Stabilizing Liquids Using Interfacial Supramolecular Assemblies

Chemistry, applications, and future prospects of structured liquids

Structured liquids are emerging functional soft materials that combine liquid flowability with solid-like structural stability and spatial organization. Here, we delve into the chemistry and underlying principles of structured liquids, ranging from nanoparticle surfactants (NPSs) to supramolecular assemblies and interfacial jamming. We then highlight recent advancements related to the design of intricate all-liquid 3D structures and examine their reconfigurability. Additionally, we demonstrate the versatility of these soft functional materials through innovative applications, such as all-liquid microfluidic devices and liquid microreactors. We envision that in the future, the vast potential of the liquid-liquid interface combined with human creativity will pave the way for innovative platforms, exemplified by current developments like liquid batteries and circuits. Although still in its nascent stages, the field of structured liquids holds immense promise, with future applications across various sectors poised to harness their transformative capabilities.

Interfacial Self-Assembly Nanostructures: Constructions and Applications

Interfacial self-assembly nanoarrays refer to the spontaneously organized nanostructures at interfaces, relying on the intrinsic properties of involved materials, such as surface energy, molecular structure, and interactions. In recent years, the exponential growth of self-assembly nanotechnology has substantially expanded the utility of nanomaterials. Particularly, non-covalent interactions-based interfacial self-assembly represents a viable and promising approach for the synthesis of novel nanostructure. This review introduces the significance and current development status of interfacial self-assembly technology, focusing on the driving mode, application, and prospects of interfacial self-assembly nanoarrays over the past few years.

Quantifying Hydrogen-Bonding Interactions in the Self-Assembly of Photoresponsive Azobenzene Amphiphiles at the Air-Water Interface

Amphiphilic azobenzene molecules offer ample scope to design functional supramolecular systems in an aqueous medium that can be controlled by light. Despite their widespread applications in photopharmacology and optoelectronics, the self-assembly pathways and energy landscapes of these systems are not well understood. Here, we report combined molecular dynamics (MD) simulation and surface manometry studies on a specially designed alkylated, meta-substituted azobenzene derivative to quantify the hydrogen-bonding interactions in the self-assembled monolayers of its photoisomers. The z-density profile, radial distribution function, order parameters, and hydrogen bond analyzed using MD simulations corroborated the experimental observations of changes in surface pressure, dipole moment, and thickness of the monolayers. Even a small change in the number of hydrogen bonds in the molecule-molecule and molecule-water interactions causes significant changes in the monolayer properties. These results are fundamentally important for engineering photoresponsive molecules with tailored properties for applications in targeted drug delivery and other industrial applications.

Building Functional Liquid-Based Interfaces: From Mechanism to Application

Functional liquid-based interfaces, with their inhomogeneous regions that emphasize the functionalized liquids, have attracted much interest as a versatile platform for a broad spectrum of applications, from chemical manufacturing to practical uses. These interfaces leverage the physicochemical characteristics of liquids, alongside dynamic behaviors induced by macroscopic wettability and microscopic molecular exchange balance, to allow for tailored properties within their functional structures. In this Minireview, we provide a foundational overview of these functional interfaces, based on the structural investigations and molecular mechanisms of interaction forces that directly modulate functionalities. Then, we discuss design strategies that have been employed in recent applications, and the crucial aspects that require focus. Finally, we highlight the current challenges in functional liquid-based interfaces and provide a perspective on future research directions.

Dynamic Electrostatic Interfacial Engineering for Block Copolymer Microparticles with Reversible Structures

Responsive nanoparticle surfactants (NPSs) can dynamically and reversibly modulate the interfacial interactions between incompatible components, which are essential in the interfacial catalysis, corrosion, and self-assembly of block copolymers (BCPs). However, NPSs with stimuli-responsive behavior often involve tedious chemical synthesis and surface modifications. Herein, we propose a strategy to in situ construct a kind of dynamic and reversible NPSs by the interfacial electrostatic interaction between the negatively charged nanoparticles (NPs) and the positively charged homopolymers. The NPSs assembled at the oil/water interface reduce the interfacial tension and direct the confined assembly of BCP. Meanwhile, the dynamic NPSs can be disassembled by increasing the pH value or introducing competitive electrostatic attractions, which can dynamically and reversibly change the interfacial properties as well as the alignment of polymer chains, enabling BCP microparticles with reversibly switchable lamellar and cylindrical structures. Furthermore, by the introduction of aggregation-induced emission luminogens as tails to the NPSs, the reversible transformation of BCP microparticles can be visualized by fluorescence emission, which is dependent on the nanostructures of microparticles. This work establishes a concept for dynamically manipulating interfacial interactions and reversibly switching BCP microparticles without time-consuming NPS synthesis, showing promising applications in the fabrication of smart materials with switchable structures and properties.

Dynamic Transformation of High-Architectural Nanocrystal Superlattices upon Solvent Molecule Exposure

The cluster-based body-centered-cubic superlattice (cBCC SL) represents one of the most complicated structures among reported nanocrystal assemblies, comprised of 72 truncated tetrahedral quantum dots per unit cell. Our previous report revealed that truncated tetrahedral quantum dots within cBCC SLs possessed highly controlled translational and orientational order owing to an unusual energetic landscape based on the balancing of entropic and enthalpic contributions during the assembly process. However, the cBCC SL's structural transformability and mechanical properties, uniquely originating from such complicated nanostructures, have yet to be investigated. Herein, we report that cBCC SLs can undergo dynamic transformation to face-centered-cubic SLs in response to post-assembly molecular exposure. We monitored the dynamic transformation process using in situ synchrotron-based small-angle X-ray scattering, revealing a dynamic transformation involving multiple steps underpinned by interactions between incoming molecules and TTQDs' surface ligands. Furthermore, our mechanistic study demonstrated that the precise configuration of TTQDs' ligand molecules in cBCC SLs was key to their high structural transformability and unique jelly-like soft mechanical properties. While ligand molecular configurations in nanocrystal SLs are often considered minor features, our findings emphasize their significance in controlling weak van der Waals interactions between nanocrystals within assembled SLs, leading to previously unremarked superstructural transformability and unique mechanical properties. Our findings promote a facile route toward further creation of soft materials, nanorobotics, and out-of-equilibrium assemblies based on nanocrystal building blocks.

Interfacial jamming of surface-alkylated synthetic nanocelluloses for structuring liquids

Nanocelluloses derived from natural cellulose sources are promising sustainable nanomaterials. Previous studies have reported that nanocelluloses are strongly adsorbed onto liquid-liquid interfaces with the concurrent use of ligands and allow for the structuring of liquids, that is, the kinetic trapping of nonequilibrium shapes of liquids. However, the structuring of liquids using nanocelluloses alone has yet to be demonstrated, despite its great potential in the development of sustainable liquid-based materials that are biocompatible and environmentally friendly. Herein, we demonstrated the structuring of liquids using rectangular sheet-shaped synthetic nanocelluloses with surface alkyl groups. Synthetic nanocelluloses with ethyl, butyl, and hexyl groups on their surfaces were readily prepared following our previous reports via the self-assembly of enzymatically synthesized cello-oligosaccharides having the corresponding alkyl groups. Among the alkylated synthetic nanocelluloses, the hexylated nanocellulose was adsorbed and jammed at water-n-undecane interfaces to form interfacial assemblies, which acted substantially as an integrated film for structuring liquids. These phenomena were attributed to the unique structural characteristics of the surface-hexylated synthetic nanocelluloses; their sheet shape offered a large area for adsorption onto interfaces, and their controlled surface hydrophilicity/hydrophobicity enhanced the affinity for both liquid phases. Our findings promote the development of all-liquid devices using nanocelluloses.