nsurfactants. The results present an efficient approach for fabricating\nand developing nanoparticle surfactant-based large-area, freestanding,\nand ultrathin membranes with finely tunable mechanical properties\non a large scale.