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Mechanical Nanosprings: Induced Coiling and Uncoiling of Ultrathin Au Nanowires
Abstract
We report the controllable coiling of colloidal gold nanowires induced by the contraction of their polymer shells. The mechanical energy stored in this process can be released upon removal or swelling of the polymer shells.
... At present, there are only a few methods known for isolating UAuNWs, all of which are derived from density gradient ultracentrifugation. It could separate UAuNWs in multiple layers of density gradients [31][32][33], but the method only works for long UAuNWs (2-4 μm), and complete removal of small (2 nm) AuNPs remains a challenge. ...
... The isolated UAuNWs always contained a significant amount of AuNPs (Figs S3, S4), highlighting the challenges in differential centrifugation. Indeed, all of the UAuNWs reported in the literature contained similar by-product AuNPs (except in small-area images, Figs S5, S6) [2,23,[30][31][32][33][34][35]37,38], consistent with our observations. ...
Ultrathin Au nanowires are always synthesized with 2 nm Au nanoparticles as the by-product, and their separation has been a long-standing problem. In this work, we show that high-purity (>99%) separation can be achieved using the solvent exclusion method: Adding hexane would cause water to be excluded from the initial water-THF mixture. The excluded water preferentially nucleates on the oleylamine-bilayer of the nanowires, transferring them into the water phase. Careful control experiments were conducted to establish the purification mechanism. The facile method can be generally applied to purify ultrathin Au nanowires with short lengths (470 and 130 nm), which has not been realized using the conventional methods.
... Their spiral growths were mainly induced by electrostatic interaction between opposite charged neighboring surfaces or by dislocation existing in crystals. Last but not least, coiled nanostructures can also be prepared in liquid circumstances and the mechanisms are usually involved with bending nanowires in confined micro-environments, or minimizing of the surface energy of nanowires [24][25][26][27][28] . Besides inorganic spiral nanostructures, organic materials of spiral nanostructures were also synthesized, mainly based on molecular self-assembly 29,30 . ...
... Unlike the case of ZnO nanorings 17 , elemental copper is isotropic material with non-polar surfaces, polarization-induced attractions between neighboring Scientific RepoRts | 5:16879 | DOI: 10.1038/srep16879 turns and closing ends cannot exist. Other helical structures prepared in liquid phase systems usually are results of template-guide or restrict [26][27][28] , those nanorings usually have diameters less than 100 nanometers, hindering their applications in certain areas, whereas copper nanocoils and nanosprings prepared in our method have much larger diameters of dozens up to hundreds of microns. Compared with products from other fabrication techniques (non-liquid phase methods, e.g. ...
Recently helical nanostructures such as nanosprings and nanocoils have drawn great interests in nanotechnology, due to their unique morphologies and physical properties, and they may be potential building blocks in sorts of electromechanical, magnetic, photoelectronic and plasmonic devices at micro/nanoscales. In this report, multi-turns copper nanocoils were synthesized through a modified solvothermal method, in which the mixture of water and N-methyl-2-pyrrolidone (NMP) were selected as reaction medium and copolymer poly(1-vinylpyrrolidone-co-vinyl acetate) (PVP/VA 64E) as reductant. In the liquid solution, nanosprings could be formed from relaxed nanocoils and demonstrated high elasticity. These nanocoils and nanosprings are of single crystalline structure, with the characteristics wire diameters ranging from tens to a few hundreds of nanometers and the ring/coil diameters mostly ~10-35 microns. Their growth and deformation mechanisms were then investigated and discussed along with that of previously reported single-turn copper nanorings. This work could be of importance for researchers working on synthesis and applications of novel 1-D helical nanomaterials and their functional devices.
... In the case of a very flexible and long filament, the encapsulated filament coils with α > 2π and the vesicle adopts an almost spherical or oblate shape (Figs. 2 A and B, SI Appendix, Fig. S3 and Fig. 4 A and B), consistent with observation of coiling for elastic spiral ESCRT-III filaments of a large target radius in dividing cells (8), for microtubules in vesicles (14,16,17), for bacterial filaments in macrophages (36), and for even ultrathin gold nanowires in polymer micelles (37). ...
A fundamental understanding of cell shaping with confined flexible filaments, including microtubules, actin filaments, and engineered nanotubes, has been limited by the complex interplay between the cell membrane and encapsulated filaments. Here, combining theoretical modeling and molecular dynamics simulations, we investigate the packing of an open or closed filament inside a vesicle. Depending on the relative stiffness and size of the filament to the vesicle as well as the osmotic pressure, the vesicle could evolve from an axisymmetric configuration to a general configuration with a maximum of three reflection planes, and the filament could bend in or out of plane or even coil up. A plethora of system morphologies are determined. Morphological phase diagrams predicting conditions of shape and symmetry transitions are established. Organization of actin filaments or bundles, microtubules, and nanotube rings inside vesicles, liposomes, or cells are discussed. Our results provide a theoretical basis to understand cell shaping and cellular stability and to help guide the development and design of artificial cells and biohybrid microrobots.
... © 2021 Wiley-VCH GmbH contraction of their polymer shells. [167,168] In the two-component system, the polymer shell can reply to changes in solvent and produce a self-attraction interaction, driving the long nanowire or nanotubes to wind into toroids. The toroid size is relatively uniform and can be regulated by the rigidity of winding objects and the contraction of the polymer shells. ...
In recent years, toroidal nanostructures have become an appealing topic in nanoscience owing to their unique structure and promising applications. Among them, polymeric toroidal self-assemblies have attracted considerable attention because of their manipulability and diversity. Despite the substantial advances in the area of polymeric nanotoroids, the universal formation principles and functions of these toroids have not been sufficiently summarized. This article aims to review recent advances in the formation and function of polymeric nanotoroids. The significant role of theoretical simulations in revealing the formation mechanism and inherent structure of toroidal assemblies is emphasized. Additionally, a perspective on the challenges of this research field is addressed.
... The redshift has been ascribed to the increase in the dielectric constant due to the miniaturization of the Au NR diameter. 272 Au UNRs and UNWs show great potential for a variety of applications, including flexible electrodes with high electrical conductivity and optical transparency, 274 pressure sensors with high sensitivity, fast response and good stability, 275 mechanical energy storage devices, 276 biosensors, 277,278 surface-enhanced Raman scattering (SERS) substrates, 279 and highly active catalysts. 280 Au NRs of small sizes (mini Au NRs) possess high photothermal efficiencies that are close to 100% because their absorption cross sections are dominant. ...
... The morphology of eukaryotic nuclei has been similarly shown to be intimately linked to the structure and mechanics of the encapsulated chromatin fibers [52][53][54], suggesting that the mutual feedback between polymer folding and membrane conformation may play an essential role in genome organization and thus in the regulation of cellular function. From a practical standpoint, the ability to control the coiling of elastic nanowires through their confinement within swelling polymer shells [55] or liquid droplets [56] has also been demonstrated experimentally, and could be exploited as the basis of a variety of applications for nanomechanical energy storage [57]. ...
We systematically explore the self-assembly of semi-flexible polymers in deformable spherical confinement across a wide regime of chain stiffness, contour lengths and packing fractions by means of coarse-grained molecular dynamics simulations. Compliant, DNA-like filaments are found to undergo a continuous crossover from two distinct surface-ordered quadrupolar states, both characterized by tetrahedral patterns of topological defects, to either longitudinal or latitudinal bipolar structures with increasing polymer concentrations. These transitions, along with the intermediary arrangements that they involve, may be attributed to the combination of an orientational wetting phenomenon with subtle density- and contour-length-dependent variations in the elastic anisotropies of the corresponding liquid crystal phases. Conversely, the organization of rigid, microtubule-like polymers evidences a progressive breakdown of continuum elasticity theory as chain dimensions become comparable to the equilibrium radius of the encapsulating membrane. In this case, we observe a gradual shift from prolate, tactoid-like morphologies to oblate, erythrocyte-like structures with increasing contour lengths, which is shown to arise from the interplay between nematic ordering, polymer and membrane buckling. We further provide numerical evidence of a number of yet-unidentified, self-organized states in such confined systems of stiff achiral filaments, including spontaneous spiral smectic assemblies, faceted polyhedral and twisted bundle-like arrangements. Our results are quantified through the introduction of several order parameters and an unsupervised learning scheme for the localization of surface topological defects, and are in excellent agreement with field-theoretical predictions as well as classical elastic theories of thin rods and spherical shells.
... Remarkable reports concerning quantum photonics, 1−3 photodynamic therapy, 4−6 and the programmable architectures 7−9 of nanoscaled gold have revealed that the dimensions, morphologies, and chemical modifications of artificial gold nanomaterials can be tailored for given applications. One-dimensional helical gold nanostructures, namely, gold nanohelices (AuNHs), 10−16 gold nanospirals (AuNSs), 17,18 and gold nanosprings, 19,20 have been shown to exhibit specific forms of atomic packing, high degrees of surface-enhanced Raman scattering (SERS), and plasmonic responses. In previous studies, several synthesis strategies, including peptide assembly, electrochemical deposition, galvanic displacement reaction, surfactant-assisted reaction, and glancing angle deposition, were utilized for the preparation of AuNHs, and growth pathways were also proposed to interpret the curved morphology of those one-dimensional gold nanomaterials. ...
Gold nanohelices (AuNHs) are synthesized using surfactant-assisted seed-mediated growth in an aqueous solution. AuNHs with diameters and lengths of 30–150 nm and several micrometers, respectively, are grown in a reaction carried out at 15 °C for 20 h by adding poly(ethylene glycol)(12)tridecyl ether, polyvinylpyrrolidone, and cetyltrimethylammonium bromide as the capping agents in an HAuCl4(aq) solution. With the addition of gold nanoparticles (AuNPs) in the reaction, the yield of the helical products is considerably increased, which indicates that AuNPs behave as the seeds for AuNH growth. The growth routes of AuNHs in the system are investigated by transmission electron microscopy measurements. Finite-difference time-domain (FDTD) simulations show that total extinction of the AuNH at 660 and 570 nm is dominantly influenced by strong e-field enhancement and the scattering of light incidence. In a practical application, surface-enhanced Raman scattering (SERS) measurements are conducted using AuNHs as the substrates and 4-mercaptobenzoic acid as the probe. A detection limit of 20 ppb is acquired using a micro-Raman spectrometer using a 633 nm He–Ne laser with a power of 3.35 mW which corresponds with the FDTD simulation results and reveals that AuNHs are superior SERS templates with resonance tuning ability in consequence of their unique helical architectures.
... Recent chemical synthesis methods have been successfully utilized to grow ultrathin gold nanowires (Au-UNWs) with diameter ∼ 2 nm and length on the micrometer scale [9]. The atomically precise Au-UNWs having high mechanical flexibility with aspect ratio > 1000 have been used in fabricating flexible transparent conductive metal grids [10], fast response pressure sensors [11], mechanical energy storage [12], and interconnects in nano-devices [13]. The dominant edge sites on their surfaces have been explored for active and selective electrochemical reductions [14] with applications in the fields of catalysis [15]. ...
Carrier dynamics in metallic nanostructures is strongly influenced by their confining dimensions. Gold nanoparticles of size \(\sim ~2\) nm which fill the transition space separating metallic and non-metallic behavior. In this work, we report carrier dynamics in high aspect ratio ultrathin gold nanowires (Au-UNWs) of average diameter \(\sim \) 2 nm using pump (3.1 eV) and coherent white light continuum as probe in the spectral range of 1.15 to 2.75 eV. The transient carrier dynamics in Au-UNWs under extreme excitation regime is slower than predicted by the often used two-temperature model. We identify Auger-assisted carrier heating process which slows down the hot carrier cooling dynamics. The rate equation model fitted to the data yields an estimate of Auger coefficient for gold nanostructures.
... Recent chemical synthesis methods have been successfully utilized to grow ultrathin gold nanowires (Au-UNWs) with diameter ∼ 2 nm and length on the micrometer scale [9]. The atomically precise Au-UNWs having high mechanical flexibility with aspect ratio > 1000 have been used in fabricating flexible transparent conductive metal grids [10], fast response pressure sensors [11], mechanical energy storage [12], and interconnects in nano-devices [13]. The dominant edge sites on their surfaces have been explored for active and selective electrochemical reductions [14] with applications in the fields of catalysis [15]. ...
Carrier dynamics in metallic nanostructures is strongly influenced by their confining dimensions. Gold nanoparticles of size $\sim 2$ nm lie at the boundary separating metallic and non-metallic behavior. In this work, we report carrier dynamics in high aspect ratio ultrathin gold nanowires (Au-UNWs) of average diameter $\sim$2 nm using pump (3.1 eV) and coherent white light continuum as probe in the spectral range of 1.15 eV to 2.75 eV. The transient carrier dynamics in Au-UNWs under extreme excitation regime is slower than predicted by the often used two temperature model. We identify Auger-assisted carrier heating process which slows down the hot carrier cooling dynamics. The rate equation model fitted to the data yields an estimate of Auger coefficient for gold nanostructures.
... 35 The modulation of encapsulating shells made of polystyrene-blockpoly(acrylic acid) led to a transformation of straight AuUNWs to circular rings in colloidal solution (Figure 5d). 36 This method gave a structure resembling that of torsion springs (Figure 5e) in which elastic energy is stored. ...
... S olvent-induced self-assembly of nanoparticles, driven by hydrophobic interactions in a liquid phase, is a convenient strategy to fabricate complex architectures in a bottom-up fashion. 1 Polystyrene-stabilized gold nanoparticles (Au@PS) of different shapes, such as spheres, 2,3 rods, 4−6 stars, 7 cubes, 8,9 and wires, 10 have been used to build a variety of structures including spherical clusters, 11,12 dynamic chain-like assemblies, 13,14 vesicles, 15,16 or low-symmetry dimers. 17 Because the major part of these architectures are kinetic products, 18 their structure (e.g., number and distribution of nanoparticles per cluster) and quality depend on the way the nonsolvent (water) is added to a dispersion of nanoparticles which are coated with a radially distributed polymer shell in a good solvent (DMF, THF). ...
The hydrophobic collapse is a structural transition of grafted polymer chains in a poor solvent. Although such a transition seems an intrinsic event during clustering of polymer-stabilized nanoparticles in the liquid phase, it has not been resolved in real time. In this work, we implemented a microfluidic 3D-flow-focusing mixing reactor equipped with real-time analytics, small-angle X-ray scattering (SAXS) and UV-Vis-NIR spectroscopy, to study the early stage of cluster formation, for polystyrene-stabilized gold nanoparticles. The polymer shell dynamics obtained by in situ SAXS analysis and numerical simulation of the solvent composition allowed us to map the interaction energy between the particles at early state of solvent mixing, 30 ms behind the crossing point. We found that the rate of hydrophobic collapse depends on water concentration, ranging between 100 and 500 nm/s. Importantly, we found that the polymer shell collapses prior to the commencement of clustering.
... Besides, with the same organic density gradient, Au nanowires were also purified from nanoparticles [91]. Further, Au nanowires can be encapsulated by copolymers (e.g., polystyrene-block-poly (acrylic acid)) to form mechanical energy stored ''nanospring" on the water/oil interface [92]. ...
In this article, we review the advancement in nanoseparation and concomitant purification of nanoparticles (NPs) by using density gradient ultracentrifugation technique (DGUC) and demonstrated by taking several typical examples. Study emphasizes the conceptual advances in classification, mechanism of DGUC and synthesis-structure-property relationships of NPs to provide the significant clue for the further synthesis optimization. Separation, concentration, and purification of NPs by DGUC can be achieved at the same time by introducing the water/oil interfaces into the separation chamber. We can develop an efficient method “lab in a tube” by introducing a reaction zone or an assembly zone in the gradient to find the surface reaction and assembly mechanism of NPs since the reaction time can be precisely controlled and the chemical environment change can be extremely fast. Finally, to achieve the best separation parameters for the colloidal systems, we gave the mathematical descriptions and computational optimized models as a new direction for making practicable and predictable DGUC separation method. Thus, it can be helpful for an efficient separation as well as for the synthesis optimization, assembly and surface reactions as a potential cornerstone for the future development in the nanotechnology and this review can be served as a plethora of advanced notes on the DGUC separation method.
... In the case of an encapsulated worm-like polymer chain with a contour length several times the circumference of the spherical vesicle (L ≫ R), the polymer chain undergoes a transition from an isotropic disordered random conformation to an ordered toroidal coil as its bending stiffness increases [39]. The coiling of confined long nanofibers has been observed in both engineering and biological circumstances including controllable coiling of gold nanowires within polymer capsules [40], filamentous morphology in bacteria [41], actin polymerization inside cellsized droplets [42]. It is of significance to take a comprehensive study on packing of nanofibers with length varying in a wide range from L/R = 2 to L/R on an order of 10 and rigidity from a persistence length on the order of tens of nanometers to several millimeters. ...
Cellular packing of flexible nanofibers, including natural cytoskeletal microtubules, actin filaments, synthetic nanotubes and nanowires, is of fundamental interest to the understanding of a wide range of cell activities, including cell shape control, cell movement, cell division, and nano-cytotoxicity. Here, we perform molecular dynamics simulations and theoretical analysis to elucidate how the geometrical and mechanical properties of a flexible nanofiber influence its encapsulation within a lipid vesicle. Our analysis indicates that the packing morphology depends on the length and stiffness of the nanofiber, the initial configuration of the nanofiber–vesicle system and the pressure difference across the vesicle membrane. We establish a packing phase diagram based on three distinct vesicle morphologies in equilibrium, including a non-axisymmetric dumpling-shaped vesicle with a strongly curved nanofiber, a cherry-shaped vesicle with a tubular membrane protrusion enclosing a significant portion of the nanofiber, and an axisymmetric lemon-shaped vesicle with a pair of protruding tips induced by the encapsulated nanofiber.
... 17 These wires are flexible enough to bend reversibly with radii of approximately 25 nm. 18 They were successfully applied in the fields of surface-enhanced Raman scattering (SERS), 19 sensing, 20,21 catalysis, 22 and transparent electronics. 23,24 Ultrahin gold nanowires interact in dispersion mainly through highly multivalent interactions between their OAm shells. ...
Hierarchical structures lend strength to natural fibers made of soft nanoscale building blocks. Intermolecular interactions connect the components at different levels of hierarchy, distribute stresses, and guarantee structural integrity under load. Here, we show that synthetic ultrathin gold nanowires with interacting ligand shells can be spun into biomimetic, free-standing microfibers. A solution spinning process first aligns the wires, then lets their ligand shells interact, and finally converts them into a hierarchical superstructure. The resulting fiber contained 80 vol.% organic ligand but was strong enough to be removed from the solution, dried, and mechanically tested. Fiber strength depended on the alignment of the wire monomers. Shear in the extrusion nozzle was systematically changed to obtain process-structure-property relations. The degree of nanowire alignment changed breaking stresses by a factor of 1.25 and the elongation at break by a factor of 2.75. Plasma annealing of the fiber to form a solid metal shell decreased the breaking stress by 65%.
... When 4 mM ( Figure S7c,j,q) to 8 mM ( Figure S7d,k,r) of C Triton X-100 was introduced into the system, the morphologies of the NW assemblies start to exhibit a distinct length-dependent effect. Consistent with a previous report, 42 the longest NWs (AuNW-I > 1 μm) gave nanorings with a diameter of about 786 nm in high yield (Figure 3a,b). The inset TEM image suggests that the Au nanoring is composed of parallel-packed AuNWs bundles. ...
Ultrathin nanowires (NWs) are considered as ideal building blocks for assembly of complex nanostructures towards future nanodevices. The polymer/particle duality of ultrathin NW plays an important role in the study of solution phase self-assembly behavior of ultrathin NWs, yet it has not been fully exploited. Herein, we demonstrate the effects of polymer/particle duality of ultrathin NWs on the morphologies of assembled complex nanostructures. The length of ultrathin AuNWs directly correlates with the flexibility of NW, and affects polymer-like assembly of NWs, while the concentration of surfactants determines interfacial tension and ligand-solvent interactions, and affects both polymer-like and colloidal assembly of NWs. By fine tuning these two factors, Ultrathin AuNWs can swing between “soft” and “hard” building block, and highly uniform nanorings, nanograins, nanobundles as well as superlattice-like nanospheres are obtained. The different assembly behavior of long and short NWs can be considered as two components to construct anisotropic complex nanostructures, in analogue with the fabrication of polymer-inorganic nanoparticle hybrid nanostructures. We synthesized anisotropic structures of Au nanodiamond rings and nanonecklaces by the co-assembly of polymer-like long NWs with particle-like short NWs or Au nanoparticles. This strategy is potential extended to the organization of anisotropic complex nanostructures with other ultrathin NWs system in the future.
... A self-rolling or polymer-induced coiling mechanism has been observed to explain the formation of ZnO nanorings, Au and Ag nanosprings, InS rings and loops and V 3 O 7 nanoscrolls. [17][18][19][20] In addition, a structural transformation via an edge-selective reaction of two-dimensional (2D) layered nanocrystals or via a Kirkendall effect has been used to prepare TiO 2 toroids, Cu 2 S nanorings and Cu-NaInS 2 nanorings. [21][22][23] Recently, the self-assembly mechanism of NPs with intrinsic polygons led to the growth of ring-like CdS, Ni-Co and PbSe nanorings. ...
Toroidal Au or Ag nanostructures are of particular interest due to their unique optical responses and superior catalytic applications. However, the fabrication of ring-like Au or Ag nanostructures is limited to either electron beam lithography or template techniques, thus hampering their applications. Here, we present a new stress-driven structure collapse and etching mechanism to synthesize Au nanorings via a direct one-pot solution-based chemical reaction. The nanoparticle-mediated recrystallization process contributes to the formation of Au nanoframes, which contain unusual stress, thus promoting the breakup of the nanoframes and finally converting them into Au nanorings. The Au nanorings with tunable hole sizes exhibit interesting localized surface plasmon features owing to the coupling of bonding and antibonding modes on the inner and outer surfaces of the nanorings. This facile approach may open the door for the preparation of toroidal nanostructures in other compositions for numerous applications.
... In reality, they are not likely to replace the ordinary transistors, but they may well provide the paradigm shift that will extend "Moore's law". One-dimensional nanoscaled materials, nanowires (NWs), nanotubes (NTs), or even composite nanowires made up of different materials represent attractive building blocks for hierarchical assembly of functional nanoscale devices, which can exhibit a real device with diverse performances and simultaneously function as the "wires", i.e., they can access and interconnect devices that could overcome fundamental limitations of conventional fabrication [3-7]. These unique properties and the intrinsically miniaturized dimensions of NWs' and NTs' building blocks may facilitate the continuation and extension of Moore's law and the evolutionary demand for even faster and smaller electronics in the future. ...
Nanoscaled materials are attractive building blocks for hierarchical assembly of functional nanodevices, which
exhibit diverse performances and simultaneous functions. We innovatively fabricated semiconductor nano-probes of tapered ZnS nanowires through melting and solidifying by electro-thermal process; and then, as-prepared nanoprobes can manipulate nanomaterials including semiconductor/metal nanowires and anoparticles through sufficiently electrostatic force to the desired location without structurally and functionally damage. With some advantages of high precision and large domain, we can move and position and interconnect individual nanowires for contracting nanodevices. Interestingly, by the manipulating technique, the nanodevice made of three vertically interconnecting nanowires, i.e., diode, was realized and showed an excellent electrical property. This technique may be useful to fabricate electronic devices based on the nanowires’ moving, positioning, and interconnecting and may overcome fundamental limitations of conventional mechanical fabrication.
... Eventually, both upper and lower faces of the shell are fully flattened, turning it into the convex hull of the enclosed coil. Similar forms have been experimentally obtained by enclosing elastic nanotubes and nanowires with emulsion droplets and polymer shells, which were then intentionally contracted [25,26]. Monte Carlo simulations at finite temperature [27,28] have likewise indicated that soft vesicles deform into obloids when enclosing a fluctuating polymer chain whose persistence length grows much larger than the vesicle diameter. ...
The packing problem of long thin filaments that are injected into confined
spaces is of fundamental interest for physicists, biologists and materials
engineers alike. How linear threads pack and coil is well known only for the
ideal case of rigid containers, however. Here, we force long elastic rods into
flexible spatial confinement borne by an elastic shell to examine under which
conditions recently acquired knowledge on wire packing in rigid spheres breaks
down. We find that unlike in rigid cavities, friction plays a key role by
giving rise to the emergence of two distinct packing patterns. At low friction,
the wire densely coils into an ordered toroidal bundle with semi-ellipsoidal
cross section, while at high friction, it packs into a highly disordered,
self-similar structure. These two morphologies are shown to be separated by a
continuous phase transition.
Recent evaluations of nanospring synthesis methods, mechanical properties, simulations, and applications are analyzed. Future perspectives focus on molecular engineering, advanced synthesis & characterizations, and machine learning.
The self-assembly of block copolymers on nanocylinders has attracted a lot of interest due to its potential application in biomedicine and other fields. In this study, the self-assembly phase behavior of AB diblock copolymers on long nanocylinders in soft confinement has been studied by using a simulated annealing method. A square phase diagram of the morphology was constructed by increasing the number of chains of copolymers (cn) and the cylindrical diameter (D). As a result, morphological transitions from striped to helical and axially stacked toroids, as well as reversible transitions, started to appear. By analyzing the chain packing in a fan-shaped region and calculating the mean-square end-to-end distance (DEE2) of the copolymers and number of AB contacts, both types of transitions were found to be driven by the competition between conformational entropy and AB interfacial energy. The number of stripes increased and the helical angle decreased with the increase in cylinder diameter. The chirality of the helix was found to be random.
Metallic nanoparticles have received a great deal of attention due to their interesting optical, electrical and catalytic properties that can be tuned by morphological control of their nanostructures. These metallic nanostructures are expected to be applied in a wide range of fields such as electronic materials, biological sensing and catalysts as nanomaterials. Various technique can be used to achieve morphological control of nanostructures. Particularly, wet-chemical synthesis using a soft-template is advantageous for large scale preparation of metal nanomaterials, and it has been successfully used to prepare metal nanocrystals with various shapes, including metallic nanowires, nanorings and nanohelices. Here, the syntheses and morphological control of noble metal nanowires using a soft-template method by the author’s group in recent years are mainly described. In addition, the features of the soft-template method using a molecular assembly are summarized.
Ultrathin Au and Au alloy nanowires upon coating of a metal layer are known to twist, and such twisting is of importance for driving motions in minuscule systems. Here, with global exploration of potential energy surface, the origin of twisting Au nanowire is investigated. Au nanowire with Face Center Cubic structure would transform into a helix with multi-shell atomic structure, driven by general increase of effective bonding (thermodynamics), where the largest contribution comes from the surface atoms. On the other hand, the rectangular nanowire comes out with Boerdijk−Coxeter−Bernal like structure. Studies on the progresses of transformations indicate that it is composed of local bending which leads to twisting of nanowire. It is conceivable that the understanding of such systems would shed light to future synthetic designs of twisting nanowires and for introducing chirality into nanowires.
Block copolymers (BCPs)-based self-assemblies with various morphological and compartmental structures can serve as universal polymeric scaffolds for the incorporation of diverse inorganic nanoparticles (NPs) within the disparate polymer domains of the formed aggregates. The properties and performance of the resulting BCPs–NPs hybrids depend not only on the organic and inorganic building moieties, but also on the spatial distribution of inorganic NPs within organic aggregates. However, few publications have so far made a systematical clarification of the effect of the critical parameters on the morphological control of BCPs–NPs hybrids and the spatial localization of NPs within the BCPs-based aggregates as well as their properties for potential applications. For this purpose, we summarized the co-operative assembly of BCPs and NPs in solution and emulsion with an emphasis on the precisely modulated localization of NPs in different domains of BCP aggregates with various morphologies. Specifically, we made detailed discussion on the effect of size, shape and surface property of NPs on the loading number and selective localization of NPs within BCP aggregates. The important guidelines drawn herein on the precise modulation of spatially distributed NPs in BCP aggregates are believed to inspire the generation of more novel hybrid materials for various applications.
The self-assembly of inorganic nanoparticles is of great importance in realizing their enormous potentials for broad applications due to the advanced collective properties of nanoparticle ensembles. Various molecular ligands (e.g., small molecules, DNAs, proteins, and polymers) have been used to assist the organization of inorganic nanoparticles into functional structures at different hierarchical levels. Among others, polymers are particularly attractive for use in nanoparticle assembly, because of the complex architectures and rich functionalities of assembled structures enabled by polymers. Polymer-guided assembly of nanoparticles has emerged as a powerful route to fabricate functional materials with desired mechanical, optical, electronic or magnetic properties for a broad range of applications such as sensing, nanomedicine, catalysis, energy storage/conversion, data storage, electronics and photonics. In this review article, we summarize recent advances in the polymer-guided self-assembly of inorganic nanoparticles in both bulk thin films and solution, with an emphasis on the role of polymers in the assembly process and functions of resulting nanostructures. Precise control over the location/arrangement, interparticle interaction, and packing of inorganic nanoparticles at various scales are highlighted.
The synthesis at room temperature of Au nanowires (NWs) in hexane solution of HAuCl4.3H2O, oleylamine and triisopropylsilane, was “in-situ” monitored by means of X-ray Absorption Fine Structure Spectroscopies and Small Angle X-Ray Scattering to determine, under identical synthesis conditions, both the changes of the oxidation state of gold atoms and the evolution of the size and shape of the objects involved in the formation of Au NWs. We propose a multi-stage process for the formation of the NWs: first, Au(III) atoms form a planar-square geometry complex that is continuously reduced to give Au(I) disc-like structures with diameters bigger than that of the final NWs. In a second stage, characteristic length/thickness ratio of these disc-like objects increases to form cylinders, presumably by aurophilic interactions between Au(I) centers and stacking of the discs. When most of the Au atoms have been reduced to Au(I), the reduction to Au(0) begins (third stage) and the NWs grow forming an hexagonal arrangement, separated by a bilayer of oleylamine molecules (fourth stage). Finally, a slow reduction leads the reaction to the final product, formed by bundles of long, ultrathin Au NWs.
Metallic nanorings have attracted much attention from researchers owing to their unique optical, electrical, and magnetic properties, and now, simple and large-scale synthesis methods must be developed for their practical application in various fields. Here, we report one-pot synthesis of ultrathin Pd nanorings through a simple and novel soft-template approach based on wet-chemical synthesis. A spindle-shaped assembly of a long-chain amidoamine derivative (C18AA) served as the soft template of Pd nanorings that were prepared in an aqueous solution containing the Pd precursor and a suitable amount of C18AA and toluene, and the chemical reduction of the Pd precursor in the aqueous solution produced an array of almost circular Pd nanorings covering the assembly. Pd nanorings that were parallel to the amine group, which is the head group of C18AA, appeared on the assembly surface. The amount of toluene strongly affected the formation of the spindle-shaped assembly and Pd nanorings. Furthermore, transmission electron microscope images were obtained at several points in time during the reaction; they revealed that the Pd nanorings were produced by the fusion of Pd nanoparticles formed on the spindle-shaped molecular assembly during an early stage of the reaction. The Pd nanorings were also found to have high structural stability against organic solvents, high temperatures, and high and low pH.
Ultrathin Au (or Ag) nanowires represent an excellent substrate for atomic layer deposition of Pt to afford highly active and cost-effective catalysts due to the large surface area and possible synergistic effect. An ideal synthesis of such nanowires should avoid using strong capping agents for convenient post-synthesis treatments, and should be easily scaled up and reproduced in a high yield, which remains a challenge. Here, we report a novel strategy to synthesize sub-2 nm Au-Ag alloy nanowires with a high quality in N, N-dimethyl formamide (DMF), which relies on Ag modification of the nanocrystal surface and Ag–halide interactions for regulating the one-dimensional growth of the nanowires, without involving strong capping agents that are usually required in conventional syntheses. Sub-monolayer Pt atoms were successfully deposited on these ultrathin Au-Ag alloy nanowires without forming ensembles albeit a high loading amount (up to 20% in terms of Pt/(Au+Ag)) due to the large surface area. The resulting Au-Ag@Pt core/shell nanowires demonstrate superior activities in the formic acid oxidation reaction (FAOR) due to the synergistic ligand effect and the absence of Pt ensembles. We believe the novel synthesis and the demonstration of the ultrathin Au-Ag alloy nanowires as a general platform for constructing cost-effective noble metal catalysts open new opportunities in designing catalysts for a broad range of reactions.
Size is one of the central issues in nanoscience. The practical meaning of the term “sub‐nanometric material (SNM)” requires two aspects: (1) its size should be at the atomic level; (2) it shows unique (size‐related) properties compared to its nano‐counterparts with larger sizes. Here, SNMs in the form of wires (SNWs) and the unique properties arising from their special size are reviewed. First, their polymer‐like behavior, including rheological behavior and self‐assembly, is dicussed. Their origins may stem from the special size and the ligands around the wire. Even a slight increase in diameter would risk the polymer‐like behavior. Meanwhile, the ligands on SNWs are proportional to the inorganic entity at this scale. Consequently, surface ligands should have a profound impact on the properties, like catalysis, self‐assembly, optics, etc. To reveal more potential applications, their applications in energy conversion are comprehensively reviewed. To some extent, characterization can greatly influence the way things are observed. Thus, some appropriate characterization techniques are briefly introduced. Finally, another emerging part of SNWs (atomic chain material) is briefly introduced. It is hoped that this review can provide new insights to this special scale.
The self-assembly of colloidal nanoparticles (NPs) medaited by block copolymers (BCPs) is an efficient way for fabricating nanocomposite superstructures with precise geometric control. Here we report a generalized liquid-air interfacial strategy by exploiting the versatility in tuning the specific affinities between the grafted polymeric ligands and BCPs, enabling the circular assembly of NPs on a liquid surface to afford unique ring-like superstructures. Fe3O4 NPs act as the model system, however, CoFe2O4 and Au NPs are also demonstrated using the proposed assembly method. Functionalizing NPs with a specific polymeric ligand is the key to achieve the circular assembly of NPs, while both the subphase and the solvent annealing temperature have profound influence on the microphase separation behaviors of BCPs and therefore the morphology of the resulting NP assemblies. Moreover, co-assembly of two types of NPs grafted with distinct polymeric ligands enables unprecendented heterogeneous concentric rings, with each ring consisting of one type of NPs.
A wide range of investigation tools and frameworks aimed at the in depth understanding of the physico-chemical properties of different nanomaterials for exploring their cellular interactions and effects have been reported in the past couple of decades. Among these, Single-molecule Force Spectroscopy (SMFS) emerges as a very important tool for characterizing nanoparticles (NPs) and one of its very valuable applications consists in the quantitative analysis of the NPs’ elasticity. In SMFS experiments that tackle this subject, a sharp tip present on the apex of a cantilever is indented into a single NP, and then the Young’s modulus is determined as a measure of its elasticity, which is one of the fundamental mechanical parameters affecting the structural and functional cellular parameters. Based on such approaches, SMFS enables the observation and analysis of significant cellular effects that are relevant to various cellular parameters. In this review, we turn our attention towards several approaches for detecting the elasticity of NPs, systematically summarizing the divergent elasticity values of different gold nanoparticles (AuNPs) with different surfaces. We carry as well a critical discussion over elasticity assesment models and fundamental factors that influence NP elasticity assesment by means of SMFS.
Self-assembly of colloidal particles is an important and challenging way to generate novel colloidal superstructures for new materials. Recent progress on syntheses of anisotropic colloids highlights opportunities for such self-assembly, particularly in defining new non-cubic superstructures. Both non-templated synthesis and templated synthesis have played an important role in preparing anisotropic colloidal particles. In this article, we briefly summarize recent progresses in anisotropic colloids by non-templated synthesis and conventional templated synthesis, and introduce a conceptual strategy of "patchy templated synthesis" that differs from the former. We illustrate this strategy with recent example emanating from colloidal rings, and discuss the future opportunities with this strategy for the synthesis of anisotropic colloids.
We present three-dimensional microshells formed by self-assembly of densely-packed 5 nm gold nanoparticles (AuNPs). Surface functionalization of the AuNPs with custom-designed mesogenic molecules drives the formation of a stable and rigid shell wall, and these unique structures allow encapsulation of cargo that can be contained, virtually leakage-free, over several months. Further, by leveraging the plasmonic response of AuNPs, we can rupture the microshells using optical excitation with ultralow power (<2 mW), controllably and rapidly releasing the encapsulated contents in less than 5 s. The optimal AuNP packing in the wall, moderated by the custom ligands and verified using small angle x-ray spectroscopy, allows us to calculate the heat released in this process, and to simulate the temperature increase originating from the photothermal heating, with great accuracy. Atypically, we find the local heating does not cause a rise of more than 50 °C, which addresses a major shortcoming in plasmon actuated cargo delivery systems. This combination of spectral selectivity, low power requirements, low heat production, and fast release times, along with the versatility in terms of identity of the enclosed cargo, makes these hierarchical microshells suitable for wide-ranging applications, including biological ones.
Metallic nanohelices are extremely rare and to date never synthesized by direct solution method. In this work, we report ultralong Au nanohelices grown in solution under ambient conditions. They are ultralong with several tens of micrometers in length, with extraordinary aspect ratio (length/diameter over 22,300) and the number of pitches (over 22,000 pitches). The pitch and width are uniform within each helix but vary widely among the helices. Crystal analyses showed that the facets, twin boundaries, grain sizes, and orientations are aperiodic along the helices. The apparent smooth curving is only possible with large number of surface steps, suggesting that these structural features are the mere consequence of the helix formation, rather than the cause. We propose that the nanowires are formed by the active surface growth mechanism and that the helicity originates from the random and assymetrical blocking of nuclei embedded within the floccules of ligand complexes, in the form of either asymmetric binding of ligands or asymmetric diffusion of growth materials through the floccules. The separate growth enviroment of these nuclei causes constant helicity within each helix but differing helicity among the individuals. The embedding also provides a robust environment for the sustained growth of the nanohelices, leading to their record length and consistency.
The recent growing interest in the applications of gold nanowires (AuNWs) as flexible materials has raised the fundamental issue of how their mechanical properties are related to their morphology. In this work, to address this issue, the systematic synthesis of AuNWs, their structural analysis, and their rheological investigation were demonstrated. The structural analysis of AuNWs was performed by TEM observation and light-scattering method. From these observations, it was found that the length of AuNWs varies from nanometer to micrometer order depending on the reaction time while a constant width of 1.6 nm is maintained. On the basis of static light-scattering experiments and a wormlike chain model, the structural parameters of AuNWs during their growth were successfully obtained. When the contour length of AuNWs reached around 5 μm, the AuNWs solution showed non-Newtonian behavior and appeared to behave as a gel. Dynamic viscoelasticity measurements indicated that such viscous behavior is responsible for entanglement between AuNWs. It is concluded that AuNWs are analogous with conventional polymers in terms of both their structure and their rheological behavior.
In nanowire-dispersed in liquid droplets, the interplay between the surface tension of the liquid and the elasticity of the nanowire determines the final morphology of the bent or buckled nanowire. Here, we investigate the fabrication of a silver nanowire (Ag NW) ring generated by encapsulation inside fine droplets. We used a hybrid aerodynamic and electrostatic atomization method to ensure the generation of droplets with scalable size in the necessary regime for ring formation. We analytically identify the compressive force of the droplet driven by surface tension as the key mechanism for the self-assembly of ring structures. Thus for potential large-scale manufacturing, the droplet size provides a convenient parameter to control the realization of ring structures from nanowires.
Due to its promising properties, honeycomb macroporous pattern (HMP) film has attracted increasing attention. It has been realized in many artificial nanomaterials, but the formation of these HMPs was attributed to templates or polymer/supermolecule/surfactant assistant assembly. Pure metal HMP film has been difficult to produce using a convenient colloidal template-free method. In this report, a unique template-free approach for preparation of Au HMP film with high transparency and conductivity is presented. Ultrathin Au nanowires, considered a linear polymer analogue, are directly assembled into HMP film on various substrates using a traditional static breath figure method. Subsequent chemical crosslinking and oxygen plasma treatment greatly enhance the stability and conductivity of the HMP film. The resulting HMP film exhibits great potential as an ideal candidate for transparent flexible conductive nanodevices.
Block copolymer-nanoparticle composite nanomaterials provide exciting opportunities as they may display distinctive properties from constituents that are desired in applications including biomedicine, photoelectric materials, and catalytic materials, etc. Block copolymers can self-assemble to various nanoscale structures. The successful distribution of nanoparticles in a particular location of the block copolymer matrix can improve the functional properties of nanoparticles. In this review, the methods for fabricating block copolymer-nonaparticle composite nanomaterials are introduced. Experimental and theoretical progress in the description of these nanostructured block copolymer based hybrid materials is represented. Furthermore, precise assembly and localization of nanoparticle in block copolymer assemblies are of great importance in realizing the formation of nano-hybrids with high performance. The properties and applications of the nanocomposites depend not only on those of individual building blocks but also on their spatial distribution within different morphological aggregates at different length scales. This review also discussed the effect of nanoparticle size, shape and surface chemistry on the selective localization of nanoparticle within block copolymer aggregates. Those factors manipulate the balance between enthalpic and entropic contributions, which provides an opportunity to precisely control the spatial distribution of nanoparticles in block copolymer aggregates. In the end, the self-assembly of block copolymer-nanoparticles in theoretical simulation is introduced. Theoretical and computational simulations offer a unique approach not only to study the evolution and formation of nanostructures,but also to investigate structure-property relationship of hybrid nanocomposites.
Ultrathin gold nanowires are unusual colloidal objects that assemble into bundles with line contacts between parallel wires. Each molecule in the contact line interacts with many ligand and solvent molecules. We used X-ray scattering and electron microscopy to study how these interactions control assembly.
Well-defined hydrophilic ultrathin tellurium nanowires (TeNWs) can be coiled into nanorings by Pickering emulsion at room temperature.
Ultrathin materials at sub-nanometer scale not only feature atomic scale size, but also possess unprecedented properties comparing with conventional nanomaterials. The two aspects endow such materials with great potential. In sub-nanometric (SN) wires, the weak interactions may overwhelm the rigidity of inorganic compounds and dominate the behaviours at this regime. Consequently intricate structures and polymer-like rheology can be obtained, shedding new lights on chemistry as well as material design. As for 0D or 2D SN materials, clusters are analogues to molecules and SN sheets show unique electronic structures. Taking SN wire as an example, their growth mechanisms are discussed, as well as their applications and potentials. The chemistry at this regime can promote their application-oriented researches, however, yet not well explored. In short, there is great potential at sub-nanometer scale, though there are also many challenges ahead.
Cu–Au dendritic nanowires (NWs) were synthesized by heating pre-synthesized Cu NWs and Au ultrathin NWs in a THF/H2O mixture. The obtained dendritic NWs were composed of a Cu/CuO stem and distributed by Au multi-branches throughout the whole structure. The formation of a dendritic structure was initiated from oxidation of Cu to CuO during the phase transition stage, giving an anisotropic dendritic precursor. Then a galvanic replacement reaction between Cu and Au ions created abundant anchor sites, facilitating Au branch formation via self-deformation of ultrathin Au NWs around the Cu NWs surface. The synthesized Cu–Au dendritic NWs could be potentially used as biosensors in detecting glucose for its high sensitivity and excellent performances, due to the demonstration of their enhanced electrochemical activity for oxidation of glucose.
Sub-1 nm, extremely long nickel molybdate nanowires are synthesized based on a good/poor solvent system. The ultrathin nanowires can be hierarchically assembled into flexible, free-standing films with good mechanical properties. Compared with the large-size counterpart, nickel molybdate ultrathin nanowires display promising oxygen evolution reaction catalytic performance derived from the ultrathin feature.
We demonstrate flow-directed production of nanoparticles of the photoresponsive block copolymer poly(o-nitrobenzyl acrylate)-b-polydimethylacrylamide in a gas-liquid microfluidic reactor. Microfluidic formation produced a variety of morphologies dependent on flow rate, with spheres and short cylinders, then large compound micelles, then unique spooled cylinders appearing as flow rate increased. The higher excess free energy of spooled cylinders relative to the quiescent equilibrium state is evidenced by their faster off-chip relaxation times (∼1 day) as compared to other flow-directed structures. Comparison of light-triggered dissociation of flow-directed nanoparticles prepared at two different flow rates shows faster disruption of nanoparticles prepared at the higher flow rate. The application of variable flow to direct both structure and responsivity suggests interesting possibilities for controlled microfluidic manufacturing of "smart" polymeric colloids.
Ultrathin Au-Ag alloy nanorods and nanowires of different lengths and ca. 1.9 nm diameter are prepared through a low-temperature decomposition of the precursor [Au2Ag2(C6F5)4(OEt2)2]n in oleic acid. This nanostructure formation has been studied through TEM, HRTEM, EDS, HS-SPME-GC-MS and (19)F NMR spectroscopy. The UNRs and UNWs display a length-dependent broad band in the mid-IR region that is related to the longitudinal mode of the surface plasmon resonance of the ultrathin nanostructures.
Controlled synthesis of gold nanorings was realized by reducing chloroauric acid in aqueous mixed solutions of cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). It is revealed that the gold nanowires are induced to fabricate the gold nanorings with an average diameter of ~300 nm. The synthesis of the nanowires and the formation of the nanorings can be achieved in one step. A variety of gold nanostructures, such as short nanowires, nanorings, nanostars with a number of soft protuberances and nanopolyhedra, could be readily obtained by simply changing the CTAB/SDS molar ratio. Both the “structural defects” and the “elastic induction”, which are closely related to the mixed bilayers (CTAB/SDS), are indispensable for the final formation of the gold nanorings. Four surfactants with similar structures were also used to further verify the formation mechanism.
The amphiphilic, pH-responsive amine derivative, 3-[(2-carboxy-ethyl)-hexadecyl-amino]-propionic acid (C16CA) was used for the functionalization of gold nanorods (Au NRs) prepared with cetyltrimethylammonium bromide (CTAB). The Au NRs could also be stabilized with C16CA owing to the selective adsorption of the amino moiety, and the Au NRs were well dispersed following one-step ligand exchange using C16CA. Based on a change in the nature of C16CA, self-assemblies of spherical micelles (pH > 5) or lamellar precipitates (pH 2-5) are formed in dispersion. Au NRs were incorporated into the precipitates at pH 2-5, but could be redispersed by redissolution of C16CA at pH > 5. The pH-induced recovery-redispersion of Au NRs was successfully accomplished without affecting the morphology of the Au NRs, the amount of Au in the dispersion, or the catalytic activity of the Au NRs for the reduction of p-nitrophenol.
Controls in coating gold nanoparticles with conductive polymers are reported, where uniform core/shell nanoparticles with tailored core aggregation and shell thickness are unambiguously demonstrated. In the presence of sodium dodecylsulfate (SDS), the adsorption and in situ polymerization of aniline or pyrrole on the surface of gold nanoparticles gives uniform polymer shells. A typical single encapsulation of 10 nm gold nanoparticles gave 99.1% monomers out of 1074 particles surveyed. The shell growth was found to be kinetically controlled; polyaniline was successively grown on 22 nm gold nanoparticles by multiple growth cycles, giving shell thicknesses of 14, 31, 61 and 92 nm, respectively. We show that the aggregation of gold nanoparticles can be controllably promoted in this system, by simply timing SDS addition, to give linearly aggregated cores of 2–20 particles. The in situ formation of conductive polymer shells has allowed the isolation and unambiguous characterization of these nanochains for the first time. The one-step, “mix-and-wait” synthesis solely utilizes inexpensive starting materials and is, therefore, well-suited for fabrication of large quantities of core/shell nanoparticles. The core/shell nanoparticles form stable colloidal suspensions and can be readily purified by centrifugation.
Single-walled carbon nanotubes (SWNT) polarize readily in the presence of electromagnetic (EM) fields, enabling a variety of electrochemical reactions. Here, we study the reaction of transition metal ion salts in the presence of surfactant-stabilized SWNT individually suspended in water when activated by alternating EM fields in the radio frequency (RF), microwave (MW), and optical regimes. Atomic force microscopy (AFM) images show formation of novel SWNT nanoparticle−nanotube structures (nanoPaNTs). The resulting nanoPaNTs include SWNT with metallic nanoparticles at one or both tips (“dumbbells”), SWNT toroids, and straight SWNT “threaded” through multiple SWNT rings to form shish-kebab structures. Mixtures of surfactants and polymer apparently modify the local environment of polarized SWNT in a manner that reduces the energy needed for ring formation. We also infer that electrodeposition reactions proceed on a significantly faster time scale than ring formation. These processes can potentially be used for self-assembly of complex 3-D structures.
Doping is a widely applied technological process in materials science that involves incorporating atoms or ions of appropriate elements into host lattices to yield hybrid materials with desirable properties and functions. For nanocrystalline materials, doping is of fundamental importance in stabilizing a specific crystallographic phase, modifying electronic properties, modulating magnetism as well as tuning emission properties. Here we describe a material system in which doping influences the growth process to give simultaneous control over the crystallographic phase, size and optical emission properties of the resulting nanocrystals. We show that NaYF(4) nanocrystals can be rationally tuned in size (down to ten nanometres), phase (cubic or hexagonal) and upconversion emission colour (green to blue) through use of trivalent lanthanide dopant ions introduced at precisely defined concentrations. We use first-principles calculations to confirm that the influence of lanthanide doping on crystal phase and size arises from a strong dependence on the size and dipole polarizability of the substitutional dopant ion. Our results suggest that the doping-induced structural and size transition, demonstrated here in NaYF(4) upconversion nanocrystals, could be extended to other lanthanide-doped nanocrystal systems for applications ranging from luminescent biological labels to volumetric three-dimensional displays.
Among the most studied processes of self-organization¹, ² are the coiling and ring formation of biopolymers such as DNA and proteins. These processes are complex, involving several different types of interaction. We have found that single-walled carbon nanotubes (SWNTs), which are renowned for their extremely high flexural rigidity³, ⁴, can also be induced to organize themselves into rings or coils, with high yields of up to 50%. But unlike coils of biopolymers, in which hydrogen bonding and ionic interactions are usually involved, coils of nanotubes can be stabilized by van der Waals forces alone.
A simple and one-step method to rapidly synthesize single crystalline ultrathin gold nanowires at room temperature within a few hours has been developed, and the self-assembled ultrathin gold nanowires demonstrated an intriguing application in surface-enhanced Raman scattering (SERS).
Manipulating the morphology of inorganic nanostructures, such as their chirality and branching structure, has been actively pursued as a means of controlling their electrical, optical and mechanical properties. Notable examples of chiral inorganic nanostructures include carbon nanotubes, gold multishell nanowires, mesoporous nanowires and helical nanowires. Branched nanostructures have also been studied and been shown to have interesting properties for energy harvesting and nanoelectronics. Combining both chiral and branching motifs into nanostructures might provide new materials properties. Here we show a chiral branched PbSe nanowire structure, which is formed by a vapour-liquid-solid branching from a central nanowire with an axial screw dislocation. The chirality is caused by the elastic strain of the axial screw dislocation, which produces a corresponding Eshelby Twist in the nanowires. In addition to opening up new opportunities for tailoring the properties of nanomaterials, these chiral branched nanowires also provide a direct visualization of the Eshelby Twist.
Carbon nanotubes and biological filaments each spontaneously assemble into kinked helices, rings, and "tennis racket" shapes due to competition between elastic and interfacial effects. We show that the slender geometry is a more important determinant of the morphology than any molecular details. Our mesoscopic continuum theory is capable of quantifying observations of these structures and is suggestive of their occurrence in other filamentous assemblies as well.
Freestanding single-crystal complete nanorings of zinc oxide were formed via a spontaneous self-coiling process during the
growth of polar nanobelts. The nanoring appeared to be initiated by circular folding of a nanobelt, caused by long-range electrostatic
interaction. Coaxial and uniradial loop-by-loop winding of the nanobelt formed a complete ring. Short-range chemical bonding
among the loops resulted in a single-crystal structure. The self-coiling is likely to be driven by minimizing the energy contributed
by polar charges, surface area, and elastic deformation. Zinc oxide nanorings formed by self-coiling of nanobelts may be useful
for investigating polar surface–induced growth processes, fundamental physics phenomena, and nanoscale devices.
A previously unknown rigid helical structure of zinc oxide consisting of a superlattice-structured nanobelt was formed spontaneously
in a vapor-solid growth process. Starting from a single-crystal stiff nanoribbon dominated by the c-plane polar surfaces, an abrupt structural transformation into the superlattice-structured nanobelt led to the formation
of a uniform nanohelix due to a rigid lattice rotation or twisting. The nanohelix was made of two types of alternating and
periodically distributed long crystal stripes, which were oriented with their c axes perpendicular to each other. The nanohelix terminated by transforming into a single-crystal nanobelt dominated by nonpolar
() surfaces. The nanohelix could be manipulated, and its elastic properties were measured, which suggests possible uses in
electromechanically coupled sensors, transducers, and resonators.
Hierarchical nanostructures of lead sulfide nanowires resembling pine trees were synthesized by chemical vapor deposition.
Structural characterization revealed a screwlike dislocation in the nanowire trunks with helically rotating epitaxial branch
nanowires. It is suggested that the screw component of an axial dislocation provides the self-perpetuating steps to enable
one-dimensional crystal growth, in contrast to mechanisms that require metal catalysts. The rotating trunks and branches are
the consequence of the Eshelby twist of screw dislocations with a dislocation Burgers vector along the 〈110〉 directions having
an estimated magnitude of 6 ± 2 angstroms for the screw component. The results confirm the Eshelby theory of dislocations,
and the proposed nanowire growth mechanism could be general to many materials.
The current drive to produce small electronic components has resulted in a considerable amount of research aimed at reducing the thickness of conductive metallic layers. In the conventional thick-film processes, this objective is usually pursued by decreasing the amount of ink deposited and/or the size of the metallic particles, which are usually spherical. Much less attention has been given to reducing the thickness of these layers by using metallic nanoflakes. This paper discusses the possibility of producing thin and conductive films using uniform, highly dispersed Ag nano-platelets produced by a cost effective aqueous precipitation process. This process yields uniform platelets of hexagonal shape exhibiting thickness of 60-80nm and the largest dimension about 0.8 μm. It is proposed that these novel materials, combined with new deposition techniques, may represent a viable route to reduce significantly the dimensions of conductive layers and, therefore, the size of the electronic components. The attributes of these platelets may also open up avenues for obtaining ultra-thin conductive films, which do not necessarily require high temperature sintering.
An individual carbon nanocoil was clamped between two AFM cantilevers and loaded in tension to a maximum relative elongation of 42%. The deformation of the nanocoil agrees well with an analytical model of the spring constant that accounts for the geometric nonlinearity. The nanocoil behaves like an elastic spring with a spring constant K of 0.12 N/m in the low strain region. No plastic deformation was detected. High-resolution microscopy images and the electron energy loss spectrum (EELS) indicate that the nanocoils are amorphous with a sp2/sp3 bonded-carbon ratio of 4:1.
Helical crystalline silicon carbide nanowires covered with a silicon oxide sheath (SiC/SiO2) have been synthesized by a chemical vapor deposition technique. The SiC core typically has diameters of 10−40 nm with a helical periodicity of 40−80 nm and is covered by a uniform layer of 30−60 nm thick amorphous SiO2. A screw-dislocation-driven growth process is proposed for the formation of this novel structure based on detailed structural characterizations. The helical nanostructures may find applications as building blocks in nanomechanical or nanoelectronic devices. The screw-dislocation-induced growth mechanism suggests that similar helical nanostructures of a wide range of materials may be synthesized.
Micelle structures from the assembly of poly(acrylic acid)-block-poly(methyl acrylate)-block-polystyrene (PAA-b-PMA-b-PS) triblock copolymers in mixed tetrahydrofuran (THF)/water solution, including disks, toroids, cylinders, and spheres, were targeted by coassembling with different diamines. At constant solution composition (THF:H2O, polymer concentration, and diamine concentration), the interfacial curvature of the assembled structures was determined primarily by diamine chain structure. It was found that interchain binding from the interaction of the two amine end groups of diamines with acid groups from different PAA corona blocks governs the final assembled structures. Diamines with hydrophilic spacers induced the formation of micelles with larger interfacial curvature as the spacer length increased. Disklike micelles, cylindrical micelles, or spherical micelles were observed with the gradual increase of hydrophilic spacer length. Diamines with variable hydrophobic spacers showed a similar effect when the spacer length was less than six methylene units. Application of longer hydrophobic diamines had a reverse effect on the interfacial curvature. This effect was attributed to the interaction of hydrophobic diamine hydrocarbon linking chains with the PMA-b-PS hydrophobic core. These findings indicate an easy method to tune micelle structure with multivalent organic counterions. Assembled morphologies were characterized by means of transmission electron microscopy, and the interaction of diamines with acidic units of the PAA block segments was studied by solution-state nuclear magnetic resonance spectroscopy.
The chemical growth of silver nanorings that possess singly twinned crystals and a circular cross section via a reductive reaction solution is reported. The wire and ring diameters of the synthesized nanorings are in the ranges 80–200 nm and 4.5–18.0 μm, respectively. By lighting up the multipolar dark plasmons with slanted illumination, the silver nanoring exhibits unique focused scattering and large local-field enhancement. We also demonstrate strong exciton–plasmon interactions between a monolayer of CdSe/ZnS semiconductor quantum dots and a single silver antenna-like nanoring (nanoantenna) at the “hot spots” located at the cross points of the incident plane and nanoring; the position of these spots are tunable by adjusting the incidence angle of illumination. The tunable plasmonic behavior of the silver nanorings could find applications as optical nanoantennae or plasmonic nanocavities.
The preparation of a new type of finite carbon structure consisting of
needlelike tubes is reported. Produced using an arc-discharge
evaporation method similar to that used for fullerene sythesis, the
needles grow at the negative end of the electrode used for the arc
discharge. Electron microscopy reveals that each needle comprises
coaxial tubes of graphitic sheets ranging in number from two up to about
50. On each tube the carbon-atom hexagons are arranged in a helical
fashion about the needle axis. The helical pitch varies from needle to
needle and from tube to tube within a single needle. It appears that
this helical structure may aid the growth process. The formation of
these needles, ranging from a few to a few tens of nanometers in
diameter, suggests that engineering of carbon structures should be
possible on scales considerably greater than those relevant to the
fullerenes.
Nanoseparation and concomitant purification of nanoparticles by ultracentrifugation in a nonhydroxylic organic density gradient has been demonstrated by separating several typical colloidal nanoparticles, including Au, Ag, and CdSe. Successful separation of Au nanowires from their spherical counterparts showed that colloidal particles can be separated not only by size but also morphology. In addition to extending the range of colloidal systems which can be separated and providing monodisperse samples that cannot be obtained by synthesis optimization alone, this method simplifies the postsynthesis treatment process and facilitates subsequent bulk assembly of the monodisperse colloids. Dissolution of organic polymers in the gradient medium both enhances the separation efficiency and also allows the direct fabrication of functional composite films with discrete monodisperse nanoparticles embedded inside.
In this study, the kinetics of vesicle formation of ABA amphiphilic triblock copolymers from an initially homogeneous state was theoretically and experimentally investigated by adding a selective solvent into the system. The pathway of spontaneous vesicle formation depended greatly on the selective solvent addition rate. At a slow addition rate, the pathway followed three stages: (1) the amphiphilic triblock copolymer combined into a large irregular aggregation; (2) the large irregular aggregation broke into big irregular spheres; and (3) some hydrophilic molecules in the big irregular spheres diffused toward the surface, and some hydrophilic molecules diffused toward the center, forming vesicles. However, at a fast addition rate, the pathway was as follows: (1) the amphiphilic triblock copolymer aggregated into many small spheres; (2) the small spheres merged to form rod-like micelles first and then oblate membranes; and (3) the oblate membranes closed up to form vesicles. This pathway difference for vesicle formation can be attributed to the existence of many metastable states in the system. This finding not only provides new insight into the origins of vesicles but also provides further understanding on the self-assembly kinetics of amphiphilic block copolymers in a selective solvent.
A templated fabrication of open nanocavities is reported, where rational control of partial polymer attachment on sacrificial metal cores introduces openings in the polymer shells. This approach provides a facile means to modify the structural features of polymer nanocavities by manipulating the surface chemistry of colloidal nanoparticles. In particular, the anisotropic geometry of gold nanorods is exploited to promote the anisotropic polymer attachment, such that two diametric openings occurred in the polymer shell. After etching the gold nanorods, this approach yields open nanochannels that are tunable in both diameter and length. The synthetic scope of the anisotropic core/shell nanoparticles is expanded, supporting the previously proposed mechanism. We demonstrate that reducing the symmetry of nano-objects could open up new ways to create structural features using simple assembly and etching techniques. The thermostability of the open polymer nanostructures is also investigated.
An effective method was developed for separating gold-nanoparticle clusters in high resolution; dimer and trimer samples were obtained with 95% and 81% purity, respectively.
A study was conducted to demonstrate the development of polymer-encapsulated metal nanoparticles (NP), as surface-enhanced Raman scattering (SERS) nanoprobes. The study demonstrated the encapsulation of analyte-tagged metal NPs by an amphiphilic polystyrene-block-poly(acrylic acid) diblock copolymer through self-assembly. It was demonstrated that the thermodynamically controlled process is suitable in polymer shells, having uniform thickness. It was found that these polymers were prepared, without the need for significant control, requiring a one-spot synthesis that involved simple heating and cooling. It was observed that the synthesis process is scalable and highly reproducible, giving large quantities of nanoprobes that can be isolated by direct centrifugation and resuspension in water. It was also observed that the polymer shells protect the encapsulated nanoprobes against salt-induced aggregation and oxidation by oxone (HSO5-.
Controlled partial attachment of polymer on gold nanoparticles breaks the symmetry of their surface functionalities, allowing tailored assembly of the nanoparticles.
Lightly etched single-walled carbon nanotubes are chemically reacted to form rings. The rings appear to be fully closed as opposed to open coils, as ring-opening reactions did not change the structure of the observed rings. The average diameter of the rings was 540 nanometers with a narrow size distribution. The nanotubes in solution were modeled as wormlike polymer chains, yielding a persistence length of 800 nanometers. Nanotubes shorter than this length behave stiffly and stay nearly straight in solution. However, nanotubes longer than the Kuhn segment length of 1600 nanometers undergo considerable thermal fluctuation, suggesting a greater flexibility of these materials than is generally assumed.
Plated gold: Self-assembly of core/shell nanostructures occurs spontaneously when gold nanoparticles are combined with amphiphilic block copolymers. Polymer cross-linking then topologically fixes the composite nanostructure (see picture). The thickness of the polymer shell, as well as the optical and chemical properties of the composite nanostructure, are precisely determined by the (Figure Presented) molecular characteristics of the assembled block copolymer.
It is well known that the morphology of block copolymer aggregates depends on polymer properties such as the molecular weight, the relative block length, and the chemical nature of the repeat unit. Recently, we have shown that if aggregates are allowed to self-assemble in solution, then in addition to the above factors, a high degree of control over the aggregate architecture can be achieved by adjusting the solution conditions. Factors such as the water content in the solvent mixture, the solvent nature and composition, the presence of additives (ions, surfactants, and homopolymer) and the polymer concentration were successfully employed to control the aggregate shape and size. In this paper, we review a series of studies performed in our group to show how solution properties can control the architecture of aggregates prepared from a given copolymer. The control mechanism is explained in terms of the effect of each property on the forces that govern the formation of any given morphology, namely the core-chain stretching, corona-chain repulsion and interfacial tension.
Free-standing Ag2V4O11 nanorings and microloops have been synthesized by a simple hydrothermal process without any template or surfactant. The Ag2V4O11 nanorings and microloops have preferred growth direction along the [30] plane and are formed by the self-rolling of Ag2V4O11 nanobelts.
A method for the synthesis of micrometer-sized gold crystals with shapes ranging from three-dimensional (3D) triangles, octahedra, and pentagonal decahedra to two-dimensional (2D) plates and one-dimensional nanowire is described. These morphologies are obtained by controlling the relative growth rates of the crystal planes by the selective use of capping ligand mixtures. The size transition and shape evolution of the crystals are monitored by electron microscopy, X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Micrometer-sized crystals with different feature shapes and sizes can be obtained by changing the composition of amine ligand mixture. The shape of the particles is determined by the relative growth rates on particular cryatallographic planes during the growth process. Several procedures exists for the preparation of 1D nanostructures such as rods and wires which includes electrochemical intemplates, photochemical synthesis and seedmediated growth.
A study is presented of the preparation of gold nanoparticles incorporated into biodegradable micelles. Poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PEO-b-PCL) copolymer was synthesized by ring-opening polymerization, and the hydroxyl end group of the PCL block was modified with thioctic acid using dicyclohexyl carbodiimide as the coupling reagent. The PEO-b-PCL-thioctate ester (TE) thus obtained was used in a later step to form monolayer protected gold nanoparticles via the thioctate spacer. Gold nanoparticles stabilized with the PEO-b-PCL block (named Au/Block (x/y), where x/y is the mole feed ratio between HAuCl4 and PEO-b-PCL-TE) were prepared and analyzed. Au/Block (1/1), Au/Block (2/1), and Au/Block (3/1) nanoparticles were found to form stable dispersions in the organic solvents commonly used to dissolve the unlabeled block copolymer. The average diameter of the nanoparticles was determined by transmission electron microscopy (TEM) and found to be 6+/-2 nm. Au/Block (4/1) nanoparticle dispersions in organic solvents, on the other hand, were not stable and produced large gold clusters (50-100 nm). Cluster formation was attributed to the low grafting density of the block copolymer, which facilitates agglomeration. For Au/Block (12/1), along the same trend, only an insoluble product was isolated. Micelles in water were prepared by the slow addition of the dilute Au/Block solution in dimethylformamide into a large excess of water with vigorous stirring. Au/Block (1/1) and Au/Block (2/1) formed nanosized structures of 5-7 nm. TEM images of stained Au/Block (1/1) micelles, made in water, clearly showed the formation of core-shell structures. Au/Block (3/1) micelles, on the other hand, were not stable and large agglomerates a few microns in size were observed. The study focuses on the synthesis, characterization, and aggregation behavior of gold-loaded PEO-b-PCL block copolymer micelles, a potential system for drug delivery in conjunction with tissue and subcellular localization studies.
Length made to order: Controlled reduction of [Pt(acac)2] and decomposition of [Fe(CO)5] in a mixture of oleylamine and octadecene leads to the facile synthesis of FePt nanowires and nanorods with diameters of 2–3 nm (see TEM image). The length of the nanowires/nanorods is tunable from greater than 200 nm down to 20 nm by simply controlling the volume ratio of oleylamine and octadecene.
The concept of a spatial-velocity hodograph is introduced to describe quantitatively the extrusion of a carbon tubule from a catalytic particle. The conditions under which a continuous tubular surface can be generated are discussed in terms of this hodograph, the shape of which determines the geometry of the initial nanotube. The model is consistent with all observed tubular shapes and explains why the formation process induces stresses that may lead to "spontaneous" plastic deformation of the tubule. This result is due to the violation of the continuity condition, that is, to the mismatch between the extrusion velocity by the catalytic particle, required to generate a continuous tubular surface, and the rate of carbon deposition.
The observation by transmission electron microscopy of six different stable aggregate morphologies is reported for the same
family of highly asymmetric polystyrene-poly-(acrylic acid) block copolymers prepared in a low molecular weight solvent system.
Four of the morphologies consist of spheres, rods, lamellae, and vesicles in aqueous solution, whereas the fifth consists
of simple reverse micelle-like aggregates. The sixth consists of up to micrometer-size spheres in aqueous solution that have
hydrophilic surfaces and are filled with the reverse micelle-like aggregates. In addition, a needle-like solid, which is highly
birefringent, is obtained on drying of aqueous solutions of the spherical micelles. This range of morphologies is believed
to be unprecedented for a block copolymer system.
Hairy micelles are obtained by using amphiphilic diblock copolymers with long hydrophilic blocks which favor single encapsulation of Au nanoparticles (ca. 5 nm, see figure). Antibody molecules can be attached to the hydrogel layers of the encapsulated Au nanoparticles to give nanoparticle/biomolecule conjugates.
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