Janus Microspheres Research Articles

Nondeterministic Wetting of Janus Microspheres at the Oil/Water Interface.

We investigate the nondeterministic wetting behaviors of Janus particles at the n-decane/water interface. Upon adsorption at the interface, only some particles reach their thermodynamically stable configuration, while many remain in random nonequilibrium states likely due to contact line pinning. Experimental data and Monte Carlo simulations show that particles in nonequilibrium states with lower three-phase contact angles exhibit reduced attractive forces due to a smaller radius of the three-phase contact line. We also find that vertical translation more easily leads to equilibrium than rotational motion. This work motivates further exploration into the effects of surface tension and surface roughness on identifying the pinning energy barrier, as well as the pinning behavior of biological materials.

Low efficiency of Janus microswimmers as hydrodynamic mixers.

The generation of fluid flows by autophoretic microswimmers has been proposed as a mechanism to enhance mass transport and mixing at the micro- and nanoscale. Here, we experimentally investigate the ability of model 2D active baths of photocatalytic silica-titania Janus microspheres to enhance the diffusivity of tracer particles at different microswimmer densities below the onset of collective behavior. Inspired by the similarities between our experimental findings and previous results for biological microorganisms, we then model our Janus microswimmers using a general squirmer framework, specifically treating them as neutral squirmers. The numerical simulations faithfully capture our observations, offer an insight into the microscopic mechanism underpinning tracer transport, and allow us to expand the parameter space beyond our experimental system. We find strong evidence that near-field interactions dominate enhancements in tracer diffusivity in active Janus baths, leading to the identification of an operating window for enhanced tracer transport by chemical microswimmers based on scaling arguments. Based on this argumentation, we suggest that for many chemically active colloidal systems, hydrodynamics alone is likely to be insufficient to induce appreciable mixing of passive components with large diffusion coefficients.

V-Doped CoSe2 Nanowire Catalysts in a 3D-Structured Electrode for Durable Li-S Pouch Cells.

Lithium-sulfur (Li-S) batteries have high theoretical energy density and are regarded as a promising candidate for next-generation energy storage systems. However, their practical applications are hindered by the slow kinetics of sulfur conversion and polysulfide shuttling. In particular, large-scale pouch cells show much poor cyclability. Here, we develop a high-efficiency catalyst of V-doped CoSe2 by studying the binary CoSe2-VSe2 system and confirming its effectiveness in accelerating polysulfide conversion. The coin cell tests reveal an initial capacity of 1414 mAh g-1 at 0.1 C and 1049 mAh g-1 at 1 C and demonstrate 1000 times cyclability with a decaying rate of 0.05% per cycle. Furthermore, the assembly and construction of pouch cells were optimized with monolithic three-dimensional (3D) electrodes and a multistacking strategy. Specifically, a 3D metallic scaffold (3MS) was developed to host V-doped CoSe2 nanowires and sulfur. In addition, Janus microspheres of C@TiO2 were synthesized to capture polar polysulfides with their polar part of TiO2 and adsorb nonpolar sulfur with their nonpolar part of carbon. By integrating with 3MS, C@TiO2 microspheres can block all ion channels of 3MS and only allow Li ions in and out. These integral designs and monolithic structures enable multistacking pouch cells with high cyclability. A high-loading pouch cell was demonstrated with a total capacity of 700 mAh. The cell can be cycled for 70 times with a capacity retention of 65.7%. In brief, this work provides an integral strategy of catalyst design and overall 3D assembly for practical Li-S batteries in a large pouch cell format.

Microreactor-Enhanced Enzymatic Breakdown: Janus microspheres with cutinase for nanoplastic removal during water treatment

While enzymatic degradation has proven to be an effective way of remediating nanoplastic-related pollution, the practical deployment of this technique is hampered by concerns over enzyme stability, costs, and the low concentration of nanoplastics in natural settings. In this study, we unveil a facile microreactor-enhanced method that improves the effective remediation capacity of cutinase for nanoplastic-polluted water systems. Our approach leverages the self-assembly capabilities of block copolymers within microfluidic droplets to fabricate Janus microspheres with distinct dual-porosity features, which have an enzyme loading capacity of up to 103.8 mg cutinase/g microsphere. The cutinase-anchored microspheres can act as microreactors to capture and degrade nanoplastics. Despite its lower enzymatic activity, the immobilized cutinase exhibits degradation performance comparable to that of its free enzyme counterpart. Moreover, it displays good operational stability over six degradation cycles. Therefore, our findings shed some light on achieving more efficient and cost-effective enzymatic nanoplastic remediation.

Optical manipulation of ratio-designable Janus microspheres

Angular optical trapping based on Janus microspheres has been proven to be a novel method to achieve controllable rotation. In contrast to natural birefringent crystals, Janus microspheres are chemically synthesized of two compositions with different refractive indices. Thus, their structures can be artificially regulated, which brings excellent potential for fine and multi-degree-of-freedom manipulation in the optical field. However, it is a considerable challenge to model the interaction of heterogeneous particles with the optical field, and there has also been no experimental study on the optical manipulation of microspheres with such designable refractive index distributions. How the specific structure affects the kinematic properties of Janus microspheres remains unknown. Here, we report systematic research on the optical trapping and rotating of various ratio-designable Janus microspheres. We employ an efficient T-matrix method to rapidly calculate the optical force and torque on Janus microspheres to obtain their trapped postures and rotational characteristics in the optical field. We have developed a robust microfluidic-based scheme to prepare Janus microspheres. Our experimental results demonstrate that within a specific ratio range, the rotation radii of microspheres vary linearly and the orientations of microsphere are always aligned with the light polarization direction. This is of great importance in guiding the design of Janus microspheres. And their orientations flip at a particular ratio, all consistent with the simulations. Our work provides a reliable theoretical analysis and experimental strategy for studying the interaction of heterogeneous particles with the optical field and further expands the diverse manipulation capabilities of optical tweezers.

Non-spherical Janus microparticles localization using equivalent geometric center and image processing

In recent years, Janus microspheres technology has been widely applied and developed in various fields. However, existing studies often rely on electron microscopy images, treating Janus microspheres as spherical to observe their submicron structures. This approach falls short in meeting the demand for precise measurement of the specific position and orientation of microspheres at the single-molecule scale. Here, we propose a standardized processing procedure that integrates multiple image processing algorithms to measure the position of Janus microspheres through the image capture. Our approach enhances the two-dimensional planar positioning accuracy of non-spherical Janus microspheres in micro-nano optical measurement systems. Utilizing this method, we can conduct a further research on the structure and motion characteristics of the microsphere at the single-particle scale. This method has been validated on a transmission illumination optical tweezers platforms, successfully calibrating the central position of the optical trap. Our work offers a greater convenience for measuring non-spherical Janus microspheres in liquid environments. It also provides a fresh perspective for subsequent studies on the motion trajectories and force dynamics of heterogeneous microspheres, showcasing its broad potential for application.

Magnetic‐optical dual functional Janus particles for the detection of metal ions assisted by machine learning

AbstractFunctional polymer microspheres have broad application prospects in various fields, such as metal ion detection, adsorption, separation, and controlled drug release. However, integrating different functions in a single microsphere system is a significant challenge in this field. In this work, we prepared multicompartmental emulsion droplets utilizing microfluidic technology. Fe3O4 magnetic nanoparticles were added to one of the compartments of the emulsion droplets as functional particles, and Janus microspheres were obtained after curing. Fluorescent probes enter the two compartments of the Janus microspheres by diffusion. The fluorescence changes of the microspheres were observed in situ and captured through a fluorescence microscope. The images are processed by image recognition software and a Python program. The “fingerprint” of the detected metal ions is obtained by dimensionality reduction of the data through Principal Component Analysis. We employ different algorithms to build Machine Learning models for predicting the metal ion species and concentration. The variation of fluorescence intensity of the three fluorescent probes and the corresponding R, G, and B channel values and time are used as descriptors. The results show that the Random Forest, K‐neighborhood (KNN), and Neural Network models demonstrated a better predicted effect with a variance (R2) greater than 0.9 and a smaller root mean square error; among them, the KNN model predicted the most accurate results.

Pickering emulsion-based TiO2@PPy janus microspheres for efficient photocatalytic degradation of 5-methylbenzotriazole

The importance of photocatalysts is indisputable in scientific research. Improving the efficiency of photocatalysis depends on appropriate catalyst structure design and synthesis strategies that enhance the separation and migration efficiency of photogenerated charge carriers. In this study, we used a Pickering emulsion-based template masking method to prepare Janus-like core-shell TiO2 @PPy under in-situ UV irradiation. Compared to non-Janus-like core-shell catalysts, Janus-like catalysts showed 1.5–10 times higher efficiency for the degradation of 5-MBT. The two catalysts were analyzed using time-resolved photoluminescence(TRPL), and the fitting analysis of the results indicated that the Janus-like catalyst exhibited a higher proportion of long-lived charge carriers. This indicates that the Janus structure has a decisive effect on the charge separation of photocatalyst particles. The electron transfer mechanism of the Janus composite catalyst was further determined by EPR and band structure analysis. This work demonstrates a simple and scalable preparation strategy to enhance the efficiency of photocatalysts.

Steering Micromotors via Reprogrammable Optoelectronic Paths

Steering micromotors is important for using them in practical applications and as model systems for active matter. This functionality often requires magnetic materials in the micromotor, taxis behavior of the micromotor, or the use of specifically designed physical boundaries. Here, we develop an optoelectronic strategy that steers micromotors with programmable light patterns. In this strategy, light illumination turns hydrogenated amorphous silicon conductive, generating local electric field maxima at the edge of the light pattern that attracts micromotors via positive dielectrophoresis. As an example, metallo-dielectric Janus microspheres that self-propelled under alternating current electric fields were steered by static light patterns along customized paths and through complex microstructures. Their long-term directionality was also rectified by ratchet-shaped light patterns. Furthermore, dynamic light patterns that varied in space and time enabled more advanced motion controls such as multiple motion modes, parallel control of multiple micromotors, and the collection and transport of motor swarms. This optoelectronic steering strategy is highly versatile and compatible with a variety of micromotors, and thus it possesses the potential for their programmable control in complex environments.

An axis-asymmetric self-driven micromotor that can perform precession multiplying “on-the-fly” mass transfer

<h2>Summary</h2> Self-driven micro/nanomotors (MNMs) can generate "on-the-fly" mass transfer, significantly advancing micro/nanofluid technologies. However, the presence of at least one symmetric axis regulates them to implement either translation or rotation, confining the enhancement efficiency for mass transfer. Here, we report axis-asymmetric hollow bowl-shaped Janus micromotors that can perform unusual precession like a spinning top and thus intriguingly enhance liquid medium convection in a large area. They are formed by self-collapse of polystyrene (PS)/platinum (Pt) hollow Janus microspheres adjacent to the boundary between the two hemispheres of PS and Pt caused by the osmotic pressure with the assistance of stirring. The synchronistic self-rotation and translation modulated by the fuel concentration and depression degree can multiply solute mixing and diffusion efficiencies by several times compared with conventional Janus counterparts. This work demonstrates a novel motion mode of self-driven MNMs, precession that greatly enhances micro-convection and rapid diffusion of liquid medium.

Self-locomotive composites based on asymmetric micromotors and covalently attached nanosorbents for selective uranium recovery

Nanosized sorbents are widely used for uranium (VI) recovery due to their high specific surface area, but the research on the integration of micromotors with nanosorbents to establish self-locomotive composites is still worth exploring. Thus, self-locomotive composites PS@PDA@Ag/SiO2-AO (PPA/SA) based on asymmetric micromotors and covalently attached nanosorbents were designed for selective uranium recovery. Pickering emulsion, as an important micro-reactor, was firstly adopted to prepare Janus microspheres with chemically distinct structure (PS@PDA@Ag), on which one hemisphere was loaded with catalytic silver (Ag) nanoparticles. Then, amidoxime (AO) decorated SiO2 nanospheres were covalently attached onto another hemisphere of PS@PDA@Ag, anisotropic configuration of as-prepared PPA/SA avoided the overlap of catalytic and binding sites. The self-propelled motion of PPA/SA induced by asymmetrical bubble evolution by H2O2 was observed, and the maximum speed was about 25 μm s−1 in case of 5 % H2O2. The uranium adsorption onto PPA/SA achieved 92 % of the equilibrium amount (29.31 mg g−1) in the first 20 min, and this value increased to 38.71 mg g−1 under the condition of H2O2, suggesting that autonomous movement achieves rapid mixing and mass transportation. The maximum adsorption amount (Qm) is 114.0 mg g−1 at 298 K according to the Langmuir model. In addition, PPA/SA exhibited remarkable selectivity for uranium even in the presence of large amounts of Na+, Mg2+, K2+, Ca2+ and other ions in the simulated seawater solution.

Robust superhydrophobic coating with hollow SiO2/PAA-b-PS Janus microspheres for self-cleaning and oil–water separation

Superhydrophobic coating can be widely used in many fields because it is not easily wetted by water like lotus leaves. However, most of superhydrophobic coating is difficult to withstand abrasion attack. Herein, hollow SiO2/PAA-b-PS Janus microspheres were synthesized via emulsion interfacial synthesis method using amphiphilic block copolymer of polyacrylic acid block polystyrene (PAA-b-PS) and hollow NH2-SiO2 microspheres as raw materials in this paper. Because the hemisphere grafting organic polymer chain was hydrophobic and the other hemisphere was hydrophilic and contained amino groups, hollow SiO2/PAA-b-PS Janus microspheres exhibited amphiphilic and asymmetrical nature, which was a typical inorganic/polymer Janus microspheres. Robust superhydrophobic coating was facilely achieved using hollow SiO2/PAA-b-PS Janus microspheres on polyurethane pretreated substrate like leather and fabric. Robust superhydrophobic coating after 90 sandpaper abrasion cycles still retained excellent superhydrophobicity. As expected, robust superhydrophobic coating had prominent self-cleaning property against different pollutants and was capable to separate a variety of oil–water mixtures with ultrahigh separation efficiency. The separation efficiency of robust superhydrophobic coating for oil–water mixture was maintained above 98% even after 40 separation cycles. In total, robust superhydrophobic coating constructed by hollow SiO2/PAA-b-PS Janus microspheres possesses distinguished superhydrophobicity, abrasion resistance, self-cleaning, oil–water separation capacity and universality, which shows a promising application in multifunctional coating.

Dual-Colored Janus Microspheres with Photonic and Plasmonic Faces.

Photonic and plasmonic colors, stemming from nanostructures of dielectric materials and metals, are promising for pigment-free coloration. In particular, nanostructures with structural colors have been employed in stimuli-responsive Janus microparticles to provide active color pixels. Here, the authors report a simple strategy to produce electro-responsive Janus microspheres composed of photonic and plasmonic faces for active color change. The photonic microspheres are first prepared by self-assembly of silica particles in emulsion droplets of photocurable resin. The silica particles form 3D crystalline arrays in the interior and 2D hexagonal arrays on the interface. The emulsion droplets are photocured and the silica particles are selectively removed to make porous photonic microspheres with hexagonal arrays of dimples on the surface. Directional deposition of gold or aluminum on the photonic microsphere develops plasmonic color on the top hemisphere while maintaining photonic color on the bottom hemisphere. Moreover, the metal deposited on one side renders the Janus microspheres electro-responsive. Therefore, the photonic and plasmonic colors are switchable by the orientation control of the Janus microspheres with an external electric field. The photonic and plasmonic colors are independently adjustable by employing two different sizes of silica particles in core-shell emulsion drops.

Amphiphilic Janus Microspheres Prepared by Caged Photoactivatable Alkoxysilane

A simple photolysis route was proposed to prepare Amphiphilic Janus Particles (AJP) based on SiO2 microspheres. The surface of SiO2 microspheres were modified by photoactive alkoxysilane, which was synthesized by dealcoholization condensation of 6-nitroveratroyloxycarbonyl and isocyanatopropyl-triethoxysilane. UV irradiation caused eater-breaking allowed for the precise control of hydrophilic modification of the hemispherical exposed particles surfaces. The component and morphology of the obtained particles were characterized by fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy, and the Janus feature was evaluated by scanning electron microscopy, transmission electron microscopy, and dispersity in the oil–water dual-phases. The following results were obtained. The AJP with 450 nm size processes the hydrophilic amino groups on one side and the hydrophobic 6-nitroveratryloxycarbonyl moieties on the other. Additionally, the AJP were located at the phase boundary between water and n-hexane, and the negative charged gold nanoparticles with 25 nm size were adsorbed only onto the side with the positive charged amino groups. The AJP have interfacial adsorption energies that can be as much as three times larger than that of homogeneous particles and thus exhibit excellent surface activities.

Janus Photonic Microspheres with Bridged Lamellar Structures via Droplet-Confined Block Copolymer Co-Assembly.

Artificial self-assembly systems typically exhibit limited capability in creating nature-inspired complex materials with advanced functionalities. Here, an effective co-assembly strategy is demonstrated for the facile creation of complex photonic structures with intriguing light reflections. Two different lipophilic and amphiphilic bottlebrush block copolymers (BCPs) are placed within shrinking droplets to enable a cooperative working mechanism of microphase segregation and organized spontaneous emulsification, respectively. Layer assemblies of the lipophilic BCP and uniform water nanodroplets stabilized by the bottlebrush surfactant are both generated, and co-assembled into a bridged lamellar structure with the alternating arrangement of layers and closely packed nanodroplet arrays. Janus microspheres with diverse dual optical characteristics are successfully fabricated, and reflected wavelengths of light are highly tunable simply by changing the formulation or molecular weight of BCP.

Janus Photonic Microspheres with Bridged Lamellar Structures via Droplet‐Confined Block Copolymer Co‐Assembly

AbstractArtificial self‐assembly systems typically exhibit limited capability in creating nature‐inspired complex materials with advanced functionalities. Here, an effective co‐assembly strategy is demonstrated for the facile creation of complex photonic structures with intriguing light reflections. Two different lipophilic and amphiphilic bottlebrush block copolymers (BCPs) are placed within shrinking droplets to enable a cooperative working mechanism of microphase segregation and organized spontaneous emulsification, respectively. Layer assemblies of the lipophilic BCP and uniform water nanodroplets stabilized by the bottlebrush surfactant are both generated, and co‐assembled into a bridged lamellar structure with the alternating arrangement of layers and closely packed nanodroplet arrays. Janus microspheres with diverse dual optical characteristics are successfully fabricated, and reflected wavelengths of light are highly tunable simply by changing the formulation or molecular weight of BCP.

Emergence of Ring‐Shaped Microstructures in Restricted Geometries Containing Self‐Propelled, Catalytic Janus Spheres

AbstractThe evaporation of liquid droplets containing colloids is an omnipresent natural phenomenon that has received much attention due to the fundamental effects it entails, as well as the multitudes of fields in which it can be applied. The deposition of particulates onto a solid surface during evaporation tends to form ring‐like stains, which are a hallmark of the “coffee‐ring effect.” A wide variety of systems has already been employed to suppress or enable this effect, however, little attention has been focused on particles in restricted geometries that are driven far from equilibrium. Here, we investigate how self‐propelled, “active” catalytic Janus microspheres affect the ring stains left behind during the drying of a geometrically confined suspension containing such particles. Self‐propulsion results indirectly from the decomposition of hydrogen peroxide (H2O2) on the catalytically active hemispherical shell, while the diametrically opposite face is inert; this is how the system is driven out of equilibrium. The magnitude of activity can be controlled by adjusting the volume concentration of aqueous H2O2 within the suspension. This parameter strongly influences the ring‐shaped microstructures obtained, especially when the concentration is sufficiently high to produce oxygen bubbles that take over the motion as opposed to auto‐phoresis.

High-throughput generation of microgels in centrifugal multi-channel rotating system

Microgels are extremely attractive in chemical engineering, food industry, energy storage, biomedical engineering, etc. However, mass production of microgels with uniform size as well as tunable components and structures remains difficult. Here, we present a novel centrifugal multi-channel rotating system for high-throughput generation of monodisperse microgels with tunable sizes. This system adopts a simple design yet being applicable to a variety of polymer components. Besides, microgels with diverse anisotropic structures including spherical, teardrop-like, tailed, stomatocyte-like, and fibrous are generated with precise control. Moreover, the system could be extended towards preparing bicomponent microgels including Janus microspheres and microcapsules. The drug loading and release performance demonstrate the potential of this system in drug delivery. These characteristics indicate that such centrifugal multi-channel rotating system has great application potentials in mass production of microgels and the related fields.

Active and selective removal of Cs from contaminated water by self-propelled magnetic illite microspheres

We report the fabrication of clay-mineral-based Janus microspheres that exhibit remotely steerable self-propulsion in water, facilitating their selective and active removal of radiocesium from a contaminated solution. The spray-drying of slurries of intrinsically Cs-selective illite containing iron oxide nanoparticles led to magnetic illite microspheres with superior 137Cs adsorption capability and superparamagnetic behavior. The Janus micromotor adsorbent was prepared by depositing catalytic Pt onto the half-surface of magnetic illite microspheres. The micromotor adsorbents exhibited self-propulsion at speeds as high as ~265 µm/s via asymmetric bubble generation in water containing H2O2 as a fuel. The self-propulsion of the adsorbent improved the Cs adsorption kinetics six-folds compared with the kinetics in the corresponding stationary liquid. The magnetic properties of the micromotor adsorbent enabled convenient separation and direction control of the adsorbents under an external magnetic field. In particular, the micromotor adsorbent could successfully remove more than 98.6% of 137Cs from aqueous media containing competing ions including K+, Na+, Ca2+ and Mg2+.

Plasmonic Janus Microspheres Created from Pickering Emulsion Drops.

Metal nanostructures have been created in a film format to develop unique plasmonic properties. Here, well-defined metal nanostructures are designed on the surface of microspheres to provide plasmonic microgranules. As conventional techniques are inadequate for nanofabrication on spherical surfaces, photocurable emulsion drops with a regular array of silica particles are employed at the interface to create periodic nanostructures. The silica particles, originating from the dispersed phase, fully cover the interface by forming a non-close-packed hexagonal array after drop generation, and slowly protrude to the continuous phase during aging while their interparticle separation decreases. Therefore, hexagonal arrays of spherical dimples with controlled geometry and separation are created on the surface of microspheres by photocuring the drops and removing the particles. Directional deposition of either aluminum or gold results in a continuous film with a hexagonal array of holes on the outermost surface and isolated curved disks in dimples, which renders the hemisphere of microspheres plasmonically colored. The resonant wavelength is controlled by adjusting the aging time, metal thickness, and size of silica particles, providing various plasmonic colors. This granular format of the plasmonic Janus microspheres will open a new avenue of optical applications including active color pixels, optical barcodes, and microsensors.