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  1. Free, publicly-accessible full text available March 16, 2023
  2. Morphological and magnetic anisotropy can be combined in colloidal assembly to create unconventional secondary structures. We show here that magnetite nanorods interact along a critical angle, depending on their aspect ratios and assemble into body-centered tetragonal colloidal crystals. Under a magnetic field, size-dependent attractive and repulsive domains develop on the ends and center of the nanorods, respectively. Our joint experiment-computational multiscale study demonstrates the presence of a critical angle in the attractive domain, which defines the equilibrium bonding states of interacting rods and leads to the formation of non–close-packed yet hard-contact tetragonal crystals. Small-angle x-ray scattering measurement attributes the perfect tetragonal phase to the slow assembly kinetics. The crystals exhibit brilliant structural colors, which can be actively tuned by changing the magnetic field direction. These highly ordered frameworks and well-defined three-dimensional nanochannels may offer new opportunities for manipulating nanoscale chemical transformation, mass transportation, and wave propagation.
  3. Building on our previous works that compared the efficacy of terpolymers vs. ternary blends in improving the performance of bulk heterojunction organic solar cells, the final piece of this series of studies focuses on comparing terpolymer and ternary blends constructed with two polymers with structurally similar backbones (monoCNTAZ and FTAZ) yet markedly different open circuit voltage ( V oc ) values. Terpolymers and ternary blends of five different ratios were studied and the results demonstrate that while the overall performance of both the systems is similar, the ternary blends exhibit higher short circuit current ( J sc ) values, while the terpolymers exhibit higher V oc values. Investigation of the charge transfer state using low-energy external quantum efficiency (EQE) indicates that the ternary blends are governed by a parallel-like mechanism, while the terpolymer does not follow this mechanism. The key morphological difference between the systems, as elucidated by resonance soft X-ray scattering (RSoXS), is the slightly smaller size (∼60 nm) of domains in the ternary blends compared to that of the terpolymer (∼80 nm), which may affect exciton harvesting in the terpolymer system and lead to lower J sc values. In addition, a lower driving force for the formation ofmore »charge transfer (CT) state is also likely to contribute to the lower J sc values in the terpolymer system. All together, the data show that structurally similar (perhaps even miscible) polymers still exhibit key differences in performance when paired in terpolymers vs. ternary blends and allow us to further illuminate the underlying mechanisms of such complex systems.« less
  4. A unique morphology for bent-core liquid crystals forming the B4 phase has been found for a class of tris-biphenyl bent-core liquid crystal molecules with a single chiral side chain in the longer para -side of the molecule. Unlike the parent molecules with two chiral side chains or a chiral side chain in the shorter meta -side, which form helical nano- or microfilament B4 phases, the two derivatives described here form heliconical-layered nanocylinders composed of up to 10 coaxial heliconical layers, which can split or merge, braid, and self-assemble into a variety of modes including feather- or herringbone-type structures, concentric rings, or hollow nest-like superstructures. These multi-level hierarchical self-assembled structures, rivaling muscle fibers, display blue structural color and show immense structural and morphological complexity.