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Janus particles

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, where BP-AZ-CN bears cyano groups as electron-withdrawing substituents on azobenzene moieties and BP-AZ-CA bears carboxyl groups as the electron-withdrawing substituents, were adopted for the investigation. The nano-scaled JPs with a narrow size distribution and different ratios of the azo polymers to PMMA were fabricated through self-assembly in solutions and 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
Hailing Yu, Andrii Kopach, Vyacheslav R Misko, Anna A Vasylenko, Denys Makarov, Fabio Marchesoni, Franco Nori, Larysa Baraban, Gianaurelio Cuniberti
Self-propelled Janus particles, acting as microscopic vehicles, have the potential to perform complex tasks on a microscopic scale, suitable, e.g., for environmental applications, on-chip chemical information processing, or in vivo drug delivery. Development of these smart nanodevices requires a better understanding of how synthetic swimmers move in crowded and confined environments that mimic actual biosystems, e.g., network of blood vessels. Here, the dynamics of self-propelled Janus particles interacting with catalytically passive silica beads in a narrow channel is studied both experimentally and through numerical simulations...
September 15, 2016: Small
Hsiao-Fan Tseng, Ming-Hsiang Cheng, Kai-Sheng Jeng, Jia-Wei Li, Jiun-Tai Chen
Anisotropic polymer particles such as Janus particles have attracted significant attention in recent years because of their unique properties and unusual self-assembly behavior. Most anisotropic polymer particles synthesized so far, however, only have different chemical regions compartmentalized on the particles. It remains a great challenge to fabricate anisotropic polymer particles with different shapes within a single particle. A novel approach is developed to prepare anisotropic polymer particles that contain two hemispheres with different curvatures by annealing polystyrene microspheres on poly(vinyl alcohol) films...
September 9, 2016: Macromolecular Rapid Communications
Alicia Boymelgreen, Gilad Yossifon, Touvia Miloh
Previously, metallodielectric Janus particles have been shown to travel with their dielectric hemisphere forward under low frequency applied electric fields as a result of asymmetric induced-charge electroosmotic flow. Here, it is demonstrated that at high frequencies, well beyond the charge relaxation time of the electric double layer induced around the particle, rather than the velocity decaying to zero, the Janus particles reverse direction, traveling with their metallic hemisphere forward. It is proposed that such motion is the result of a surface force, arising from localized nonuniform electric field gradients, induced by the dual symmetry-breaking of an asymmetric particle adjacent to a wall, which act on the induced dipole of the particle to drive net motion even in a uniform AC field...
September 20, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
Yang Liu, Bei Peng, Salman Sohrabi, Yaling Liu
Nanoparticles (NPs) are promising carriers for targeted drug delivery, photodynamic therapy, and imaging probes. A fundamental understanding of the dynamics of polymeric NP targeting to bilayer membranes is important to enhance the design of NPs for higher adhesion, binding percentage, and efficiency. In this study, dissipative particle dynamics simulations are applied to investigate the adhesion and uptake processes of the rod, spherical, and striped NPs to cell membranes. It is observed that the striped ligands can prevent NPs from rotating even in active rotation...
October 4, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
Wesley F Reinhart, Athanassios Z Panagiotopoulos
Triblock Janus colloids, which are colloidal spheres decorated with attractive patches at each pole, have recently generated significant interest as potential building blocks for functional materials. Their inherent anisotropy is known to induce self-assembly into open structures at moderate temperatures and pressures, where they are stabilized over close-packed crystals by entropic effects. We present a numerical investigation of the equilibrium phases of triblock Janus particles with many different patch geometries in three dimensions, using Monte Carlo simulations combined with free energy calculations...
September 7, 2016: Journal of Chemical Physics
Xing Ma, Seungwook Jang, Mihail N Popescu, William E Uspal, Albert Miguel-López, Kersten Hahn, Dong-Pyo Kim, Samuel Sánchez
Self-motile Janus colloids are important for enabling a wide variety of microtechnology applications as well as for improving our understanding of the mechanisms of motion of artificial micro- and nanoswimmers. We present here micro/nanomotors which possess a reversed Janus structure of an internal catalytic "chemical engine". The catalytic material (here platinum (Pt)) is embedded within the interior of the mesoporous silica (mSiO2)-based hollow particles and triggers the decomposition of H2O2 when suspended in an aqueous peroxide (H2O2) solution...
September 27, 2016: ACS Nano
Laura C Bradley, Kathleen J Stebe, Daeyeon Lee
Janus particles are colloidal analogues of molecular amphiphiles that can self-assemble to form diverse suprastructures, exhibit motility under appropriate catalytic reactions, and strongly adsorb to fluid-fluid interfaces to stabilize multiphasic fluid mixtures. The chemistry of Janus particles is the fundamental parameter that controls their behavior and utility as colloid surfactants in bulk solution and at fluid interfaces. To enable their widespread utilization, scalable methods that allow for the synthesis of Janus particles with diverse chemical compositions and shapes are highly desirable...
September 14, 2016: Journal of the American Chemical Society
Younan Xia
The 191st Faraday Discussion meeting on "Nanoparticles with Morphological and Functional Anisotropy" offers a broad range of new insights into an interdisciplinary research field converged at the forefronts of chemistry, colloid science, and materials science. It was held on the campus of University of Strathclyde, Glasgow, UK. Across the street of the meeting place, one could see a large portrait of Thomas Graham, the father of physical chemistry who coined the term of "colloid" in the 19th century, painted on the outside wall of a tall building...
October 6, 2016: Faraday Discussions
Mengqi Li, Dongqing Li
This paper presents experimental investigations of the fabrication and the motion of electrically anisotropic Janus droplets in a microchannel under externally applied direct current (DC) electrical field. The fabrication method of the Janus droplets is presented first. To begin, oil droplets are coated uniformly with positively charged nanoparticles in the aluminum oxide nanoparticle suspension. The electrically anisotropic Janus droplets are formed when the nanoparticles are accumulated to one side of the droplets in response to externally applied direct-current electric field...
August 8, 2016: Electrophoresis
W E Uspal, M N Popescu, S Dietrich, M Tasinkevych
Catalytically active Janus particles suspended in solution create gradients in the chemical composition of the solution along their surfaces, as well as along any nearby container walls. The former leads to self-phoresis, while the latter gives rise to chemiosmosis, providing an additional contribution to self-motility. Chemiosmosis strongly depends on the molecular interactions between the diffusing chemical species and the wall. We show analytically, using an approximate "point-particle" approach, that by chemically patterning a planar substrate one can direct the motion of Janus particles: the induced chemiosmotic flows can cause particles to either "dock" at the chemical step between the two materials or follow a chemical stripe...
July 22, 2016: Physical Review Letters
M Labbé-Laurent, S Dietrich
Recently there has been strong experimental and theoretical interest in studying the self-assembly and the phase behavior of patchy and Janus particles, which form colloidal suspensions. Although in this quest a variety of effective interactions have been proposed and used in order to achieve a directed assembly, the critical Casimir effect stands out as being particularly suitable in this respect because it provides both attractive and repulsive interactions as well as the potential of a sensitive temperature control of their strength...
August 21, 2016: Soft Matter
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