Electrostatic Interaction-Driven Fabrication of Large-Area, Freestanding Nanoparticle Surfactant Membranes with Controllable Elastic Properties.

Nanoparticle surfactants assembled at water-oil interfaces can significantly lower the interfacial tension and can be used to stabilize liquids. Understanding and actively tuning the mechanical properties of the generated membranes, which comprise the nanoparticle surfactants, are of significant fundamental interest for the interfacial behavior of nanoparticles and of interest for water purification, drug encapsulation, enhanced oil recovery, and innovative energy transduction applications. Here, we present electrostatic interaction-driven fabrication of freestanding and close-packed SiO surfactant membranes with diameters up to 0.10 mm. The membranes of 20-30 nm in thickness were spanned over holes with a diameter of 2 μm, exhibiting a Young's modulus ranging from 1.5 to 5.9 GPa. The controllable elastic properties of the fabricated nanoparticle surfactant membranes are found to be dictated by the strength of interactions between nanoparticles and ligands, between ligands and ligands, and between the nanoparticle surfactants. The results present an efficient approach for fabricating and developing nanoparticle surfactant-based large-area, freestanding, and ultrathin membranes with finely tunable mechanical properties on a large scale.