Precise Synthesis of Polymer Particles Spanning from Anisotropic Janus Particles to Heterogeneous Nanoporous Particles

Anisotropic Microparticles with a Controllable Structure via Soap-Free Seeded Emulsion Polymerization

Anisotropic particles have a wide range of applications in materials science such as emulsion stabilization, oil-water separation, and catalysis due to their asymmetric structure and properties. Nevertheless, designing and synthesizing large quantities of anisotropic particles with controlled morphologies continue to present considerable challenges. In this study, we successfully synthesized anisotropic microspheres using a soap-free seed emulsion polymerization method. This approach combines the benefits of seed emulsion polymerization with emulsion interfacial polymerization. By varying the concentrations of dissolved polymeric monomers, 3-methacryloyloxypropyltrimethoxysilane (MPS), and the initiator of potassium persulfate (KPS), different shapes of bowl, cap, and three-sided concave particles were obtained in surfactant-free aqueous solutions, simplifying the post-treatment process. The cap particles are Janus particles with good emulsion stability to toluene/water emulsions over 30 days. The catalytic degradation of 4-nitrophenol (4-NP) was investigated after loading silver nanoparticles on the surface of the particles by in situ deposition. The anisotropic particles obtained in this work have potential applications in emulsion stabilization and catalysis.

Two sides of the coin: synthesis and applications of Janus particles

Named after the two-faced Roman god, Janus particles (JPs) are defined by their distinct dual chemical compositions on a single particle. Research on micron-sized JPs has yielded remarkable insights, showcasing their unique assembly behaviors both in bulk and at interfaces. However, significant challenges persist, particularly in the synthesis of smaller (<500 nm) JPs, which remains complex and difficult to scale up. To date, there has been no commercial success with JPs. Recently, seeded synthesis methods, such as emulsion polymerization that is already employed in industrial-scale manufacturing, have shown great promise. These methods enable the production of high-quality JPs with different sizes, morphologies, and functionalities. This advancement has inspired more efforts in exploring JP applications across various fields, including emulsion stabilization, drug delivery, electronic devices, and coatings. This review provides a comprehensive overview of the recent progress in the synthesis and application of polymeric JPs, with an emphasis on the seeded synthesis approach. It discusses the underlying reaction mechanisms and explores different strategies for controlling JP morphology. Serving as a roadmap, this review aims to guide the design of novel functional JPs and their potential future applications. The successful implementation of JPs will require careful consideration and a deep understanding of both synthesis and applications, as these are indeed two sides of the same coin.

Colloidal bubble propulsion mediated through viscous flows

Bubble-propelled catalytic colloids stand out as a uniquely efficient design for artificial controllable micromachines, but so far lack a general theoretical framework that explains the physics of their propulsion. Here we develop a combined diffusive and hydrodynamic theory of bubble growth near a spherical catalytic colloid, that allows us to explain the underlying mechanism and the influence of environmental and material parameters. We identify two dimensionless groups, related to colloidal activity and the background fluid, that govern a saddle-node bifurcation of the bubble growth dynamics, and calculate the generated flows analytically for both slip and no slip boundary conditions on the bubble. We finish with a discussion of the assumptions and predictions of our model in the context of existing experimental results, and conclude that some of the observed behaviour, notably the ratchet-like gait, may stem from peculiarities of the experimental setup rather than fundamental physics of the propulsive mechanism.

Janus particle-engineered structural lipiodol droplets for arterial embolization

Embolization (utilizing embolic materials to block blood vessels) has been considered one of the most promising strategies for clinical disease treatments. However, the existing embolic materials have poor embolization effectiveness, posing a great challenge to highly efficient embolization. In this study, we construct Janus particle-engineered structural lipiodol droplets by programming the self-assembly of Janus particles at the lipiodol-water interface. As a result, we achieve highly efficient renal embolization in rabbits. The obtained structural lipiodol droplets exhibit excellent mechanical stability and viscoelasticity, enabling them to closely pack together to efficiently embolize the feeding artery. They also feature good viscoelastic deformation capacities and can travel distally to embolize finer vasculatures down to 40 μm. After 14 days post-embolization, the Janus particle-engineered structural lipiodol droplets achieve efficient embolization without evidence of recanalization or non-target embolization, exhibiting embolization effectiveness superior to the clinical lipiodol-based emulsion. Our strategy provides an alternative approach to large-scale fabricate embolic materials for highly efficient embolization and exhibits good potential for clinical applications.

Amphiphilic Bowl-Shaped Janus Particles Prepared via Thiol-Ene Click Reaction for Effective Oil-Water Separation

Janus particles for oil-water separation have attracted widespread attention in recent years. Herein, we prepared a bowl-shaped Janus particle that could rapidly separate oil and water through a thiol-ene click reaction and selective etching. Firstly, snowman-like composite microspheres based on silica and mercaptopropyl polysilsesquioxane (SiO₂@MPSQ) were prepared by a hydrolytic condensation reaction and phase separation, and the effects of the rotational speed and molar ratios on their microscopic morphologies were investigated. Subsequently, bowl-shaped Janus particles with convex hydrophilic and concave oleophilic surfaces were prepared via a thiol-ene click reaction followed by HF etching. Our amphiphilic bowl-shaped Janus particles could remarkably separate micro-sized oil droplets from an n-heptane-water emulsion with a separation efficiency of >98% within 300 s. Based on the experimental and theoretical results, we proposed the underlying mechanism for the coalescence of oil droplets upon the addition of the amphiphilic bowl-shaped Janus particles.

Shedding Light on Luminescent Janus Nanoparticles: From Synthesis to Photoluminescence and Applications

Luminescent Janus nanoparticles refer to a special category of Janus-based nanomaterials that not only exhibit dual-asymmetric surface nature but also attractive optical properties. The introduction of luminescence has endowed conventional Janus nanoparticles with many alluring light-responsive functionalities and broadens their applications in imaging, sensing, nanomotors, photo-based therapy, etc. The past few decades have witnessed significant achievements in this field. This review first summarizes well-established strategies to design and prepare luminescent Janus nanoparticles and then discusses optical properties of luminescent Janus nanoparticles based on downconversion and upconversion photoluminescence mechanisms. Various emerging applications of luminescent Janus nanoparticles are also introduced. Finally, opportunities and future challenges are highlighted with respect to the development of next-generation luminescent Janus nanoparticles with diverse applications.

Self-Propelled Janus Mesoporous Micromotor for Enhanced MicroRNA Capture and Amplified Detection in Complex Biological Samples

The slow mass transport of the target molecule essentially limits the biosensing performance. Here, we report a Janus mesoporous microsphere/Pt-based (meso-MS/Pt) nanostructure with greatly enhanced target transport and accelerated recognition process for microRNA (miRNA) amplified detection in complex biological samples. The mesoporous MS was synthesized via double emulsion interfacial polymerization, and Pt nanoparticles (PtNPs) were deposited on the half-MS surface to construct Janus meso-MS/Pt micromotor. The heterogeneous meso-MS/Pt with a large surface available was attached to an entropy-driven DNA recognition system, termed meso-MS/Pt/DNA, and the tremendous pores network was beneficial to enhanced receptor-target interaction. It enabled moving around complex biological samples to greatly enhance target miRNA mass transport and accelerate recognition procedure due to the self-diffusiophoretic propulsion. Coupling with the entropy-driven signal amplification, extremely sensitive miRNA detection in Dulbecco's modified Eagle medium (DMEM), and cell lysate without preparatory and washing steps was realized. Given the free preparatory and washing steps, fast mass transport, and amplified capability, the meso-MS/Pt/DNA micromotor provides a promising method for miRNAs analysis in real biological samples.

Synthetic Strategies for Polymer Particles with Surface Concavities

Over the past decade or so, there has been increasing interest in the synthesis of polymer particles with surface concavities, which mainly include golf ball-like, dimpled and surface-wrinkled polymer particles. Such syntheses generally can be classified into direct polymerization and post-treatment on preformed polymer particles. This review aims to provide an overview of the synthetic strategies of such particles. Some selected examples are given to present the formation mechanisms of the surface concavities. The applications and future development of these concave polymer particles are also briefly discussed. This article is protected by copyright. All rights reserved.

Synthesis of Shape-Controllable Anisotropic Microparticles and "Walnut-like" Microparticles via Emulsion Interfacial Polymerization

Anisotropic microparticles have plenty of applications for their asymmetric structure and precisely modified surface. In our research, the uniform anisotropic microparticles with benzyl chloride group were synthesized successfully via emulsion interfacial polymerization. By varying the degree of cross-linking and the concentration of slightly hydrophilic monomer 4-vinyl benzyl chloride (VBC), several types of microparticles with different concavities and different shapes of microparticles (hemisphere, bowl-like, egg-like, etc.) were obtained. Nanoporous microparticles with a walnut-like heterostructure were achieved with modified hydrophilic seeds with the same strategy. The potential applications of shape-controllable fluorescent microparticles and surface modification of microparticles by thiol-click reaction were explored. The modified microparticles achieved in this study are very useful in labeling, tracing, protein separation, and other biomedical fields.

Janus Nanoparticles: From Fabrication to (Bio)Applications

Janus nanoparticles (JNPs) refer to the integration of two or more chemically discrepant composites into one structure system. Studies into JNPs have been of significant interest due to their interesting characteristics stemming from their asymmetric structures, which can integrate different functional properties and perform more synergetic functions simultaneously. Herein, we present recent progress of Janus particles, comprehensively detailing fabrication strategies and applications. First, the classification of JNPs is divided into three blocks, consisting of polymeric composites, inorganic composites, and hybrid polymeric/inorganic JNPs composites. Then, the fabrication strategies are alternately summarized, examining self-assembly strategy, phase separation strategy, seed-mediated polymerization, microfluidic preparation strategy, nucleation growth methods, and masking methods. Finally, various intriguing applications of JNPs are presented, including solid surfactants agents, micro/nanomotors, and biomedical applications such as biosensing, controlled drug delivery, bioimaging, cancer therapy, and combined theranostics. Furthermore, challenges and future works in this field are provided.

Structurally Anisotropic Janus Particles with Tunable Amphiphilicity via Polymerization of Dynamic Complex Emulsions

A facile one-step approach for the synthesis of physically and chemically anisotropic polymer particles with tunable size, shape, composition, wettability, and functionality is reported. Specifically, dynamically reconfigurable oil-in-water Janus emulsions containing photocurable hydrocarbon or fluorocarbon acrylate monomers as one of the droplet phases are used as structural templates to polymerize them into precision Janus particles with highly uniform anomalous morphologies including (hemi-) spheres, lenses, and bowls. During polymerization, each interface is exposed to a different chemical environment, yielding particles with an intrinsic Janus character that can be amplified via side-selective postfunctionalization. The fabrication method allows to start with various common emulsification techniques, thus generating particles in the range of 200 nm –150 μm, also at a technical scale. The anisotropic shape combined with the asymmetric wettability profile of the produced particles promotes their directed self-assembly into colloidal clusters as well as their directional alignment at fluid interfaces. We foresee the application of such Janus particles in technical emulsions or oil recovery, for the manufacturing of programmed self-assembled architectures, and for the engineering of microstructured interfaces.

Molecular Patchy Clusters with Controllable Symmetry Breaking for Structural Engineering

Anisotropic patchy particles with molecular precision are exquisite building blocks for constructing diverse meso-structures of high complexity. In this research, a library of molecular patchy clusters consisting of a collection of functional polyhedral oligomeric silsesquioxane cages with exact regio-configuration and composition were prepared through a robust and modular approach. By meticulously tuning the composition, molecular symmetry, and other parameters, these patchy clusters could assemble into diverse nanostructures, including unconventional complex spherical phases (i.e., Frank-Kasper σ phase and dodecagonal quasicrystalline phase). As the size of the hydrophilic patch expands, a transition sequence from disorder to hexagonally packed cylinders and then to double gyroids was recorded, corresponding to a progressive decrease of interfacial curvature. On the other hand, regioisomers with the same composition but different regio-configuration adopt similar molecular packing but varied phase stability, as a result of the local self-sorting process to alleviate excess unfavorable interfacial contact. These precisely defined molecular patchy clusters provide a model system for a general understanding of the hierarchical structure formation and evolution based on anisotropic spherical building blocks at the nanoscale.

Impact of Surface Amphiphilicity on the Interfacial Behavior of Janus Particle Layers under Compression

Langmuir monolayers of silica/gold Janus particles with two different degrees of amphiphilicity have been examined to study the significance of particle surface amphiphilicity on the structure and mechanical properties of the interfacial layers. The response of the layers to the applied compression provides insight into the nature and strength of the interparticle interactions. Different collapse modes observed for the interfacial layers are linked to the amphiphilicity of Janus particles and their configuration at the interface. Molecular dynamics simulations on nanoparticles with similar contact angles provide insight on the arrangement of particles at the interface and support our conclusion that the interfacial configuration and collapse of anisotropic particles at the air/water interface are controlled by particle amphiphilicity.