Morphological Control in Aggregates of Amphiphilic Cylindrical Metal–Polymer “Brushes”

Controlled self-assembly of gold nanorods (AuNRs) into nanostructures of various morphologies has attracted considerable interest because it provides a high degree of freedom in tailoring the properties of the nanostructures by the coupling of the optical and electronic properties of the individual AuNRs. This paper presents a new strategy for making AuNR aggregates of tunable morphologies. In this approach, the surface of AuNRs is chemically coated with an amphiphilic diblock copolymer. The coating gives the AuNRs a cylindrical brush structure. By varying the nature of the common solvent or the interparticle electrostatic repulsion, the self-assembly of the amphiphilic cylindrical AuNR–polymer “brushes” can produce water-soluble aggregates of controllable morphologies, including single-rod ellipsoidal micelles, curved circular lamellae, and nanospheres. The AuNRs in the various aggregates generate different surface plasmon resonance (SPR) absorption patterns, with the longitudinal SPR band in the near-infrared spectral window shifting as the aggregate morphology changes

Formation of Diverse Ordered Structures in ABC Triblock Terpolymer Templated Macroporous Silicas

The macroporous silica synthesis system with the ABC triblock terpolymer poly­(ethylene oxide)-<i>block</i>-polystyrene-<i>block</i>-poly­(<i>tert</i>-butyl acrylate) (denoted as OSA) as template and tetraethyl orthosilicate as silica source under acidic conditions in a mixture solvent of tetrahydrofuran and H₂O has been investigated, and two synthesis–field phase diagrams are plotted. Eight different structures varied from normal-phase (oil in water) cage-type (<i>n</i>-C), normal-phase 2D hexagonal (<i>n</i>-H), and lamellar (L) to unique inverse-phase (water in oil) hyperbolic-surface (<i>i</i>-HS) structures, including the shifted double-diamond (<i>i</i>-SDD), single-gyroid (<i>i</i>-SG), and shifted double-primitive (<i>i</i>-SDP), inverse-phase 2D hexagonal (<i>i</i>-H) and inverse-phase micellar (<i>i</i>-M) structures, have been formed by varying the degree of polymerization of the hydrophobic blocks in OSA. From the two-component phase diagram, it can be concluded that the macroporous structures formation is affected by the packing parameter <i>p</i> and the segregation product (χ<i>N</i>) of the hydrophilic and hydrophobic blocks. With an increase in <i>p</i>, the structures <i>n</i>-C and <i>n</i>-H were found in the range of low χ<i>N</i>, whereas the structures <i>i</i>-HS, <i>i</i>-H, and <i>i</i>-M were found in the range of higher χ<i>N</i>, while L is in between. In the three-component phase diagram, different volume fraction ratios (VFR) of the hydrophobic/hydrophilic block (S/O, A/O) and those of hydrophobic/hydrophobic block (S/A) in this co-assembly system divided the resultant ordered structures in various regions. The <i>n</i>-C, <i>n</i>-H, and L structures were found in low VFRs of S/O and A/O; <i>i</i>-H and <i>i</i>-M structures were formed in high VFRs of S/O and A/O. The formations of the <i>i</i>-HS structures including <i>i</i>-SDD, <i>i</i>-SDP, and <i>i</i>-SG are depending on low VFRs regions of S/O and S/A with similar packing parameter

Growth of 2D Mesoporous Polyaniline with Controlled Pore Structures on Ultrathin MoS₂ Nanosheets by Block Copolymer Self-Assembly in Solution

The development of versatile strategies toward two-dimensional (2D) porous nanocomposites with tunable pore structures draws immense scientific attention in view of their attractive physiochemical properties and a wide range of promising applications. This paper describes a self-assembly approach for the directed growth of mesoporous polyaniline (PANi) with tunable pore structures and sizes on ultrathin freestanding MoS₂ nanosheets in solution, which produces 2D mesoporous PANi/MoS₂ nanocomposites. The strategy employs spherical and cylindrical micelles, which are formed by the controlled solution self-assembly of block copolymers, as the soft templates for the construction of well-defined spherical and cylindrical mesopores in the 2D PANi/MoS₂ nanocomposites, respectively. With potential applications as supercapacitor electrode materials, the resultant 2D composites show excellent capacitive performance with a maximum capacitance of 500 F g^–1 at a current density of 0.5 A g^–1, good rate performance, as well as outstanding stability for charge–discharge cycling. Moreover, the 2D mesoporous nanocomposites offer an opportunity for the study on the influence of different pore structures on their capacitive performance, which helps to understand the pore structure–property relationship of 2D porous electrode materials and to achieve their electrochemical performance control

Effect of Side Chains on the Low-Dimensional Self-Assembly of Polyphenylene-Based “Rod–Coil” Graft Copolymers in Solution

We synthesized a series of “rod–coil” graft copolymers containing a laterally expanded poly-<i>p</i>-phenylene (PPP) backbone grafted with nonionic poly­(ethylene oxide) (PEO) or ionic poly­(acrylic acid) (PAA) side chains (denoted as PPP-<i>g</i>-PEO or PPP-<i>g</i>-PAA). The effect of the side chains on the self-assembly of the graft copolymers in THF–water mixed solvents was investigated. The PPP-<i>g</i>-PEO copolymers exhibited temperature-dependent self-assembly behavior, which is affected by the grafting percentage (GP) and the degree of polymerization (DP) of PEO. At 25 °C, which is higher than the crystallization temperature (<i>T</i>_c) of the PEO chains, PPP-<i>g</i>-PEO self-assembled into ultralong helices with controlled pitches when <i>P</i>N > 6<i>l</i>_m/4<i>b</i>, where <i>P</i> represents GP, <i>N</i> denotes DP of PEO, <i>l</i>_m expresses the length of a repeating unit in PPP, and <i>b</i> is Kuhn monomer length of a free jointed PEO chain; when <i>P</i>N < 6<i>l</i>_m/4<i>b</i>, only nonhelical nanowires were observed. At 10 °C, which is below <i>T</i>_c of PEO, PPP-<i>g</i>-PEO self-assembled into polygonal multilayer nanosheets when <i>P</i>N ≥ 85.8<i>l</i>_m/4<i>b</i>, while ultralong helices or nanowires were formed when <i>P</i>N < 85.8<i>l</i>_m/4<i>b</i>. The PPP-<i>g</i>-PAA copolymer showed pH-sensitive self-assembly behavior. An increase in the electrostatic repulsion among the PAA coils in response to the pH change of the aggregate solution from 3 to 7 resulted in the formation of multiple low-dimensional nanostructures, including multilayer nanosheets, nanostrips, and helical nanostrips

Synthesis and Characterization of Macroporous Photonic Structure that Consists of Azimuthally Shifted Double-Diamond Silica Frameworks

A macroporous silica with azimuthally shifted double-diamond frameworks has been synthesized by the self-assembly of an amphiphilic ABC triblock terpolymer poly­(<i>tert</i>-butyl acrylate)-<i>b</i>-polystyrene-<i>b</i>-poly­(ethylene oxide) and silica source in a mixture of tetrahydrofuran and water. The structure of the macroporous silica consists of a porous system separated by two sets of hollow double-diamond frameworks shifted 0.25<i>c</i> along ⟨001⟩ and adhered to each other crystallographically due to the loss of the mutual support in the unique synthesis, forming a tetragonal structure (space group <i>I</i>4₁/<i>amd</i>). The unit cell parameter was changed from <i>a</i> = 168 to ∼240 nm with <i>c</i> = √2<i>a</i> by tuning the synthesis condition and the wide edge of the macropore size was ∼100 to ∼140 nm. Electron crystallography was applied to solve the structure. Our studies demonstrate electron crystallography is the only way to solve the complex structure in such length scale. Besides, this structure exhibits structural color that ranged from violet to blue from different directions with the bandgap in the visible wavelength range, which is attributed to the structural feature of the adhered frameworks that have lower symmetry. Calculations demonstrate that this is a new type of photonic structure. A complete gap can be obtained with a minimum dielectric contrast of 4.6, which is inferior to the single diamond but superior to the single gyroid structure. A multilayer core–shell bicontinuous microphase templating route was speculated for the formation of the unique macroporous structure, in which common solvent tetrahydrofuran in hydrophobic shell and selective solvent water in hydrophilic core to enlarge each microphase sizes

Nonplanar Ladder-Type Polycyclic Conjugated Molecules: Structures and Solid-State Properties

Using an efficient intramolecular carbon–carbon cross-coupling reaction, a series of new ladder-type conjugated molecules have been prepared successfully in high yields. Such a pyran-fused polycylic structure possesses an extended π-conjugated backbone with flexible conformation, which gives these molecules interesting properties, including high solubility in common organic solvents, excellent thin film-forming abilities, blue fluorescent emission with good quantum yields, and aggregate formation in a binary solvent. The self-assembly behaviors of these molecules as well as various nanostructures can be finely tailored by varying the substituted group on the molecular periphery. The powder and single-crystal X-ray diffraction analyses revealed that the synergetic effect of π–π stacking and van der Waals interactions play a key role in controlling the morphologies of these aggregates. More importantly, self-assembled molecules exhibit good fluorescent performance, due to their twist backbone conformation

Electronic Structure of Isolated Graphene Nanoribbons in Solution Revealed by Two-Dimensional Electronic Spectroscopy

Structurally well-defined graphene nanoribbons (GNRs) are nanostructures with unique optoelectronic properties. In the liquid phase, strong aggregation typically hampers the assessment of their intrinsic properties. Recently we reported a novel type of GNRs, decorated with aliphatic side chains, yielding dispersions consisting mostly of isolated GNRs. Here we employ two-dimensional electronic spectroscopy to unravel the optical properties of isolated GNRs and disentangle the transitions underlying their broad and rather featureless absorption band. We observe that vibronic coupling, typically neglected in modeling, plays a dominant role in the optical properties of GNRs. Moreover, a strong environmental effect is revealed by a large inhomogeneous broadening of the electronic transitions. Finally, we also show that the photoexcited bright state decays, on the 150 fs time scale, to a dark state which is in thermal equilibrium with the bright state, that remains responsible for the emission on nanosecond time scales