Janus Particles Research Articles

Deciphering Long-Range Order in Active Matter: Insights from Swimming Bacteria in Quasi-2D and Electrokinetic Janus Particles

Deciphering Long-Range Order in Active Matter: Insights from Swimming Bacteria in Quasi-2D and Electrokinetic Janus Particles

Janus particles: features, synthesis and potential uses, including surface functionalisation

ABSTRACTAs the development of nanostructured materials continues to blossom, there is increasing attention to functionalised particles. The so-called Janus particles are anisotropic regions having different physicochemical properties. The recent development of their synthesis in a pH field during suspension as bipolar particles between electrodes has opened the door to improved scalability due to the ease of entraining particles as a slurry in a flowing electrolyte stream. Potential application areas span catalysis of chemical synthesis, sustainable energy conversion and pharmaceutical and biomedical sectors of industry. In view of their versatility, the ability to undergo surface modification and opportunities for facile scale-up, Janus particles might be deployed as building blocks to fabricate functional surfaces having tailored chemical, structural and surface anisotropy. They could prove to be valuable feedstock in 3-D printing and surface finishing of fast prototype components and devices.

Phase separation of a magnetic fluid: Asymptotic states and nonequilibrium kinetics.

We study self-assembly in a colloidal suspension of magnetic particles by performing comprehensive molecular dynamics simulations of the Stockmayer (SM) model, which comprises spherical particles decorated by a magnetic moment. The SM potential incorporates dipole-dipole interactions along with the usual Lennard-Jones interaction and exhibits a gas-liquid phase coexistence observed experimentally in magnetic fluids. When this system is quenched from the high-temperature homogeneous phase to the coexistence region, the nonequilibrium evolution to the condensed phase proceeds with the development of spatial as well as magnetic order. We observe density-dependent coarsening mechanisms-a diffusive growth law ℓ(t)∼t^{1/3} in the nucleation regime and hydrodynamics-driven inertial growth law ℓ(t)∼t^{2/3} in the spinodal regimes. [ℓ(t) is the average size of the condensate at time t after the quench.] While the spatial growth is governed by the expected conserved order parameter dynamics, the growth of magnetic order in the spinodal regime exhibits unexpected nonconserved dynamics. The asymptotic morphologies have density-dependent shapes which typically include the isotropic sphere and spherical bubble morphologies in the nucleation region, and the anisotropic cylinder, planar slab, cylindrical bubble morphologies in the spinodal region. The structures are robust and nonvolatile, and exhibit characteristic magnetic properties. For example, the oppositely magnetized hemispheres in the spherical morphology impart the characteristics of a Janus particle to it. The observed structures have versatile applications in catalysis, drug delivery systems, memory devices, and magnetic photonic crystals, to name a few.

On the Interfacial Assembly of Anisotropic Amphiphilic Janus Particles

AbstractIt has been shown both theoretically and experimentally that amphiphilic Janus particles are the most effective solid surfactants to stabilize interfaces. In most cases, the Janus particles investigated have uniform morphologies with Janus boundaries dividing the particle into halves. However, there are many examples of Janus particles where the hydrophilic and hydrophobic domains are not equally distributed. The effects of this uneven domain distribution on the mechanism and kinetics of Janus particle assembly, and final equilibrium state are not well‐understood. Dynamic pendant drop tensiometry offers a means to probe both the equilibrium assembly and the kinetics and mechanism of assembly. Here, the interfacial kinetics and assembly of spherical anisotropic Janus particles are investigated using dynamic pendant drop tensiometry. Systematic studies quantifying the time‐dependent interfacial behavior as a function of Janus particle morphology, chemical composition, particle concentration, and NaOH and HCl concentration are performed. These studies shed light on the assembly mechanism of more complex Janus particle morphologies and highlight their effectiveness as interface stabilizers.

Self-Assembly Pathways of Triblock Janus Particles into 3D Open Lattices.

The self-assembly of triblock Janus particles is simulated from a fluid to 3D open lattices: pyrochlore, perovskite, and diamond. The coarse-grained model explicitly takes into account the chemical details of the Janus particles (attractive patches at the poles and repulsion around the equator) and it contains explicit solvent particles. Hydrodynamic interactions are accounted for by dissipative particle dynamics. The relative stability of the crystals depends on the patch width. Narrow, intermediate, and wide patches stabilize the pyrochlore-, the perovskite-, and the diamond-lattice, respectively. The nucleation of all three lattices follows a two-step mechanism: the particles first agglomerate into a compact and disordered liquid cluster, which does not crystallize until it has grown to a threshold size. Second, the particles reorient inside this cluster to form crystalline nuclei. The free-energy barriers for the nucleation of pyrochlore and perovskite are ≈10kBT, which are close to the nucleation barriers of previously studied 2D kagome lattices. The barrier height for the nucleation of diamond, however, is much larger (>20kBT), as the symmetry of the triblock Janus particles is not perfect for a diamond structure. The large barrier is associated with the reorientation of particles, i.e., the second step of the nucleation mechanism.

Synthesis of Anisotropic Magnetic Polymeric Janus Particles by In Situ Separation of Magnetic Nanoparticles in a Microfluidic Device.

Magnetic Janus particles have been studied extensively for medical and biological applications owing to their controllable mobility in fluid media. In this work, we report a novel microfluidic device designed for the synthesis of magnetically anisotropic Janus particles made of poly(ethylene glycol) diacrylate and embedded with magnetic iron oxide nanoparticles. Our method consists of a droplet generation step followed by magnetic separation using an external magnetic field and ultraviolet polymerization. The synthesized particles exhibit a monodisperse size distribution with a standard deviation of less than 3.5%, which is among the best size distributions obtained in the literature for magnetic Janus particles. The anisotropic magnetic property of the particles enable them to rotate about their own axes in the presence of an external magnetic field, introducing another degree of freedom to their motion. This microfluidic technique is simple, one-step, and versatile, offering control over the size distribution to synthesize magnetically anisotropic Janus particles.

One-pot two-step production of nano-CaCO3 with tunable Janus balance decorated by self-crosslinked admicelle of conjugated linoleate

BackgroundIn mass production of Janus nanoparticles, tunable Janus balance, nanoscale decoration, environmental and biological compatibility, and response to environmental stimuli are challenges. MethodsBy manipulating the self-assembly and self-crosslinking of sodium conjugated linoleate (SCL), we established a facile one-pot synthesis with two-step addition of SCL under wax protection on partial surface of the microspheres to synthesize CaCO3 Janus nanoparticles with above features simultaneously. Significant findingsThe self-crosslinked admicelle (SCA) of SCL decorated on the nano-CaCO3 surface to produce SCA-CaCO3 Janus nanoparticles, and their Janus balance is tunable by simply regulating the primary SCL dosage in the preparation of molten wax emulsions. Afterwards, O/W Pickering emulsions are stabilized by 0.25 wt% of the selected SCA-CaCO3 Janus nanoparticle with a proper Janus balance at primary SCL dosage of 60 mg·L−1; the obtained high internal phase emulsion is reversibly switchable by pH or CO2−N2 triggers. This strategy of one-pot two-step production of Janus particles may provide a facile mass production tool to create hierarchical Janus structures for various inorganic nanoparticles with different sizes and chemical compositions, endowing variable Janus surfaces with tunable Janus balance, providing a nanoscale SCA decoration layer of SCL with biocompatibility, environmental friendliness and multi-stimuli responses.

Demixing behavior of Pickering emulsions stabilized by Janus particles and uniform Pickering particles at different pH values

This work investigates the demixing behavior of Pickering emulsions consisting of water, n-hexadecane, and two different types of Pickering particles. The first type is uniform, and the second consists of one-side modified Janus particles influencing the emulsion behavior significantly. Both particle types are able to stabilize the emulsions, but lead to clear differences in the emulsion drop size and size distribution. This results in different creaming times varying between minutes and hours and different clearance processes of the water excess phase. Large pH effects were found in addition. At some conditions, non-adsorbed particles were observed that sediment over time in addition to the creaming of the emulsion.

Waterproof and Flame-Retardant Fabric Coating with Nail-Tie Structure was Constructed by Janus Particles with Strong Mechanical, Physical, and Chemical Durability.

Oil spills are one of the most dangerous sources that cause serious environmental pollution and fire and explosion. In this work, multifunctional separator silica@polydivinylbenzene/poly 2,6-dimethyl-1, 4-phenyl ether (silica@PDVB/PPE) Janus particles were fabricated via seed emulsion polymerization, causing phase segregation as well as selective modification. The epoxy modified silica is partially covalently bonded to the fabric substrate surface by simple spraying to achieve a strong composite coating. The low surface energy PDVB/PPE forms a micronano rough layered surface, which can achieve a super hydrophobic and lipophile surface (WCA = 155°) and obtain a high flux separation of water and oil at 32,700 L·m-2·h-1. At the same time, the Janus composite fabric coating has the advantages of high heat resistance and flame retardant, which is realized by halogen-free flame-retardant unsaturated polyphosphate (PPE), making Janus fabric have potential value in separating oil-water mixtures and fire protection applications. In addition, the coating shows excellent chemical durability. After soaking in various aqueous solvents and organic solvents for 30 h, it can still maintain superhydrophobicity and flame retardant. The coating still has water repellency and flame retardant after 50 washings and mechanical wear and has good mechanical durability.

Hollow Superstructure In Situ Assembled by Single-Layer Janus Nanospheres toward Electromagnetic Shielding Flame-Retardant Polyurea Composites.

A dodecahedral superstructure consisting of a single layer of Janus spheres containing ZIF-67 nanodots is prepared by in situ polymerization, with ZIF-67 and bio-based phytic acid (PA) as templates and dopants. It is used to improve the flame retardant, electromagnetic (EMI) shielding, and thermal conductivity properties of polyurea (PUA). By adding 5wt% polyaniline@cobalt phytate-2.0 (PANI@Co-PA-2.0), the peak of heat release rate and the peak of smoke production rate are reduced by 54.9 and 59.9%, respectively. The peak of CO and CO2 production also decreased by 46.2 and 53.1%, respectively. A decrease in the absorption intensity of aliphatic and aromatic volatiles is also observed. The fire safety of PUA is greatly improved. In addition, PUA/PANI@Co-PA-2.0 exhibits an EMI shielding capability of 22.4dB with the help of reduced graphene oxide, which confirms the possibility of PUA material application in the field of electromagnetic shielding. The 5wt% filler increases the tensile strength of the PUA matrix to 6.3MPa, and the composite material obtains good thermal conductivity. This work provides a viable method for the preparation of a flame-retardant, conductive, and electromagnetic refractory PUA substrate.

Anisotropic Multitentacle Janus Particles Synthesized by Selective Asymmetric Growth.

Anisotropic colloidal particles with asymmetric morphology possess functionally rich heterogeneous structures, thus offering potential for intricate superstructures or nanodevices. However, it is a challenge to achieve controlled asymmetric surface partitioned growth. In this work, an innovative strategy is developed based on the selective adsorption and growth of emulsion droplets onto different regions of object which is controlled by wettability. It is found that the emulsion droplets can selectively adsorb on the hydrophilic surface but not the hydrophobic one, and further form asymmetric tentacle by the interfacial sol-gel process along its trajectory. Janus particles with an anisotropic shape and multitentacle structure are achieved via integration of emulsion droplet (soft) and seed (hard) templates. The size and number of tentacles exhibit tunability mediated by soft and hard templates, respectively. This general strategy can be expanded to a variety of planar substrates or curved particles, further confirming the correlation between tentacle growth and Brownian motion. Most interestingly, it can be employed to selectively modify one region of surface partitioned particles to achieve an ABC three-component Janus structure.

Preparation of amphiphilic Janus nanosheets based on thermally expandable microspheres and evaluation of their physical and chemical properties

Janus nanosheets can reduce the interfacial tension of oil and water and are of great significance for improving the recovery efficiency of remaining oil. A novel strategy for preparing amphiphilic Janus nanosheets is presented in this paper. Trialkoxysilane is adsorbed on the surface of thermally expandable microspheres (TEMS), and Janus spheres (TEMS@SiO2) are obtained by sol-gel treatment. Dodecyltrimethoxysilane (DTES) is used to modify TEMS@SiO2, which is combined with the thermal expansion of TEMS and the breaking of the outer shell of Janus spheres to prepare amino/alkyl composite silicon-based amphiphilic Janus nanosheets (ASAJN). Characterization of ASAJN is carried out via FTIR, TG, SEM, TEM, and contact angle tester, with the results showing that ASAJN boasts amphiphilicity and two-sidedness, and a sheet structure with a thickness of 210 nm. The stability, wettability evaluation, emulsification properties, and interface properties of ASAJN nanofluids have been evaluated, with the results showing that ASAJN nanofluids boast good stability without delamination after 30 days. ASAJN nanofluid can convert oil-wet core slices into water-wettable ones. ASAJN nanofluid manifests excellent emulsification, with the 240-hour emulsification index of ASAJN nanofluid and silica fluid respectively at0.40 and 0.021 under ultra-low concentration (1000 mg/L). ASAJN is obviously able to reduce oil–water interfacial tension. At 1000 mg/L (60 ℃) concentration, the oil-water interfacial tension is reduced to 2.6 mN/m, while that of nano-silica at the same concentration is 15.1 mN/m. ASAJN flooding can significantly improve the recovery efficiency of low-permeability reservoirs, increasing the recovery efficiency by 32.8 % at a permeability of 7.5 × 10-3 μm2.

Multimode microdimer robot for crossing tissue morphological barrier

Swimming microrobot energized by magnetic fields exhibits remotely propulsion and modulation in complex biological experiment with high precision. However, achieving high environment adaptability and multiple tasking capability in one configuration is still challenging. Here, we present a strategy that use oriented magnetized Janus spheres to assemble the microdimer robots with two magnetic distribution configurations of head-to-side configuration (HTS-config) and head-to-head configuration (HTH-config), achieving performance of multiple tasks through multimode transformation and locomotion. Modulating the magnetic frequency enables multimode motion transformation between tumbling, rolling, and swing motion with different velocities. The dual-asynchronization mechanisms of HTS-config and HTH-config robot dependent on magnetic dipole-dipole angle are investigated by molecular dynamic simulation. In addition, the microdimer robot can transport cell crossing morphological rugae or complete drug delivery on tissues by switching motion modes. This microdimer robot can provide versatile motion modes to address environmental variations or multitasking requirements.

Driven transport of active particles through arrays of symmetric obstacles.

We numerically examine the driven transport of an overdamped self-propelled particle through a two-dimensional array of circular obstacles. A detailed analysis of transport quantifiers (mobility and diffusivity) has been performed for two types of channels, channel I and channel II, that respectively correspond to the parallel and diagonal drives with respect to the array axis. Our simulation results show that the signatures of pinning actions and depinning processes in the array of obstacles are manifested through excess diffusion peaks or sudden drops in diffusivity, and abrupt jumps in mobility with varying amplitude of the drive. The underlying depinning mechanisms and the associated threshold driving strength largely depend on the persistent length of self-propulsion. For low driving strength, both diffusivity and mobility are noticeably suppressed by the array of obstacles, irrespective of the self-propulsion parameters and direction of the drive. When self-propulsion length is larger than a channel compartment size, transport quantifiers are insensitive to the rotational relaxation time. Transport with diagonal drives features self-propulsion-dependent negative differential mobility. The amplitude of the negative differential mobility of an active particle is much larger than that of a passive one. The present analysis aims at understanding the driven transport of active species like, bacteria, virus, Janus particle etc. in porous medium.

Tailored Morphology in Polystyrene/Poly(lactic acid) Blend Particles: Solvent's Effect on Controlled Janus/Core-Shell Structures.

Controlling the morphology of polymeric particles is vital for their diverse applications. In this study, we explored how solvent composition influences the morphology of poly(styrene)/poly(lactic acid) (PS/PLA) particles prepared via the emulsion solvent evaporation method. We used toluene, dichloromethane (DCM), and various mixtures to prepare these particles. We investigated phase separation within the PS/PLA/solvent system using the Flory-Huggins ternary phase diagram and MesoDyn simulation, revealing pronounced immiscibility and phase separation in both PS/PLA/DCM and PS/PLA/toluene systems. We employed scanning electron microscopy (SEM) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) to characterize the resulting morphologies. Our study unveiled the substantial impact of solvent composition on particle structure. Using pure toluene resulted in acorn-shaped Janus particles. However, incorporating DCM into the solvent induced a transition from Janus to core-shell morphology. Remarkably, core-shell particles exhibited a single-core structure in a mixed toluene/DCM solvent, indicating thermodynamic stability. In contrast, pure DCM favored kinetically controlled multicore morphology, leading to lower PLA crystallinity due to increased PS-PLA interfaces. Samples with high Janus balance formed a self-assembled, two-dimensional (2-D) monolayer film, demonstrating the interfacial activity of the Janus particles. This 2-D monolayer film exhibits desirable emulsification properties with potential applications in various fields. Our study combines theoretical and experimental analyses, shedding light on the profound impact of solvent composition on the PS/PLA particle morphology. We observed transitions from Janus to core-shell structures, highlighted the influence of solvent viscosity on particle size, and uncovered the formation of self-assembled 2-D monolayer films. These insights are pivotal for tailoring polymeric particle structures. Furthermore, our findings advance macromolecular science in interface design, offering promising prospects for innovative materials development.

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.

A Quorum Sensing Active Matter in a Confined Geometry

Inspired by the problem of biofilm growth, we numerically investigate clustering in a two-dimensional suspension of active (Janus) particles of finite size confined in a circular cavity. Their dynamics is regulated by a non-reciprocal mechanism that causes them to switch from active to passive above a certain threshold of the perceived near-neighbor density (quorum sensing). A variety of cluster phases, i.e., glassy, solid (hexatic) and liquid, are observed, depending on the particle dynamics at the boundary, the quorum sensing range, and the level of noise.

On-chip screening of SARS-CoV-2 cDNA by LAMP-integrated rotational diffusometry

The unprecedented pandemic has raised the demand for prompt, precise, and large-scale virus detection techniques to control the transmission of contagious illnesses. In this study, a loop-mediated isothermal amplification (LAMP) based on-chip platform was developed to address this challenge using rotational diffusometry and functionalized Janus particles. A recombinant plasmid containing a cDNA sequence of the SARS-CoV-2 non-structural protein 2 (nsp2) gene was employed here as a proof-of-concept for COVID-19 detection. Specifically, designed primers and the functionalized Janus particles were simultaneously loaded on a microfluidic chip to perform the LAMP reaction on a hot plate. The optimal Janus particle concentrations for diffusometric analysis were thoroughly validated, and the performance of the on-chip LAMP reaction was assessed using thermal image analysis. Utilization of the highly sensitive rotational diffusometry achieved a limit of detection of 1 pg/μL in just 10 min with a sample volume of 20 μL. Our method delivered a tenfold higher sensitivity than the conventional method by utilizing only half of its usual required time. Overall, this study proposes a potential nucleic acid (NA) amplification device to aid the rapid diagnosis of various diseases by modifying the primers for different target genes.

Fabrication of Versatile Janus Microparticles through Geometry and Surface Chemistry Control.

Amphiphilic Janus particles typically comprise two distinct hemispheres with spatially dispersed physicochemical properties. The anisotropic structure and physicochemical properties of Janus particles can be exploited for various applications. However, their preparation typically requires complex and sophisticated processes and expensive equipment to control the formation of different structures and chemical compositions. Herein, a simple synthetic approach for the facile fabrication of versatile Janus particles with efficient control of the Janus ratio and wettability based on particle fixation at a three-phase interface and photopolymerization is reported. Agarose gel and surfactant are used to control the surface-coated boundaries of the Janus particles through the equilibrium of a floating microparticle at the fluid interface. poly(propylene glycol) diacrylate or poly(N-isopropylacrylamide) coating on polystyrene-based microparticles allows easy control of the chemical functionality of the particle surfaces. Depending on the particle morphology and wettability, the interfacial behavior between two immiscible liquids can be adjusted, which allows the stabilization of Pickering emulsions that encapsulate independent oil droplets in water or vice versa. This facile approach has the potential to enable more efficient mass production of Janus particles and their use in various applications, such as biomedical and environmental engineering.

Janus particle amphiphilicity and capillary interactions at a fluid interface

AbstractStudying the behavior of anisotropic particles at fluid interfaces is a rapidly expanding field, as understanding how the introduced anisotropy affects the resulting properties is essential in the engineering of interfacial systems. Surface anisotropic particles, also known as Janus particles (JPs), offer new possibilities for novel applications due to their amphiphilicity and stronger binding to fluid interfaces compared to homogeneous particles. Introducing surface anisotropy creates complexity as the orientation of interfacially bound particles affects interparticle interactions, a contributing factor to the microstructure formation. In this work, we have investigated the microstructure of JP monolayers formed at the air–water interface using particles with different degrees of amphiphilicity and examined the response of the networks to applied compressions. Our findings demonstrate that JPs amphiphilicity is a crucial factor governing their orientation at the interface, which in turn dictates the complexity of the capillary interactions present and the mechanical properties of the ensuing networks.