Polymeric Janus nanorods via anodic aluminum oxide templating

We report a novel method for the fabrication of polymeric Janus nanorods via sequential polymerization from anodic aluminum oxide (AAO) templates. Dual compositions can be incorporated into individual nanorods and endow versatile potential applications. This fabrication strategy paves the way for constructing multifunctional nanostructures and brings together different materials in a single entity.

Regioselective Seeded Polymerization in Block Copolymer Nanoparticles: Post-Assembly Control of Colloidal Features

Post-assembly modifications are efficient tools to adjust colloidal features of block copolymer (BCP) particles. However, existing methods often address particle shape, morphology, and chemical functionality individually. For simultaneous control, we transferred the concept of seeded polymerization to phase separated BCP particles. Key to our approach is the regioselective polymerization of (functional) monomers inside specific BCP domains. This was demonstrated in striped PS-b-P2VP ellipsoids. Here, polymerization of styrene preferably occurs in PS domains and increases PS lamellar thickness up to 5-fold. The resulting asymmetric lamellar morphology also changes the particle shape, i.e., increases the aspect ratio. Using 4-vinylbenzyl azide as co-monomer, azides as chemical functionalities can be added selectively to the PS domains. Overall, our simple and versatile method gives access to various multifunctional BCP colloids from a single batch of pre-formed particles.

Electrochemically Initiated Synthesis of Polyacrylamide Microgels and Core-shell Particles

Herein, we developed a simple procedure for synthesizing micrometer-sized microgel particles as a suspension in an aqueous solution and thin films deposited as shells on different inorganic cores. A sufficiently high constant potential was applied to the working electrode to commence the initiator decomposition that resulted in gelation. Under hydrodynamic conditions, this initiation allowed preparing different morphology microgels at room temperature. Importantly, neither heating nor UV-light illumination was needed to initiate the polymerization. Moreover, thin films of the cross-linked gel were anchored on different core substrates, including silica and magnetic nanoparticles. Scanning electron microscopy and transmission electron microscopy imaging confirmed the microgel particles' and films' irregular shape and porous structure. Energy-dispersive X-ray spectroscopy indicated that the core coating with the microgel film was successful. Dynamic light scattering measured the micrometer size of gel particles with different combinations of acrylic monomers. Thermogravimetric analysis and the first-derivative thermogravimetric analysis revealed that the microgels' thermal stability of different compositions was different. Fourier-transform infrared and 13C NMR spectroscopy showed successful copolymerization of the main, functional, and cross-linking monomers.

Janus particles by simplified RAFT-based emulsion polymerization process for polymer coating

We describe a simplified method to synthesize film forming polymer Janus particles by phase separation during RAFT-based free radical emulsion polymerization. Fully crosslinked snowman- or football-shaped polystyrene Janus particles (PSJPs) were first produced in a one-step batch process using amphiphilic triblock macro-RAFT copolymers as stabilizers. Such particles were in turn employed as seeds in a continuous emulsion polymerization in which a monomer mixture of methyl methacrylate (MMA) and butyl acrylate (BA) (1/1 by weight) was constantly injected into the reaction in the presence of a water soluble initiator. The added monomers wetted seed particle surface and their polymerization led to formations of 93-nm film forming single- or two-headed Janus particles. The resulted latex was successfully used to disperse and encapsulate solid calcite extender.

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Enhanced thermal conductivity of nanofluids by introducing Janus particles

The addition of nanoparticles to a base fluid (i.e., nanofluids) is an effective strategy to achieve a higher thermal conductivity of a fluid. In a common nanofluid, the suspended nanoparticles are mostly symmetrical spheres. In the present paper, we propose to add Janus nanoparticles into a fluid (termed as Janus nanofluids), to further enhance the thermal conductivity of nanofluids. By using molecular dynamics simulations, it is found that the thermal conductivity can be distinctly improved by introducing Janus particles into the nanofluids in contrast with common nanofluids. Based on the calculation results of the molecular radial distribution function around the nanoparticle, and the diffusion coefficient of the base fluid and the Janus nanoparticle, the enhancement in the thermal conductivity of Janus nanofluids is attributed to the enhanced Brownian motion of Janus nanoparticles, which increases the probability of inter-molecular collisions and leads to enhanced energy transfer in nanofluids. The Janus nanofluids proposed in this work provide insights for the design of nanofluids with high thermal conductivity.

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.

Soft–hard Janus nanoparticles for polymer encapsulation of solid particulate

Janus nanoparticles with soft lobes can self-assemble on the surface of solid substrates in aqueous phase and coalesce to form a complete polymer shell encapsulating the entire solid substrate.

Cold-Responsive Nanoparticle Enables Intracellular Delivery and Rapid Release of Trehalose for Organic-Solvent-Free Cryopreservation

Conventional cryopreservation of mammalian cells requires the use of toxic organic solvents (e.g., dimethyl sulfoxide) as cryoprotectants. Consequently, the cryopreserved cells must undergo a tedious washing procedure to remove the organic solvents for their further applications in cell-based medicine, and many of the precious cells may be lost or killed during the procedure. Trehalose has been explored as a nontoxic alternative to traditional cryoprotectants. However, mammalian cells do not synthesize trehalose or express trehalose transporters in their membranes, and the lack of an approach for the efficient intracellular delivery of trehalose has been a major hurdle for its use in cell cryopreservation. In this study, a cold-responsive polymer (poly(N-isopropylacrylamide-co-butyl acrylate)) is utilized to synthesize nanoparticles for the encapsulation and intracellular delivery of trehalose. The trehalose-laden nanoparticles can be efficiently taken up by mammalian cells. The nanoparticles quickly and irreversibly disassemble upon cold treatment, enabling the controlled and rapid release of trehalose from the nanoparticles inside cells. The latter is confirmed by an evident increase in cell volume upon cold treatment. This rapid cold-triggered intracellular release of trehalose is crucial to developing a fast protocol to cryopreserve cells using trehalose. Cells with intracellular trehalose delivered using the nanoparticles show comparable postcryopreservation viability compared to that of cells treated with DMSO, eliminating the need for the tedious and cell-damaging washing procedure required for using the DMSO-cryopreserved cells in vivo. This cold-responsive nanoparticle may greatly facilitate the use of trehalose as a nontoxic cryoprotectant for banking cells and tissues to meet their high demand by modern cell-based medicine.

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.

Synthesis of Janus and Patchy Particles Using Nanogels as Stabilizers in Emulsion Polymerization

Polymer nanogels are used as colloidal stabilizers in emulsion polymerization. The nanogels were made by the covalent cross-linking of block copolymer micelles, the macromolecular building blocks of which were synthesized using a combination of catalytic chain transfer emulsion polymerization and reversible addition-fragmentation chain transfer (RAFT) of methacrylate monomers. The use of the nanogels in an emulsion polymerization led to anisotropic Janus and patchy colloids, where a latex particle was decorated by a number of patches on its surface. Control of the particle size and patch density was achieved by tailoring of the reaction conditions, such as varying the amount of nanogels, pH, and salt concentration. Overall, the emulsion polymerization process in the presence of nanogels as stabilizers is shown to be a versatile and easily scalable route toward the fabrication of Janus and patchy polymer colloids.

Effect of the addition of salt to Pickering emulsion polymerizations using polymeric nanogels as stabilizers

Nanogels made from crosslinked block copolymer micelles are used as stabilizers in the Pickering emulsion polymerization of styrene.

Characterization of oligo(acrylic acid)s and their block co-oligomers

Oligo(acrylic acid), oligoAA are important species currently used industrially in the stabilization of paints and also for the production of self-assembled polymer structures which have been shown to have useful applications in analytical separation methods and potentially in drug delivery systems. To properly tailor the synthesis of oligoAA, and its block co-oligomers synthesized by Reversible-Addition Fragmentation chain Transfer (RAFT) polymerization to applications, detailed knowledge about the chemical structure is needed. Commonly used techniques such as Size Exclusion Chromatography (SEC) and Electrospray Ionization-Mass Spectrometry (ESI-MS) suffer from poor resolution and non-quantitative distributions, respectively. In this work free solution Capillary Electrophoresis (CE) has been thoroughly investigated as an alternative, allowing for the separation of oligoAA by molar mass and the RAFT agent end group. The method was then extended to block co-oligomers of acrylic acid and styrene. Peak capacities up to 426 were observed for these 1D CE separations, 10 times greater than what has been achieved for Liquid Chromatography (LC) of oligostyrenes. To provide a comprehensive insight into the chemical structure of these materials ¹H and ¹³C Nuclear Magnetic Resonance (NMR) spectroscopy was used to provide an accurate average chain length and reveal the presence of branching. The chain length at which branching is detected was investigated with the results showing a degree of branching of 1% of the monomer units in oligoAA with an average chain length of 9 monomer units, which was the shortest chain length at which branching could be detected. This branching is suspected to be a result of both intermolecular and intramolecular transfer reactions. The combination of free solution CE and NMR spectroscopy is shown to provide a near complete elucidation of the chemical structure of oligoAA including the average chain length and branching as well as the chain length and RAFT agent end group distribution. Furthermore, the purity in terms of the dead chains and unreacted RAFT agent was quantified. The use of free solution CE and ¹H NMR spectroscopy demonstrated in this work can be routinely applied to oligoelectrolytes and their block co-oligomers to provide an accurate characterization which allows for better design of the materials produced from these oligomers.

Investigating Switchable Nanostructures in Shape Memory Process for Amphipathic Janus Nanoparticles

Janus particles (JPs) have attracted increasing attention from the communities of materials science, chemistry, physics, and biology. However, the nanoscale JPs that can switch shapes in response to an environmental stimulus is a significant challenge. In this article, we have demonstrated a simple procedure to fabricate the amphipathic Janus nanoparticles (JNPs) composed of hydrophilic body and hydrophobic lobe via using sudden negative pressure technique. Moreover, in response to temperature, the nanoparticles can recover to their initial nanosphere state by a switchable process, showing promising shape memory effect. Here, we can monitor the switchable nanostructures with hydrophilic and hydrophobic changes in the shape memory process of the JNPs by transmission electron microscope, dynamic light scattering, and water contact angle. Furthermore, we successfully compare the differences in shape deformation ratio and shape recovery ratio using the three test methods by the statistical analysis of Student's t-test for independent samples. In addition, we also develop hybrid magnetic Janus nanoparticles, changed from the amphipathic JNPs by the selective attachment of magnetic nanoparticles with hydrophobic molecules, which show new Janus nanostructure and shape memory property.

Polymeric Janus Nanoparticles: Recent Advances in Synthetic Strategies, Materials Properties, and Applications

Polymeric Janus nanoparticles with two sides of incompatible chemistry have received increasing attention due to their tunable asymmetric structure and unique material characteristics. Recently, with the rapid progress in controlled polymerization combined with novel fabrication techniques, a large array of functional polymeric Janus particles are diversified with sophisticated architecture and applications. In this review, the most recently developed strategies for controlled synthesis of polymeric Janus nanoparticles with well-defined size and complex superstructures are summarized. In addition, the pros and cons of each approach in mediating the anisotropic shapes of polymeric Janus particles as well as their asymmetric spatial distribution of chemical compositions and functionalities are discussed and compared. Finally, these newly developed structural nanoparticles with specific shapes and surface functions orientated applications in different domains are also discussed, followed by the perspectives and challenges faced in the further advancement of polymeric Janus nanoparticles as high performance materials.

Janus or homogeneous nanoparticle mediated self-assembly of polymer electrolyte fuel cell membranes

The functionality of polymer electrolyte fuel cell membranes depends on the self-assembled structure of the graft polymer. To control self-assembly, nanoparticles (NPs) are often used as catalysts. Hence, we investigate the effect of hydrophilic (HI), hydrophobic (HO), and Janus nanoparticles (JNPs) for the self-assembly of graft polymers using dissipative particle dynamics (DPD) simulations. We found that the differences that appeared among the self-assembled structures of water depended on the concentration of PEFC. We also calculated the diffusion constant of water (D(H2O)) from the slopes of the time-averaged mean square displacement (MSD) curves. HI NPs had the largest effect in suppressing the diffusion of water because the HI NPs incorporated into the water particles. It was also seen that D(H2O) with various NPs gradually decreased as the number of NPs increased for three PEFC concentrations (70%, 80%, and 90%). Thus, a close correlation between the position and chemical composition of NPs in polymer electrolyte fuel cell (PEFC) membrane systems has been found. Moreover, the mean square radius of gyration 〈R g〉 and the mean square end-to-end distance 〈R〉 was calculated to analyse the self-assembled structures of PEFC. The 〈R g〉 and 〈R〉 increased as the concentration of PEFC was increased, with and without various NPs.

Artificial molecular and nanostructures for advanced nanomachinery

Artificial nanomachines can be broadly defined as manmade molecular and nanosystems that are capable of performing useful tasks, very often, by means of doing mechanical work at the nanoscale. Recent advances in nanoscience allow these tiny machines to be designed and made with unprecedented sophistication and complexity, showing promise in novel applications, including molecular assemblers, self-propelling nanocarriers and in vivo molecular computation. This Feature Article overviews and compares major types of nanoscale machines, including molecular machines, self-assembled nanomachines and hybrid inorganic nanomachines, to reveal common structural features and operating principles across different length scales and material systems. We will focus on systems with feature size between 1 and 100 nm, where classical laws of physics meet those of quantum mechanics, giving rise to a spectrum of exotic physiochemical properties. Concepts of nanomachines will be illustrated by selected seminal work along with state-of-the-art progress, including our own contribution, across the fields. The Article will conclude with a brief outlook of this exciting research area.

Biodistribution and Clearance of Stable Superparamagnetic Maghemite Iron Oxide Nanoparticles in Mice Following Intraperitoneal Administration

Nanomedicine is an emerging field with great potential in disease theranostics. We generated sterically stabilized superparamagnetic iron oxide nanoparticles (s-SPIONs) with average core diameters of 10 and 25 nm and determined the in vivo biodistribution and clearance profiles. Healthy nude mice underwent an intraperitoneal injection of these s-SPIONs at a dose of 90 mg Fe/kg body weight. Tissue iron biodistribution was monitored by atomic absorption spectroscopy and Prussian blue staining. Histopathological examination was performed to assess tissue toxicity. The 10 nm s-SPIONs resulted in higher tissue-iron levels, whereas the 25 nm s-SPIONs peaked earlier and cleared faster. Increased iron levels were detected in all organs and body fluids tested except for the brain, with notable increases in the liver, spleen, and the omentum. The tissue-iron returned to control or near control levels within 7 days post-injection, except in the omentum, which had the largest and most variable accumulation of s-SPIONs. No obvious tissue changes were noted although an influx of macrophages was observed in several tissues suggesting their involvement in s-SPION sequestration and clearance. These results demonstrate that the s-SPIONs do not degrade or aggregate in vivo and intraperitoneal administration is well tolerated, with a broad and transient biodistribution. In an ovarian tumor model, s-SPIONs were shown to accumulate in the tumors, highlighting their potential use as a chemotherapy delivery agent.

Recent advances in RAFT-mediated surfactant-free emulsion polymerization

We summarized the RAFT-mediated surfactant-free emulsion polymerization using various RAFT agents and the polymerization types for the preparation of organic/inorganic hybrid materials.

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.

H2O2 Enables Convenient Removal of RAFT End-Groups from Block Copolymer Nano-Objects Prepared via Polymerization-Induced Self-Assembly in Water

RAFT-synthesized polymers are typically colored and malodorous due to the presence of the sulfur-based RAFT end-group(s). In principle, RAFT end-groups can be removed by treating molecularly dissolved copolymer chains with excess free radical initiators, amines, or oxidants. Herein we report a convenient method for the removal of RAFT end-groups from aqueous dispersions of diblock copolymer nano-objects using H2O2. This oxidant is relatively cheap, has minimal impact on the copolymer morphology, and produces benign side products that can be readily removed via dialysis. We investigate the efficiency of end-group removal for various diblock copolymer nano-objects prepared with either dithiobenzoate- or trithiocarbonate-based RAFT chain transfer agents. The advantage of using UV GPC rather than UV spectroscopy is demonstrated for assessing both the kinetics and extent of end-group removal.

Janus nanoparticles inside polymeric materials: interfacial arrangement toward functional hybrid materials

Recent advances and successes in interfacial behavior of Janus NPs at interfaces are summarized, with the hope to motivate additional efforts in the studies of Janus NPs in polymer matrix for the design of functional hybrid nanostructures and devices with engineered, desired and tailored properties for real-life applications.

The in situ formation of nanoparticles via RAFT polymerization-induced self-assembly in a continuous tubular reactor

Amphiphilic poly(poly(ethylene glycol)methyl ether methacrylate)-b-poly(methyl methacrylate) (PPEGMA-b-PMMA) diblock copolymer nanoparticles were successfully synthesized via polymerization-induced self-assembly (PISA) at 70 °C in a continuous tubular reactor.

Methacrylic block copolymers by sulfur free RAFT (SF RAFT) free radical emulsion polymerisation

We demonstrate the use of sulfur free reversible addition–fragmentation chain transfer polymerisation (RAFT) as a versatile tool for the controlled synthesis of methacrylic block and comb-like copolymers.

A simple strategy to improve the interfacial activity of true Janus gold nanoparticles: a shorter hydrophilic capping ligand

Janus gold nanoparticles (JPs) of ∼4 nm-diameter half functionalized with 1-hexanethiol as a hydrophobic capping ligand exhibit significantly higher interfacial activity, reproducibility and rheological response when the other half is functionalized with 1,2-mercaptopropanediol (JPs-MPD) than with 2-(2-mercaptoethoxy)ethanol (JPs-MEE), both acting as hydrophilic capping ligands. The interfacial pressure measured by pendant drop tensiometry reaches 50 mN m(-1) and 35 mN m(-1) for the JPs-MPD at the water/air and water/decane interface, respectively. At the same area per particle, the JPs-MEE reveal significantly lower interfacial pressure: 15 mN m(-1) and 5 mN m(-1) at the water/air and water/decane interface, respectively. Interfacial dilatational rheology measurements also show an elastic shell behaviour at higher compression states for JPs-MPD while the JPs-MEE present near-zero elasticity. The enhanced interfacial activity of JPs-MPD is explained in terms of chemical and hydration differences between the MPD and MEE ligands, where MPD has a shorter hydrocarbon chain and twice as many hydroxyl terminal groups as MEE.

Controlled fabrication of polymeric Janus nanoparticles and their solution behaviors

Well-defined Janus particles with tunable Janus balances are achieved, and the influences of Janus balance have been discussed in detail.

Control of cross-linking and reactions in one-step dispersion polymerization toward particles with combined anisotropies

Particles with a combination of anisotropies in morphology, surface roughness, structure and composition are synthesized by one-step dispersion polymerization.

One-step fabrication of polymeric hybrid particles with core–shell, patchy, patchy Janus and Janus architectures via a microfluidic-assisted phase separation process

We report in this paper a one-step route for the preparation of core–shell, patchy, patchy Janus and Janus particles via a microfluidic-assisted phase separation process.

One-step synthesis of Janus hybrid nanoparticles using reverse atom transfer radical polymerization in emulsion

Janus hybrid nanoparticles have been synthesized by one-step reverse atom transfer radical polymerization in emulsion, which reduces the requirement of reaction conditions.

Polymeric Janus nanoparticles from triblock terpolymer micellar dimers

Well-defined polymeric Janus nanoparticles have been synthesized by a novel method of combining self-assembly of simple ABC linear triblock terpolymers into nanostructured dimers and crosslinking of the conjunction between the opposite hemispheres.