Robust Reactive Janus Composite Particles of Snowman Shape

Charge-dominated phase separation synthesis method of Janus particles with well-defined separated lobes and patternable surface chemistries

Synthesizing Janus particles (JPs) with well-defined separated lobes and customizable surface chemistries has broad scientific and engineering application prospects but has proven extremely challenging. Here, we report a novel phase-separation-based fabrication method leveraging charge-dominated seeded emulsion polymerization, which enables the synthesis of JPs with multi-scale lobe architectures (ranging from isotropic asymmetric shapes to chemically anisotropic forms such as ellipses, dumbbells, and triblock structures) and customizable surface chemistries (including functional groups like carboxyl, sulfate, and sulfonate). Our method is based on the principles of multicomponent systems' heterogeneous nucleation and growth, where the interfacial energy is meticulously controlled by fine-tuning the surface charges/chemical properties of polystyrene (PS) seeds and methacryloxypropyl trimethoxysilane (MPS) emulsions, while the growth kinetics of polymethacryloxypropyl trimethoxysilane (PMPS) lobes are guided through a synergistic combination of radical polymerization and hydrolysis-condensation reactions. Charge-dominated repulsive forces at the interface play a crucial role in driving the phase separation, enabling the synthesis of well-defined JPs and making this strategy broadly applicable to a variety of negatively charged PS seeds or MPS emulsions for customizable two-lobe surface chemistries. Furthermore, the PMPS hemisphere can be selectively modified, enabling applications in Pickering emulsions. This work offers a scalable method for the controllable fabrication of JPs with programmable architectures and surface chemistries.

TEMPO-Grafted Polystyrene/Polymethacrylate Organosiloxane Janus Nanohybrids as Efficient Pickering Interfacial Catalyst for Selective Aerobic Oxidation of Cinnamyl Alcohol

The novel 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) groups immobilized on functional polymers or nanoparticles emerged as potential Pickering interfacial catalysts (PICs) for effective catalysis in biphasic systems. In this study, a snowman-shaped Janus-structured polymer with TEMPO-anchored nanohybrid particles (SM-JPP-TEMPO) was prepared and employed as a potential PIC in the Anelli-Montanari system for the selective oxidation of alcohol. The amphiphilic character of SM-JPP-TEMPO particles plays a dual role as an emulsifier and catalyst in the Pickering emulsion. As a result, it enables smaller droplets (102 μm) at the water-in-oil (W/O) interface and reduces the interfacial tension from 26.58 to 17.38 mN/m, which improves the stability of the Pickering emulsion system. This constructed Pickering emulsion microreactor offers a larger interface contact area and shortens the mass transfer distance of the substrate of cinnamyl alcohol, which significantly enhances the catalytic conversion at the Anelli-Montanari oxidation system, thus achieving remarkable conversion efficiency of (92.3%) with excellent selectivity (99%) in static (stirring-free) condition. It was found that the Janus nanohybrid catalyst (SM-JPP-TEMPO) enhanced 1.29-fold catalytic efficiency compared to the TEMPO grafted spherical polystyrene nanoparticle (PS-NPs-TEMPO) catalyst (72%). Moreover, after seven consecutive cycles, the Janus nanocatalyst (SM-JPP-TEMPO) maintained the conversion significantly. Hence, these results collectively highlight that the amphiphilic SM-JPP-TEMPO catalyst provides an efficient and eco-friendly strategy for the intensification of liquid-liquid biphasic reaction systems for potential applications in industries.

Interfacial Activity of Janus Particle: Unity of Molecular Surfactant and Homogeneous Particle

Janus particles with different compositions and properties segmented to different regions on the surface of one objector provide more opportunities for interfacial engineering. As a novel interfacial active material, Janus particles integrate the amphiphilic properties of molecular surfactants and the Pickering effect of homogeneous particles. In this research, the outstanding properties of Janus particles on various interfaces are examined from both theoretical and practical perspectives, and the advantages of Janus particles over molecular surfactants and homogeneous particle surfactants are analyzed. We believe that Janus particles are ideal tools for interface regulation and functionalization in the future.

Preparation of Non-Spherical Janus Particles via an Orthogonal Dissolution Approach

Post-synthesis modifications are valuable tools to alter functionalities and induce morphology changes in colloidal particles. Non-spherical polymer particles with Janus characteristics are prepared by combining seeded growth polymerization and selective dissolution. First, spherical polystyrene (PS) particles have been swollen with methyl methacrylate (MMA) with an activated swelling method. This is followed by polymerization that led to particles with two well-separated faces: one made of PS and the second of polymethyl methacrylate (PMMA). Subsequently, non-spherical particles are obtained by exposing the Janus colloids to various solvents. Using the two polymers' orthogonal solubility, solvents are identified to selectively dissolve only one face, leading to hemispherical PS or PMMA particles. It is further investigated how changing the composition of the PMMA face - by either co-polymerization with glycidyl methacrylate or by adding a cross-linker - affects the particles' morphology. The poly-methacrylate face can gain total or partial resistance towards the solvents, resulting in intriguing shapes, such as mushroom-like and Janus dimpled particles. The dissolution mechanisms are investigated via optical microscopy, where total or partial dissolutions can be directly observed. Lastly, prematurely quenching the dissolution of the particle's lobes with water can be used to control the Janus mushroom-like particle aspect ratio.

Janus Composite Particles and Interfacial Catalysis Thereby

Janus composite particles (JPs) with distinct compartmentalization of varied components thus performances and anisotropic shape display a variety of properties and have demonstrated great potentials in diversify practical applications. Especially, the catalytic JPs are advantageous for multi-phase catalysis with much easier separation of products and recycling the catalysts. In the first section of this review, typical methods to synthesize the JPs with varied morphologies are briefly surveyed in the category of polymeric, inorganic and polymer/inorganic composite. In the main section, recent progresses of the JPs in emulsion interfacial catalysis are summarized covering organic synthesis, hydrogenation, dye degradation, and environmental chemistry. The review will end by calling more efforts toward precision synthesis of catalytic JPs at large scale to meet the stringent requirements in practical applications such as catalytic diagnosis and therapy by the functional JPs.

Synthesis of dimpled polymer particles and polymer particles with protrusions - Past, present, and future

Since the development of emulsion polymerization techniques, polymer particles have become the epitome of standard colloids due to the exceptional control over size, size distribution, and composition the synthesis methods allow reaching. The exploration of different variations of the synthesis methods has led to the discovery of more advanced techniques, enabling control over their composition and shape. Many early investigations focused on forming particles with protrusions (with one protrusion, called dumbbell particles) and particles with concavities, also called dimpled particles. This paper reviews the literature covering the synthesis, functionalization, and applications of both types of particles. The focus has been on the rationalization of the various approaches used to prepare such particles and on the discussion of the mechanisms of formation not just from the experimental viewpoint but also from the standpoint of thermodynamics. The primary motivation to combine in a single review the preparation of both types of particles has been the observation of similarities among some of the methods developed to prepare dimpled particles, which sometimes include the formation of particles with protrusions and vice versa. The most common applications of these particles have been discussed as well. By looking at the different approaches developed in the literature under one general perspective, we hope to stimulate a more ample use of these particles and promote the development of even more effective synthetic protocols.

Reactive Janus Particle Compatibilizer with Adjustable Structure and Optimal Interface Location for Compatibilization of Highly Immiscible Polymer Blends

Highly immiscible blend materials with distinctive and excellent properties play a key role in meeting the application needs, especially in extreme environments, and reactive nanoparticles are used to increase the interface adhesion and optimize the morphology of highly immiscible blending. However, these reactive nanoparticles tend to aggregate and even agglomerate during reactive blending, which significantly deteriorates their compatibilization efficiency. Herein, reactive Janus particles with the epoxy group and various siloxane molecular long chain grafting ratios (E-JP-PDMS) were synthesized using SiO₂@PDVB Janus particles (JP) and used as compatibilizers for polyamide and methyl vinyl silicone elastomer (PA/MVQ) blends, which were highly immiscible. The effects of the structure of E-JP-PDMS Janus nanoparticles on their location at the interfaces between the PA and MVQ as well as their compatibilization efficiency for the PA/MVQ blends were investigated. The location and dispersion of E-JP-PDMS at the interfaces were improved by increasing the PDMS content in E-JP-PDMS. The average diameter of the MVQ domains of the PA/MVQ (70/30, w/w) was 79.5 μm and was reduced to 5.3 μm in the presence of 3.0 wt % of the E-JP-PDMS with 65 wt % PDMS. As a comparison, it was 45.1 μm in the presence of 3.0 wt % of a commercial compatibilizer (ethylene-butylacylate-maleic anhydride copolymer, denoted as EBAMAH), which provides a guideline for the design and preparation of efficient compatibilizers for highly immiscible polymer blends.

Facile Fabrication of Monodisperse Micron-Sized Dual Janus Silica Particles with Asymmetric Morphology and Chemical Environment

Janus particles are a kind of materials with asymmetric morphology or surface chemical environment. But so far, the preparation of particles with dual asymmetry is still a challenging problem. Hence the cation surfactant hexadecyl trimethyl ammonium bromide and co-surfactant octadecylamine are applied to improve the Pickering emulsion stability, and the micron-sized silica particles are arranged in a single layer at the toluene-water interface through electrostatic interaction. Furthermore, organosilane reagents are added in the preparation process, resulting in the construction of asymmetric hydrophilic or hydrophobic mesoporous precisely onto the micron-sized silica particles surface. The cation surfactant-assisted Pickering emulsion method is simple, effective, and convenience, which can be applied in the synthesis of various dual Janus silica particles for specific applications.

Liquid-liquid phase separation of immiscible polymers at double emulsion interfaces for configurable microcapsules

Liquid-liquid phase separation at complex interfaces is a common phenomenon in biological systems and is also a fundamental basis to create synthetic materials in multicomponent mixtures. Understanding the liquid-liquid phase separation in well-defined macromolecular systems is anticipated to shed light on similar behaviors in cross-disciplinary areas. Here we study a series of immiscible polymers and reveal a generic phase diagram of liquid-liquid phase separation at double emulsion interfaces, which depicts the equilibrium structures by interfacial tension and polymer fraction. We further reveal that the interfacial tensions in various systems fall on a linear relationship with spreading coefficients. Based on this theoretical guideline, the liquid-liquid phase separation can be modulated by a low fraction of amphiphilic block copolymers, leading the double emulsion droplets configurable between compartments and anisotropic shapes. The solidified anisotropic microcapsules could provide unique orientation-sensitive optical properties and thermomechanical responses. The theoretical analysis and experimental protocol in this study yield a generalizable strategy to prepare multiphase double emulsions with controlled structures and desired properties.

Orientation-Controlled Ultralong Assembly of Janus Particles Induced by Bubble-Driven Instant Quasi-1D Interfaces

Constructing precisely oriented assemblies and exploring their orientation-dependent properties remain a challenge for Janus nanoparticles (JNPs) due to their asymmetric characteristics. Herein, we propose a bubble-driven instant quasi-1D interfacial strategy for the oriented assembly of JNP chains in a highly controllable manner. It is found that the rapid formation of templated bubbles can promote the interfacial orientation of JNPs kinetically, while the confined quasi-1D interface in the curved liquid bridge can constrain the disordered rotation of the particles, yielding well-oriented JNP chains in a long range. During the evaporation process, the interfacial orientation of the JNPs can be transferred to the assembled chains. By regulating the amphiphilicity of the JNPs, both heteraxial and coaxial JNP assemblies are obtained, which show different polarization dependences on light scattering, and the related colorimetric logic behaviors are demonstrated. This work demonstrates the great potential of patterned interfacial assembly with a manageable orientation and shows the broad prospect of asymmetric JNP assembly in constructing novel optoelectronic devices.

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.

A Janus Au-Polymersome Heterostructure with Near-Field Enhancement Effect for Implant-Associated Infection Phototherapy

Polymer-inorganic hybrid Janus nanoparticles (PI-JNPs) have attracted extensive attention due to their special structures and functions. However, achieving the synergistic enhancement of photochemical activity between polymer and inorganic moieties in PI-JNPs remains challenging. Herein, the construction of a novel Janus Au-porphyrin polymersome (J-AuPPS) heterostructure by a facile one-step photocatalytic synthesis is reported. The near-field enhancement (NFE) effect between porphyrin polymersome (PPS) and Au nanoparticles in J-AuPPS is achieved to enhance its near-infrared (NIR) light absorption and electric/thermal field intensity at their interface, which improves the energy transfer and energetic charge-carrier generation. Therefore, J-AuPPS shows a higher NIR-activated photothermal conversion efficiency (48.4%) and generates more singlet oxygen compared with non-Janus core-particle Au-PPS nanostructure (28.4%). As a result, J-AuPPS exhibits excellent dual-mode (photothermal/photodynamic) antibacterial and anti-biofilm performance, thereby significantly enhancing the in vivo therapeutic effect in an implant-associated-infection rat model. This work is believed to motivate the rational design of advanced hybrid JNPs with desirable NFE effect and further extend their biological applications.

Optically active polymer particles with programmable surface microstructures constructed using chiral helical polyacetylene

Micro/nanoparticles with surface microstructures have attracted tremendous attention due to their fascinating structures and properties. Herein, we present the first strategy for producing optically active polymer particles with varying surface microstructures via a template surface modification process in which achiral particles act as the template and helical substituted polyacetylene acts as the chiral component. To prepare the designed chiral-functionalized particles, template particles were first reacted with propargylamine to produce alkynylated template particles. The alkynylated templates further participated in the polymerization of chiral alkyne monomers through a surface grafting precipitation polymerization approach, resulting in achiral particles with surface microstructures covalently bonded with a chiral helical polymer. SEM images ascertain the production of chiral-functionalized particles showing various shapes (jar-like, golf ball-like, and raspberry-like particles). Furthermore, CD and UV-vis absorption spectra demonstrate that the grafted polyacetylene chains adopt a predominantly single-handed helical conformation, thereby affording composite particles with optical activity. Using the established protocol, numerous advanced chiral-functionalized micro/nanostructures are expected to be designed and constructed.

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.

Temperature-Sensitive Anti-Inflammatory Organohydrogels Containing Janus Particle Stabilized Phase-Change Microinclusions

A fabrication strategy for multifunctional organohydrogels is proposed, which combines phase-change microinclusions within a double-network (DN) hydrogel under the stabilization of Janus particles. Janus particles possess reactivity and colloidal stability for more robust organohydrogels, while the interstice among Janus particles enhances the mass transfer between the phase interfaces. Moreover, DN hydrogels are achieved through dynamic cross-linking networks, endowing organohydrogels with injectability and self-healing performance. Phase-change microinclusions are beneficial to the organohydrogels with temperature-responsive mechanical property and temperature-programed shape-memory performance. Organohydrogels can be employed for temperature therapy through the melting-crystallization process of phase-change microinclusions. Simultaneously, the payloads within microinclusions can be released for antibacteria upon melting the encapsulated wax. The organohydrogels can be served as an ideal dressing with temperature-responsive mechanical property, temperature therapy effectiveness, and temperature-triggered antibacterial ability.

Anisotropic Particle Fabrication Using Thermal Scanning Probe Lithography

Size, shape, and chemical properties of nanoparticles are powerful tools to modulate the optical and physicochemical properties of a particle suspension. Despite having many methods to synthesize anisotropic nanoparticles, often there are challenges in terms of controlling the polydispersity, shape, size, or composition of anisotropic nanoparticles. This work has been inspired by the potential for developing a unique pathway to make different shaped monodispersed anisotropic nano- and microparticles with large flexibility in material choice. Compared to existing methods, this state-of-the-art nanolithographic method is fast, easy to prototype, and much simple in terms of its mechanical requirement. We show that this technique has been efficiently used to make a variety of anisotropic nano- and microparticles of different shapes, such as triangular prisms, ovals, disks, flowers, and stairs following the same pathway, at the same time showing the potential of being flexible with respect to the composition of the particles. The thermal scanning probe lithographic method in combination with dry reactive ion etching was used to make two-dimensional and three-dimensional templates for the fabrication of anisotropic nano- and microparticles. Deposition of different metal/metal oxides by the electron-beam evaporation method onto these templates allowed us to fabricate a range of nanomaterials according to the required functionality in potential applications. The particles were characterized by atomic force microscopy, He-ion microscopy, scanning electron microscopy, and dynamic light scattering to ensure that the developed method is reproducible, flexible, and robust in choosing the shapes for making monodispersed anisotropic nanoparticles with great control over shape and size.

Shape-tunable polymeric Janus nanoparticles with hollow cavities derived from polymerization induced self-assembly based crosslinked vesicles

The fabrication of shape-tunable polymeric Janus nanoparticles with hollow cavities derived from polymerization induced self-assembly based crosslinked vesicles is reported for the first time in this work. These novel polymeric JNPs can be applied to an extensive range of applications, wherein nanoparticles with controllable hollow morphologies are needed.

Kinetics-Controlled Super-Assembly of Asymmetric Porous and Hollow Carbon Nanoparticles as Light-Sensitive Smart Nanovehicles

The rational design and controllable synthesis of hollow nanoparticles with both a mesoporous shell and an asymmetric architecture are crucially desired yet still significant challenges. In this work, a kinetics-controlled interfacial super-assembly strategy is developed, which is capable of preparing asymmetric porous and hollow carbon (APHC) nanoparticles through the precise regulation of polymerization and assembly rates of two kinds of precursors. In this method, Janus resin and silica hybrid (RSH) nanoparticles are first fabricated through the kinetics-controlled competitive nucleation and assembly of two precursors. Specifically, silica nanoparticles are initially formed, and the resin nanoparticles are subsequently formed on one side of the silica nanoparticles, followed by the co-assembly of silica and resin on the other side of the silica nanoparticles. The APHC nanoparticles are finally obtained via high-temperature carbonization of RSH nanoparticles and elimination of silica. The erratic asymmetrical, hierarchical porous and hollow structure and excellent photothermal performance under 980 nm near-infrared (NIR) light endow the APHC nanoparticles with the ability to serve as fuel-free nanomotors with NIR-light-driven propulsion. Upon illumination by NIR light, the photothermal effect of the APHC shell causes both self-thermophoresis and jet driving forces, which propel the APHC nanomotor. Furthermore, with the assistance of phase change materials, such APHC nanoparticles can be employed as smart vehicles that can achieve on-demand release of drugs with a 980 nm NIR laser. As a proof of concept, we apply this APHC-based therapeutic system in cancer treatment, which shows improved anticancer performance due to the synergy of photothermal therapy and chemotherapy. In brief, this kinetics-controlled approach may put forward new insight into the design and synthesis of functional materials with unique structures, properties, and applications by adjusting the assembly rates of multiple precursors in a reaction system.

Anisotropic Janus materials: from micro-/nanostructures to applications

Janus materials have led to great achievements in recent years owing to their unique asymmetric structures and properties. In this review, recent advances of Janus materials including Janus particles and Janus membranes are summarized, and then the microstructures and applications of Janus materials are emphasized. The asymmetric wettability of Janus materials is related to their microstructures; hence, the microstructures of Janus materials were analyzed, compared and summarized. Also presented are current and potential applications in sensing, drug delivery, oil-water separation and so on. Finally, a perspective on the research prospects and development of Janus materials in more fields is given.

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.

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.

Responsive polymeric Janus cage

A robust thermo-responsive polymeric Janus cage with a PNIPAM-cPVBC-PEO sandwiched shell is synthesized. The Janus cage provides a general method of thermally triggered separation of oil/water emulsions independent of the type of surfactant and emulsion. It can selectively capture organic compounds at a higher temperature and release them at a lower temperature.

Compatibilization Behavior of Double Spherical TETA-SiO2@PDVB Janus Particles Anchored at the Phase Interface of Acrylic Resin/Epoxy Resin (AR/EP) Polymer Blends

The inorganic particles used as a compatibilizer play a role in crack termination and heat resistance. However, the poor compatibility of inorganic particles and polymer hinders their application. Herein, the double spherical SiO₂@PDVB Janus particles (JPs) were modified with triethylenetetramine (TETA), and the obtained anisotropic TETA-SiO₂@PDVB JPs were used as the compatibilizer of acrylic resin/epoxy resin (AR/EP) composites. The modification and the compatibilization of TETA-SiO₂@PDVB JPs were studied by scanning electron microscopy, X-ray photoelectron spectroscopy, differential scanning calorimetry, and dynamic mechanical analyzer, impact test, tensile test, and so forth. Results show that amino groups grafted onto the SiO₂ lobe can react with epoxy groups of EP, which results in the TETA-SiO₂ lobe being embedded in the EP phase and the PDVB lobe being pushed toward the AR phase. The TETA-SiO₂@PDVB JPs anchored at the interface of AR and EP increase their interfacial adhesion, decrease the domain phase size and distribution of dispersed AR, and improve the compatibility of AR/EP composites. The compatibilization of nanoparticles (NPs) is realized by the cavitation and blunting of different scaled AR phase domain distributions and that of JPs is realized by the strong interfacial force originated by JPs. Moreover, the desorption energy of TETA-SiO₂@PDVB JPs is higher than that of SiO₂-TETA; so the glass transition temperature (T _g) of AR/EP/JP composites is higher than that of AR/EP/NP composites. The strong interfacial adhesion and high desorption energy endow TETA-SiO₂@PDVB JPs with a toughening effect and enhancing effect. The impact strength and the tensile strength of AR/EP/TETA-SiO₂@PDVB composites are 16.03 kJ/m² and 63.12 MPa, which are 9.91 kJ/m² and 16.32 MPa higher than those of AR/EP composites, respectively. JPs used in the thermosetting EP is benefit to its toughening study and the new anisotropic Janus compatibilizer.

Morphology evolution of Janus dumbbell nanoparticles in seeded emulsion polymerization

Emulsion polymerization is a versatile approach to produce different polymeric nanoparticle morphologies, which can be useful in a variety of applications. However, the detailed mechanism of the morphology formation is not entirely clear. We study the kinetics of nanoparticle morphology evolution during a seeded emulsion polymerization using both experimental and computational tools. Lightly crosslinked polystyrene seeds were first synthesized using dispersion polymerization. Then the seed particles were swollen in tert-butyl acrylate and styrene monomers, and subsequently polymerized into nanoparticles of dumbbell and multilobe morphologies. It was discovered that both the seed and final particle morphology were affected by the methanol concentration during the seed synthesis. Systematically adjusting the methanol amount will not only yield spherical seed particles of different size, but also dumbbell particles even without the second monomer polymerization. In addition to methanol concentration, morphology can be controlled by crosslinking density. The kinetics studies revealed an interesting transition from multilobe to dumbbell geometries during the secondary polymerization. Based on the results, a nucleation-growth model has been proposed to describe the morphology evolution and verification was offered by computer simulation. The key discovery is that nanoparticle morphology can be kinetically controlled by diffusion of the protrusions on the seed particles. The condition of seed synthesis and crosslinking density will drastically change the seed and final nanoparticle morphology.

Bi-continuous emulsion using Janus particles

Bi-continuous emulsion stabilized with amphiphilic Janus particles was achieved.

Biodegradable Anisotropic Microparticles for Stepwise Cell Adhesion and Preparation of Janus Cell Microparticles

The biomimetic anisotropic particles have different physicochemical properties on the opposite two sides, enabling diverse applications in emulsion, photonic display, and diagnosis. However, the traditional anisotropic particles have a very small size, ranging from submicrons to a few microns. The design and fabrication of anisotropic macron-sized particles with new structures and properties is still challenging. In this study, anisotropic polycaprolactone (PCL) microparticles well separated with each other were prepared by crystallization from the dilute PCL solution in a porous 3D gelatin template. They had fuzzy and smooth surfaces on each side, and a size as large as 70 μm. The fuzzy surface of the particle adsorbed significantly larger amount of proteins, and was more cell-attractive regardless of the cell types. The particles showed stronger affinity toward fibroblasts over hepatocytes, which paved a new way for cell isolation merely based on the surface morphology. After a successive seeding process, Janus cell microparticles with fibroblasts and endothelial cells (ECs) on each side were designed and obtained by making use of the anisotropic surface morphology, which showed significant difference in EC functions in terms of prostacyclin (PGl2) secretion, demonstrating the unique and appealing functions of this type of anisotropic microspheres.

Janus Colloids toward Interfacial Engineering

Janus colloids are functional particles consisting of two surfaces (or internal materials) with distinct physical or chemical properties in the same particle. Owing to their amphiphilic nature, Janus colloids composed of both hydrophilic and hydrophobic faces provide a powerful tool to generate functional surfaces and to manipulate the properties of interfaces. Amphiphilic Janus colloids have shown promising applications as particulate surfactants in oil/water separation, as interfacial compatibilizers in polymer blends, and as assembly blocks in robust coatings with unique wettability. In this Feature Article, we summarize recent advances in engineering interfaces by using Janus colloids.

Janus Nanoparticles for Improved Dentin Bonding

The amphiphilic monomer 2-hydroxyethyl methacrylate (HEMA) is widely used in dental adhesives as a priming component, especially for dentin bonding. It behaves as a compatibilizer between hydrophilic and hydrophobic components and stabilizes the multicomponent adhesive system. However, there are several drawbacks associated with using HEMA, such as water retention within the adhesive layer, hydrolysis in oral environments, and cytotoxicity. These drawbacks lead to the failure of tooth restoration and represent a heavy medical burden. Thus, it is imperative to find a new compatibilizer to substitute for HEMA. Because of their superior compatibilization capabilities as functional solid surfactants, amphiphilic Janus particles are chosen as candidates for an alternative to HEMA in dental adhesives. Reactive amphiphilic Janus nanoparticles are synthesized by selectively etching and modifying at the interface of a Pickering emulsion. This approach could be extended to the synthesis of a series of other Janus nanoparticles. The Janus nanoparticles were verified to be better for the reduction of the phase separation and stabilization of dentin adhesives than HEMA. It is also demonstrated that these reactive Janus nanoparticles can strongly enhance the dentin bonding interface without cytotoxicity. It is clearly illustrated by this study that Janus nanoparticles may be promising materials to substitute for HEMA in dental adhesives.

Fabrication of shape-tunable macroparticles by seeded polymerization of styrene using non-cross-linked starch-based seed

Nonspherical colloidal particles with various geometries and different compositions have attracted tremendous attention and been widely researched. The preparation of polymer colloidal particles with controlled shapes by seeded polymerization is recognized as the most promising technique owing to the precise control of various morphologies and using non-cross-linked seed particles are of particular interest. Seeds particles derived from natural biopolymers are seldom applied. Hence, non-cross-linked starch-based seed could be used to fabricate the anisotropic particles by soap-free seed polymerization. Non-cross-linked starch-based seed particles were prepared by a nanoprecipitation method. Starch/polystyrene composite colloidal particles with shape-tunable were fabricated by soap-free seeded polymerization using starch-based seed. The effect of the polymerization time, monomer feed ratio and seed type were investigated. The seed particles with a single- or multi-hole structure were obtained after swelling with styrene. The resulting particles including golf-like, raspberry-like, octahedron-like and snowman-like structures, was fabricated on the polymerization process. This study firstly reports that the morphology of composite particles from golf-like to snowman-like at high monomer feed ratio using starch-based seed. At low monomer feed ratio, raspberry-like particles were obtained by surface nucleation increasing process. In addition, seed type also effect the morphology of composite particles.

Intriguing Morphology Evolution from Noncrosslinked Poly(tert-butyl acrylate) Seeds with Polar Functional Groups in Soap-Free Emulsion Polymerization of Styrene

Herein, we demonstrate a facile approach to prepare anisotropic poly(tert-butyl acrylate)/polystyrene (PtBA/PS) composite particles with controllable morphologies by soap-free seeded emulsion polymerization (SSEP). In the first step, noncrosslinked PtBA seeds with self-stabilizing polar functional groups (e.g., ester groups and radicals) are synthesized by soap-free emulsion polymerization. During the subsequent SSEP of styrene (St), PS bulges are nucleated on the PtBA seeds due to the microphase separation confined in the latex particles. The morphology evolution of PtBA/PS composite particles is tailored by varying the monomer/seed feed ratio, polymerization time, and polymerization temperature. Many intriguing morphologies, including hamburger-like, litchi-like, mushroom-like, strawberry-like, bowl-like, and snowman-like, have been acquired for PtBA/PS composite particles. The polar groups on the PtBA seed surface greatly influence the formation and further merging of PS/St bulges during the polymerization. A possible formation mechanism is proposed on the basis of experimental results. These complex composite particles are promising for applications in superhydrophobic coatings.

Polarity Reversal in Homologous Series of Surfactant-Free Janus Nanoparticles: Toward the Next Generation of Amphiphiles

The ability to finely tune the amphiphilic balance of Janus nanoparticles (JNPs) could represent a step forward toward creating the next generation of solid-state amphiphiles with significant potential for applications. The inherent amphiphilicity of JNPs stemming from an intrinsic polarity contrast between two surface regions is well-acknowledged, but remained difficult to demonstrate experimentally in the absence of surfactants and stabilizers. We have designed two homologous series of surfactant-free polymeric JNPs starting from polystyrene (PS) seed nanoparticles (NPs) on which we grew Janus lobes of different sizes via seed polymerization and phase separation of the 3-(triethoxysilyl)propyl-methacrylate (3-TSPM) monomer. The two series differ only by the radical initiator used in the seed polymerization: polar ionic ammonium persulfate (APS) vs nonpolar oil-soluble 2,2'-azobis(2-methylpropionitrile) (AIBN). To compare the two series, we employed them in the emulsification of water with heptane or molten paraffin wax. A polarity reversal of the JNPs within AIBN-JNP series could be observed from the catastrophic and transitional emulsion phase inversions and occurred when the more polar lobe was larger than the nonpolar seed PS lobe. Furthermore, the AIBN-JNPs appeared to be amphiphilic and adopt preferred orientation within the monolayer at the oil/water interface. We therefore demonstrated that in the absence of surfactants the amphiphilicity of the JNPs depends not only on the relative size of the lobes, but also on the surface polarity contrast, which can be tuned by changing the nature of radical initiator.

Janus Particles in a Nonpolar Solvent

Amphiphilic Janus particles are currently receiving great attention as "solid surfactants". Previous studies have introduced such particles with a variety of shapes and functions, but there has so far been a strong emphasis on water-dispersible particles that mimic the molecular surfactants soluble in polar solvents. Here we present an example of lipophilic Janus particles which are selectively dispersible in very nonpolar solvents such as alkanes. Interfacial tension measurements between the alkane dispersions and pure water indicate that these particles do have interfacial activity, and like typical hydrophobic, nonionic surfactants, they do not partition to the aqueous bulk. We also show that the oil-borne particles, by retaining locally polar domains where charges can reside, generate electric conductivity in nonpolar liquids-another feature familiar from molecular surfactants and one commonly exploited to mitigate explosion hazards due to flow electrification during petroleum pumping and in the formulation of electronic inks.