4 research outputs found

    Synthesis of Liquid Core–Shell Particles and Solid Patchy Multicomponent Particles by Shearing Liquids Into Complex Particles (SLICE)

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    We report a simple method that uses (i) emulsion shearing with oxidation to make core–shell particles, and (ii) emulsion shearing with surface-tension driven phase segregation to synthesize particles with complex surface compositions and morphologies. Subjecting eutectic gallium–indium, a liquid metal, to shear in an acidic carrier fluid we synthesized smooth liquid core–shell particles 6.4 nm to over 10 μm in diameter. Aggregates of these liquid particles can be reconfigured into larger structures using a focused ion beam. Using Field’s metal melts we synthesized homogeneous nanoparticles and solid microparticles with different surface roughness and/or composition through shearing and phase separation. This extension of droplet emulsion technique, SLICE, applies fluidic shear to create micro- and nanoparticles in a tunable, green, and low-cost approach

    Grooved Nanowires from Self-Assembling Hairpin Molecules for Solar Cells

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    One of the challenges facing bulk heterojunction organic solar cells is obtaining organized films during the phase separation of intimately mixed donor and acceptor components. We report here on the use of hairpin-shaped sexithiophene molecules to generate by self-assembly grooved nanowires as the donor component in bulk heterojunction solar cells. Photovoltaic devices were fabricated <i>via</i> spin-casting to produce by solvent evaporation a percolating network of self-assembled nanowires and fullerene acceptors. Thermal annealing was found to increase power conversion efficiencies by promoting domain growth while still maintaining this percolating network of nanostructures. The benefits of self-assembly and grooved nanowires were examined by building devices from a soluble sexithiophene derivative that does not form one-dimensional structures. In these systems, excessive phase separation caused by thermal annealing leads to the formation of defects and lower device efficiencies. We propose that the unique hairpin shape of the self-assembling molecules allows the nanowires as they form to interact well with the fullerenes in receptor–ligand type configurations at the heterojunction of the two domains, thus enhancing device efficiencies by 23%

    Odd–Even Effect in the Hydrophobicity of <i>n</i>‑Alkanethiolate Self-Assembled Monolayers Depends upon the Roughness of the Substrate and the Orientation of the Terminal Moiety

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    The origin of the odd–even effect in properties of self-assembled monolayers (SAMs) and/or technologies derived from them is poorly understood. We report that hydrophobicity and, hence, surface wetting of SAMs are dominated by the nature of the substrate (surface roughness and identity) and SAM tilt angle, which influences surface dipoles/orientation of the terminal moiety. We measured static contact angles (θ<sub>s</sub>) made by water droplets on <i>n</i>-alkanethiolate SAMs with an odd (SAM<sup>O</sup>) or even (SAM<sup>E</sup>) number of carbons (average θ<sub>s</sub> range of 105.8–112.1°). When SAMs were fabricated on smooth “template-stripped” metal (M<sup>TS</sup>) surfaces [root-mean-square (rms) roughness = 0.36 ± 0.01 nm for Au<sup>TS</sup> and 0.60 ± 0.04 nm for Ag<sup>TS</sup>], the odd–even effect, characterized by a zigzag oscillation in values of θ<sub>s</sub>, was observed. We, however, did not observe the same effect with rougher “as-deposited” (M<sup>AD</sup>) surfaces (rms roughness = 2.27 ± 0.16 nm for Au<sup>AD</sup> and 5.13 ± 0.22 nm for Ag<sup>AD</sup>). The odd–even effect in hydrophobicity inverts when the substrate changes from Au<sup>TS</sup> (higher θ<sub>s</sub> for SAM<sup>E</sup> than SAM<sup>O</sup>, with average Δθ<sub>s |<i>n</i> – (<i>n</i> + 1)|</sub> ≈ 3°) to Ag<sup>TS</sup> (higher θ<sub>s</sub> for SAM<sup>O</sup> than SAM<sup>E</sup>, with average Δθ<sub>s |<i>n</i> – (<i>n</i> + 1)|</sub> ≈ 2°). A comparison of hydrophobicity across Ag<sup>TS</sup> and Au<sup>TS</sup> showed a statistically significant difference (Student’s <i>t</i> test) between SAM<sup>E</sup> (Δθ<sub>s |Ag evens – Au evens|</sub> ≈ 5°; <i>p</i> < 0.01) but failed to show statistically significant differences on SAM<sup>O</sup> (Δθ<sub>s |Ag odds – Au odds|</sub> ≈ 1°; <i>p</i> > 0.1). From these results, we deduce that the roughness of the metal substrate (from comparison of M<sup>AD</sup> versus M<sup>TS</sup>) and orientation of the terminal −CH<sub>2</sub>CH<sub>3</sub> (by comparing SAM<sup>E</sup> and SAM<sup>O</sup> on Au<sup>TS</sup> versus Ag<sup>TS</sup>) play major roles in the hydrophobicity and, by extension, general wetting properties of <i>n</i>-alkanethiolate SAMs
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