Janus Nanosheets Research Articles

Mussel-Inspired Two-Dimensional Freestanding Alkyl-Polydopamine Janus Nanosheets.

Mussel-inspired two-dimensional freestanding, alkyl-polydopamine (alkyl-PDA) Janus nanosheets, with a well-controlled nanometer thickness and a lateral size of up to micrometers, have been developed. A self-assembled octadecylamine (ODA) bilayer is used as the reactive template for the dopamine polymerization, resulting in the formation of well-defined nanosheets. The alkyl-PDA nanosheets show an amphiphilic nature with hydrophilic PDA and hydrophobic alkyl chains on opposing sides. The nanosheets can be used to functionalize many substrates and is dependent on the configuration of surface of the nanosheets. The nanosheets are quite stable, as the morphology is preserved after carbonization at 900 °C. Post-modification of the nanosheets can be easily achieved because of the reactive nature of PDA. This work will provide a new strategic approach for fabricating polymeric Janus nanosheets, which can find applications for surface modifications, catalyst supports, and guided self-assembly.

Janus Nanosheets Synchronously Strengthen and Toughen Polymer Blends

Strength is usually compromised with toughness of polymer blends. We report a new way to synchronously strengthen and toughen a typical blend of epoxy resin/nitrile-butadiene rubber (EP/LNBR) with ...

Preparation of Janus nanosheets via reusable cross-linked polymer microspheres template

Janus nanosheets have great potential applications in diverse fields to provide improved performance over conventional homogenous nanoparticles. A novel strategy to prepare Janus nanosheets by surface adsorption and the sol–gel process of trialkoxy silanes onto the reusable cross-linked polymer microspheres template is presented in this paper. Polymer microspheres were synthesized by inverse suspension polymerization, and the matched silanes were screened by molecular simulations. After adsorption and sol–gel of silanes onto microspheres surface, the microspheres were covered with silica-based membranes. The silica-based membranes were further selective modified and exfoliated from the microspheres surface to obtain Janus nanosheets. Microspheres could be easily recycled and reused. Two kinds of silica-based Janus nanosheets of carboxyl/alkyl composite and amide/alkyl composite were successfully prepared by the above approach. The synthesized nanosheets exhibited sheet-like morphology, Janus nature, interfacial activity and excellent ability to stabilize emulsions. This study provides a scalable method for the controllable synthesis of Janus nanosheets, which may provide a new avenue for their fundamental studies and practical applications.

Aggregation Kinetics and Colloidal Stability of Amphiphilic Janus Nanosheets in Aqueous Solution

Although amphiphilic Janus nanosheets have great potential applications in diverse fields to provide improved performance over conventional homogeneous nanoparticles, its aggregation characteristics are still mostly uncovered. Anisotropic shape and chemistry should play a critical role in the interactions between two colloidal particles. Hence, the amphiphilic Janus nanosheets are expected to have unique aggregation behavior different from homogeneous nanoparticles. In this paper, a representative silica-based amphiphilic Janus nanosheets was synthesized, and the influences of temperature, pH, ionic strength, ion valence on their aggregation and stability were probed by batch static multiple light scattering, zeta potential, and electrophoretic mobility measurements. Particularly, the interactions energy between two adjacent amphiphilic Janus nanosheets were calculated based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The aggregation kinetics and colloidal stability of amphiphilic Janus nanoshe...

Magnetic-Responsive Janus Nanosheets with Catalytic Properties.

In this article, we describe a method to fabricate magnetic-responsive Janus nanosheets with catalytic properties via the surface protection method. Fe3O4 nanoparticles and PW12O403--based ionic liquid are located on the two opposite sides of the Janus nanosheets, respectively. The Janus nanosheets are characterized by Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and ζ-potential analyses. They are used as recyclable catalysts to the esterification reaction of methanol and oleic acid for their magnetic-responsive and catalytic properties. The esterification ratio is up to 80% and there is nearly no change when Fe3O4 nanoparticles/PW12O403--based ionic liquid composite nanosheets were recycled four times.

Residue-Specific Solvation-Directed Thermodynamic and Kinetic Control over Peptide Self-Assembly with 1D/2D Structure Selection.

Understanding the self-organization and structural transformations of molecular ensembles is important to explore the complexity of biological systems. Here, we illustrate the crucial role of cosolvents and solvation effects in thermodynamic and kinetic control over peptide association into ultrathin Janus nanosheets, elongated nanobelts, and amyloid-like fibrils. We gained further insight into the solvation-directed self-assembly (SDSA) by investigating residue-specific peptide solvation using molecular dynamics modeling. We proposed the preferential solvation of the aromatic and alkyl domains on the peptide backbone and protofibril surface, which results in volume exclusion effects and restricts the peptide association between hydrophobic walls. We explored the SDSA phenomenon in a library of cosolvents (protic and aprotic), where less polar cosolvents were found to exert a stronger influence on the energetic balance at play during peptide propagation. By tailoring cosolvent polarity, we were able to achieve precise control of the peptide nanostructures with 1D/2D shape selection. We also illustrated the complexity of the SDSA system with pathway-dependent peptide aggregation, where two self-assembly states (i.e., thermodynamic equilibrium state and kinetically trapped state) from different sample preparation methods were obtained.

Interactions between amphiphilic Janus nanosheets and a nonionic polymer in aqueous and biphasic systems.

It is of great significance to understand the interactions between nanoparticles and polymers since they guide the development of tremendous applications, for example, in optoelectronic devices, biomedicine, and enhanced oil extraction. However, few studies have probed into this fundamental science as the emerging amphiphilic Janus nanosheets have a more complicated structure than homogeneous nanoparticles, which makes their interactions more complex. In this work, we try to understand the interactions between amphiphilic Janus nanosheets and a model nonionic polymer, hydroxyethyl cellulose (HEC), under different electrolyte and temperature conditions in both aqueous and biphasic systems by employing molecular dynamics simulations as well as experiments. It is found that the attachment of HEC onto the nanosheet surfaces exhibits ion-concentration-dependent behavior in the aqueous phase, helping to colloidally stabilize the nanosheets even in an environment with an extremely high salt concentration for a long duration. In the oil and water biphasic system, only elevated temperature promotes both Janus nanosheets and HEC to individually remain at the interface.

Electrostatic-attraction-induced high internal phase emulsion for large-scale synthesis of amphiphilic Janus nanosheets.

We report a novel and scalable method to obtain amphiphilic Janus nanosheets in large quantities. By inducing electrostatic attraction using alkylamine with further tuned particle interactions, a highly stable water-in-oil high internal phase emulsion was generated while simultaneously performing single-side graphene oxide hydrophobization at the fluid interface.

Amphiphilic Janus nanosheets by grafting reactive rubber brushes for reinforced rubber materials

An amphiphilic Janus nanosheet with different reactive rubber brushes on two opposite sides can simultaneously strengthen and toughen rubber blends.

Physicochemical properties and potential applications of silica-based amphiphilic Janus nanosheets for enhanced oil recovery

Nanofluid flooding has recently garnered significant attention as a novel enhanced oil recovery (EOR) technology; however, there are limitations to the current simple nanofluid flooding. Compared with the commonly used homogeneous spherical nanoparticles, amphiphilic Janus nanosheets have a higher interfacial activity and greater application potential for EOR. In this paper, a carboxyl/alkyl composite silica-based amphiphilic Janus nanosheets (CSAJN) were prepared by a bottom-up synthesis strategy, and the physicochemical properties and EOR potential were systematically investigated. The results showed that the CSAJN displayed a distinct ultrathin flake-like morphology and a lateral size in the range of hundreds of nanometres. More specifically, the CSAJN had two different sides, one side containing a carboxyl group that was hydrophilic, and the other side containing an alkyl group that was hydrophobic. Because of the amphiphilic and Janus nature, the CSAJN could be dispersed in different polar solvents, reduce the oil-water interfacial tension and enhance the oil-water interfacial film strength. Core displacement experiments showed that the CSAJN nanofluid could significantly increase the efficiency of oil recovery to ∼18.31% even at an ultralow concentration of 0.005 wt% and cause minimal impairment to the permeability. By observing and analysing the interfacial behaviour of CSAJN in a toluene/brine system, it was found that the formation of a climbing film and high-strength elastic oil-water interfacial film by CSAJN may play an important role in EOR mechanism. This work reveals the physicochemical properties of silica-based amphiphilic Janus nanosheets and provides a novel efficient nanofluid system for EOR.

2D Particles at Fluid-Fluid Interfaces: Assembly and Templating of Hybrid Structures for Advanced Applications.

Fluid-fluid interfaces have widespread applications in personal care products, the food industry, oil recovery, mineral processes, etc. and are also important and versatile platforms for generating advanced materials. In Pickering emulsions, particles stabilize the fluid-fluid interface, and their presence reduces the interfacial energy between the two fluids. To date, most Pickering emulsions stabilized by 2D particles make use of clay platelets or GO nanosheets. These systems have been used to template higher order hybrid, functional materials, most commonly, armored polymer particles, capsules, and Janus nanosheets. This review discusses the experimental and computational study of the assembly of sheet-like 2D particles at fluid-fluid interfaces, with an emphasis on the impact of chemical composition, and the use of these assemblies to prepare composite structures of dissimilar materials. The review culminates in a perspective on the future of Pickering emulsions using 2D particle surfactants, including new chemical modification and types of particles as well as the realization of properties and applications not possible with currently accessible systems, such as lubricants, porous structures, delivery, coatings, etc.

Enthalpy-Enhanced Janus Nanosheets for Trapping Nonequilibrium Morphology of Immiscible Polymer Blends

Janus particles are promising for self-assembly at the liquid/liquid interface due to coexistence of the Pickering effect and the different wettability of both sides. In this study, we synthesize a Janus nanosheet and evaluate its ability to trap nonequilibrium morphology by interfacial self-assembly. The Janus nanosheet was synthesized by selectively grafting polymer chains, polystyrene (PS) or polyisoprene (PI), on each side of a silica nanosheet. The selective grafting method endow the nanosheet with two different wettabilities, which make it ideal for self-assembly and further jamming at the PS/PI interface. The interfacial jamming of the nanosheet trapped the intermediate, nonequilibrium morphology during phase separation of the polymer blends. Compared to other Janus materials, the Janus nanosheet has higher interfacial activity and reduces the free energy of the system more effectively due to its 2D structure. Only 2 wt % of Janus nanosheet is required to break the threshold and reach the jammed st...

Poly(sodium 4-styrenesulfonate) Stabilized Janus Nanosheets in Brine with Retained Amphiphilicity.

Maintaining colloidal stability in unfriendly environments while retaining surface chemical properties is challenging for fundamental science and crucial for many applications. Here, we report for the first time that by using a low concentration of poly(sodium 4-styrenesulfonate) (PSS), graphene-based amphiphilic Janus nanosheets (AJNs) can be stabilized in high salt brine (3 wt % NaCl and 0.5 wt % CaCl2), whereas the interfacial behavior of the nanosheets is not affected. The adsorption of PSS on the hydrophilic and hydrophobic surfaces of AJNs in brine was investigated experimentally and by molecular dynamics simulations. Simulations further showed that the spatial configuration of absorbed PSS molecules with sulfonate functional groups facing outward favored the generation of electrosteric repulsive interactions. Calculations of the interaction energy between PSS molecules and the nanosheet revealed surface charge as a key parameter to stabilize AJNs in the salt environment, as demonstrated by the case of graphene oxide with higher surface charge. Simulations were also used to examine the interfacial behavior of graphene-based AJNs in biphasic systems. The AJNs, which exhibited asymmetry in surface wettability, remained at the oil/brine interface because of PSS detachment from the hydrophobic surface. The results were subsequently experimentally confirmed, consistent with our previously reported graphene-based AJN fluid prepared in fresh water. The process was thermodynamically supported by the demonstrated negative change of Gibbs free energy. We believe that such a strategy could benefit for the stabilization of other AJNs with surface chemical accessibility under harsh conditions.

Inorganic Janus nanosheets bearing two types of covalently bound organophosphonate groups via regioselective surface modification of K4Nb6O17·3H2O.

Janus nanosheets were prepared from K4Nb6O17·3H2O by modifying surfaces of their two distinct interlayers in a regioselective and sequential manner and subsequent exfoliation. The surface properties of nanosheets were investigated by phase atomic force microscopy imaging and two types of surfaces were discriminated, indicating that Janus nanosheets were successfully prepared.

Polymeric Janus Nanosheets by Template RAFT Polymerization

We report a general method to synthesize polymeric Janus nanosheets (PJS) by sequential RAFT grafting from a template particle surface. Layer number and composition of the PJS are tunable by feeding sequence and type of monomers. The cPNIPAM–PS PJS is flexible and thermal responsive, which can form a scrolled superstructure. A dually responsive cPAA–PNIPAM PJS is derived by hydrolysis of cPtBA–PNIPAM. Accordingly, stability of the emulsion with the cPAA–PNIPAM PJS is triggered by alternation of pH or/and temperature.

Synthesis of graphene-based amphiphilic Janus nanosheets via manipulation of hydrogen bonding

The economical synthesis of amphiphilic Janus nanosheets in large amounts for practical applications is a grand challenge. This work reports a facile and scalable method to prepare graphene-based amphiphilic Janus nanosheets with much higher efficiency than the previously-reported wax template masking method. Graphene oxide (GO) was immobilized by hydrogen bonding on the surfaces of starch microspheres, confirmed by both experiments and Molecular Dynamics simulations. After selective functionalization of the exposed surface with alkylamine, amphiphilic Janus nanosheets (AJN) were obtained by releasing the nanosheets from the starch microspheres via breaking the hydrogen bonding. The interfacial behavior of AJN shows its amphiphilicity and the asymmetrical surface wettability indicated from the difference of contact angles, further demonstrated its Janus nature. In addition, avoiding of dissolving the template materials in comparison with wax masking method was also benefit for environment and recycling.

Secondary Oil Recovery Using Graphene-Based Amphiphilic Janus Nanosheet Fluid at an Ultralow Concentration

Nanofluid of graphene-based amphiphilic Janus nanosheets produced high-efficiency tertiary oil recovery at a very low concentration (0.01 wt %). The more attractive way is to use nanofluid during the secondary oil recovery stage, which can eliminate the tertiary stage and save huge amounts of water, especially at times when the price of oil is low. Here, we continue to report our findings on the application of the same nanosheets in secondary oil recovery, which increased oil recovery efficiency by ≤7.5% at an ultralow concentration (0.005 wt %). Compared with nanofluids of homogeneous nanoparticles, our nanofluid achieved a higher efficiency at a much lower concentration. The nanosize dimension of this two-dimensional carbon material improves transport in rock pores. After single-side surface hydrophobization of oxidized graphene with alkylamine, the partial restoration of the graphitic sp2 network was detected by Raman, ultraviolet–visible, etc. The amphiphilic Janus nature of nanosheets led to their un...

Self-Assembled 2D Free-Standing Janus Nanosheets with Single-Layer Thickness.

We report the thermodynamically controlled growth of solution-processable and free-standing nanosheets via peptide assembly in two dimensions. By taking advantage of self-sorting between peptide β-strands and hydrocarbon chains, we have demonstrated the formation of Janus 2D structures with single-layer thickness, which enable a predetermined surface heterofunctionalization. A controlled 2D-to-1D morphological transition was achieved by subtly adjusting the intermolecular forces. These nanosheets provide an ideal substrate for the engineering of guest components (e.g., proteins and nanoparticles), where enhanced enzyme activity was observed. We anticipate that sequence-specific programmed peptides will offer promise as design elements for 2D assemblies with face-selective functionalization.

Phosphomolybdic acid-responsive Pickering emulsions stabilized by ionic liquid functionalized Janus nanosheets

A type of ionic liquid functionalized high-aspect-ratio Janus SiO2 nanosheets (IL-Janus nanosheets), which possesses a side terminated by imidazolin salt groups and the opposite side terminated by phenyl groups, was prepared and its emulsification performance was investigated. The surface wettability of ionic liquid functionalized side could be tailored via simple anion exchanging, giving the amphiphilic or totally hydrophobic Janus nanosheets. The influence of several parameters including surface wettability, particle concentration, oil composition, oil-water ratio as well as initial location of the nanosheets on the stability, morphology and type of the Pickering emulsions (O/W or W/O) stabilized by the amphiphilic IL-Janus nanosheets was evaluated. The research results revealed that average emulsion droplets size was decreased with increase of nanosheets concentration below a concentration value but had almost no change beyond the concentration; catastrophic phase inversion phenomenon occurred by varying volume fraction of water phase in the oil-water systems, and transitional phase inversion could be achieved by in-situ exchanging Cl− anion of the IL-Janus nanosheets with phosphomolybdate H2PMo12O40−. The responsiveness of Pickering emulsions towards phosphomolybdic acid is resulted from irreversible anion exchanging of Cl− by H2PMo12O40− and the variation of surface wettability of the nanosheets.

Distinct Chemical and Physical Properties of Janus Nanosheets.

Janus particles have recently garnered significant attention for their distinct properties compared to particles that are homogeneously functionalized. Moreover, high aspect ratio Janus particles that are rod-like or planar (i.e., nanosheets) are especially intriguing considering their interfacial properties as well as their ability to assemble into higher order and hybrid structures. To date, major challenges facing the exploration and utilization of 2D Janus particles are scalability of synthesis, characterization of tailored chemical functionalization, and ability to introduce a diverse set of functionalities. Herein, a facile method to access Janus 2D graphene oxide (GO) nanosheets by combining a Pickering-type emulsion and grafting-from polymerization via ATRP is reported. Janus GO nanosheets bearing PMMA on one face as well as the symmetrically functionalized analogue are prepared, and the chemical, thermal, structural, surface, and interfacial properties of these materials are characterized. Time-of-flight secondary ion mass spectrometry coupled with Langmuir-Blodgett films is shown to be an ideal route to conclusively establish asymmetric functionalization of 2D materials. This work not only provides a facile route for the preparation of Janus nanosheets but also demonstrates the direct visualization of polymer grown from the surface of GO.