P2VP Domains Research Articles

CdS/C60 binary nanocomposite films prepared via phase transition of PS-b-P2VP block copolymer

We demonstrate the well-defined control of phase transition of a polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer from spherical micelles to lamellar structures, in which CdS and C60 nanoparticles (NPs) are selectively positioned at the P2VP domains. The CdS NPs are in situ synthesized using PS-b-P2VP block copolymer templates that are self-assembled in PS-selective solvents. The CdS-PS-b-P2VP micellar structures are transformed to lamellar phase by adjusting a solvent selectivity for both blocks. In addition, a binary system of CdS/C60 embedded in PS-b-P2VP lamellar structures (CdS/C60-PS-b-P2VP) is fabricated by embedding C60 molecules into P2VP domain though charge-transfer complexation between pyridine units of PS-b-P2VP and C60 molecules. The CdS/C60-PS-b-P2VP nanostructured films are characterized by transmission electron microscopy (TEM) and UV–Vis spectrometer.

Microstructure and Optoelectronic Properties of P3HT-b-P4VP/PCBM Blends: Impact of PCBM on the Copolymer Self-Assembly

Block copolymers have been widely investigated over the past decades for their ability to microphase separate into well-defined nanostructured thin films with tailored physical properties. The aim of the present study is to investigate the thin film properties of rod–coil block copolymer/phenyl-C61-butyric acid methyl ester (PCBM) blends as a function of the blend weight ratio, using a copolymer which is based on a poly(3-hexylthiophene) (P3HT) rod block and poly(4-vinylpyridine) (P4VP) coil block. Atomic force microscopy, transmission electron microscopy and grazing incidence X-ray diffraction analysis are used to study the influence of PCBM on the copolymer self-assembling. UV–visible absorption and photoluminescence spectroscopies as well as field-effect mobility measurements are performed in order to get further insight into the blend optoelectronic properties. It is found that the block copolymer phase-separated morphology and charge carrier mobilities strongly depend on the PCBM loading and thermal annealing. In particular, the results point out that PCBM enhances the block copolymer microphase separation within a narrow range of the polymer:PCBM weight ratio. In addition, clear evidence for PCBM accumulation within the P4VP domains is found by monitoring the P3HT fluorescence and charge carrier mobilities.

Multimodal imaging of heterogeneous polymers at the nanoscale by AFM and scanning near-field ellipsometric microscopy

Scanning near field ellipsometric microscopy (SNEM) was used to simultaneously obtain optical images and tapping mode topography images of the microphase separated morphology of PS-b-P2VP block copolymer thin films. Optical images revealed a spatial resolution well below the diffraction limit. The SNEM setup used consisted of an AFM and an ellipsometer that were commercially available and that did not require major changes in their design to build the hybrid microscope. The observed increase in optical contrast for gold coated tips compared to silicon AFM probe tips was in qualitative agreement with the calculated increase in scattering amplitude according to the point dipole model for a gold AFM probe tip compared to a bare silicon AFM probe tip of the same size. The dielectric constant difference between the two blocks of the diblock copolymer was increased by selectively staining the P2VP block with iodine vapor. This resulted in an increase in the optical contrast between the PS and P2VP domains. Furthermore, the decrease in optical contrast as a function of increasing tip-sample separation was studied. It was observed that at 50nm tip sample separation the optical contrast was significantly reduced. The non-linear decay of the near-field amplitude signal as a function of the tip-sample separation calculated with the point dipole model supported this experimental result. The use of tapping mode in SNEM opens novel opportunities to study soft matter down to the macromolecular level.

Self-assembly of PS-b-P4VP block copolymers of varying architectures in aerosol nanospheres

Poly(styrene-block-4-vinylpyridine) (PS-b-P4VP) nanospheres are prepared in an aerosol phase where the self-assembly is induced by initial solvent evaporation and subsequent thermal annealing. The block copolymers self-assemble into different structures within solid aerosol nanospheres depending on the relative lengths of the polymer blocks, annealing temperature in the aerosol phase, and solvent composition. The obtained structures are worm-like P4VP domains in a PS matrix with low relative P4VP block lengths whereas alternating lamellae of P4VP and PS in a stacked or onion-like order are found with equal block lengths. With specified solvents and annealing below a glass transition temperature (Tg) this results in phase dimensions smaller than in the corresponding bulk copolymer. At the temperature significantly higher than the Tg the chain segments reach thermal equilibrium, which results in equilibrium structures as in the bulk. The results here show that the instantaneous assembly of polymers blocks in nanospheres can be manipulated in the gas phase to obtain various nanoscale structures which are advantageous, for instance, in designing novel nanosphere-based carrier systems for controlled drug delivery.

Hierarchical Structures of Hydrogen-Bonded Liquid-Crystalline Side-Chain Diblock Copolymers in Nanoparticles

Here we show that it is possible to control the overall morphology as well as hierarchical microstructure of lamellae-forming block copolymers within nanoparticles by altering side-chain content and processing temperature. We used cholesteryl hemisuccinate (CholHS) as hydrogen-bonded side chains and poly(styrene)-block-poly(4-vinylpyridine) (PS–P4VP) as backbone to produce submicrometer particles with the aerosol method. With CholHS-to-P4VP repeat unit ratio of 0.25 and 0.50, we obtained onion-like particles with either single CholHS layers sandwiched between P4VP rich lamellae or smectic P4VP(CholHS) layers perpendicular to the polymer domain interfaces. When the fraction of CholHS was increased to 0.75, the onion-like structure broke down due to increased splay deformation energy of the liquid crystalline P4VP(CholHS) domains. The onion-like structure could be re-established, however, when the particles were produced at a higher temperature which made the CholHS molecules partially soluble into the PS phase. Because of the reversible nature of the hydrogen bonds, it was possible to selectively remove the CholHS side chains from the particles.

Effect of Confinement on Proton Transport Mechanisms in Block Copolymer/Ionic Liquid Membranes

Nanostructured membranes containing structural and proton-conducting domains are of great interest for a wide range of applications requiring high conductivity coupled to high thermal stability. Understanding the effect of nanodomain confinement on proton-conducting properties in such materials is essential for designing new, improved membranes. This relationship has been investigated for a lamellae-forming mixture of poly(styrene-b-2-vinyl pyridine) (PS-b-P2VP) with ionic liquid composed of imidazole and bis(trifluoromethylsulfonyl)imide, where the ionic liquid selectively resides in the P2VP domains of the block copolymer. Quasi-elastic neutron scattering and NMR diffusion measurements reveal increased prevalence of a fast proton hopping transport mechanism, which we hypothesize is due to changes in the hydrogen bond structure of the ionic liquid under confinement. This, in combination with unique ion aggregation behavior, leads to a lower activation energy for macroscopic ion transport compared with that in a mixture of ionic liquid with P2VP homopolymer. The proton transference number in both samples is significantly higher than that in the neat ionic liquid, which could be taken advantage of for applications such as proton exchange membrane fuel cells and actuators. These results portend the rational design of nanostructured membranes having improved mechanical properties and conductivity.

Gold-Decorated Block Copolymer Microspheres with Controlled Surface Nanostructures

Gold-decorated block copolymer microspheres (BCP-microspheres) displaying various surface morphologies were prepared by the infiltration of Au precursors into polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) microspheres. The microspheres were fabricated by emulsifying the PS-b-P4VP polymers in chloroform into a surfactant solution in water, followed by the evaporation of chloroform. The selective swelling of the P4VP domains in the microspheres by the Au precursor under acidic conditions resulted in the formation of Au-decorated BCP-microspheres with various surface nanostructures. As evidenced by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) measurements, dotted surface patterns were formed when microspheres smaller than 800 nm were synthesized, whereas fingerprint-like surface patterns were observed with microspheres larger than 800 nm. Au nanoparticles (NPs) were located inside P4VP domains near the surfaces of the prepared microspheres, as confirmed by TEM. The optical properties of the BCP-microspheres were characterized using UV-vis absorption spectroscopy and fluorescence lifetime measurements. A maximum absorption peak was observed at approximately 580 nm, indicating that Au NPs are densely packed into P4VP domains on the microspheres. Our approach for creating Au-NP-hybrid BCP-microspheres can be extended to other NP systems such as iron-oxide or platinum NPs. These precursors can also be selectively incorporated into P4VP domains and induce the formation of hybrid BCP-microspheres with controlled surface nanostructures.

Morphology Evolution of PS-b-P2VP Diblock Copolymers via Supramolecular Assembly of Hydroxylated Gold Nanoparticles

We report on the strong segregation of core–shell Au nanoparticles, with a shell layer consisting of a random copolymer brush of styrene and vinylphenol (PS-r-PVPh-SH), in poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) diblock copolymer. Because of the formation of multiple hydrogen bonds between the hydroxyl groups within the shell of the nanoparticles and the pyridine group in PS-b-P2VP, the Au nanoparticles were strongly localized into P2VP domains with a very high volume fraction of nanoparticles (ϕp ∼ 0.53). The spatial distribution of Au nanoparticles, observed by transmission electron microscopy (TEM), is compared with results of previous experiments where homopolymers were blended with block copolymers. If the diameter d of the nanoparticles is much less than the width D of the P2VP lamellar domains, these nanoparticles are more uniformly distributed across the P2VP domain than if d is comparable to D, in which case the nanoparticles are pushed toward the center of the P2VP domains. This behavior is ...

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.

Synthesis of Well‐defined Amphiphilic Block Copolymers by Organotellurium‐Mediated Living Radical Polymerization (TERP)

Low-molecular weight amphiphilic diblock copolymers, polystyrene-block-poly (2-vinylpyridine) (PS-b-P2VP), and (P2VP-b-PS) with different block ratios were synthesized for the first time via organotellurium-mediated living radical polymerization (TERP). For both the homo- and block copolymerizations, good agreement between the theoretical, and experimental molecular weights was found with nearly 100% yield in every case. The molecular weight distribution for all the samples ranged between 1.10 and 1.24, which is well below the theoretical lower limit of 1.50 for a conventional free radical polymerization. Furthermore, a very simple approach to producing highly dense arrays of titania nanoparticles (TiO2 ) is presented using a site-selective reaction of titanium tetraisopropoxide within the P2VP domains of micellar film of P2VP-b-PS in toluene through the sol-gel method.

Domain Coalescence-Induced Nucleation and Anomalous Growth of Holes in Thin Polymer Blend Film

The phase evolution of a thin polymer blend film of polystyrene (PS) and poly(2-vinyl pyridine) (P2VP) triggered by solvent annealing is examined at both the bulk and single-(macro)molecule levels using wide-field microscopy (WFM). The transitions between different evolutionary stages in the nucleation and growth process are clearly visualized in real time and without intermittent breaks. The nucleation of PS holes arises from the coalescence and growth of P2VP domains and the holes expand in a complex manner involving the dewetting of PS and the absorption of P2VP domains into the holes.

The fabrication of graphitic thin films with highly dispersed noble metal nanoparticles by direct carbonization of block copolymer inverse micelle templates

Ordered arrays of Au or Ag nanoparticles supported on two-dimensional graphitic carbon films were prepared by direct carbonization of stabilized asymmetric polystyrene- block-poly(4-vinyl pyridine) (PS- b-P4VP) inverse micellar films loaded with metal precursors. Crosslinked PS- b-P4VP thin film templates with metal precursors selectively distributed in P4VP domains were converted to carbonaceous thin films having well-defined, highly dispersed metal nanoparticle (NP) arrays by ultraviolet (UV) irradiation under vacuum and subsequent carbonization. Mesoporous carbon films were also obtained after extracting the metal NPs by sonication in selected solvents. PS- b-P4VP was employed not only as carbon source, but also as template for introducing metal NPs in a nanopatterned configuration. The characteristic features and properties of thus generated hybrid carbon nanostructures were investigated by microscopy, UV–visible spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction measurement, and Raman spectroscopy.

Perforated Lamellae Morphology in Novel P2VP(PDMS-b-PI-b-PS)2 3-Miktoarm Star Quarterpolymer

The melt morphology of a novel P2VP(PDMS-b-PI-b-PS)2 3-miktoarm star quarterpolymer is investigated. The melt morphology is determined using rheology and small-angle neutron and X-ray scattering data in conjunction with dissipative particle dynamics simulations of a model molecule matching the volume fractions of the experimental system. The simulations are used to interpret the scattering data and identify the melt morphology as a new perforated lamellae structure. In this structure the P2VP forms hexagonally perforated lamellae containing close-packed protrusions of PS connecting adjacent lamellae layers of PS. The PI part forms a lining between the P2VP and PS domains constrained by the molecular architecture.

Reversible submergence of nanoparticles into ultrathin block copolymer films

In this study we report on the responsive behavior of organic/inorganic nanocomposite films. Specifically, the heat treatment of the films in the vapor of different solvents resulted in reversible rising and submerging of the nanoparticles incorporated into the film. The thin nanocomposite films consisting of silver nanoparticles (100–130 nm) evenly dispersed in a poly(styrene-b-2-vinylpyridine) (PS–P2VP) block copolymer were formed via melt incorporation. To fabricate the films the nanoparticles were first attached to the P2VP domains exposed to the surface of the block copolymer film. Next, the substrates covered with nanoparticles were annealed at 130 °C. The thermal treatment caused incorporation of the nanoparticles into the polymeric film. Thermal annealing of the film in a vapor of solvent selective for the PS block caused the nanoparticles to rise to the surface. The annealing of the same film in a vapor of solvent selective for the P2VP block led to submerging of the nanoparticles into the polymer film. The submerging and rising behavior of the nanoparticles was completely reversible.

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.

Selective embedding of P2VP coated Pd nanoparticles in PS-b-P2VP block copolymers

Nanocomposite films with palladium nanoparticles were prepared in a block copolymer with different morphologies. Poly(2-vinylpyridine) (P2VP) and polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymers were synthesized by living anionic polymerization using a vacuum apparatus system. To fabricate the nanocomposites, palladium nanoparticles with P2VP chains on their surfaces, which were prepared by alcohol reduction (Pd-P2VP) were introduced to the block copolymers. These palladium nanoparticles (4 nm) were embedded selectively in the P2VP domain of PS-b-P2VP. Various nanocomposites with different morphologies were obtained as the volume ratio of the block copolymer and the amount of Pd-P2VP nanoparticles. The block copolymers, nanoparticles and nanocomposites were analyzed by size exclusion chromatography (SEC), 1H nuclear magnetic resonance spectroscopy (1H NMR), UV/Vis spectroscopy (UV/Vis), and energy filtering-transmission electron microscopy (EF-TEM). Open image in new window

Hexagonally ordered arrays of metallic nanodots from thin films of functional block copolymers

We demonstrate a new and simple route to fabricate highly dense arrays of hexagonally close packed inorganic nanodots using functional diblock copolymer (PS-b-P4VP) thin films. The deposition of pre-synthesized inorganic nanoparticles selectively into the P4VP domains of PS-b-P4VP thin films, followed by removal of the polymer, led to highly ordered metallic patterns identical to the order of the starting thin film. Examples of Au, Pt and Pd nanodot arrays are presented. The affinity of the different metal nanoparticles towards P4VP chains is also understood by extending this approach to PS-b-P4VP micellar thin films. The procedure used here is simple, eco-friendly, and compatible with the existing silicon-based technology. Also the method could be applied to various other block copolymer morphologies for generating 1-dimensional (1D) and 2-dimensional (2D) structures.

Self-Assembly of Heteroarms Core−Shell Polymeric Nanoparticles (HCPNs) and Templated Synthesis of Gold Nanoparticles within HCPNs and the Superparticles

Here we report the self-assembly of heteroarm core−shell polymeric nanoparticles (HCPNs) into spherical superparticles and synthesis of gold nanoparticles within the HCPNs and the superparticles. HCPNs with polystyrene (PS)/poly(4-vinylpyridine) (P4VP) as the heteroarms and the cross-linked network poly(4VP-co-divinylbenzene) as the core were synthesized via a two-step anionic polymerization method. In the first step, living PS chains were prepared by initiating styrene using n-butyllithium in THF. In the second step, copolymerization of 4VP and DVB was initiated by the living PS chains. The HCPNs thus prepared have two features in the structure. (1) The HCPNs are large (the average hydrodynamic radius ⟨Rh⟩ of the HCPNs in DMF is 111 nm, whereas ⟨Rh⟩ of reported heteroarms star polymers are less than 10 nm) and flexible when they are dispersed in the solvents such as DMF and acidic water. (2) The PS arms are designed to be considerably longer than the P4VP arms. These two features led to interesting behaviors of the HCPNs in both the common solvent and the selective solvents for the heteroarms. In DMF, the common solvent, the HCPNs were swollen and with a ⟨Rh⟩ of 111 nm. In toluene, the selective solvent for PS, the longer PS arms shielded the short insoluble P4VP chains so that the HCPNs were individually dispersed with a ⟨Rh⟩ of 80 nm; the short P4VP arms collapsed, and the core shrank. In acidic water, which is a selective solvent for the shorter P4VP arms, the HCPNs self-assembled into large spherical superparticles with an average ⟨Rh⟩ of 187 nm. The above-mentioned two structural features are thought necessary for the regular self-assembly of such large and isotropic HCPNs. Furthermore, both HCPNs in toluene and the superparticles in acidic aqueous solution were used as templates to prepare gold nanoparticles (Au NPs). When HCPNs in toluene were used as the template, the Au NPs with a size of ca. 2−7 nm were scattered at the periphery of the cross-linked cores, forming raspberry-like morphology. When the superparticles were used as the template, the morphology of AuNP/superparticle composite nanoparticles depended on the solvent composition. In 0.1 M aqueous HCl solution, Au NPs were located at the periphery of the superparticles, forming gold shells with a thickness of ca. 50 nm. However, in 0.1 M HCl aqueous solution/DMF mixed solvent (9:1, v/v), the HAuCl4 precursor could penetrate into the P4VP domains within the superparticles, forming dendron-like Au NP clusters within the template after the reduction.

Responsive Hybrid Nanotubes Composed of Block Copolymer and Gold Nanoparticles

We demonstrate the facile fabrication of high aspect ratio nanotubes from responsive block copolymer, polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP), and in situ grown gold nanoparticles. PS-b-P2VP nanotubes are fabricated by template-assisted assembly by utilizing cylindrical pores of porous alumina membranes followed by its dissolution. Solvent annealing was employed to facilitate ordered phase separation of the block copolymer with in the nanotube structure, followed by in situ formation of gold nanoparticles in the P2VP domains occupying the inner and outer shell of the nanotubes. Owing to the pH-sensitive nature of P2VP block, which exhibits a coil to globule transition above pH 3.6, the PS-b-P2VP−gold nanoparticles hybrid nanotubes show reversible changes in topology, size (up to 25%), and collective plasmon resonance appearance. We suggest that PS-b-P2VP−gold nanoparticles hybrid nanotubes with their pH-responsive properties, large surface-to-volume ratio, and through open pore can find intriguing applications in sensing and microfluidic systems.

Full Color Stop Bands in Hybrid Organic/Inorganic Block Copolymer Photonic Gels by Swelling−Freezing

We report a facile way of fabricating hybrid organic/inorganic photonic gels by selective swelling and subsequent infiltration of SiO(2) into one type of lamellar microdomain previously self-assembled from modest-molecular-weight block copolymers. Transparent, in-plane lamellar films were first prepared by assembly of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP), and subsequently the P2VP domains were swollen with a selective solvent, methanol. The swollen structures were then fixated by synthesizing SiO(2) nanoparticles within P2VP domains. The resulting frozen photonic gels (f-photonic gels) exhibited strong reflective colors with stop bands across the visible region of wavelengths.