Self-Assembly of Polymer End-Tethered Gold Nanorods into Two-Dimensional Arrays with Tunable Tilt Structures

Entropy-driven formation of binary superlattices assembled from polymer-tethered nanorods and nanospheres

Integrating binary mixtures of nanoparticles (NPs) into well-defined superstructures gives rise to novel collective properties depending on the shapes and individual properties of both species. In this paper, we studied the entropy-driven formation of binary superlattices assembled from polymer-tethered nanorods and nanospheres. The results indicated that the conformational entropy of the polymer chains and the mixing entropy of the nanorods and nanospheres are two parameters that determine the formation of binary superlattices.

Large-Area Arrays of Polymer-Tethered Gold Nanorods with Controllable Orientation and Their Application in Nano-Floating-Gate Memory Devices

In this work, it is reported that large-area (centimeter-scale) arrays of non-close-packed polystyrene-tethered gold nanorod (AuNR@PS) can be prepared through a liquid-liquid interfacial assembly method. Most importantly, the orientation of AuNRs in the arrays can be controlled by changing the intensity and direction of electric field applied in the solvent annealing process. The interparticle distance of AuNR can be tuned by varying the length of polymer ligands. Moreover, the AuNR@PS with short PS ligand are favorited to form orientated arrays with the assistance of electric field, while long PS ligands make the orientation of AuNRs difficult. The orientated AuNR@PS arrays are employed as the nano-floating gate of field-effect transistor memory device. Tunable charge trapping and retention characteristics in the device can be realized by electrical pulse with visible light illumination. The memory device with orientated AuNR@PS array required less illumination time (1 s) at the same onset voltage in programming operation, compared to the control device with disordered AuNR@PS array (illumination time: 3 s). Moreover, the orientated AuNR@PS array-based memory device can maintain the stored data for more than 9000 s, and exhibits stable endurance characteristic without significant degradation in 50 programming/reading/erasing/reading cycles.

Anisotropic nanocluster arrays to a diminished zone: different regimes of surface deposition of gold nanocolloids

Evaporation-induced assembly of nanoparticles has emerged as a versatile technique for the production of large-scale ordered structures and materials with complex features. In this study, we show that a dried particulate of an anisotropic nanocolloid undergoes non-ubiquitous surface morphological transitions at varying particle concentrations. Below 5 nM, deposits reveal the formation of linear arrays of AuNR clusters outside of the coffee ring and an annular CTAB-rich depletion zone in the inner vicinity of the coffee ring. For nanoparticle concentrations ≥5 nM, the outer cluster deposits disappear and a region of reduced AuNR density, sandwiched between the coffee ring and the depletion zone, analogous to the diminished zone, is observed. Within the coffee-ring deposits, nanoscale smectic AuNR assembly occurs via the expulsion of the cetyltrimethyl ammonium bromide (CTAB) bilayer, which contributes to the inward solutal Marangoni flow. An enhanced inward solutal Marangoni flow at high particle concentrations assists in the formation of a wider depletion zone, the emergence of the diminished zone and suppression of the width of the coffee-ring deposits. Through detailed analysis of data from ex situ (scanning electron microscopy, SEM) and in situ (contact angle and confocal imaging) measurements, we establish a direct correlation between the different evaporation modes and the various deposition regimes. A detailed mechanism for the surface morphology modulation of AuNR deposits by tuning the nanoparticle concentration in the drying sessile drop is discussed.

Influence of the Crystal Structure of Melamine Trimetaphosphate 2D Supramolecules on the Properties of Polyamide 6

To explore the influence of the crystal structure difference of melamine trimetaphosphate (MAP) on the application performance of its polymer composites, an intumescent flame retardant with the optimal crystal type was designed and synthesized to improve the mechanical properties and flame retardancy of polyamide 6 (PA6). I-MAP and II-MAP were obtained using different concentrations of MA and sodium trimetaphosphate (STMP) in an acidic aqueous solution. The morphology, chemical composition, and thermal stability were comprehensively characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The dispersion, mechanical properties, and flame retardancy of PA6/I-MAP and PA6/II-MAP were evaluated by SEM, stress and strain, limiting oxygen index test (LOI), vertical burning test (UL-94), cone calorimetry (CONE) test, and char residue analysis. The conclusion is as follows: I-MAP and II-MAP have a greater influence on the physical properties of PA6 but less influence on the chemical properties. Compared with PA6/I-MAP, the tensile strength of PA6/II-MAP is 104.7% higher, the flame rating reaches V-0, and PHRR is reduced by 11.2%.

Magnetic Alignment for Plasmonic Control of Gold Nanorods Coated with Iron Oxide Nanoparticles

Plasmonic nanoparticles that can be manipulated with magnetic fields are of interest for advanced optical applications, diagnostics, imaging, and therapy. Alignment of gold nanorods yields strong polarization-dependent extinction, and use of magnetic fields is appealing because they act through space and can be quickly switched. In this work, cationic polyethyleneimine-functionalized superparamagnetic Fe₃ O₄ nanoparticles (NPs) are deposited on the surface of anionic gold nanorods coated with bovine serum albumin. The magnetic gold nanorods (MagGNRs) obtained through mixing maintain the distinct optical properties of plasmonic gold nanorods that are minimally perturbed by the magnetic overcoating. Magnetic alignment of the MagGNRs arising from magnetic dipolar interactions on the anisotropic gold nanorod core is comprehensively characterized, including structural characterization and enhancement (suppression) of the longitudinal surface plasmon resonance and suppression (enhancement) of the transverse surface plasmon resonance for light polarized parallel (orthogonal) to the magnetic field. The MagGNRs can also be driven in rotating magnetic fields to rotate at frequencies of at least 17 Hz. For suitably large gold nanorods (148 nm long) and Fe₃ O₄ NPs (13.4 nm diameter), significant alignment is possible even in modest (<500 Oe) magnetic fields. An analytical model provides a unified understanding of the magnetic alignment of MagGNRs.

Effect of rhodamine 6G dye molecular interactions on counterintuitive self-assembly of noble metal nanorods

HYPOTHESIS

Self-assembled nanostructures with highly ordered and diversified patterns can be obtained by adding additives that directionally control the interparticle interactions. However, due to the complex non-covalent weak interactions in the self-assembly process, the active mechanism of additives is not fully understood, resulting in the limitation of obtaining the nano-superstructures. The introduction of rhodamine 6G (R6G) enables gold nanorods (GNRs) self-assembled into a counterintuitive tetragonal superlattice, during which the exploration of the influence of R6G molecular interactions on the GNRs self-assembly is of importance.

EXPERIMENTS

We present the detailed investigations of spacial configuration, binding modes, and aggregated degree of R6G molecule on formation of the tetragonal GNRs superlattices by combining the experimental and simulated results.

FINDINGS

By analyzing the peak position and peak intensity in the fluorescent spectra of assembled samples and pure R6G samples, H-dimer is verified as the main cause for inducing the tetragonal superstructures. Molecular dynamics simulations reveal that 2-3 H-dimers adsorbed obliquely in a zigzag chain manner on the surface of GNRs is the most stable state of the self-assembly. This work would contribute to a deeper understanding of the complex colloidal nanoparticle self-assemblies and push forward the development of the bottom-up nanoscale superstructures.

Fabrication of Oriented Colloidal Crystals from Capillary Assembly of Polymer-Tethered Gold Nanoparticles

Self-assembled colloidal crystals (CCs) or nanoparticle (NPs) superlattices have attracted significant attention due to their potential applications in many fields. However, due to the complex interactions that govern the self-assembly, it is difficult to predict and control the superstructure organization of CCs. Herein, a facile yet effective way is demonstrated to fabricate oriented CCs from capillary assembly of polymer-tethered gold NPs (AuNPs). Assembly mechanism of polymer-tethered AuNPs and their superlattice structures are systematically studied by in situ small-angle X-ray scattering (SAXS) technology. The results show that the oriented CCs of polymer-tethered AuNPs can be obtained upon solvent evaporation in a capillary tube and the oriented structure is mainly determined by the chain length of polymer ligands and size of AuNPs. Assembly of AuNPs tethered by short-chain ligand can result in oriented face-centered cubic (fcc) superlattice, whereas AuNPs tethered by long-chain ligand can assemble into an oriented body-centered tetragonal (bct) superlattice structure. Interestingly, in situ SAXS study shows that for the sample of bct superlattice structure, a transformation from fcc to bct superlattice upon solvent evaporation is observed, which strongly depends on chain length of ligands. This work provides a useful guide for polymer-tethered AuNPs to prepare orientation colloidal crystals.

Switchable Anion Exchange in Polymer-Encapsulated APbX3 Nanocrystals Delivers Stable All-Perovskite White Emitters

We report a one-step synthesis of halide perovskite nanocrystals embedded in amphiphilic polymer (poly(acrylic acid)-block-poly(styrene), PAA-b-PS) micelles, based on injecting a dimethylformamide solution of PAA-b-PS, PbBr₂, ABr (A = Cs, formamidinium, or both) and "additive" molecules in toluene. These bifunctional or trifunctional short chain organic molecules improve the nanocrystal-polymer compatibility, increasing the nanocrystal stability against polar solvents and high flux irradiation (the nanocrystals retain almost 80% of their photoluminescence after 1 h of 3.2 w/cm² irradiation). If the nanocrystals are suspended in toluene, the coil state of the polymer allows the nanocrystals to undergo halide exchange, enabling emission color tunability. If the nanocrystals are suspended in methanol, or dried as powders, the polymer is in the globule state, and they are inert to halide exchange. By mixing three primary colors we could prepare stable, multicolor emissive samples (for example, white emitting powders) and a UV-to-white color converting layer for light-emitting diodes entirely made of perovskite nanocrystals.