Janus Particles
“Originally the term Janus particle was coined by C. Casagrande et al. in 1988to describe spherical glass particles with one of the hemispheres hydrophilic and the other hydrophobic. In that work the amphiphilic beads were synthesized by protecting one hemisphere with varnish and chemically treating the other hemisphere with a silane reagent. This method resulted in a particle with equal hydrophilic and hydrophobic areas. Since then, and as anticipated by Pierre-Gilles de Gennes, on the occasion, of his Nobel lecturethe surface properties of these Janus particles have become an area of great interest for a variety of applications like: drug delivery, catalysis, sensors, stabilization of water-oil emulsions and gas-liquid foams.”
“These particles are composed of at least two physically (or chemically) distinctive surfaces. The name Janus arises from the double-faced roman god Janus.”
(Wikipedia, Janus Particles, 12/29/2010)
“Micrometer-sized Janus particles of many kinds can be formed using droplet microfluidics, but in existing methods, the microfluidic templating is strongly coupled to the material synthesis, since droplet solidification occurs through rapid polymerization right after droplet formation. This circumstance limits independent control of the material properties and the morphology of the resultant particles.”
”In this paper, we demonstrate a microfluidic technique to produce functional Janus microgels from prefabricated, cross-linkable precursor polymers. This approach separates the polymer synthesis from the particle gelation, thus allowing the microfluidic droplet templating and the functionalization of the matrix polymer to be performed and controlled in two independent steps. We use microfluidic devices to emulsify semidilute solutions of cross-linkable, chemically modified or unmodified poly(N-isopropylacrylamide) precursors and solidify the drops via polymer-analogous gelation. The resultant microgel particles exhibit two distinguishable halves which contain most of the modified precursors, and the unmodified matrix polymer separates these materials. The spatial distribution of the modified precursors across the particles can be controlled by the flow rates during the microfluidic experiments. We also form hollow microcapsules with two different sides (Janus shells) using double emulsion droplets as templates, and we produce Janus microgels that are loaded with a ferromagnetic additive which allows remote actuation of the microgels.”
(Seiffert, Romanowsky and Weltz, Lagmuir, 100823083433027 [2010]5/19/2011
Recent Journal Articles
Self-Assembly of Janus Composite Droplets at the Interface in Quaternary Immiscible Polymer Blends
(5850–5856) Macromolecules 44 #15 (2011)
Effects of pH and temperature on assembly of multiresponsive Janus microgels
(729-737) Colloid and Polymer Science 289 #5-6 (2011)
Umeda et al of Shinshu University, Japan, fabricated the multiresponsive Janus microgels by post-polymerization modification at an oil/water interface. To prevent the microgels from wobbling at the interface during the modification process, oil droplets stabilized by microgels were solidified by cooling. By changing temperature and pH, behaviors of Janus microgels could be controlled; they dispersed individually or assembled into specific structures. The stimuli-responsive behaviors of Janus microgels may be used as microactuators or candidates in developing more precisely controlled particle clusters. (RDC 5/17/2011)
Compartmentalized Photoreactions within Compositionally Anisotropic Janus Microstructures
(431–437)Macromolecular Rapid Communications 32 #5 (2011)
Lee et al of the University of Michigan, Michigan demonstrated spatially controlled photoreactions within bicompartmental microparticles and microfibers. Selective photoreactions are achieved by anisotropic incorporation of photocrosslinkable poly(vinyl cinnamate) in one compartment of either colloids or microfibers. Prior to photoreaction, bicompartmental particles, and fibers were prepared by electrohydrodynamic co-jetting of two compositionally distinct polymer solutions. Subsequent exposure of poly(vinyl cinnamate)-based particles and fibers to UV light at 254 nm resulted in spatially controlled crosslinking. Treatment of the crosslinked bicompartmental colloids with chloroform produced half-moon shaped objects. These hemishells exhibited a distinct porous morphology with pore sizes in the range of 70 nm. Based on this novel synthetic approach, Janus-type particles and fibers can be prepared by electrohydrodynamic co-jetting and can be selectively photocrosslinked without the need for masks or selective laser writing. (RDC 2/24/2011)
Janus composite nanorings by combinational template synthesis and skiving micro-process
( 3606-3611) Polymer 51 #16 (2010)
Zhou et al of the Institute of Chemistry, China fabrication Janus composite nanorings by skiving the corresponding arrayed nanotubes. The polymer nanotubes and their arrays are polymerized from the pore surface via ATRP inside porous anodic aluminium oxide membrane (AAO) templates. As examples, Janus composite nanorings of sulfonated PS/PS, titania/PS, silica/PS and PANi/PS are prepared. (RDC 12/22/2010)
Janus gold nanoparticle with bicompartment polymer brushes templated by polymer single crystals
(4814-4822) Polymer 51 #21 (2010)
Wang et al synthesized Janus nanoparticles by growing polymer brushes on polymer-single-crystal-immobilized 6 and 15 nm diameter gold nanoparticles (AuNPs) using atom transfer radical polymerization. JNPs with bicompartment polymer brushes, such as poly(ethylene oxide) (PEO)/poly(methyl methacrylate), PEO/poly(tert-butyl acrylate), and PEO/poly(acrylic acid), were synthesized. By using polymer single crystal as the templates, small size (<20 nm diameter) JNPs having bicompartment polymer brushes can be readily obtained. The ability to tune grafting density and molecular weight of polymer brushes can lead to controlled particle amphiphilicity. (RDC 12/19/2010)