Fabrication of an open Au/nanoporous film by water-in-oil emulsion-induced block copolymer micelles

Water-in-oil (W/O) emulsion-induced micelles with narrow size distributions of approximately 140 nm were prepared by sonicating the polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer in the toluene/water (50:1 vol %). The ordered nanoporous block copolymer films with the hydrophilic P2VP interior and the PS matrix were distinctly fabricated by casting the resultant solution on substrates, followed by evaporating the organic solvent and water. The porous diameter was estimated to be about 70 nm. Here, we successfully prepared the open nanoporous nanocomposites, the P2VP domain decorated by Au (5+/-0.4 nm) nanoparticles based on the methodology mentioned. We anticipate that this novelty enhances the specific function of nanoporous films.     

Controlled supramolecular assembly of micelle-like gold nanoparticles in PS-b-P2VP diblock copolymers via hydrogen bonding

We report a facile strategy to synthesize amphiphilic gold (Au) nanoparticles functionalized with a multilayer, micelle-like structure consisting of a Au core, an inner hydroxylated polyisoprene (PIOH) layer, and an outer polystyrene shell (PS). Careful control of enthalpic interactions via a systematic variation of structural parameters, such as number of hydroxyl groups per ligand (N(OH)) and styrene repeating units (N(PS)) as well as areal chain density of ligands on the Au-core surface (Σ), enables precise control of the spatial distribution of these nanoparticles. This control was demonstrated in a lamellae-forming poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) diblock copolymer matrix, where the favorable hydrogen-bonding interaction between hydroxyl groups in the PIOH inner shell and P2VP chains in the PS-b-P2VP diblock copolymer matrix, driving the nanoparticles to be segregated in P2VP domains, could be counter balanced by the enthalphic penalty of mixing of the PS outer brush with the P2VP domains. By varying N(OH), N(PS), and Σ, the nanoparticles could be positioned in the PS or P2VP domains or at the PS/P2VP interface. In addition, the effect of additives interfering with the hydrogen-bond formation between hydroxyl groups on Au nanoparticles and P2VP chains in a diblock copolymer matrix was investigated, and an interesting pea-pod-like segregation of Au nanoparticles in PS domains was observed.     

One-step route to the fabrication of highly porous polyaniline nanofiber films by using PS-b-PVP diblock copolymers as templates

We report a new method to control both the nucleation and growth of highly porous polyaniline (PANI) nanofiber films using porous poly(styrene-block-2-vinylpyridine) diblock copolymer (PS-b-P2VP) films as templates. A micellar thin film composed of P2VP spheres within a PS matrix is prepared by spin coating a PS-b-P2VP micellar solution onto substrates. The P2VP domains are swollen in a selective solvent of acetic acid, which results in the formation of pores in the block copolymer film. PANI is then deposited onto the substrates modified with such a porous film using electrochemical methods. During the deposition, the nucleation and growth of PANI occur only at the pores of the block copolymer film. After the continued growth of PANI by the electrochemical deposition, a porous PANI nanofiber film is obtained.     

Ordering evolution of block copolymer thin films upon solvent-annealing process

Morphologies of polystyrene-block-poly(2-vinylpyridine) copolymer (S2VP) thin films, which are forming poly(2-vinylpyridine) cylinders in bulk phase, were investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM) to account for their ordering behavior induced by solvent annealing. Initially, when the copolymer was dissolved in toluene, which is selective solvent for majority polystyrene (PS) blocks, and was spin-coated on Si substrates, dimple-type micellar structures of S2VP were formed. After the film was placed in a solvent-annealing chamber covered with a lid under the existence of chloroform, surface morphologies of S2VP were measured as a function of annealing time. In this study, it was found that the morphologies of S2VP thin film repeated the cycle of the creation and extinction of various morphologies on ordering process. Namely, S2VP exhibited the various transformations between different morphologies, including highly disordered state, cylinders normal to the plane, and cylinders parallel to the plane. Each of the morphologies observed here was employed as a template to synthesize gold (Au) nanoparticles or nanowires. The arrays of Au nano-objects were used to tune a surface plasmon resonance.     

Creating surfactant nanoparticles for block copolymer composites through surface chemistry

A simple strategy to tailor the surface of nanoparticles for their specific adsorption to and localization at block copolymer interfaces was explored. Gold nanoparticles coated by a mixture of low molecular weight thiol end-functional polystyrene (PS-SH) (Mn = 1.5 and 3.4 kg/mol) and poly(2-vinylpyridine) homopolymers (P2VP-SH) (Mn = 1.5 and 3.0 kg/mol) were incorporated into a lamellar poly(styrene-b-2-vinylpyridine) diblock copolymer (PS-b-P2VP) (Mn = 196 kg/mol). A library of nanoparticles with varying PS and P2VP surface compositions (FPS) and high polymer ligand areal chain densities was synthesized. The location of the nanoparticles in the PS-b-P2VP block copolymer was determined by transmission electron microscopy. Sharp transitions in particle location from the PS domain to the PS/P2VP interface, and subsequently to the P2VP domain, were observed at FPS = 0.9 and 0.1, respectively. This extremely wide window of FPS values where the polymer-coated gold nanoparticles adsorb to the interface suggests a redistribution of PS and P2VP polymers on the Au surface, inducing the formation of amphiphilic nanoparticles at the PS/P2VP interface. In a second and synthetically more challenging approach, gold nanoparticles were covered with a thiol terminated random copolymer of styrene and 2-vinylpyridine synthesized by RAFT polymerization. Two different random copolymers were considered, where the molecular weight was fixed at 3.5 kg/mol and the relative incorporation of styrene and 2-vinylpyridine repeat units varied (FPS = 0.52 and 0.40). The areal chain density of these random copolymers on Au is unfortunately not high enough to preclude any contact between the P2VP block of the block copolymer and the Au surface. Interestingly, gold nanoparticles coated by the random copolymer with FPS = 0.4 were dispersed in the P2VP domain, while those with FPS = 0.52 were located at the interface. A simple calculation for the adsorption energy to the interface of the nanoparticles with different surface arrangements of PS and P2VP ligands supports evidence for the rearrangement of thiol terminated homopolymers. An upper limit estimate of the adsorption energy of nanoparticles uniformly coated with a random arrangement of PS and P2VP ligands where a 10% surface area was occupied by P2VP -mers or chains was approximately 1 kBT, which indicates that such nanoparticles are unlikely to be segregated along the interface, in contrast to the experimental results for nanoparticles with mixed ligand-coated surfaces.     

Ordered complex nanostructures from bimodal self-assemblies of diblock copolymer micelles with solvent annealing

We report the formation of ordered complex nanostructures from single-layered films of mixtures of polystyrene-poly(2-vinylpyridine) (PS-P2VP) and polystyrene-poly(4-vinylpyridine) (PS-P4VP) diblock copolymer micelles by THF (tetrahydrofuran) annealing. We first examined the influence of THF vapor on PS-P2VP and PS-P4VP micelles in their single-layered films. Due to the different solubility of PS-P2VP and PS-P4VP copolymers in THF, a hexagonal array of PS-P2VP micelles was changed into cylindrical nanodomains, but that of PS-P4VP micelles was not changed. The different influence of THF on PS-P2VP and PS-P4VP micelles was combined in single-layered films of mixtures of both micelles. For the purpose, we prepared mixture solutions of independently prepared small PS-P2VP and large PS-P4VP micelles. Then, bimodal self-assemblies of micelles were prepared from the mixtures, for which the hexagonal array of large PS-P4VP micelles was surrounded by small PS-P2VP micelles. When the bimodal self-assembly was annealed by THF vapor, PS-P2VP micelles were transformed into cylindrical nanodomains, but their reorganization was guided by hexagonally arranged PS-P4VP micelles. As a result, we were able to produce ordered complex nanostructures in the form of a hexagonal array of PS-P4VP micelles surrounded by PS-P2VP cylinders, which was further utilized for the synthesis of Au nanoparticles.     

Effect of TiO2 nanoparticles on self-assembly behaviors and optical and photovoltaic properties of the P3HT-b-P2VP block copolymer

An ordered nanostructure can be created from the hybrid materials of self-assembly poly(3-hexyl thiophene-b-2-vinyl pyridine) and nicotinic acid-modified titanium dioxide nanoparticles (P3HT-b-P2VP/TiO(2)). TEM and XRD analyses reveal that the TiO(2) nanoparticles (NPs) are preferentially confined in the P2VP domain of P3HT-b-P2VP whereas TiO(2) NPs interact with either pure P3HT or a blend of P3HT and P2VP to produce microsized phase segregation. The morphologies of lamellar and cylindrical structures are disturbed when the loading of TiO(2) NPs is 40 wt % or higher. Cylindrical P3HT-b-P2VP/TiO(2) exhibits a small blue shift in absorption and photoluminescence spectra with increasing TiO(2) loading as compared to P3HT/TiO(2). The NPs cause a slightly misaligned P3HT domain in the copolymer. Furthermore, the PL quenching of P3HT-b-P2VP/TiO(2) becomes very large as a result of efficient charge separation in the ordered nanodomain at 16 nm. Solar cells fabricated from self-assembly P3HT-b-P2VP/TiO(2) hybrid materials exhibit a >30 fold improvement in power conversion efficiency as compared to the corresponding 0.3P3HT-0.7P2VP/TiO(2) polymer blend hybrid. This study paves the way for the further development of high-efficiency polymer-inorganic nanoparticle hybrid solar cells using a self-assembled block copolymer.     

Fabrication of CdSe composite by using the amphiphilic block copolymer as template

CdSe nanoparticles of improved stability against aggregation were synthesized by using amphiphilic block copolymer polyacrylonitrile-block-poly(ethylene glycol)-block-polyacrylonitrile (PAN-b-PEG-b-PAN, PEA). The products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopic (HRTEM). The optical properties were characterized by UV-vis spectrophotometer and the room temperature photoluminescence (PL). The results revealed that the CdSe nanoparticles have been uniformly distributed throughout the copolymer with diameters of 6-7 nm and the produced novel hybrid nanocomposites displayed obviously quantum size effects and interesting fluorescence features. FTIR results provided the information on the interaction between the copolymer and the nanoparticles. The TGA revealed that the thermal property of the copolymer enhanced due to the interaction of the nanoparticles and the groups of the copolymer.     

High-density arrays of titania nanoparticles using monolayer micellar films of diblock copolymers as templates

Highly dense arrays of titania nanoparticles were fabricated using surface micellar films of poly(styrene-block-2-vinylpyridine) diblock copolymers (PS-b-P2VP) as reaction scaffolds. Titania could be introduced selectively within P2VP nanodomains in PS-b-P2VP films through the binary reaction between water molecules trapped in the P2VP domains and the TiCl(4) vapor precursors. Subsequent UV exposure or oxygen plasma treatment removed the organic matrix, leading to titania nanoparticle arrays on the substrate surface. The diameter of the titania domains and the interparticle distance were defined by the lateral scale present in the microphase-separated morphology of the initial PS-b-P2VP films. The typical diameter of titania nanoparticles obtained by oxygen plasma treatment was of the order of approximately 23 nm. Photoluminescence (PL) properties were investigated for films before and after plasma treatment. Both samples showed PL properties with major physical origin due to self-trapped excitons, indicating that the local environment of the titanium atoms is similar.     

Electrostatic force microscopy measurements of CdSe-PS nanoparticles and CdSe-PS/poly(styrene-b-butadiene-b-styrene) nanocomposites

Electrostatic force microscopy (EFM) measurements were performed to analyze the conductive properties of CdSe nanoparticles functionalized with polystyrene (PS) brushes and embedded in a poly(styrene-b-butadiene-b-styrene) triblock copolymer. CdSe nanoparticles were synthesized aqueously and functionalized with polystyrene chains by the grafting through technique. CdSe-PS nanoparticles obtained after 5 and 8 h of polymerization were analyzed, in order to study the effect of the molecular weight of PS chains on conductive properties. EFM results showed the maintenance of the conductive properties of CdSe nanoparticles through functionalization reactions and even when they were confined in the block copolymer. Due to the low differences between the values obtained in the response of the samples to the charged tip, no effect of the molecular weight of brushes was confirmed.     

Optical and Electronic Properties of Different Kinds of Water‐Soluble Porphyrin Films

Water‐soluble porphyrin‐porphyrin and porphyrin‐CdSe nanoparticle monolayer films were self‐assembled on different substrates. The influence of substrates, types of films, and heat treatment temperature on fluorescence of different kinds of porphyrin films was investigated. The SEM images showed the formation of monolayer films on porous alumina foil. The films assembled on porous alumina foil possessed higher fluorescence intensity and thermal stability. The result of conductance measurement indicated that the interaction of trimethylamidophenylporphyrin iodide (TAPPI) molecules with hydroxyl groups on porous alumina foil was weakened after CdSe nanoparticles assembled with TAPPI.     

Fluorescent and pH-responsive diblock copolymer-coated core-shell CdSe/ZnS particles for a color-displaying, ratiometric pH sensor

A color distinctive, ratiometric pH sensor was demonstrated using pH responsive and fluorescent (PyMMP-b-P2VP) diblock copolymer coated CdSe/ZnS QDs. Due to the change in the P2VP conformations in response to pH change, the color of QDs in solution changes distinctly from blue to red.     

Generation of nanocomposites based on polystyrene-grafted CdSe nanoparticles by grafting through and block copolymer

Continuing with our previous work, in which CdSe nanoparticles were functionalized with polystyrene (PS) brushes (CdSe-PS) by the grafting through method, nanocomposites were prepared by adding them to a poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer. After characterizing CdSe-PS nanoparticles obtained at different polymerization times of 3, 5, and 8 h by means of thermogravimetric analysis and gel permeation chromatography, CdSe-PS nanoparticles obtained after 5 h of polymerization (CdSe-PS(5h)) were chosen as the most adequate for the generation of nanocomposites. Atomic force microscopy (AFM) was used for morphological characterization of SBS/CdSe-PS(5h) nanocomposites. AFM images showed a good dispersion of the nanoparticles in the block copolymer, with the placement of the nanoparticles in the PS domains due to the improved affinity obtained by their functionalization with PS brushes.     

Enhanced ordering in gold nanoparticles self-assembly through excess free ligands

Self-assembly of nanometer-sized particles is an elegant and economical approach to achieve dense patterns over large areas beyond the resolution and throughput capabilities of electron-beam lithography. In this paper, we present results of self-assembly of oleylamine-capped gold nanoparticles with 8.0 ± 0.3 nm diameter into densely packed and well-ordered monolayers with center-to-center distance of ～11 nm. Self-assembly was done in a Langmuir-Blodgett trough and picked up onto Si substrates. The nanoparticles undesirably assembled within micrometer-sized "droplets" that were organic in nature. However, within these droplets, we observed that the addition of the excess ligand, oleylamine, drastically enhanced the self-assembly of the nanoparticles into monolayers with near-perfect ordering. This approach has the potential use in templated self-assembly of nanoparticles for rearranging poorly ordered assembly into a commensurate prepatterned substrate.     

Controlled placement of polystyrene-grafted CdSe nanoparticles in self-assembled block copolymers

Surface functionalization of semiconductor CdSe nanoparticles has been achieved with polystyrene (PS) brushes by “grafting from” technique for further addition to a polystyrene-b-polybutadiene-b-polystyrene (SBS) block copolymer in order to obtain self-assembled composites. For modification of nanoparticle surface 3-glycidoxypropyltrimethoxysilane (GPS) was used at first for the later attachment of the 4,4′-azobis(4-cyanopentanoic acid) azo initiator. Fourier-transform infrared spectroscopy confirmed the presence of GPS and PS on the surface of nanoparticles. Atomic force microscopy was used for morphological characterization of SBS/CdSe nanocomposites. Modification of nanoparticles with PS brushes by radical polymerization improved their affinity with PS block and the dispersion of nanoparticles avoiding agglomeration. CdSe nanoparticle size was measured to be around 2 nm by the use of X-ray diffraction and UV–Vis techniques. Optical properties were characterized using fluorescence measurements.     

Multicomponent nanoparticles via self-assembly with cross-linked block copolymer surfactants

We describe a simple and versatile protocol to prepare water-soluble multifunctional nanostructures by encapsulation of different nanoparticles in shell cross-linked, block copolymer micelles. This method permits simultaneous incorporation of different nanoparticle properties within a nanoscale micellar container. We have demonstrated the co-encapsulation of magnetic (gamma-Fe2O3 and Fe3O4), semiconductor (CdSe/ZnS), and metal (Au) nanoparticles in different combinations to form multicomponent micelles that retain the precursor particles' distinct properties. Because these multifunctional hybrid nanostructures spontaneously assemble from solution by simultaneous desolvation of nanoparticles and amphiphilic block copolymer components, we anticipate that this can be used as a general protocol for preparing multifunctional nanostructures without explicit multimaterial synthesis or surface functionalization of nanoparticles.     

Organization of nanoscale objects via polymer demixing

We present an extremely versatile method for the lateral organization of nano-scale objects (NOs) based on the phenomenon of polymer demixing. NOs are suspended in a solution of two immiscible polymers, which is used to form a thin polymer film by spin coating. During spin coating the two polymers separate to give a microphase structure, whose length scale depends on the experimental conditions. The NOs spontaneously partition into one or other of the polymer phases resulting in their lateral organization. In this work, the organization of CdSe nanoparticles and fluorescent organic dyes was studied by fluorescence microscopy. The NOs were organized in the polymer film in stochastic patterns or in ordered designs on substrates pre-patterned by soft-lithography techniques. Single-particle measurements, using confocal microscopy, showed that at low concentrations there was little aggregation of the particles.     

Two-dimensional arrays of luminescent metal-selenide nanoparticle

The direct synthesis of CdSe nanoparticles inside the core of PS-P4VP micellar structures has been utilized for the easy fabrication of 2-D CdSe nanoparticle arrays with variable sizes on a solid substrate.     

Tin Domain Growth on Quasi-Two-Dimensional CdTe and CdSe Nanoparticles

Tin domain growth on quasi-two-dimensional colloidal CdSe and CdTe nanoparticles having the zinc blende structure has been studied. The initial quasi-two-dimensional CdSe and CdTe nanoparticles having lateral sizes of 100–200 nm were prepared by a colloidal method. Tin domain growth was accomplished in tetrahydrofuran via the reduction of a tin(II) salt by tetrabutylammonium borohydride. The tin domains had sizes of 10–20 nm as probed by TEM. In case of CdSe nanoparticles, tin domains were grown inside the inner cavities of initially rolled nanoparticles. A β-tin phase was identified by X-ray diffraction. The absorption spectra featured the broadening of exciton bands corresponding to quasi-two-dimensional nanoparticles, the spectral positions of absorption peaks remaining almost unchanged.     

Mechanism of titania deposition into cylindrical poly(styrene-block-4 vinyl pyridine) block copolymer templates

A simple and effective way for TiO(2) to be deposited on silicon or indium tin oxide (ITO) substrates has been achieved by using a poly(styrene-block-4-vinyl pyridine) (PS-b-P4VP) block copolymer template. In particular, a mechanism for the formation of TiO(2) within the P4VP phase was developed. Within this model, the TiO(2) deposition occurs by swelling of the protonated P4VP segments followed by transport of Ti precursor, probably protonated Ti(OH)(4) given the low pH conditions used, into the swollen P4VP followed by condensation into TiO(2) during the heating/plasma etch processes. TiO(2) nanostructure morphology is affected by pH and deposition temperatures, because these parameters affect the degree of protonation of P4VP segments and diffusion of the titanium(IV) bis(ammonium lactato)dihydroxide (TALH) precursor into the film. A pH range of 2.1-2.5 for silicon substrates and pH = 2.1 for ITO substrates gave the narrower TiO(2) nanostructures distributions, and deposition at 70 °C gave TiO(2) nanostructures with more regular arrangements and smoother surface than those deposited at room temperature. The use of 1,4-diiodobutane as a P4VP cross-linking compound is demonstrated to be a critical parameter for maintaining good cylindrical surface morphology for both the block copolymer template and the TiO(2) nanostructures.