Browsing by Subject "Self-assembly (Chemistry)"
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Item The self-assembly of colloidal particles into 2D arrays(2007-12) Rabideau, Brooks Douglas, 1979-; Bonnecaze, R. T. (Roger T.)As the feature size of new devices continues to decrease so too does the feasibility of top-down methods of patterning them. In many cases bottom-up methods are replacing the existing methods of assembly, as having building blocks self-organize into the desired structure appears, in many cases, to be a much more advantageous route. Self-assembled nanoparticulate films have a wide range of potential applications; high-density magnetic media, sensing arrays, meta-materials and as seeds for 3D photonic crystals to name a few. Thus, it is critical that we understand the fundamental dynamics of pattern formation on the nanoparticulate and colloidal scale so that we may have better control over the formation and final quality of these structures. We study computationally the self-organization of colloidal particles in 2D using both Monte Carlo and dynamic simulation We present 3 studies employing Monte Carlo simulation. In the first study, Monte Carlo simulations were used to understand the experimental observation of highlyordered 2D arrays of bidisperse, stabilized gold nanoparticles. It was shown that the LS lattice forms with the addition of interparticle forces and a simple compressive force, revealing that bidisperse lattice formation is, in fact, a dynamic process. It was evident that the LS lattice forms in large part because the particles within the lattice reside in their respective interparticle potential wells. In the second Monte Carlo study, this information was used to predict size-ratios and surface coverages for novel lattice structures. These predictions are intended to guide experimentalists in their search for these exciting new structures. In the third study it was shown that polydisperse amounts of amorphous-silicon nanoparticles could form 2D clusters exhibiting long-range orientational order even in the absence of translational order. Monte Carlo simulations were performed, which included lateral capillary forces and a simple stabilizing repulsion, resulting in structures that were strikingly similar to the experimentally observed In the fourth study we used dynamic simulation to study the hydrodynamicallyassisted self-organization of DNA-functionalized colloids in 2D. It was shown that hydrodynamic forces allow a more thorough sampling of phase space than through thermal or Brownian forces alone.Item Self-assembly of nanomaterials into films and fibers using genetically engineered viruses(2003) Lee, Seung-wuk; Belcher, Angela M.; Vanden Bout, David A.Genetically engineered M13 bacteriphage (viruses) were used to self-assemble various nanomaterials (ZnS, Au, fluorescein, and phycoerythrin) into films and fibers. The filamentous viruses, which were the basic building block of the self-ordering system, were selected through phage display for their specific recognition moieties for desired materials surfaces. The M13 viruses coupled with ZnS nanocrystals spontaneously evolved a self-supporting hybrid film material that was ordered at the nano-scale and micron-scales. Periodic domains were continuously propagated over a centimeter length scale, an observance that was verified using various optical and electron microscopy techniques. Anti-streptavidin viruses, which could specifically bind to streptavidin, were conjugated with many nanomaterials and used to modulate the nanomaterials in the self- assembled virus system. The resulting virus composite films had chiral smectic C structures due to the helical surface of the M13 virus. In addition, ~20 micrometer diameter fibers were fabricated with liquid crystalline virus suspensions using a wetspinning process that mimicked the spinning process of silk spiders. The virus was also blended with highly soluble polyvinyl pyrolidone and electrospun, resulting in nanoscale diameter fibers. This approach to aligning nanomaterials in a genetically engineered M13 virusbased liquid crystal system has several advantages. Monodisperse biopolymers (M13 viruses) of specified lengths can be easily prepared by molecular cloning techniques. By genetic selection of a peptide recognition moiety, one can easily modulate and align different types of nanomaterials into 3D ordered structures. We anticipate that our approach using recognition as well as a liquid crystalline self-assembly system of engineered viruses may provide new pathways to organizing electronic, optical, and magnetic materials.Item Topics in colloidal nanocrystals: synthesis and characterization, polymorphism, and self-assembly(2006) Ghezelbash, Hossein-Ali; Korgel, Brian A.The first step in the utilization of the unique and potentially technologically impactful size- and shape-dependent properties of nanocrystals is to develop reproducible methods to synthesize monodisperse nanocrystals. The development of the solventless synthetic approach showed a new pathway towards the synthesis of high quality rodshaped and triangular prism-shaped rhombohedral NiS nanocrystals. The nanorods and nanoprims both form via the thermal decomposition of the nickel thiolate single-source precursor. The length on the nanorods was dependent on growth conditions, varying between 15 and 50 nm. The solventless approach was also capable of producing triangular nanoprisms in a 1:1 ratio with the nanorods, depending on the overall concentration of the reactant species. We have demonstrated that synthetic pathway chosen can also dictate the shapes and phases accessible to the nanocrystal product with our comparisons between the solution-phase and solventless syntheses of nickel sulfide and copper sulfide. The solution-phase approach to nickel sulfide resulted only in polydisperse cubic Ni3S4 nanocrystals, which were a reaction byproduct in the solventless synthesis, shaped either as quasi-spheres or quasi-cubes. The stoichiometery of the copper sulfide product synthesized in solution was dependent on the Cu:S reactant molar ratio, with either CuS (covellite) and Cu1.8S (digenite) forming. CuS, Cu1.8S and Ni3S4 differ from the Cu2S and NiS nanocrystals obtained by solventless decomposition of metal thiolate single source precursors, in terms of stoichiometry for copper sulfide, and both stoichiometry and morphology for nickel sulfide. CuS nanodisks self-assembled into well-ordered columnar phases. Sterically-stabilized CdS nanorods were observed to self-align into networks of stripes several micrometers long when dropcast from dispersions at sub-monolayer coverage. The nanorods assemble side-by-side with their long axes parallel to the stripe direction. Nanorods 3 to 5 nm in diameter, with aspect ratios ranging from 4 to 12 were found to form stripe patterns. We propose that interparticle attractions between the rods drive the formation of the stripes, and that the rods are trapped in the stripe networks by solvent evaporation dynamics.