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We have developed a new method to produce hybrid particles with polyhedral shapes in very high yield (liter quantities at up to 70% purity) using a combination of emulsion polymerization and inorganic surface chemistry. The procedure has been generalized to create complex geometries, including hybrid line segments, triangles, tetrahedra, octahedra, and more. The optical properties of these particles are tailored for studying their dynamics and self-assembly. For example, we produce systems that consist of index-matched spheres allowing us to define the position of each elementary particle in three-dimensional space. We present some preliminary studies on the self-assembly of these complex shaped systems based on electron and optical microscopy.
Self-propulsion and directed movement of nano- and micro-particles can in principle provide novel components for applications in microrobotics and MEMS. Our research involves the design of catalytic propulsion systems and the control of colloidal movement based on this principle. We have designed autonomous nanomotors that mimic biological motors by using catalytic reactions to generate forces derived from chemical gradients. Through architectural control of bimetallic catalytic particles, we have recently developed systems that undergo more complex movement. For example, we have constructed 10-micron scale rotary motors by contact lithography. In these chiral motors, bimetallic Au-Pt patterns are free-standing and move in the pattern predicted by theory. These studies demonstrate that by designing the proper architecture, one can tailor the pattern of movement to specific applications, such as changing from translational to rotational movement. The potential for elaboration of these designs to more complex micro-machine assemblies is discussed.
A coarse-grained model of peptide amphiphiles (PA) dissolved in aqueous solution was presented, where the effects of PA concentration, temperature and shear stress upon the self-assembly of PA were numerically studied by dissipative particle dynamics (DPD) simulation. We technically investigate the repulsion parameter aHW which indicates the repulsion force between the hydrophilic head of PA and water molecules, hence, at the same time, indicating the change in temperature. It was found that aHW played an important role in the self-assembly dynamics and in the resulting micro-structures of PA. By imposing shear strain on the simulation system, the formation of wormlike PA micelles was accelerated. The simulation results were in good agreement with our previous experimental results and the mechanism of shear-induced transition was proposed.
Polyvinyl alcohol/Poly-aniline/Vanadium Oxide nanocomposite-based macroscopic fibers have been generated by using a redox reaction addressed while performing an extrusion shaping process. The resulting composites have been thoroughly characterized via a large set of techniques such as SEM, SAXS, XRD and FTIR, in order to determine aniline effects over final materials' structures and properties. Thus, the perturbation of the preferential orientation of the V2O5 nano-ribbons toward the fiber main axis, induced by aniline Red-ox intercalation, has been observed. Also, the partial reduction of V5+ species to V4+ ones, due to the strongly oxidizing character of the first ones toward aniline, has been revealed by Electron Spin Resonance (ESR). Moreover, these fibers are able to detect 5 ppm of ethanol within 3-5 seconds at 42 °C, and possess a toughness of 12 J.g-1.
We have designed a novel technique for fabrication of magnetic Janus microparticles based on “trapping” the alignment of magnetite nanoparticles dispersed within the oil drops of polymerizable oil-in-water emulsion. We polymerized the oil drops after gelling the continuous aqueous phase in the presence of an external magnetic filed. This allowed us to produce magnetic Janus particles with optical and magnetic anisotropy which form unusual zigzag chains and structures when an external magnetic field is applied to a suspension of such particles. These novel microparticles retain high remanence magnetization and coercivity values indicative of ferromagnetic behavior, which indicates that the composite polymeric Janus microparticles posses a net magnetic dipole and behave like micro-magnets due to the “trapped” orientation of the magnetite nanoparticles in their polymeric matrix.
The aim of this study is to understand the crosslinked system of poly(styrene)-bpoly(isoprene) copolymer using cold vulcanization process as a facile method to produce anisometric nanoparticles. The morphologies of block copolymers could be controlled by the type of monomers, block junction, composition, and block size. A systematic methodology, utilizing cylindrical and lamellar morphologies of PS-b-PI copolymer, was used for producing fiber and sheet shaped nanoparticles. The cold vulcanization process was accomplished using sulfur monochloride (S2Cl2) as crosslinking agent. The microstructures and crosslinking density of crosslinked PS-b-PI copolymers were imaged and characterized. This study demonstrated the crosslinking of microphase separated block copolymer as a method to create particles with controlled size, shape, and physical properties.