Well-defined Superstructure Research Articles

Self-assembly of superstructures at all scales

Summary Controllable assembly of molecular and nanoscale building blocks into uniform superstructures up to bulk dimensions remains a key challenge in the next phase of nanotechnology development. Here, we report the self-assembly of superstructures at all scales by taking advantage of the partial miscibility of water and 1-butanol to generate transient aqueous emulsion droplets that can encapsulate the target materials and introduce them into template holes. Further diffusion of water into 1-butanol depletes the emulsion droplets, assembling the building blocks into one well-defined superstructure in each hole. Superstructuring of various types and shapes of nanoparticles, biomolecules, and inorganic compounds could be achieved without the need for surfactants and chemical modifications. The versatility, scalability, low-cost, and accurate positioning are crucial advantages for the future development of advanced precision manufacturing.

Synthesis and characterization of a hexagonal polymorph of GdAlO3

The structure and basic properties of a hexagonal polymorph of GdAlO3 aluminate (GAH) were studied using a set of experimental methods (XRD, FTIR, Raman spectroscopy, diffuse reflectance spectroscopy, luminescence spectroscopy, magnetic susceptibility, and TEM). The GAH crystallized at 900 °C from an amorphous precursor and decomposed into perovskite GdAlO3 (GAP) at 1000 °C. XRD pattern of polycrystalline GAH could be indexed in P63/mmc space group with unit cell parameters a = 0.3734 nm, c = 1.0535 nm, following literature data. The electron diffraction revealed, however, the presence of well-defined superstructure reflections due to defects ordering. Contrary to a recent report suggesting the presence of CO3 groups in the structure of similar hexagonal YAlO3, we did not observe such groups in the FTIR spectra of GAH. On the other hand, the stoichiometry of GAH differs from ideal GdAlO3, with Al/Gd atomic ratio close to 1.2, similar to reported for hexagonal YAlO3. GAH exhibits paramagnetic behavior over 1.8–300 K temperature range, with the effective Gd magnetic moment μeff = 7.90 μB, close to the theoretical value for free Gd3+ ion. No paramagnetic – antiferromagnetic phase transition at ~4 K, characteristic for perovskite-type GdAlO3, was observed. The reason is probably a less "dense" structure of GAH, with longer Gd-Gd and Gd-O-Gd interatomic distances. Emission spectra of Dy doped (~1 at%) GAH and GAP revealed dramatic differences in Dy3+ emission bands, despite similar mean crystallite size of the host material. An almost structureless 4F9/2→6H13/2 and 4F9/2→6H15/2 emission bands, observed for GAH, indicate, following TEM data, that Dy ions occupy numerous nonequivalent sites due to the presence of a large concentration of crystal defects.

Fabrication of NiFe layered double hydroxide with well-defined laminar superstructure as highly efficient oxygen evolution electrocatalysts

Structure–activity relationship (SAR) is the key problem of nanoscience, thus to fabricate novel and well-defined nanostructure will provide a new insight on catalyst preparation method. Highly active and low cost electrocatalysts for oxygen evolution reaction (OER) are of great importance for future renewable energy conversion and storage. Herein, NiFe-based layered double hydroxides with laminar structure (NFLS) were successfully fabricated via a one-step hydrothermal approach by using sodium dodecyl sulfate as surfactant. The as-fabricated NFLS showed a well-defined periodic layered-stacking geometry with a scale down to 1-nm. Benefitting from the unique structure, NFLS exhibited an excellent catalytic activity towards OER with current densities of 10 mA·cm−2 at overpotential of 197 mV. The synergistic effect of Ni and Fe plays a key role in electrode reactions. The present work provides a new insight to improve the OER performance by rational design of electrocatalysts with unique structures.

Strand Displacement Amplification Reaction on Quantum Dot-Encoded Silica Bead for Visual Detection of Multiplex MicroRNAs.

The combination of microbead array, isothermal amplification, and molecular signaling enables the continuous development of next-generation molecular diagnostic techniques. Herein we reported the implementation of nicking endonuclease-assisted strand displacement amplification reaction on quantum dots-encoded microbead (Qbead), and demonstrated its feasibility for multiplexed miRNA assay in real sample. The Qbead featured with well-defined core-shell superstructure with dual-colored quantum dots loaded in silica core and shell, respectively, exhibiting remarkably high optical encoding stability. Specially designed stem-loop-structured probes were immobilized onto the Qbead for specific target recognition and amplification. In the presence of low abundance of miRNA target, the target triggered exponential amplification, producing a large quantity of stem-G-quadruplexes, which could be selectively signaled by a fluorescent G-quadruplex intercalator. In one-step operation, the Qbead-based isothermal amplification and signaling generated emissive "core-shell-satellite" superstructure, changing the Qbead emission-color. The target abundance-dependent emission-color changes of the Qbead allowed direct, visual detection of specific miRNA target. This visualization method achieved limit of detection at the subfemtomolar level with a linear dynamic range of 4.5 logs, and point-mutation discrimination capability for precise miRNA analyses. The array of three encoded Qbeads could simultaneously quantify three miRNA biomarkers in ∼500 human hepatoma carcinoma cells. With the advancements in ease of operation, multiplexing, and visualization capabilities, the isothermal amplification-on-Qbead assay could potentially enable the development of point-of-care diagnostics.

Compact hybrid (gold nanodendrite-quantum dots) assembly: plasmon enhanced fluorescence-based platform for small molecule sensing in solution.

In this study, we have presented a novel plasmon enhanced fluorescence (PEF) system for label-free sensing of small molecules in bulk solution. The amine-terminated gold nanodendrite (AuND) and carboxyl-terminated QDs directly assemble each other by amine-carboxyl attraction. Without any spacer layers, PEF can be increased by 4 times during the formation of the compact hybrid (AuND-QDs) assembly. Both experiment and finite-difference time domain calculation results indicate that the distinct solution-PEF effect is ascribed to two reasons: (1) The used AuNDs simultaneously possess four features in morphology and topology, well-defined superstructure, sharp tips and edges, moderately elongated subunits, and smaller size. (2) The hybrid (AuND-QDs) assembly has a very compact structure. So, the fluorescence is well enhanced by the effective increase of excitation and radiative decay rates with the decrease of scattering effect. The (AuND-QDs) assembly is then employed for sensing of trinitrotoluene (TNT), one of the highly explosive and environmentally detrimental substances, in bulk solution. The sensing principle is that the analytes can react with primary amines on the AuND surface and form Meisenheimer complexes, which break the preformed assemblies and result in the fluorescence recovery of the QDs. The linear range is 0-8.8 nM with 0.05 nM detection limit. The present quasi-picomole level sensitivity is one of the best results for fluorescent TNT sensing. The developed method is successfully applied to TNT sensing in real environmental samples, indicating the practical potential.

In situ STM studies of Bi(111)|1-ethyl-3-methylimidazolium tetrafluoroborate + 1-ethyl-3-methylimidazolium iodide interface

Formation of an interfacial structure at an electrochemically polished Bi(111) surface in 1wt.% 1-ethyl-3-methylimidazolium iodide+1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid mixture has been analysed using the high-resolution in situ electrochemical scanning tunneling microscopy, cyclic voltammetry and electrochemical impedance methods. At 22±1°C, a well-defined 2-dimensional superstructure has been demonstrated within the electrode potential (E) region from −0.7V to −0.3V (vs. Ag|AgCl in the same mixture of the ionic liquids), where a strong specific I− anion adsorption and coadsorption of counter-ions occurs. At E<−0.8V, the superstructure disappears as a result of desorption of the specifically adsorbed iodide anions from the Bi(111) surface. At E≥−0.2V, where Bi(111) surface oxidation process starts, the 2D-superstructure cannot be observed due to a quick atomic-scale roughening of the Bi(111) plane.

Dynamic Origin and Thermally Induced Evolution of New Self‐Assembled Aggregates from an Amphiphilic Comb‐Like Graft Copolymer: A Multiscale and Multimorphological Procedure

In the past several decades, the self-assembly of block copolymers in selective solvents has attracted extensive interest due to the formation of various aggregates including spherical and cylindrical micelles, vesicles, tubes, helices, toroids, and other complex forms. Research has been focused on aggregates with spherical, flowerlike, tubular or sheet-like superstructures, obtained through the hierarchical self-assembly of Janus micelles or Janus nanoparticles, owning to their formation mechanisms and potential applications in biomedical materials and new nanodevices. The self-assembled aggregates can also be constructed from amphiphilic comb-like graft copolymers in water or organic solvents. Despite that many interesting aggregates including petal-like micelles, spindle-like micelles, wormlike micelles, chiral helices, and so on, are obtained by the change of structural and environmental parameters, in most cases conventional spherical micelles and vesicles are observed. In comparison with block copolymers, self-assembled aggregates of amphiphilic comb-like graft copolymers reveal the morphological characteristics of obviously low diversity and complexity. Considering the shape plays a crucial role in determining physical and chemical properties of aggregates, the controlled fabrication and switch of morphologies have been paid a great attention, which has been implemented by regulating the conditions, such as solvent, pH, redox, and so on. Typically, crystallization is an important factor utilized to control the self-assembly of semicrystalline block copolymers consisting of the crystallizable block and amorphous block, which has been actively researched recently. Inspired by this specific class of copolymer, we have designed an amphiphilic comb-like graft copolymer consisting of poly(p-dioxanone) (PPDO) as a crystallizable hydrophobic side chain and poly(vinyl alcohol) (PVA) as a hydrophilic main chain, and found that this copolymer presented an unique self-assembled behavior. In fact, recently we reported a “star anise”-like nanoaggregate from a PPDO-based branched alternating multi-block copolymer. Herein, by directly dispersing this PPDO-based amphiphilic comb-like graft copolymer into water, more complex and regular aggregates with a well-defined snowflake-like superstructure was obtained, and their origin involving a dynamically disorder–order change from nanoto submicroscale was visualized. Moreover, the aggregates showed thermally induced multimorphological evolution from a snowflake-like to cluster-like structure. As an original and significant work, this superstructure enriches the self-assembled morphology of amphiphiles, especially comb-like macromolecules. Furthermore, the direct water phase self-assembled strategy of PPDO-based amphiphilic copolymers and temperature-adjusted morphological change could provide a new idea to construct complex multimorphological and multiscale objects. The precursors of the copolymers were synthesized through ring-opening polymerization and the acylation, respectively. The copolymers were prepared in DMSO by a coupling reaction between carboxyl groups presenting on PPDO chain-end and hydroxyl groups of PVA (Scheme 1). The information of the molecular structure of copolymers is listed in the Supporting Information, Table S1. The self-assembly was achieved by adding PVA500-g5.6%PPDO15 to water at room temperature, heating the system to homogenous phase (to erase the thermal history), and aging it at 25 8C. Tests of dynamic light scattering (DLS) indicated the presence of monodispersed and stable particles with 791 nm of intensity-averaged hydrodynamic diameter ( ) and a polydispersity index (PDI) of 0.053 (Figure 1a, their and PDI after 7 days was shown in the Supporting Information, Figure S1). Transmission electron microscopy (TEM) images revealed well-defined snowflakelike aggregates having about 260 nm of average thickness, 530 nm of average width, and 620 nm of average length, respectively (marked by short arrows in Figure 1band 1c). For monodisperse spherical aggregates, they have same diffusion coefficient in every direction, and their size from CONTIN analysis is independent of scattering angles. Conversely, for the anisotropic or polydisperse aggregates, the results of DLS are dependent of scattering angles. By multi-angle DLS experiment, we found that the diameter and apparent [a] G. Wu, Dr. S.-C. Chen, Dr. X.-L. Wang, Dr. K.-K. Yang, Prof. Y.-Z. Wang National Engineering Laboratory of Eco-Friendly Polymeric Materials (Sichuan) State Key Laboratory of Polymer Materials Engineering College of Chemistry, Sichuan University 29 Wangjiang Road, Chengdu 610064 (P.R. China) Fax: (+86)28-85410259 E-mail : chensichong@scu.edu.cn yzwang@scu.edu.cn Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201103961.

Quadruple-layered perovskite (CuCl)Ca2NaNb4O13

We will present the synthesis, structure and magnetic properties of a new quadruple-layered perovskite (CuCl)Ca2NaNb4O13. Through a topotactic ion-exchange reaction with CuCl2, the precursor RbCa2NaNb4O13 presumably having an incoherent octahederal tliting changes into (CuCl)Ca2NaNb4O13 with a 2ap×2ap×2cp superstructure (tetragonal; a=7.73232(5)Å, c=39.2156(4)Å). The well-defined superstructure for the ion-exchanged product should be stabilized by the inserted CuCl4O2 octahedral layers that firmly connect with neighboring perovskite layers. Magnetic studies show the absence of long-range magnetic ordering down to 2K despite strong in-plane interactions. Aleksandrov′s group theory and Rietveld refinement of synchrotron X-ray diffraction data suggest the structure to be of I4/mmm space group with in-phase tilting along the a and b axes, a two-tilt system (++0).

LADDER SUPERSTRUCTURE-DIRECTED SYNTHESIS OF A WELL-DEFINED m-PHENELENEDIIMINO-BRIDGED LADDER POLYMETHYLSILOXANE

A well-defined m-phenylenediimino-bridged ladder polymethylsiloxane (LP) was first synthesized through a well-defined ladder superstructure (LS) acting as synthetic template, which was self-assembled by concerted interaction of hydrogen bonding and aromatic π-π stacking of the monomer (M), N,N′-bis(phenyldichlorosilyl)-m-phenylenediamine. Some key characterization data of LP and, in particular, the extremely vulnerable LS with very unstable Si–Cl and Si–N groups were given. The molecular weights (Mn) of LS and LP are 5010 and 10480, corresponding to about 15 and 46 monomer units, respectively. To monitor the real in situ status of LS in solution the XRD measurements of special freeze-drying samples were performed, demonstrating two characteristic peaks of ladder structure. Most importantly, both LP and LS display exceedingly sharp resonance absorption peaks with a half peak width (Δ1/2) as small as < 0.3 of MeSi(NH)O2/2 moieties in 29Si-NMR spectra. It is well-known that the higher the regularity of the l...

Growth of 3,4,9,10-perylenetetracarboxylic-dianhydride (PTCDA) on Cu(110) studied by STM

The structure of thin 3,4,9,10-perylenetetracarb-oxylic-dianhydride (PTCDA) films on Cu(110) was studied by scanning tunnelling microscopy (STM) from submonolayer to monolayer coverage. While no long-range ordering was found after deposition at room temperature, the formation of a well-defined superstructure is observed after thermal annealing. It appears that the formation of the superstructure is driven by the interaction between the oxygen atoms of the PTCDA and the copper atoms of the substrate. While the distance between the molecules fits well to the atomic lattice of the Cu(110) surface along the [1\(\)0] direction, the mismatch along the [001] direction leads to a periodic buckling normal to the surface accompanied by a restructuring of the substrate.

Thermomechanical behaviors and antiferroelectric superstructures in Pb(Yb1/2Nb1/2)O3–rich Pb(Yb1/2Nb1/2)O3–Pb(Fe1/2Nb1/2)O3solution system

Abstract The phase transition behavior of the pseudo-binary (1-x Pb(Yb1/2Nb1/2)O3–xPb(Fe1/2Nb1/2)O3 solid solution has been investigated by thermal expansion and x-ray diffraction. The deviation from the high temperature thermal expansion at temperature near the paraelectric-antiferoelectric (ferroelectric) transition can be explained by the elastic strain coupling to the dipole moments via the electrostriction. For 0<x<0.11, the transition is characteristically sharp, whereas for 0.14≤x≤0.3 it is diffise. X-ray diffraction of pure Pb(Ybl/2Nb1/2)O3 shows a well-defined antiferroelectric superstructure. With the increasing Pb(Fe1/2Nb1/2)O3 concentration, the order-disorder as well as displacement superstructure is observed to diminish. Such structural manifestation on transition seems to be connected with the dielectric behavior.