Stabilizing Liquids Using Interfacial Supramolecular Polymerization

Tuning the Stability of Liquids by Controlling the Formation of Interfacial Surfactants

Currently, the stability of liquids by nanoparticle surfactants is widely investigated, while the stability of liquids by supramolecular polymer surfactants is rarely involved. Herein, we combine small organic molecules dissolved...

The Assembly and Jamming of Nanoparticle Surfactants at Liquid-Liquid Interfaces

Using the interactions between nanoparticles (NPs) and polymeric ligands to generate nanoparticle surfactants (NPSs) at the liquid-liquid interface, the binding energy of the NP to the interface can be significantly increased, irreversibly binding the NPSs to the interface. By designing a simplified NPS model, where the NP size can be precisely controlled and the characteristic fluorescence of the NPs be used as a direct probe of their spatial distribution, we provide new insights into the attachment mechanism of NPSs at the liquid-liquid interface. We find that the binding energy of NPSs to the interface can be reduced by competitive ligands, resulting in the dissociation and disassembly of NPSs at the interface, and allowing the construction of responsive, reconfigurable all-liquid systems. Smaller NPSs that are loosely packed (unjammed) and irreversibly bound to the interface can be displaced by larger NPSs, giving rise to a size-dependent assembly of NPSs at the interface. However, when the smaller size NPSs are densely packed and jam at the interface, the size-dependent assembly of NPSs at the interface can be completely suppressed.

Responsive Interfacial Assemblies Based on Charge-Transfer Interactions

Charge transfer (CT) interactions have been widely used to construct supramolecular systems, such as functional nanostructures and gels. However, to date, there is no report on the generation of CT complexes at the liquid-liquid interface. Here, by using an electron-deficient acceptor dissolved in water and an electron-rich donor dissolved in oil, we present the in situ formation and assembly of CT complex surfactants (CTCSs) at the oil-water interface. With time, CTCSs can assemble into higher-order nanofilms with exceptional mechanical properties, allowing the stabilization of liquids and offering the possibility to structure liquids into nonequilibrium shapes. Moreover, due to the redox-responsiveness of the electron-deficient acceptor, the association and dissociation of CTCSs can be reversibly manipulated in a redox process, leading to the switchable assembly and disassembly of the resultant constructs.

Surfactant-Induced Interfacial Aggregation of Porphyrins for Structuring Color-Tunable Liquids

Locking nonequilibrium shapes of liquids into targeted architectures by interfacial jamming of nanoparticles is an emerging area in material science. 5,10,15,20-tetrakis(4-sulfonatophenyl) porphyrin (H₆ TPPS) shows three different aggregation states that present an absorption imaging platform to monitor the assembly and jamming of supramolecular polymer surfactants (SPSs) at the liquid/liquid interface. The interfacial interconversion of H₆ TPPS, specifically H₄ TPPS^2- dissolved in water, from J- to an H-aggregation was induced by strong electrostatic interactions with amine-terminated polystyrene dissolved in toluene at the water/toluene interface. This resulted in color-tunable liquids due to interfacial jamming of the SPSs formed between H₄ TPPS^2- and amine-terminated polystyrene. However, the formed SPSs cannot lock in nonequilibrium shapes of liquids. In addition, a self-wrinkling behavior was observed when amphiphilic triblock copolymers of PS-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) were used to interact with H₄ TPPS^2- . Subsequently, the SPSs formed can lock in nonequilibrium shapes of liquids.

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

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.