Synthesis of Nano/Microstructures at Fluid Interfaces

Stimuli-responsive nanoparticle self-assembly at complex fluid interfaces: a new insight into dynamic surface chemistry

The self-assembly of core/shell nanoparticles (NPs) at fluid interfaces is a rapidly evolving area with tremendous potential in various fields, including biomedicine, display devices, catalysts, and sensors. This review provides an in-depth exploration of the current state-of-the-art in the programmed design of stimuli-responsive NP assemblies, with a specific focus on inorganic core/organic shell NPs below 100 nm for their responsive adsorption properties at fluid and polymer interfaces. The interface properties, such as ligands, charge, and surface chemistry, play a significant role in dictating the forces and energies governing both NP-NP and NP-hosting matrix interactions. We highlight the fundamental principles governing the reversible surface chemistry of NPs and present detailed experimental examples in the following three key aspects of stimuli-responsive NP assembly: (i) stimuli-driven assembly of NPs at the air/liquid interface, (ii) reversible NP assembly at the liquid/liquid interface, including films and Pickering emulsions, and (iii) hybrid NP assemblies at the polymer/polymer and polymer/water interfaces that exhibit stimuli-responsive behaviors. Finally, we address current challenges in existing approaches and offer a new perspective on the advances in this field.

Tunable Approach to Induce the Formation of Flexible Nanofilms from Small (3 nm) Gold Nanoparticles at Oil-Water Interfaces

The self-assembly of gold nanoparticles (AuNPs) into thin films at the liquid-liquid interface has promising applications in industries such as catalysis, optics, and sensors. However, precise control over their formation is complex, influenced by several factors which scale differently with core size. Due to their small free energy of adsorption, there are few examples of AuNPs with core diameters <10 nm. The present research evaluates the adsorption of ∼3 nm AuNPs from either side of the oil-aqueous interface with variations in ligand shell composition, the oil phase composition, and the structure of alcohol additives to best drive thin-film formation. Film formation and quality are evaluated, and a recent thermodynamic model is used to gain insight into the primary forces promoting this adsorption. Results demonstrate that longer-chain alcohol additives (namely, n-butanol and n-hexanol) induced adsorption more efficiently than shorter-chain alcohols (ethanol). The volume of alcohol additive needed to induce adsorption was dependent upon the ligand composition, suggesting that the mechanism for induced interfacial adsorption is via interaction with the AuNP ligand shell. Comparison with the thermodynamic model indicates that the driving force for this induced adsorption is the alteration of the three-phase contact angle. Additionally, the use of various oils demonstrates that as oil-water interfacial tension increases, more AuNPs adsorb to the interface. This relationship is also supported by the model. Insight gained for favorable conditions of adsorption for AuNPs < 10 nm as well as the underlying thermodynamic mechanism is important in working toward the ability to fine-tune such films for industrial applications.

Supramolecular Interfaces and Reconfigurable Liquids Derived from Cucurbit[7]uril Surfactants

Nanoparticle surfactants (NPSs) offer a powerful means to stabilize the oil-water interface and construct all-liquid devices with advanced functions. However, as the nanoparticle size decreases to molecular-scale, the binding energy of the NPS to the interface reduces significantly, leading to a dynamic adsorption of NPS and "liquid-like" state of the interfacial assemblies. Here, by using the host-guest recognition between a water-soluble small molecule, cucurbit[7]uril (CB[7]) and an oil-soluble polymer ligand, methyl viologen-terminated polystyrene, a supramolecular NPS model, termed CB[7] surfactant, is described. CB[7] surfactants form and assemble rapidly at the oil-water interface, generating an elastic film with excellent mechanical properties. The binding energy of CB[7] surfactant to the interface is sufficiently high to hold it in a jammed state, transforming the interfacial assemblies from a "liquid-like" to "solid-like" state, enabling the structuring of liquids. With CB[7] surfactants as the emulsifier, O/W, W/O and O/W/O emulsions can be prepared in one step. Owing to the guest-competitive responsiveness of CB[7] surfactants, the assembly/disassembly and jamming/unjamming of CB[7] surfactants can be well controlled, leading to the reconfiguration of all-liquid constructs.

MXene-Based Porous Monoliths

In the past decade, a thriving family of 2D nanomaterials, transition-metal carbides/nitrides (MXenes), have garnered tremendous interest due to its intriguing physical/chemical properties, structural features, and versatile functionality. Integrating these 2D nanosheets into 3D monoliths offers an exciting and powerful platform for translating their fundamental advantages into practical applications. Introducing internal pores, such as isotropic pores and aligned channels, within the monoliths can not only address the restacking of MXenes, but also afford a series of novel and, in some cases, unique structural merits to advance the utility of the MXene-based materials. Here, a brief overview of the development of MXene-based porous monoliths, in terms of the types of microstructures, is provided, focusing on the pore design and how the porous microstructure affects the application performance.

Individual Coating of Entomopathogenic Nematodes with Titania (TiO2) Nanoparticles Based on Oil-in-Water Pickering Emulsion: A New Formulation for Biopesticides

This study presents a new eco-friendly formulation of entomopathogenic nematodes (EPNs) based on individual coating of EPNs with titanium dioxide (TiO₂) nanoparticles (NPs) and mineral oil via oil-in-water Pickering emulsions. Mineral oil-in-water emulsions stabilized by amine-functionalized titanium dioxide (TiO₂-NH₂) particles were prepared. 40:60 and 50:50 oil-water volume ratios using 2 wt % TiO₂-NH₂ particles were found to be the most stable emulsions with a droplet size suitable for the formulation and were further studied for their toxicity against the incorporated EPNs. Carboxyfluorescein was covalently bonded to TiO₂-NH₂ NPs, and the resulting composite was observed via fluorescence confocal microscopy. The dry coating was evaluated using SEM and confocal microscopy, which showed significant nematode coverage by the particles and oil. The final formulation was biocompatible with the studied EPNs, where the viability of the EPNs in the formulation was equivalent to control aqueous suspension after 120 days. Finally, yields of nematodes from infected Galleria mellonella cadavers collected for 150 days showed no significant differences (P > 0.05) using the tested emulsions compared to the control containing nematodes in water.

Pickering Emulsion Catalysis: Interfacial Chemistry, Catalyst Design, Challenges, and Perspectives

Pickering emulsions are particle-stabilized surfactant-free dispersions composed of two immiscible liquid phases, and emerge as attractive catalysis platform to surpass traditional technique barrier in some cases. In this review, we have comprehensively summarized the development and the catalysis applications of Pickering emulsions since the pioneering work in 2010. The explicit mechanism for Pickering emulsions will be initially discussed and clarified. Then, summarization is given to the design strategy of amphiphilic emulsion catalysts in two categories of intrinsic and extrinsic amphiphilicity. The progress of the unconventional catalytic reactions in Pickering emulsion is further described, especially for the polarity/solubility difference-driven phase segregation, "smart" emulsion reaction system, continuous flow catalysis, and Pickering interfacial biocatalysis. Challenges and future trends for the development of Pickering emulsion catalysis are finally outlined.

Temperature-responsive Pickering high internal phase emulsions for recyclable efficient interfacial biocatalysis

The field of biocatalysis is expanding owing to the increasing demand for efficient low-cost green chemical processes. However, a feasible strategy for achieving product separation, enzyme recovery, and high catalytic efficiency in biocatalysis remains elusive. Herein, we present thermoresponsive Pickering high internal phase emulsions (HIPEs) as controllable scaffolds for efficient biocatalysis; these HIPEs demonstrate a transition between emulsification and demulsification depending on temperature. Ultra-high-surface-area Pickering HIPEs were stabilized by Candida antarctica lipase B immobilized on starch particles modified with butyl glycidyl ether and glycidyl trimethyl ammonium chloride, thus simplifying the separation and reuse processes and significantly improving the catalytic efficiency. In addition, the switching temperature can be precisely tuned by adjusting the degree of substitution of the modified starches to meet the temperature demands of various enzymes. We believe that this system provides a green platform for various interfacial biocatalytic processes of industrial interest.

The thermoresponsive Pickering high internal phase emulsions stabilized by starch particles as controllable scaffolds for efficient biocatalysis, which simplified the separation and reuse processes and significantly improved the catalytic efficiency.

Instant interfacial self-assembly for homogeneous nanoparticle monolayer enabled conformal "lift-on" thin film technology

Thin film fabrication is of great importance in modern engineering. Here, we propose a universal and conformal thin film technique enabled by the wetting empowered interfacial self-assembly. By tailoring the contact angle of nanoparticle (NP), a NP monolayer can be assembled instantly (within 5 seconds) with an excellent harvesting efficiency (up to 97.5 weight %). This self-assembly strategy presents a universal applicability on various materials, e.g., nonmetal, metal, and core-shell structures, and can achieve a monolayer with same in-plane area as a 95 cm² wafer in a single process, indicating great potential for scale-up manufacturing. Through a template transfer, we coat the surface of different substrates (plastic, paper, etc.) with the assembled film in a conformal and nondestructive “lift-on” manner and subsequently demonstrate fluorescent micropatterns. This self-assembly strategy has great implications in advancing thin film technology in a user-friendly and cost-effective fashion for applications in anti-counterfeiting, actuators, and wearable/flexible electronics.

Gated Molecular Diffusion at Liquid-Liquid Interfaces

The jamming of nanoparticle surfactants (NPSs) at liquid-liquid interface imparts attractive properties to the interfacial assemblies and enables the structuring of liquids. Herein, we report photoresponsive supramolecular microcapsules with jammed NPS assemblies at the oil-water interface, taking advantage of host-guest molecular recognition. The permeability of the colloidal membrane can be effectively manipulated by switching the NPSs from a jammed state to an unjammed state with a photo trigger, leading to a controlled molecular diffusion and release, affording a versatile platform for the construction of next generation smart microcapsule systems.

Hierarchical Assembly of Two-Dimensional Polymers into Colloidosomes and Microcapsules

Hierarchical assembly of two-dimensional (2D) polymers to 3D microstructures provides new means of creating functional materials with exotic properties for extensive applications. Herein, we report an approach of assembling 2D covalent organic framework (COF) colloidosomes or microcapsules from small molecules. We polymerized monomers to produce narrowly distributed COF particles with average particle sizes greater than 490 nm, which were further used as stabilizers to prepare various water-in-oil Pickering emulsions with droplet sizes of 10-120 μm on average. The emulsion droplets were subsequently applied as templates for interfacial polymerization of the same monomers. The COF microcapsules with varied diameters and shell thicknesses of 0.2-3.1 μm were thus obtained, which possessed good stability, high crystallinity, and surface areas no less than 540 m²/g. The approach also permits facile loading of water-soluble substances such as salts, dyes, or proteins. The loaded molecules demonstrated different permeability against the shell, in which 98% of the encapsulated salts could be released in 1 h while only 18% of dye molecules and almost none of the fluorescent proteins diffused out from the microcapsules. Such an assembling approach may greatly extend the applications of 2D polymers and their microcapsules.

Adhesion and Aggregation of Spherical Nanoparticles on Lipid Membranes

We present a review of recent results on the adhesion, wrapping and aggregation of spherical nanoparticles (NPs) on lipid membranes via molecular dynamics simulations of an implicit solvent model. We show that the degree of wrapping of small NPs, by tensionless planar membranes, can increase continuously with the adhesion strength. However, the degree of wrapping exhibits a discontinuity for large NPs or short interaction range. The adhesion of NPs to small vesicles, without volume constraint, also exhibits a discontinuity between weakly wrapped states and fully endocytosed states. Multiple spherical NPs, bound to tensionless planar membranes are either in a gas state, at weak adhesion strength, or aggregate, at relatively high adhesion strength, into a multitude of structures, corresponding to in-plane chains, out-of-plane tubes and rings, and out-of-plane single-chain tubes. Annealing scans and free energy calculations show that the gas and tube phases are the predominantly stable phases. In-plane chains are only stable for small aggregates and the out-of-plane bitubes are long-lived metastable states.

Porous Ceramics via Processable Pickering Emulsion Stabilized by Oppositely Charged Colloids

We report a method to produce processable Pickering emulsions in which electrostatic heteroaggregation of oppositely charged fumed silica and alumina particles is exploited. The ability of weakly charged heteroaggregates to adsorb to the oil-water interface favors the formation of highly stable emulsions. A control over the microstructure and rheology of the Pickering emulsion is demonstrated by tuning parameters such as composition, pH, and total concentration of particles. The Pickering emulsions formed under optimal conditions are found to be gel-like and are excellent templates for the fabrication of porous ceramics. Furthermore, the porous mullite ceramic structure which has exceptional thermal and chemical resistance under harsh environments is obtained by drying and sintering of the emulsion template. The phase evolution, microstructure, and porosity of the resulting ceramic are characterized.

Interfacial Assembly and Jamming of Polyelectrolyte Surfactants: A Simple Route To Print Liquids in Low-Viscosity Solution

Nanoparticle surfactants (NPSs) assembled at the oil-water interface can significantly lower the interfacial tension and be used to structure liquids. However, to realize the three-dimensional printing of one liquid in another, high-viscosity liquids, for example, silicone oil, have been generally used. Here, we present a simple, low-cost approach to print water in low-viscosity toluene by using a new type of polyelectrolyte surfactant, sodium carboxymethyl cellulose surfactant (CMCS), that forms and assembles at the oil-water interface. The interfacial activity of CMCSs can be enhanced by tuning parameters, such as pH and concentration, and the incorporation of a rigid ligand affords excellent mechanical strength to the resultant assemblies. With CMCS jammed at the interface, liquids can be easily printed or molded to the desired shapes, with biocompatible walls that can be used to encapsulate and adsorb active materials. This study opens a new pathway to generate complex, all-liquid devices with a myriad of potential applications in biology, catalysis, and chemical separation.

Fabrication of ultrathin nanocellulose shells on tough microparticles via an emulsion-templated colloidal assembly: towards versatile carrier materials

Here, we develop a robust approach to forming an ∼8 nm thick cellulose nanofiber (CNF) shell on polymer microparticles through an emulsion-templated assembly. The median diameter of the CNF-shelled microparticles was 3.0 μm. The microparticles showed good dispersibility in water with a ζ-potential of -46.7 ± 0.5 mV and had good mechanical resistance. The surface CNF shells showed pH-sensitive drug loading/releasing properties, which suggest potential for a range of therapeutic and biomedical applications.

Interfacial Activity of Amine-Functionalized Polyhedral Oligomeric Silsesquioxanes (POSS): A Simple Strategy To Structure Liquids

Amine-functionalized polyhedral oligomeric silsesquioxane (POSS), the smallest, monodisperse cage-shaped silica cubic nanoparticle, is exceptionally interfacially active and can form assemblies that jam the toluene/water interface, locking in non-equilibrium shapes of one liquid phase in another. The packing density of the amine-functionalized POSS assembly at the water/toluene interface can be tuned by varying the concentration, the pH value, and the degree of POSS functionalization. Functionalized POSS gives a higher interface coverage, and hence a lower interfacial tension, than nanoparticle surfactants formed by interactions between functionalized nanoparticles and polymeric ligands. Hydrogen-bonded POSS surfactants are more stable at the interface, offering some unique advantages for generating Pickering emulsions over typical micron-sized colloidal particles and ligand-stabilized nanoparticle surfactants.

Microgels Adsorbed at Liquid-Liquid Interfaces: A Joint Numerical and Experimental Study

Soft particles display highly versatile properties with respect to hard colloids and even more so at fluid-fluid interfaces. In particular, microgels, consisting of a cross-linked polymer network, are able to deform and flatten upon adsorption at the interface due to the balance between surface tension and internal elasticity. Despite the existence of experimental results, a detailed theoretical understanding of this phenomenon is still lacking due to the absence of appropriate microscopic models. In this work, we propose an advanced modeling of microgels at a flat water/oil interface. The model builds on a realistic description of the internal polymeric architecture and single-particle properties of the microgel and is able to reproduce its experimentally observed shape at the interface. Complementing molecular dynamics simulations with in situ cryo-electron microscopy experiments and atomic force microscopy imaging after Langmuir-Blodgett deposition, we compare the morphology of the microgels for different values of the cross-linking ratios. Our model allows for a systematic microscopic investigation of soft particles at fluid interfaces, which is essential to develop predictive power for the use of microgels in a broad range of applications, including the stabilization of smart emulsions and the versatile patterning of surfaces.

Symmetry-Breaking Synthesis of Multicomponent Nanoparticles

Multicomponent nanoparticles (MCNs) composed of disparate inorganic colloidal components have attracted great attention from researchers in both the academic and industrial community, because of their unique properties and diverse applications in energy conversion and storage; heterogeneous catalysis; optics and electronics; and biomedical imaging, diagnosis, and therapy. Compared with single-component nanoparticles (NPs), new or advanced properties of MCNs arise from the synergistic effect between their constituent components and the presence of nanoscale interfaces between distinct materials within the particles. Consequently, the spatial arrangement of nanoscale domains of MCNs becomes equally important in property or function control of MCNs as their size, shape, and composition, if not more. In particular, compositionally asymmetric MCNs may outperform their symmetric counterparts in many of their applications. To this end, the seed-mediated growth (SMG) method, which involves depositing a second material onto seed NPs, has been considered as the most common strategy for the synthesis of asymmetric MCNs with desired complexity. In this approach, the control of symmetry breaking during MCN growth is usually achieved by manipulating the growth kinetics or using seed NPs with asymmetric shapes or surfaces. Although great progress has been made in the past decade, there remains a challenge to control the shape, orientation and organization of colloidal components of MCNs with a high yield and reproducibility. Recently, several unconventional methods have been developed as an important addition to the synthetic toolbox for the production of complex MCNs that otherwise may not be readily attainable. This Account summarizes recent advancements on the development of unconventional synthetic strategies for breaking the growth symmetry in the synthesis of asymmetric MCNs. We start with a brief discussion of the achievements and limitations of the conventional strategies for symmetry breaking synthesis. In the subsequent section, we present three unconventional approaches toward symmetry-breaking synthesis of asymmetric MCNs, namely, surface-protected growth, interface-guided growth, and welding-induced synthesis. First, we discuss how commonly used soft agents (e.g., collapsed polymer) and hard agents (e.g., silica) can be asymmetrically coated on seed NPs to template the asymmetric growth of secondary material, generating a broad range of MCNs with complex architectures. The unique features and key factors of this surface-protected synthesis are discussed from the viewpoints of the surface chemistry of seed NPs. We further discuss the use of a solid/liquid or liquid/liquid interface to guide the synthesis of Janus or more complex MCNs through two general mechanisms; that is, selective blocking or impeding the access of precursors to one side of seed NPs and interfacial reaction-enabled generation of asymmetric seeds for further growth. Finally, we discuss a symmetry-breaking method beyond the SMG mechanism, directed welding of as-synthesized single-component NPs. Moreover, we discuss how the unique structural symmetry and compositional arrangement of these MCNs significantly alter the physical and chemical properties of MCNs, thus facilitating their performance in exemplary applications of photocatalysis and electrocatalysis. We finally conclude this Account with a summary of recent progress and our future perspective on the future challenges.

Time-dependent FTIR microscopy for mechanism investigations and kinetic measurements in interfacial polymerisation: a microporous polymer film study

The real-time characterisation of interfacial polymerization is demonstrated by using FTIR-mapping spectroscopy with microscopy to deduce the reaction kinetics.

Polymeric raspberry-like particles via template-assisted polymerisation

Functional monodisperse raspberry-like colloids are fabricated via template-assisted polymerisation, leading to optical materials with high dispersion stability in an aqueous environment.

Nanoparticle Assembly at Liquid-Liquid Interfaces: From the Nanoscale to Mesoscale

In the past few decades, novel syntheses of a wide range of nanoparticles (NPs) with well-defined chemical composition and structure have opened tremendous opportunities in areas ranging from optical and electronic devices to biomedical markers. Controlling the assembly of such well-defined NPs is important to effectively harness their unique properties. The assembly of NPs at liquid-liquid interfaces is becoming a central topic both in surface and colloid science. Hierarchical structures, including 2D films, 3D capsules, and structured liquids, have been generating significant interest and are showing promise for physical, chemical, and biological applications. Here, a brief overview of the development of the self-assembly of NPs at liquid-liquid interfaces is provided, from theory to experiment, from synthetic NPs to bio-nanoparticles, from water-oil to water-water, and from "liquid-like" to "solid-like" assemblies.

Rapid fabrication of flexible and transparent gold nanorods/poly (methyl methacrylate) membrane substrate for SERS nanosensor application

Flexible substrates have been proposed for daily-life applications in SERS detection due to the prominent sample collection properties such as they can be wrapped around non-planar object surface. Combining the noble metals with polymers, flexible SERS substrates could be fabricated with advantages of light weight, transparency and high SERS sensitivity. Herein, we prepare a gold nanorods (AuNRs)/poly(methyl methacrylate) (PMMA) film as flexible SERS substrate by self-assembling a uniformly AuNRs array layer on PMMA template. This AuNRs/PMMA film performs excellently on thiram trace detection with the lowest detection concentration of 0.5 ppb. The fabricated substrates were applied for practical detection with cucumber by directly covering the AuNRs/PMMA flexible film on the target surface. Furthermore, the high SERS sensitivity as well as great reproducibility present a wide range of prospections for the further application of non-plane surface.

Sandwich-interface inspired strategy for controlled formation of nanoparticles

Nanoparticles are functional materials able to offer improved or new synergetic properties. By manipulating the interfacial properties, we demonstrate an innovative sandwich-interface method capable of forming various monodispersed nanostructures including metals, semiconductors, and inorganic and coordinated nanoparticles. By analysing of the reaction mechanism, we show that reaction time, the height of transition and presence of surfactant have the greatest influence on the formation of the products. These advances in the sandwich-interface synthesis significantly extend the scope of interface synthetic methods, facilitating a new level of structural-architectural control which may lead to future developments in the field of crystallography.

Insights in the Diffusion Controlled Interfacial Flow Synthesis of Au Nanostructures in a Microfluidic System

Continuous segmented flow interfacial synthesis of Au nanostructures is demonstrated in a microchannel reactor. This study brings new insights into the growth of nanostructures at continuous interfaces. The size as well as the shape of the nanostructures showed significant dependence on the reactant concentrations, reaction time, temperature, and surface tension, which actually controlled the interfacial mass transfer. The microchannel reactor assisted in achieving a high interfacial area, as well as uniformity in mass transfer effects. Hexagonal nanostructures were seen to be formed in synthesis times as short as 10 min. The wettability of the channel showed significant effect on the particle size as well as the actual shape. The hydrophobic channel yielded hexagonal structures of relatively smaller size than the hydrophilic microchannel, which yielded sharp hexagonal bipyramidal particles (diagonal distance of 30 nm). The evolution of particle size and shape for the case of hydrophilic microchannel is also shown as a function of the residence time. The interfacial synthesis approach based on a stable segmented flow promoted an excellent control on the reaction extent, reduction in axial dispersion as well as the particle size distribution.

Self-Assembly of Mesoscale Artificial Clathrin Mimics

Fluidic control and sampling in complex environments is an important process in biotechnology, materials synthesis, and microfluidics. An elegant solution to this problem has evolved in nature through cellular endocytosis, where the dynamic recruitment, self-assembly, and spherical budding of clathrin proteins allows cells to sample their external environment. Yet despite the importance and utility of endocytosis, artificial systems which can replicate this dynamic behavior have not been developed. Guided by clathrin's unusual structure, we created simplified metallic microparticles that capture the three-legged shape, particle curvature, and interfacial attachment characteristics of clathrin. These artificial clathrin mimics successfully recreate biomimetic analogues of clathrin's recruitment, assembly, and budding, ultimately forming extended networks at fluid interfaces and invaginating immiscible phases into spheres under external fields. Particle curvature was discovered to be a critical structural motif, greatly limiting irreversible aggregation and inducing the legs' selective tip-to-tip attraction. This architecture provides a template for a class of active self-assembly units to drive structural and dimensional transformations of liquid-liquid interfaces and microscale fluidic sampling.

Highly Transparent w/o Pickering Emulsions without Adjusting the Refractive Index of the Stabilizing Particles

Pickering emulsions with a remarkable transmittance of up to 86% across the visible spectrum have been prepared without adjusting the refractive index (RI) of the stabilizing particles to those of the aqueous and oil phases. Commercially available hydrophilic silica particles with a diameter of 20 nm, which are hydrophobized partially in situ, were used to stabilize water droplets with diameters below 400 nm in IsoparM. In this system, the stabilizing particles and the emulsion droplets act as one single scattering object, which renders RI-matching of the particles unnecessary. By either evaporation of some water from the droplets or addition of an appropriate organic liquid to the oil phase, it is possible to match the RI of the droplets (aqueous phase + particles) with that of the continuous phase, which minimizes scattering and results in highly transparent emulsions.

Liquid Tubule Formation and Stabilization Using Cellulose Nanocrystal Surfactants

Structured liquids, generated by the interfacial formation, assembly, and jamming of nanoparticle (NP)-surfactants at liquid/liquid interfaces, maintain all the desirable characteristics of each liquid, while providing a spatially structured framework. Herein, we show that rod-like cellulose nanocrystal (CNC)-based NP-surfactants, termed CNC-surfactants, are formed rapidly at the liquid/liquid interface, assemble into a monolayer, and, when jammed, offer a robust assembly with exceptional mechanical properties. Plateau-Rayleigh (PR) instabilities of a free-falling jet of an aqueous medium containing the CNCs into a toluene solution of amine end-functionalized polystyrene are completely suppressed, allowing the jetting of aqueous tubules that are stabilized when the CNC-surfactants are jammed at the interface. These results open a new platform for the additive manufacturing techniques, for example, three-dimensional (3D) printing, of all-liquid constructs.

Self-Regulated Nanoparticle Assembly at Liquid/Liquid Interfaces: A Route to Adaptive Structuring of Liquids

The controlled structuring of liquids into arbitrary shapes can be achieved in biphasic liquid media using the interfacial assemblies of nanoparticle surfactants (NP-surfactants), that consist of a polar nanoparticle "head group" bound to one or more hydrophobic polymer "tails". The nonequilibrium shapes of the suspended liquid phase can be rendered permanent by the jamming of the NP-surfactants formed and assembled at the interface between the liquids as the system attempts to minimize the interfacial area between the liquids. While critical to the structuring process, little is known of the dynamic mechanical properties of the NP-surfactant monolayer at the interface as it is dictated by the characteristics of the component, including NP size and concentration and the molecular weight and concentration of polymers bound to the NPs. Here we provide the first comprehensive understanding of the dynamic mechanical character of two-dimensional NP-surfactant assemblies at liquid/liquid interfaces. Our results indicate that the dynamics of NP-polymer interactions are self-regulated across multiple time scales and are associated with specific mesoscale interactions between self-similar and cross-complementary components. Furthermore, the mechanical properties of the NP-surfactant monolayer are tunable over a broad range and deterministic on the basis of those component inputs. This control is key to tailoring the functional attributes of the reconfigurable structured liquids to suit specific applications.

A general method for determining molecular interfaces and layers

A general and direct computational scheme to locate the surface separating arbitrarily shaped domains made up of molecules (or any other particles) has been developed and is described and illustrated for several, both artificial and physical examples. The proposed scheme consists of two modules: (i) triangulation and (ii) assignment of simplices to domains. Three different triangulation methods are employed, viz., the Delaunay triangulation, regular triangulation, and quasi-triangulation. In the triangulated system, the assignment step is carried out in two different ways, one based on the characteristic metric of a particular triangulation procedure and the other on the concept of a touching sphere. Some of the combinations of the triangulation and assignment steps lead to methods already used by others to find interfacial or surface molecules, namely the alpha-shape-based method of Usabiaga nad Duque [Phys. Rev. E 79 (2009) 046709] and GITIM of Sega et al. [J. Chem. Phys. 138 (2013) 044110]. The resulting surface is defined not only as a discrete set of particles, but it is build up of facets of the triangulation forming a broken line in two dimensions or a polyhedral surface in three dimensions. Individual molecular layers are identified in a very straightforward manner, starting with the interfacial layer itself and proceeding into the interior of the phase. The proposed scheme is illustrated first by identifying border molecules of pre-sampled domains of several shapes in a plane and then applied to five physically meaningful examples: thin films, near critical water, liquid water slab in an electric field, liquid water at a solid wall, and water at condition of electric-field-induced jetting. Performance of the considered methods is critically assessed. Treatment of domains forming percolating clusters through periodic boundary conditions is also described along with the determination of their periodicity and dimensionality.

Dynamic Self-Assembly of Homogenous Microcyclic Structures Controlled by a Silver-Coated Nanopore

The self-assembly of nanoparticles is a challenging process for organizing precise structures with complicated and ingenious structures. In the past decades, a simple, high-efficiency, and reproducible self-assembly method from nanoscale to microscale has been pursued because of the promising and extensive application prospects in bioanalysis, catalysis, photonics, and energy storage. However, microscale self-assembly still faces big challenges including improving the stability and homogeneity as well as pursuing new assembly methods and templates for the uniform self-assembly. To address these obstacles, here, a novel silver-coated nanopore is developed which serves as a template for electrochemically generating microcyclic structures of gold nanoparticles at micrometers with highly homogenous size and remarkable reproducibility. Nanopore-induced microcyclic structures are further applied to visualize the diffusion profile of ionic flux. Based on this novel strategy, a nanopore could potentially facilitate the delivery of assembled structures for many practical applications including drug delivery, cellular detection, catalysis, and plasmonic sensing.

Submicron Colloidosomes of Tunable Size and Wall Thickness

We present a simple method for the fabrication of colloidal capsules of different sizes ranging from below 100 nm up to one micron. The capsules are produced by self-assembling 5 nm gold nanoparticles at the interface of oil-in-water emulsion droplets. The size of the capsules is regulated by tuning the wetting properties of the nanoparticles by changing either the composition of their ligand shell or the composition of the oil phase. The modified wettability affects not only the size but also the thickness of capsule walls. The wall can be thin if it is made of a single layer of the nanoparticles or thick when composed of multilayers. The durability of such capsules is quite high, although it can be improved by chemical cross-linking with UV light. Such capsules have low permeability, so they can store a molecular cargo and then release it on demand.

Anisotropic Self-Assembly of Supramolecular Polymers and Plasmonic Nanoparticles at the Liquid-Liquid Interface

The study of supramolecular polymers in the bulk, in diluted solution, and at the solid-liquid interface has recently become a major topic of interest, going from fundamental aspects to applications in materials science. However, examples of supramolecular polymers at the liquid-liquid interface are mostly unexplored. Here, we describe the supramolecular polymerization of triarylamine molecules and their light-triggered organization at a chloroform-water interface. The resulting interfacial nematic layer of these 1D supramolecular polymers is further used as a template for the precise alignment of spherical gold nanoparticles coming from the water phase. These hybrid thin films are spontaneously formed in a single process, without chemical prefunctionalization of the metallic nanoparticles, and their ordering is improved by centrifugation. The resulting polymer chains and strings of nanoparticles can be co-aligned with high anisotropy over very large distances. By using a combination of experimental and theoretical investigations, we decipher the full sequence of this oriented self-assembly process. In such a highly anisotropic configuration, electron energy loss spectroscopy reveals that the self-assembled nanoparticles behave as plasmonic waveguides.