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.

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.

Emulsions are important in numerous fields, including cosmetics, coatings, and biomedical applications. A subset of these structures, oil-in-oil emulsions, are especially intriguing for water sensitive reactions such as polymerizations and catalysis. Widespread use and application of oil-in-oil emulsions is currently limited by the lack of facile and simple methods for preparing suitable surfactants. Herein, we report the ready preparation of oilin-oil emulsions using 2D nanomaterials as surfactants at the interface of polar and nonpolar organic solvents. Both the edges and basal plane of graphene oxide nanosheets were functionalized with primary alkyl amines and we demonstrated that the length of the alkyl chain dictates the continuous phase of the oil-in-oil emulsions (i.e., nonpolar-in-polar or polar-in-nonpolar). The prepared emulsions are stable at least 5 weeks and we demonstrate they can be used to compartmentalize reagents such that reaction occurs only upon physical agitation. The simplicity and scalability of these oil-in-oil emulsions render them ideal for applications impossible with traditional oil-in-water emulsions, and provide a new interfacial area to explore and exploit.

Oil-in-oil emulsions are especially attractive for compartmentalized reactions with water-sensitive monomers which cannot be used with traditional oil/water emulsions.

Poly(lactic acid) (PLA) is a commercially available bio‐based polymer that is a potential alternative to many commodity petrochemical‐based polymers. However, PLA's thermomechanical properties limit its use in many applications. Incorporating polymer‐grafted cellulose nanocrystals (CNCs) is one potential route to improving these mechanical properties. One key challenge in using these polymer‐grafted nanoparticles is to understand which variables associated with polymer grafting are most important for improving composite properties. In this work, poly(ethylene glycol)‐grafted CNCs are used to study the effects of polymer grafting density and molecular weight on the properties of PLA composites. All CNC nanofillers are found to reinforce PLA above the glass transition temperature, but non‐grafted CNCs and CNCs grafted with short PEG chains (<2 kg mol−1) are found to cause significant embrittlement, generally resulting in less than 3% elongation‐at‐break. By grafting higher molecular weight PEG (10 kg mol−1) onto the CNCs at a grafting density where the polymer chains are predicted to be in the semi‐dilute polymer brush conformation (~0.1 chains nm−2), embrittlement can be avoided.