A versatile colloidal Janus platform: surface asymmetry control, functionalization, and applications

Functionalization of Emulsion Interfaces: Surface Chemistry Made Liquid

Disperse systems, and emulsions in particular, are currently massively used in fields as varied as food industry, cosmetics, health care and environmentally-friendly materials. To meet increasingly precise needs or targeted applications, these systems need to be endowed with new functionalities at their interfaces, in addition to their composition and structural properties. However, due to the fragility of drops and the low reactivity of their surface, conventional solid surface chemistry cannot be used for such a purpose. Several specific emulsion interface functionalization techniques have thus been developed for targeted systems and applications, but a general framework has yet to be drawn. In this review, we attempt to present these methods in a unified way through the prism of what we may call "liquid surface chemistry". We propose to categorize existing methods into drop-coating strategies, including layer-by-layer techniques and polymer coating, with a particular focus on polydopamine, and emulsifier-carrier approaches involving particles and/or amphiphilic molecules. They are discussed in a transversal way, highlighting the underlying physico-chemical principles and providing a comparative analysis of their advantages, current limitations and potential for improvement. We also propose future directions and opportunities, involving for instance DNA-based programmability or artificial intelligence, which could make liquid surface chemistry more versatile and controlled.

Modular Attachment of Nanoparticles on Microparticle Supports via Multifunctional Polymers

Nanoparticles are key to a range of applications, due to the properties that emerge as a result of their small size. However, their size also presents challenges to their processing and use, especially in relation to their immobilization on solid supports without losing their favorable functionalities. Here, we present a multifunctional polymer-bridge-based approach to attach a range of presynthesized nanoparticles onto microparticle supports. We demonstrate the attachment of mixtures of different types of metal-oxide nanoparticles, as well as metal-oxide nanoparticles modified with standard wet chemistry approaches. We then show that our method can also create composite films of metal and metal-oxide nanoparticles by exploiting different chemistries simultaneously. We finally apply our approach to the synthesis of designer microswimmers with decoupled mechanisms of steering (magnetic) and propulsion (light) via asymmetric nanoparticle binding, aka Toposelective Nanoparticle Attachment. We envision that this ability to freely mix available nanoparticles to produce composite films will help bridge the fields of catalysis, nanochemistry, and active matter toward new materials and applications.

Task-Specific Janus Materials in Heterogeneous Catalysis

Janus materials are anisotropic nano- and microarchitectures with two different faces consisting of distinguishable or opposite physicochemical properties. In parallel with the discovery of new methods for the fabrication of these materials, decisive progress has been made in their application, for example, in biological science, catalysis, pharmaceuticals, and, more recently, in battery technology. This Minireview systematically covers recent and significant achievements in the application of task-specific Janus nanomaterials as heterogeneous catalysts in various types of chemical reactions, including reduction, oxidative desulfurization and dye degradation, asymmetric catalysis, biomass transformation, cascade reactions, oxidation, transition-metal-catalyzed cross-coupling reactions, electro- and photocatalytic reactions, as well as gas-phase reactions. Finally, an outlook on possible future applications is given.

Preparation of asymmetric particles by controlling the phase separation of seeded emulsion polymerization with ethanol/water mixture

Alcohols are discovered for the first time to tune the morphology of poly(vinyl benzyl chloride)-poly(3-methacryloxypropyltrimethoxysilane) (PVBC-PMPS) composite particles through seeded emulsion polymerization within the alcohol/water mixture. Here, monodispersed linear PVBC particles was synthesized through the dispersion polymerization and employed as the seeds. The as-obtained PVBC-PMPS composite particles could be dramatically tuned from core-shell structures to snowman-like particles, to dumbbell-shaped particles, to inverse snowman-like particles when the ethanol content in reaction mixtures is only adjusted within a narrow range. The morphology of fresh PMPS bulges was observed after removing the linear PVBC seeds with N,N'-dimethyl formamide, and their formation mechanism was studied by monitoring the free radical polymerization and sol-gel process of 3-methacryloxypropyltrimethoxysilane. It has been confirmed that the sol-gel kinetics were the main factor on the particles' morphology. In addition, morphologies of PVBC-PMPS particles were also varied by the MPS feeding amount, types of the co-solvent and pH values of alcohol/water mixtures.

Fabrication of a nanocomposite film decorated with highly dispersive nanoparticles by following an interface-induced strategy

A polymer nanocomposite film decorated with highly dispersive nanoparticles was prepared by a liquid-liquid interface induced self-assembly method based on a breath figure process. The distribution as well as the orientation preference of the Janus particles within the polymer matrix could be dynamically controlled by adjusting the environmental conditions. Antibacterial and photocatalytic functionality was obtained for the nanocomposite films decorated with silver and titanium dioxide nanoparticles, respectively.

Janus bifunctional periodic mesoporous organosilica

Synthesis of a Janus periodic mesoporous organosilica material (JPMO) is presented here. In this strategy, the surface of the hollow silica material was selectively functionalized with two different bridged organic-inorganic hybrid groups. It was found that the resulting bifunctional material is able to form a stable Pickering emulsion. This new type of PMO material may be suitable for widespread applications in various fields related to material science and catalysis.

Construction multifunctional nanozyme for synergistic catalytic therapy and phototherapy based on controllable performance

Advances in nanozyme involve an efficient catalytic process, which has demonstrated great potential in tumor therapy. The key to improving catalytic therapy is to solve the limitation of the tumor microenvironment on Fenton reaction. In this work, Prussian blue nanoparticles doped with different rare earth ions (Yb³⁺, Gd³⁺, Tm³⁺) were screened to perform synergistic of photothermalandcatalytictumortherapy. The optimized catalytic performance can be further enhanced through photothermal effect to maximize the Fenton reaction to solve the limitation of the tumor microenvironment. Yb-PB, with the optimal photothermal and catalytic performance, was screened out. In order to avoid the scavenging effect of glutathione (GSH) on ·OH in tumor cells and the reaction with a bit H₂O₂ in normal cells, GSH targeted polydopamine (PDA) was wrapped on the surface of Yb-PB to obtain Yb-PB@PDA. It was found that enough hydroxyl radicals (·OH) can be generated even if at high GSH concentration and the NIR irradiation can help produce more ·OH. Cell fluorescence imaging (FOI) and in vivo magnetic resonance imaging (MRI) experiments showed the potential application in FOI/MRI dual-mode imaging guided therapy. In vivo anti-tumor experiments showed that Yb-PB@PDA has a satisfactory anti-cancer effect through the combined effect of catalytic/photothermal therapy. Thus, a multifunctional nanozyme for tumor therapy is constructed.

Optically Active Janus Particles Constructed by Chiral Helical Polymers through Emulsion Polymerization Combined with Solvent Evaporation-Induced Phase Separation

Polymer Janus particles (PJPs) have been extensively investigated due to their intriguing features which cannot be achieved in traditional counterparts. Chiral polymer particles also have constituted a unique research area in polymer science. However, how to construct PJPs derived from chiral polymers, especially chiral helical polymers, still remains a significant academic challenge. This contribution reports the first success in preparing optically active PJPs constructed by chiral helical substituted polyacetylene via emulsion polymerization combined with solvent evaporation to induce phase separation. In emulsion polymerization systems, polymethyl methacrylate worked as a template and separated from polyacetylene domains in the course of acetylenic monomers' polymerization and evaporation of the solvent, by which optically active PJPs were formed. The major influencing factors were explored to elucidate their effects on the formation and morphology of PJPs. Mushroom- and bowl-like PJPs were obtained. Scanning electron microscopy (SEM) images ascertain nonspherical morphologies of the obtained PJPs. Circular dichroism and UV-vis absorption spectra demonstrate their optical activity, which originated in the predominantly one-handed helical polyacetylene chains constructing the PJPs. A formation mechanism was then proposed for understanding this unprecedented type of PJPs.

Structural characterization of Janus nanoparticles with tunable geometric and chemical asymmetries by small-angle scattering

Recent advances in polymer chemistry allow a facile, large-scale synthesis of nanoscale Janus particles (JP) with tunable structural and physical properties. Both the structures and distributions of regions with different chemical compositions within JP play an important role in chemical and optical sensing, or in bio-medical applications, such as drug delivery. The structural properties of symmetric JP can be accurately characterized by small-angle scattering (SAS), yet the structure of JP with tunable geometrical and chemical asymmetries (AJP) can be described only qualitatively (e.g., globular, elongated or planar), depending on the value of the scattering exponent in the Porod region of SAS intensity. Here it is shown that identification of AJP and a quantitative description of their morphology can be achieved by using the method of SAS together with contrast variation. This approach is illustrated by providing analytic expressions for SAS intensities and for contrast matching points for two kinds of common multiphase AJP: spheres with one cap and those with two caps. The influence of the model's parameters is presented and discussed, and the structural evolution of AJP upon solvent deuteration is characterized. The results suggest that the combination of the SAS technique with multiphase modeling provides unprecedented detailed information about the structural conformation of AJP, which allows their identification from experimental SAS data. Monte Carlo simulations are performed both to validate the obtained results and to illustrate the above findings for complex AJP for which analytic expressions are not available.

Synthesis of sandwich-structured silver@polydopamine@silver shells with enhanced antibacterial activities

The unique antibacterial characteristics of Ag nanomaterials offer a wide potential range of applications, but achieving rapid and durable antibacterial efficacy is challenging. This is because the speed and durability of the antibacterial function make conflicting demands on the structural design: the former requires the direct exposure of Ag to the surrounding environment, whereas the durability requires Ag to be protected from the environment. To overcome this incompatibility, we synthesize sandwich-structured polydopamine shells decorated both internally and externally with Ag nanoparticles, which exhibit prompt and lasting bioactivity in applications. These shells are biocompatible and can be used in vivo to counter bacterial infection caused by methicillin-resistant Staphylococcus aureus superbugs and to inhibit biofilm formation. This work represents a new paradigm for the design of composite materials with enhanced antibacterial properties.