A drop of solution containing nonvolatile solute is allowed to evaporate from a sphere-on-flat geometry. Left behind is a striking pattern of gradient concentric rings with unprecedented regularity. The center-to-center distance between adjacent rings, lambda(C-C), and the height of the ring, h(d), are strongly affected by the concentration of the solution and the properties of the solvent. The nature of the formation of regular gradient ring patterns during the course of irreversible solvent evaporation is revealed through theoretical calculations based on the mass conservation of the solution.

Self-assembly of nanoscale materials to form ordered structures promises new opportunities for developing miniaturized electronic, optoelectronic, and magnetic devices. [1][2][3][4] In this regard, several elegant methods based on self-assembly have emerged, [5][6][7][8] for example, self-directed self-assembly, [5] and electrostatic self-assembly.[8] Self-assembly of nanoparticles by irreversible solvent evaporation has been recognized as an extremely simple route to intriguing structures. [9][10][11][12] However, these dissipative structures are often randomly organized without controlled regularity. Herein, we show a simple, onestep technique to produce concentric rings and spokes comprising quantum dots or gold nanoparticles with high fidelity and regularity by allowing a drop of a nanoparticle solution to evaporate in a sphere-on-flat geometry. The rings and spokes are nanometers high, submicrons to a few microns wide, and millimeters long. This technique, which dispenses with the need for lithography and external fields, is fast, cheap and robust. As such, it represents a powerful strategy for creating highly structured, multifunctional materials and devices.Quantum dots (QDs) are highly emissive, spherical, inorganic nanoparticles a few nanometers in diameter. They provide a functional platform for a new class of materials for use in light emitting diodes (LEDs), [13] photovoltaic cells, [14] and biosensors. [15] Because of the quantum-confined nature of QDs such as CdSe, the variation of particle size provides continuous and predictable changes in fluorescence emission. Passivating the vacancies and trap sites on the CdSe surface with higher-band-gap materials, such as ZnS, produces CdSe/ ZnS core/shell QDs that have strong photoluminescence. [16] Two CdSe/ZnS core/shell QDs (4.4 and 5.5 nm in diameter, D) were used as the first nonvolatile solutes in our experiments. The surface of CdSe/ZnS was passivated with a monolayer of tri-n-octylphosphine oxide (TOPO) to impart solubility to the host environment and retain the spectroscopic properties of the materials by preventing them from aggregating. A drop of CdSe/ZnS in toluene was loaded in a confined geometry consisting of a spherical silica lens in contact with an Si substrate (i.e., sphere-on-flat geometry; see Experimental Section), [17][18][19][20][21] which led to the formation of a capillary bridge of the solution as illustrated in Figure 1 a. In situ optical microscopy (OM) revealed two main types of pattern formations, namely, concentric rings and spokes, which depend on whether fingering instabilities of thin film of the evaporating front took place or not.The formation of ringlike deposits in an evaporating drop that contains nonvolatile solutes on a single surface is known as the "coffee-ring" phenomenon. [9,10,22,23] Maximum evaporative loss of the solvent at the perimeter triggers the jamming of the solutes and creates a local roughness (i.e., the contact Figure 1. a) Sphere-on-flat geometry in which a drop of nanoparticle solution is constrai...

A sodium metal anode protected by an ion-rich polymeric membrane exhibits enhanced stability and high-Columbic efficiency cycling. Formed in situ via electropolymerization of functional imidazolium-type ionic liquid monomers, the polymer membrane protects the metal against parasitic reactions with electrolyte and, for fundamental reasons, inhibits dendrite formation and growth. The effectiveness of the membrane is demonstrated using direct visualization of sodium electrodeposition.

Nanocomposites of poly(3-hexylthiophene)-cadmium selenide (P3HT-CdSe) were synthesized by directly grafting vinyl-terminated P3HT onto [(4-bromophenyl)methyl]dioctylphosphine oxide (DOPO-Br)-functionalized CdSe quantum dot (QD) surfaces via a mild palladium-catalyzed Heck coupling, thereby dispensing with the need for ligand exchange chemistry. The resulting P3HT-CdSe nanocomposites possess a well-defined interface, thus significantly promoting the dispersion of CdSe within the P3HT matrix and facilitating the electronic interaction between these two components. The photophysical properties of nanocomposites were found to differ from the conventional composites in which P3HT and CdSe QDs were physically mixed. Solid-state emission spectra of nanocomposites suggested the charge transfer from P3HT to CdSe QDs, while the energy transfer from 3.5 nm CdSe QD to P3HT was implicated in the P3HT/CdSe composites. A faster decay in lifetime further confirmed the occurrence of charge transfer in P3HT-CdSe nanocomposites.

We present a method for organizing metallic nanoparticles in solution that is based on the hydrophobic effect and does not require either hydrogen bonding or molecular recognition. When amphiphilic V-shaped molecules are attached to a gold cluster, an aggregation process ensues in aqueous solution and leads to the formation of well-defined cylindrical and vesicular nanoarrays of particles. The metallic clusters densely pack at the boundary separating the hydrophobic core from the hydrophilic corona of the hybrid micelle-like aggregates. This design allows one to assemble and disassemble the nanoparticles in a reversible manner and control the size and the morphology of the arrays by changing the conditions of the solution preparation. The versatility of this method is demonstrated by its applicability to different metals with covalently attached amphiphilic arms with various chemical compositions (PS-PEO and PB-PEO) and molecular weights.

Low bandgap copolymers are prepared by incorporating thiophene‐modified benzo[1,2‐b:4,5‐b′]dithiophene and alkyloxy or fluorine‐modified benzothiadiazole as donor and acceptor units. These copolymers exhibit a high open‐circuit voltage and short‐circuit current density. Good power conversion efficiencies are demonstrated in solar cell studies, indicating their promising photovoltaic application as donor materials.

Poly(ferrocenylsilanes) (PFS) are a novel class of transition metal-containing polymers with a main chain that consists of alternating organosilane and ferrocene units. 1-17 They possess intriguing physical properties that have potential applications in magnetic data storage, 1,2,4-7,10,12,13 photonic device, 1,9 and redox-active materials. 2,5 In addition, they are ideal precursors for producing magnetoceramics whose magnetic properties can be tuned by pyrolysis temperature. 1,2,[4][5][6][7][8][10][11][12][13] For example, pyrolysis of poly(ferrocenyldimethylsilane) at 1000°C turns it into ferromagnetic R-iron (R-Fe) nanoparticles embedded in an amorphous silicon carbide/carbon (SiC/C) matrix. 1,7 It has been demonstrated that the patterned, micron-scale PFS bars, circles, and lines exhibit a significant increase in coercivity in magnetic properties measurements. 12 Furthermore, these patterned PFS can also serve as etch barriers in nano-and microlithographic applications, for example, transferring the patterns into silicon substrate. 11,15-17 PFS is stable in reactive ion etching process compared to common organic polymers due to the presence of iron and silicon in the polymer backbone. 17 However, the creation of these micrometer size patterns involves the preparation and use of either a mask in UV-lithography 11,14 or a stamp in capillary force lithography, 16,17 or requires the use of expensive electron-beam lithography that is not costeffective and operated under high vacuum chamber. 11,12 Moreover, a subsequent step of removal of unexposed PFS is required. 11,12,14 Self-assembly via irreversible solvent evaporation of a droplet containing nonvolatile elements (dyes, nanoparticles, or polymers) represents an extremely versatile way for onestep creation of complex large-scale 18-34 or long-range ordered structures. 35,36 However, the flow instabilities within the evaporating droplet often result in irregular dissipative structures (e.g., convection patterns and fingering instabilities). Therefore, to fully utilize the evaporation as a simple, non-lithography route to produce well-ordered structures that have numerous technological applications, it requires delicately controlling the evaporative flux, the solution concentration, and the interfacial interactions among the solvent, solute, and substrate. To date, a few attempts have been made to control the droplet evaporation in a confined geometry in which self-organized mesoscale patterns are readily obtained. [37][38][39] Recently, patterns of remarkably high fidelity and regularity have been reported. 37 They are formed simply by allowing a drop to evaporate in a confined geometry (1) MacLachlam, M. J.; Ginzburg, M.; Coombs, N.; Coyle, T. W.; Raju, N. P.; Greedan, J. E.; Ozin, G. Cheng, A.; Bartole, A.; Greenberg, S.; Resendes, R.; Coombs, N.; Safa-Sefat, A.; Greedan, J. E.; Stover, H. D. H.; Ozin, G. A.; Manners, I. Resendes, R.; Cheng, A. Y.; Bartole, A.; Safa-Sefat, A.; Coombs, N.; Stover, H. D. H.; Greedan, J. E.; Ozin, G. A.; Manners, I. AdV. Ma...

Here we describe a very efficient method to produce well-defined amphiphilic gold nanoparticles (Au NPs) with an equal number of hydrophobic and hydrophilic arms which are distributed along the surface of a 2-nm gold core in an alternating fashion. The strategy involves direct coupling of V-shaped block copolymer amphiphile 2 with a carboxylic group at its junction point to mercaptophenol-terminated Au NPs. The reaction proceeds under mild esterification conditions and yields the product with a molecular weight of 40 kDa, high grafting density (2.9 chains/nm2), and extremely low polydispersity (1.07). The big advantage of this approach is the opportunity to avoid the use of expensive and often inaccessible polymeric thiols. The method described here is applicable to any carboxyl-terminated molecules and can be used for the preparation of complex, yet well-defined, macromolecular hybrid structures such as 1 (Au(PB-PEG)n). The new product, which was characterized by a combination of SEC, NMR, UV-vis, DLS, and TEM, represents a unique example of gold nanoparticles soluble in any conventional solvent.