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Janus particles

Bas G P van Ravensteijn, Willem K Kegel
Chemically anisotropic dumbbell-shaped colloids are prepared starting from cross-linked polymer seed particles coated with a chlorinated outer layer. These chlorinated seeds are swollen with monomer. Subsequently, a liquid protrusion is formed on the surface of the seed particle by phase separation between the monomer and the swollen polymer network. Solidification of these liquid lobes by polymerization leads to the desired dumbbell-shaped colloids. The chlorine groups remain confined on the seed lobe of the particles, ensuring chemical anisotropy of the resulting particles...
November 15, 2016: Journal of Colloid and Interface Science
Yijiang Liu, Jiankang Hu, Xiaotian Yu, Xinyu Xu, Yong Gao, Huaming Li, Fuxin Liang
Two Janus-type catalysts were synthesized by selective modification and further functionalization with metal nanoparticles on one or both beads of snowman-like Janus particles. The catalytic performance of Janus-type catalysts both in homogeneous and interfacial reaction systems was systematically investigated using the reduction of nitro-compound as model reaction. The results showed that Janus-type catalysts have excellent catalytic activity in homogeneous reaction system and they are easy to recycle. Further, the Janus-type catalysts exhibited more efficient catalytic activity at emulsion interface than that of oil-water biphasic interface due to the exposed Au nanoparticles on snowman-like Janus particles offer high accessibility to reactants...
November 15, 2016: Journal of Colloid and Interface Science
Lucero Sanchez, Yi Yi, Yan Yu
Controlling the internalization of synthetic particles by immune cells remains a grand challenge for developing successful drug carrier systems. Polyethylene glycol (PEG) is frequently used as a protective coating on particles to evade immune clearance, but it also hinders the interactions of particles with their intended target cells. In this study, we investigate a spatial decoupling strategy, in which PEGs are coated on only one hemisphere of particles, so that the other hemisphere is available for functionalization of cell-targeting ligands without the hindrance effect from the PEGs...
December 2, 2016: Nanoscale
Pingwei Cai, Yuan Hong, Suqin Ci, Zhenhai Wen
Electrochemical catalysis of O2-incorporated reactions is a promising strategy for metal-air batteries. The performance of metal-air batteries is determined by the catalytic activities of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Therefore, developing efficient catalysts with superior activities for the ORR and OER is of great significance to expand the application range of metal-air batteries. Herein, CoFe alloy nanoparticles adhered to the inside wall of nitrogen doped carbon nanotubes (CoFe@NCNTs) are synthesized and can function as a Janus particle to efficiently catalyze the ORR and OER with desirable activities in 0...
November 24, 2016: Nanoscale
Jing Liu, Hong-Lian Guo, Zhi-Yuan Li
Controlled propulsion of microparticles and micromachines in fluids could revolutionize many aspects of technology, such as biomedicine, microfluidics, micro-mechanics, optomechanics, and cell biology. We report the self-propelled cyclic round-trip motion of metallo-dielectric Janus particles in static line optical tweezers (LOT). The Janus particle is a 5 μm-diameter polystyrene sphere half-coated with 3 nanometer thick gold film. Both experiment and theory show that this cyclic translational and rotational motion is a consequence of the collective and fine action of the gold-face orientation dependent propulsion optical force, the gradient optical force, and the spontaneous symmetry breaking induced optical torque in different regions of the LOT...
December 1, 2016: Nanoscale
Francisca Guzmán-Lastra, Andreas Kaiser, Hartmut Löwen
Fission and fusion processes of particle clusters occur in many areas of physics and chemistry from subnuclear to astronomic length scales. Here we study fission and fusion of magnetic microswimmer clusters as governed by their hydrodynamic and dipolar interactions. Rich scenarios are found that depend crucially on whether the swimmer is a pusher or a puller. In particular a linear magnetic chain of pullers is stable while a pusher chain shows a cascade of fission (or disassembly) processes as the self-propulsion velocity is increased...
November 22, 2016: Nature Communications
Nicolò Castro, Doru Constantin, Patrick Davidson, Benjamin Abécassis
Janus nanoparticles bearing two different properties on a single particle are amenable to self-assembly into higher-order structures via their directional interaction. We show that gold/silica Janus nanoparticles self-assemble in solution into clusters resembling colloidal micelles upon addition of a hydrophobic thiol which provides them with a surface active amphiphilic character. As the nanoparticles spontaneously assemble, the color of the solution evolves due to the coupling of the surface plasmons. Time resolved spectrophotometry in the visible and near-infrared ranges coupled to simulations were used to probe the assembly process...
November 21, 2016: Soft Matter
Ana Armada-Moreira, Essi Taipaleenmäki, Fabian Itel, Yan Zhang, Brigitte Städler
Therapeutic cell mimicry is an approach in nanomedicine aiming at substituting for missing or lost cellular functions employing nature-inspired concepts. Pioneered decades ago, only now is this technology empowered with the arsenal of nanotechnological tools and ready to provide radically new solutions such as assembling synthetic organelles and artificial cells. One of these tools is droplet microfluidics (D-μF), which provides the flexibility to generate cargo-loaded particles with tunable size and shape in a fast and reliable manner, an essential requirement in cell mimicry...
December 1, 2016: Nanoscale
Huanxin Wu, Ming Han, Erik Luijten
Spherical Janus colloids, particles with different surface properties on their two hemispheres, are generally heterogeneous in permittivity. This dielectric heterogeneity may affect their behavior in electrolytes and external electric fields, but is typically not taken into account in computational studies. We apply the iterative dielectric solver developed by Barros and Luijten [Phys. Rev. Lett., 2014, 113, 017801] in combination with preconditioning techniques that can accurately and efficiently compute the polarization of dielectrically anisotropic particles...
November 16, 2016: Soft Matter
Mariah Chambers, Stewart Anthony Mallory, Heather Malone, Yuan Gao, Stephen M Anthony, Yi Yi, Angelo Cacciuto, Yan Yu
Amphiphilic Janus particles self-assemble into complex metastructures, but little is known about how their assembly might be modified by weak interactions with a nearby biological membrane surface. Here, we report an integrated experimental and molecular dynamics simulation study to investigate the self-assembly of amphiphilic Janus particles on a lipid membrane. We created an experimental system in which Janus particles are allowed to self-assemble in the same medium where zwitterionic lipids form giant unilamellar vesicles (GUVs)...
November 16, 2016: Soft Matter
Wen Yan, John F Brady
Diffusiophoresis is the process by which a colloidal particle moves in response to the concentration gradient of a chemical solute. Chemically active particles generate solute concentration gradients via surface chemical reactions which can result in their own motion - the self-diffusiophoresis of Janus particles - and in the motion of other nearby particles - normal down-gradient diffusiophoresis. The long-range nature of the concentration disturbance created by a reactive particle results in strong interactions among particles and can lead to the formation of clusters and even coexisting dense and dilute regions often seen in active matter systems...
October 7, 2016: Journal of Chemical Physics
Bhuvnesh Bharti, David Rutkowski, Koohee Han, Aakash Umesh Kumar, Carol K Hall, Orlin D Velev
Janus and patchy particles are emerging as models for studying complex directed assembly patterns and as precursors of new structured materials and composites. Here we show how lipid induced capillary bridging could serve as a new and non conventional method of assembling patchy particles into ordered structures. Iron oxide surface patches on latex microspheres were selectively wetted with liquid lipids, driving the particle assembly into 2D and 3D clusters via interparticle capillary bridge formation. The liquid phase of the bridges allows local reorganization of the particles within the clusters and assists in forming true equilibrium configurations...
October 24, 2016: Journal of the American Chemical Society
Gianmaria Falasco, Richard Pfaller, Andreas P Bregulla, Frank Cichos, Klaus Kroy
Symmetries constrain dynamics. We test this fundamental physical principle, experimentally and by molecular dynamics simulations, for a hot Janus swimmer operating far from thermal equilibrium. Our results establish scalar and vectorial steady-state fluctuation theorems and a thermodynamic uncertainty relation that link the fluctuating particle current to its entropy production at an effective temperature. A Markovian minimal model elucidates the underlying nonequilibrium physics.
September 2016: Physical Review. E
Martin Walker, Mark R Wilson
Dissipative particle dynamics (DPD) simulations are used to model the aqueous self-assembly of three variants of the non-ionic triphenylene-based chromonic mesogen, TP6EO2M. In the variants studied, one to three of the six methoxy poly(ethylene glycol) chains of TP6EO2M are replaced by short hydrophobic-lipophobic chains, causing a remarkable change in the structure of the mesophases formed. In the 100 wt% limit, corresponding to pure thermotropic phases, complex columnar phases arise, in which the underlying hexagonal packing is supplemented by additional order resulting from microphase separation of hydrophobic-lipophobic regions...
September 26, 2016: Soft Matter
Jeong Hoon Byeon, Jae Hong Park
Gold (Au)-decorated iron oxide (Fe3O4), Au/Fe3O4, Janus nanoparticles were fabricated via the continuous route for aerosol Au incorporation with Fe3O4 domains synthesized in an aqueous medium as multifunctional nanoplatforms. The fabricated nanoparticles were subsequently exposed to 185-nm UV light to generate positive charges on Au surfaces, and their activities were tested in computed tomography (CT) and magnetic resonance (MR) imaging, gene-delivery and photothermal therapy. No additional polymeric coatings of the Janus particles also had a unique ability to suppress inflammatory responses in macrophages challenged with lipopolysaccharide, which may be due to the absence of amine groups...
October 7, 2016: Scientific Reports
Xinran Zhou, Shouping Chen, Bingyang Liu, Xiaogong Wang
We report the successful fabrication of photoresponsive Janus particles (JPs) composed of an epoxy-based azo polymer and poly(methyl methacrylate) (PMMA). Two representative azo polymers, of which one polymer (BP-AZ-CN) has cyano groups as electron-withdrawing substituents on the azobenzene moieties and the other polymer (BP-AZ-CA) has carboxyl groups as the electron-withdrawing substituents, were adopted for the investigation. The nanoscaled JPs, with a narrow size distribution and different azo polymer/PMMA ratios, were fabricated through self-assembly in solution and as dispersions...
October 5, 2016: Chemistry, An Asian Journal
Shang Yik Reigh, Mu-Jie Huang, Jeremy Schofield, Raymond Kapral
Active media, whose constituents are able to move autonomously, display novel features that differ from those of equilibrium systems. In addition to naturally occurring active systems such as populations of swimming bacteria, active systems of synthetic self-propelled nanomotors have been developed. These synthetic systems are interesting because of their potential applications in a variety of fields. Janus particles, synthetic motors of spherical geometry with one hemisphere that catalyses the conversion of fuel to product and one non-catalytic hemisphere, can propel themselves in solution by self-diffusiophoresis...
November 13, 2016: Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
Brenda Sanchez-Vazquez, Adérito J R Amaral, Deng-Guang Yu, George Pasparakis, Gareth R Williams
This work is a proof of concept study establishing the potential of electrosprayed Janus particles for combined photodynamic therapy-chemotherapy. Sub-micron-sized particles of polyvinylpyrrolidone containing either an anti-cancer drug (carmofur) or a photosensitiser (rose bengal; RB), and Janus particles containing both in separate compartments were prepared. The functional components were present in the amorphous form in all the particles, and infrared spectroscopy indicated that intermolecular interactions formed between the different species...
September 30, 2016: AAPS PharmSciTech
Hossein Rezvantalab, Daniel J Beltran-Villegas, Ronald G Larson
We demonstrate through Brownian dynamics simulations a phase transition in plastic crystalline assemblies of Janus spheres through controlled pressure anisotropy. When the pressure in plane with hexagonally ordered layers is increased relative to that normal to the layers, a rapid first-order rotator-to-lamellar transition of Janus sphere orientation occurs at constant temperature. We show that the underlying mechanism closely follows the Maier-Saupe theory, originally developed for isotropic-to-nematic transition in positionally disordered materials but here applied to positionally ordered ones...
September 16, 2016: Physical Review Letters
Gabi Steinbach, Sibylle Gemming, Artur Erbe
Despite its prominent role in the dynamics of soft materials, rotational friction remains a quantity that is difficult to determine for many micron-sized objects. Here, we demonstrate how the Stokes coefficient of rotational friction can be obtained from the driven torsional oscillations of single particles in a highly viscous environment. The idea is that the oscillation amplitude of a dipolar particle under combined static and oscillating fields provides a measure for the Stokes friction. From numerical studies we derive a semi-empirical analytic expression for the amplitude of the oscillation, which cannot be calculated analytically from the equation of motion...
September 29, 2016: Scientific Reports
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