Direct observation of nanoparticle-surfactant assembly and jamming at the water-oil interface

Abstract

Electrostatic interactions between nanoparticles (NPs) and functionalized ligands lead to the formation of NP surfactants (NPSs) that assemble at the water-oil interface and form jammed structures. To understand the interfacial behavior of NPSs, it is necessary to understand the mechanism by which the NPSs attach to the interface and how this attachment depends on the areal coverage of the interface. Through direct observation with high spatial and temporal resolution, using laser scanning confocal microscopy and in situ atomic force microscopy (AFM), we observe that early-stage attachment of NPs to the interface is diffusion limited and with increasing areal density of the NPSs, further attachment requires cooperative displacement of the previously assembled NPSs both laterally and vertically. The unprecedented detail provided by in situ AFM reveals the complex mechanism of attachment and the deeply nonequilibrium nature of the assembly.

Self‐Assembly of Strongly Amphiphilic Janus Nanoparticles into Freestanding Membranes

“…This wrinkle formation is similar to interface jamming and buckling, and has been observed for a variety of nanoparticles strongly anchored at oilwater interfaces by oil-soluble ligands, surfactants or a polymer corona grafted on the nanoparticle. [25][26][27][28][29] This freestanding membrane is rather sturdy and could be picked up from the water surface by manual dipping of a microscope glass slide and can be subsequently detached with tweezers (Figure 5f,g).…”

Gated Molecular Diffusion at Liquid–Liquid Interfaces

“…Nanoparticle surfactants (NPSs) provide an alternative strategy to construct interfacial NP assemblies by dispersing NPs in one liquid and dissolving functionalized polymer ligands in a second liquid immiscible with the first [21, 22] . Unlike polymer‐capped NPs where NPs are fully covered with polymer ligands, [23] “Janus‐like” NPSs form in situ at the interface by the electrostatic interactions between NPs and polymer ligands, assemble into a monolayer and, when jammed, generate a robust assembly with exceptional mechanical properties [24–26] . By taking advantage of the interfacial jamming of NPSs, liquids can be sculpted into complex shapes using all‐liquid moulding and 3D printing, [27, 28] showing tremendous potentials for all‐liquid microfluidics, biphasic micro‐reactors and chemical separation systems [29–32] .…”

“…[21,22] Unlike polymer-capped NPs where NPs are fully covered with polymer ligands, [23] "Janus-like" NPSs form in situ at the interface by the electrostatic interactions between NPs and polymer ligands, assemble into a monolayer and, when jammed, generate a robust assembly with exceptional mechanical properties. [24][25][26] By taking advantage of the interfacial jamming of NPSs, liquids can be sculpted into complex shapes using all-liquid moulding and 3D printing, [27,28] showing tremendous potentials for all-liquid microfluidics, biphasic micro-reactors and chemical separation systems. [29][30][31][32] On the other hand, with NPSs, ultra-stable, structured Pickering emulsion can be produced via a simple shearing process, that can be used as templates to fabricate microcapsules and 3D porous materials.…”

Spontaneous emulsification induced by nanoparticle surfactants

“…1(a)]. These nanoparticle surfactant assemblies have been shown to form monolayers at the liquid-liquid interface using grazing incidence x-ray scattering, 38 atomic force microscopy, 39 and x-ray photon correlation spectroscopy. 40 Here, we use carboxy-functionalized Noria, a nanoporous organic cage, 41,42 chosen for its high charge density.…”