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.     

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.     

Hybrid Compound Block Copolymer Micelles Encapsulating Gold Nanoparticles

We report here on the formation of hybrid compound block copolymer micelles encapsulating gold nanoparticles, utilizing a direct and general preparation method. The giant hybrid compound micelles are structured with micelles of PS‐b‐P2VP with gold nanoparticles in their P2VP core and PI‐b‐PS chains as the outer part of the compound micelles. The gold nanoparticles were produced using gold ion‐loaded PS‐b‐P2VP micelles as a nanoreactor, in a PS selective solvent (toluene), by the subsequent reduction of gold ions. The synthesis of the gold nanoparticles was monitored by UV‐vis spectroscopy. The gold containing micelles were then encapsulated in larger micelles of PI‐b‐PS copolymer, by successive utilization of toluene and heptane with the intermediate evaporation of toluene. The nanoassembly of the compound materials comprised a PI corona and a PS compound core, with P2VP/Au⁰ domains, and was characterized using UV‐vis spectroscopy, dynamic light scattering and transmission electron microscopy.

     

Nucleating pattern formation in spin-coated polymer blend films with nanoscale surface templates

We use Dip-Pen Nanolithography (DPN) to generate monolayer surface templates for guiding pattern formation in spin-coated polymer blend films. We study template-directed pattern formation in blends of polystyrene/poly(2-vinylpyridine) (PS/P2VP) as well as blends of PS and the semiconducting conjugated polymer poly(3-hexylthiophene) (P3HT). We show that acid-terminated monolayers can be used to template pattern formation in PS/P3HT blends, while hydrophobic monolayers can be used to template pattern formation in PS/P2VP blends. In both blends, the polymer patterns comprise laterally-phase separated regions surrounded by vertically separated bilayers. We hypothesize that the observed patterns are formed by template-induced dewetting of the bottom layer of a polymer bilayer during the spin-coating process. We compare the effects of template feature size and spacing on the resulting polymer patterns with predictions from published models of template-directed dewetting in thin films and find the data in good agreement. For both blends we observe that a minimum feature size is required to nucleate dewetting/phase separation. We find this minimum template diameter to be approximately 180 nm in 50/50 PS/P2VP blends, and approximately 100 nm in 50/50 PS/P3HT blends. For larger template diameters, PS/P2VP blends show evidence for pattern formation beginning at the template boundaries, while PS/P3HT blends rupture randomly across the template features.     

Micellar structures of poly(styrene-b-4-vinylpyridine)s in THF/toluene mixtures and their functionalization with gold

The effects of the block copolymer composition and the solvent selectivity on the micellar morphologies of poly(styrene- b-4-vinylpyridine)s (PS- b-P4VPs) and their functionalizations with gold were studied in 10 mg/mL solutions using small-angle X-ray scattering and transmission electron microscopy (TEM). The solvent selectivity for the PS block was controlled by toluene/tetrahydrofuran (THF) mixtures in which toluene and THF are selective for PS and nonselective, respectively. The micellar structure was strongly dependent on phi (wt % toluene in toluene/THF mixture) and the composition of the block copolymers. PS(12K)- b-P4VP(11.8K) (symmetric) showed spherical micelles in the entire range of phi except phi = 0 (THF, nonselective solvent). PS(3.3K)- b-P4VP(18.7K) (asymmetric, longer P4VP) showed multiple morphologies with transitions from spheres to cylinders and finally to vesicles with an increase in phi. PS(19.6K)- b-P4VP(5.1K) (asymmetric, longer PS) showed spherical micelles only at the narrow ranges of 90 wt % 相似文献   

Synthesis and morphology of model 3‐miktoarm star terpolymers of styrene,isoprene and 2‐vinyl pyridine

The combination of anionic polymerization and controlled chlorosilane chemistry made possible for the first time the synthesis of model 3‐miktoarm star terpolymers of styrene (PS), isoprene (PI) and 2‐vinylpyridine (P2VP) (3μ‐SIV). The morphology of a nearly symmetric 3μ‐SIV star terpolymer, was also studied. From the preliminary results, it seems that the PI and P2VP phases form hexagonally packed adjoined cylinders, whereas the PS phase occupies the remaining space forming non‐regular curved hexagons, hexagonally packed as well. The star junction points reside on periodically spaced, parallel lines defined by the intersection of the three microdomain interfaces. Non of the phases form the matrix. The star molecular architecture gives the molecule the ability to “choose” which arms directly interact in the microphase segregate state, in order to minimize the most highly unfavorable contact between the PI and P2VP arms.     

Au/CdS Hybrid Nanoparticles in Block Copolymer Micellar Shells

A polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) micellar structure with a P2VP core containing 5 nm CdS nanoparticles (NPs) and a PS shell formed in toluene that is a good solvent for PS block undergoes the core‐shell inversion by excess addition of methanol that is a good solvent for P2VP block. It leads to the formation of micellar shell‐embedded CdS NPs in the methanol major phase. The spontaneous crystalline growth of Au NPs on the CdS surfaces positioned at micellar shells without a further reduction process is newly demonstrated. The nanostructure of Au/CdS/PS‐b‐P2VP hybrid NPs is confirmed by transmission electron microscopy, energy‐dispersive X‐ray, and UV‐Vis absorption.

     

A Facile Synthesis of Dynamic,Shape‐Changing Polymer Particles

We herein report a new facile strategy to ellipsoidal block copolymer nanoparticles that exhibit a pH‐triggered anistropic swelling profile. In a first step, elongated particles with an axially stacked lamellae structure are selectively prepared by utilizing functional surfactants to control the phase separation of symmetric polystyrene‐b‐poly(2‐vinylpyridine) (PS‐b‐P2VP) in dispersed droplets. In a second step, the dynamic shape change is realized by cross‐linking the P2VP domains, thereby connecting glassy PS discs with pH‐sensitive hydrogel actuators.     

A Facile Synthesis of Dynamic,Shape‐Changing Polymer Particles

We herein report a new facile strategy to ellipsoidal block copolymer nanoparticles that exhibit a pH‐triggered anistropic swelling profile. In a first step, elongated particles with an axially stacked lamellae structure are selectively prepared by utilizing functional surfactants to control the phase separation of symmetric polystyrene‐b‐poly(2‐vinylpyridine) (PS‐b‐P2VP) in dispersed droplets. In a second step, the dynamic shape change is realized by cross‐linking the P2VP domains, thereby connecting glassy PS discs with pH‐sensitive hydrogel actuators.     

An approach for the surface functionalized gold nanoparticles with pH-responsive polymer by combination of RAFT and click chemistry

In this report, we demonstrated a novel efficient post-modification route for preparation of smart hybrid gold nanoparticles with poly(4-vinylpyridine) (P4VP) based on RAFT and click chemistry. A new azide terminated ligand was first synthesized to modify gold nanoparticles by ligand exchange reaction, and then click reaction was used to graft alkyne terminated P4VP which was prepared by RAFT onto the surface of gold nanoparticles. The functionalized hybrid gold nanoparticles were characterized by TEM, FTIR, and XPS etc. The results indicated that the P4VP was successfully grafted onto the surface of gold nanoparticles by click reaction. The surface grafting density was calculated to be about 6 chains/nm²_. In addition, the hybrid gold nanoparticles showed a pH responsive phenomenon as the pH value changed around 5.     

Functional colloidal particles stabilized by layered silicate with hydrophilic face and hydrophobic polymer brushes

In this study, we describe a new strategy for producing narrowly dispersed functional colloidal particles stabilized by a nanocomposite with hydrophilic clay faces and hydrophobic polystyrene (PS) brushes on the edges. This method involves preparation of polymer brushes on the edges of clay layers and Pickering suspension polymerization of styrene in the presence of the nanocomposites. PS brushes on the edges of clay layers were prepared by atom transfer radical polymerization. X‐ray diffraction and thermogravimetric analysis results indicated that PS chains were grafted to the edges of clay platelets. Transmission electron microscope results showed that different morphologies of clay‐PS particles could be obtained in different solvents. In water, clay‐PS particles aggregated together, in which PS chains collapsed forming nanosized hydrophobic domains and hydrophilic clay faces stayed in aqueous phase. In toluene, clay‐PS particles formed face‐to‐face structure. Narrowly dispersed PS colloidal particles stabilized by clay‐PS were prepared by suspension polymerization. Because of the negatively charged clay particles on the surface, the zeta potential of the PS colloidal particles was negative. Positively charged poly(2‐vinyl pyridine) (P2VP) chains were adsorbed to the surface of PS colloidal particles in aqueous solution at a low pH value, and gold nanoparticles were prepared in P2VP brushes. Such colloidal particles may find important applications in a variety of fields including waterborne adhesives, paints, catalysis of chemical reactions, and protein separation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1535–1543, 2009     

Transformation from ordered islands to holes in phase-separating P2VP/PS blend films by adding Triton X-100

Our previous investigation showed that the ordered hexagonal island pattern in the phase-separating polymeric blend films of polystyrene and poly(2-vinylpyridine) (PS/P2VP) formed due to the convection effect by proper control of PS molecular weight, solvent evaporation rate, and the weight ratio of PS to P2VP. In this paper, we further illustrate that, by adding a proper amount of the surfactant Triton X-100 to the PS/P2VP toluene solution, the ordered hexagonal island pattern can be transformed to the ordered honeycomb pattern. The effects of the amount of Triton X-100 on the surface morphology evolution and the pattern transformation are discussed in terms of the collapse of Triton X-100, phase separation between Triton X-100/P2VP and PS, the interfacial interaction between Triton X-100/P2VP and the mica substrate, and the Bénard-Marangoni convection.     

Structural isomer effects on the morphology of block copolymer/metal salts hybrids

The structural isomer effects on phase behavior of block copolymer/FeCl₃ hybrids were investigated by comparing structures of two series of blends based on polystyrene‐b‐poly(4‐vinylpyridine) (PS‐P4VP) and polystyrene‐b‐poly(2‐vinylpyridine) (PS‐P2VP), with the same molecular weight and the same composition. By conbining fourier transform infrared (FT‐IR) spectroscopy and differencial scaninng calorimetry, successful achievements of selective dispersion of FeCl₃ into poly(vinylpyridine) phase via coordination were verified. Complementary morphological observation by transmission electron microscopy and small‐angle X‐ray scattering (SAXS), it has been clarified that phase behavior for two isomer series is considerably different. That is, neat PS‐P4VP formed thicker cylindrical domains than that of neat PS‐P2VP due to much stronger Flory‐Huggins interaction parameter χ, χ_PS‐P4VP » χ_PS‐P2VP. As for PS‐P2VP/FeCl₃ hybrids, morphological transition can be taken place at the smaller amount of metal salt; furthermore, P2VP blend series form lamellar structures with evidently larger periodic length at the same amount of metal salt. This is probably caused by the event that excess metal salt also contributes to lamellar expansion by localizing at the center of P2VP lamellar phase. Moreover, the saturation limit of introduced metal salt in P2VP was smaller than that in P4VP due to the steric hindrance for a lone pair electrons on nitrogen atoms directed to the main chain of P2VP. These results can be explained by the structural isomer effects on the conformation of the P2VP chains at coordinated state with FeCl₃, that is, P2VP chains prefer to form the intramolecular coordination due to the short range interaction so as to make themselves stiffer, whereas P4VP chains tend to adopt the long range interaction including intra‐ and intermolecular coordinations. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 377–386     

Adhesion between chemically heterogeneous switchable polymeric brushes and an elastomeric adhesive

We investigated the adhesive properties of binary heterogeneous polymer brushes made from end-functionalized polystyrene (PS) and poly(2-vinylpyridine) (P2VP) chains. The molecular organization of the mixed brush could be varied reversibly by exposure to selective solvents for PS (toluene) and for P2VP (acidic water). This exposure results in reversible switching of adhesive and wetting properties. The manner in which the adhesion switching occurs can be tuned by the composition of mixed brushes. However, the outer surface composition could be enriched more effectively in PS after the toluene treatment than in P2VP after the acidic water treatment. As a result, the mixed brush compositions that showed the largest difference in properties between an exposure to toluene and an exposure to water were the P2VP-rich compositions. Adhesive properties, tested against a soft hydrophobic pressure-sensitive adhesive (PSA) using a probe test, always showed smaller differences between solvent treatments than wetting properties with water, suggesting a much higher sensitivity of the hydrophobic/hydrophilic brushes to polar molecules than to nonpolar molecules.     

Mixed polymer brushes by sequential polymer addition: anchoring layer effect

Smart surfaces can be described as surfaces that have the ability to respond in a controllable fashion to specific environmental stimuli. A heterogeneous (mixed) polymer brush (HPB) can provide a synthetic route to designing smart polymer surfaces. In this research we study HPB comprised of end-grafted polystyrene (PS) and poly(2-vinyl pyridine) (P2VP). The synthesis of the HPB involves the use of an "intermolecular glue" acting as a binding/anchoring interlayer between the polymer brush and the substrate, a silicon wafer. We compare anchoring layers of epoxysilane (GPS), which forms a self-assembled monolayer with epoxy functionality, to poly(glycidyl methacrylate) (PGMA), which forms a macromolecular monolayer with epoxy functionality. The PS and P2VP were deposited onto the wafers in a sequential fashion to chemically graft PS in a first step and subsequently graft P2VP. Rinsing the HPB in selective solvents and observing the change in water contact angle as a function of the HPB composition studied the switching nature of the HPB. Scanning probe microscopy was used to probe the topography and phase imagery of the HPB. The nature of the anchoring layer significantly affected the wettability and morphology of the mixed brushes.     

Nanowear studies in chemically heterogeneous responsive polymeric brushes by surface force microscopy

In this study, we present nanowear studies using surface force microscopy (SFM), on nanoscopic thin films of reversibly switchable binary polymer brushes [polystyrene (PS) + poly(2-vinylpyridine) (P2VP)] and respective monobrushes [polystyrene and poly(2-vinylpyridine)] synthesized via “grafting to” method. The aim was to tune the wear in nanothin polymer brush surfaces. Therefore, the effect of conformational switching of PS + P2VP brush on treatment with selective solvents for PS and P2VP chains on the wear process was investigated. Wear process on thick spin-coated films of PS and P2VP was also investigated for comparison. Nanowear experiments were performed using SFM tip by repeating scans over the surface to follow the wear process closely. The wear process on different surfaces was explained on the basis of molecular entanglement as well as adhesion and friction on the sample surface. For spin-coated PS film as well as PS and PS + P2VP brush surfaces (treated with toluene) with molecular entanglements at surface, wear mechanism involved formation of ripples. However, in case of spin-coated P2VP films as well as P2VP and PS + P2VP brush surfaces (treated with ethanol) with no molecular entanglements at surface, wear occurred via removal of polymer chains and their accumulation at the rim. For PS + P2VP surface treated with acidic water, wear mechanism was complex and inhomogeneous ripple formation was followed by formation of heaps of polymeric material in the center of scanned area. The extent of wear as measured either by root mean square roughness of the surface or spacing between the ripples, increased with the number of scans for all the surfaces. Our study shows that wear mode of polymer brush surfaces is different for different polymers and can be controlled/tuned by the use of binary polymer brushes.     

Preparation and thermal characterization of poly(2‐vinylpyridine) copolymers coordinated to Cr nanoparticles

In this study, polystyrene‐block‐poly(2‐vinylpyridine), PS‐b‐P2VP, polyisoprene‐block‐poly(2‐vinylpyridne), PI‐b‐P2VP and poly(methyl metacrylate)‐block‐poly(2‐vinylpyridine), PMMA‐b‐P2VP, coordinated to Cr metal were synthesized and characterized by Fourier transform infrared, transmission electron microscopy and direct pyrolysis mass spectrometry techniques. Both thermal degradation mechanism and thermal stability of P2VP blocks were affected by the coordination of Cr nanoparticles to nitrogen of pyridine rings. Thermal decomposition of P2VP blocks was started by loss of pyridine units leaving an unsaturated and/or crosslinked polymer backbone that degraded at relatively high temperatures. Incorporation of Cr metal did not noticeably influence thermal behavior of PS and PI blocks. However, increase in thermal stability of PMMA block was detected and associated with inhibition of the interactions between carbonyl groups of MMA chains with nitrogen atom of pyridine ring as a consequence of coordination to metal. Copyright © 2015 John Wiley & Sons, Ltd.     

Ordered CdSe nanoparticles within self-assembled block copolymer domains on surfaces

Hierarchical, high-density, ordered patterns were fabricated on Si substrates by self-assembly of CdSe nanoparticles within approximately 20-nm-thick diblock copolymer films in a controlled manner. Surface-modified CdSe nanoparticles formed well-defined structures within microphase-separated polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) domains. Trioctylphosphine oxide (TOPO)-coated CdSe nanoparticles were incorporated into PS domains and polyethylene glycol-coated CdSe nanoparticles were located primarily in the P2VP domains. Nearly close-packed CdSe nanoparticles were clearly identified within the highly ordered patterns on Si substrates by scanning electron microscopy (SEM). Contact angle measurements together with SEM results indicate that TOPO-CdSe nanoparticles were partially placed at the air/copolymer interface.     

Directed Self‐Assembly of Diblock Copolymer Thin Films on Prepatterned Metal Nanoarrays

The sequential layer by layer self‐assembly of block copolymer (BCP) nanopatterns is an effective approach to construct 3D nanostructures. Here large‐scale highly ordered metal nano­arrays prepared from solvent annealed thin films of polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) diblock copolymer are used to direct the assembly of the same BCP. The influence of initial loading concentration of metal precursor, the type of metal nanoparticle (gold, platinum, and silver), and the nanoparticle–substrate interaction on the directed assembly behavior of the upper BCP layer have been focused. It is found that the upper BCP film can be completely directed by the gold nanoarray with P2VP domain exclusively located between two adjacent gold nanowires or nanodots, which behaves the same way as on the platinum nanoarray. While the silver nanoarray can be destroyed during the upper BCP self‐assembly with the silver nanoparticles assembled into the P2VP domain. Based on the discussions of the surface energy of nanoparticles and the interplay between nanoparticle–substrate interaction and nanoparticle–polymer interaction, it is concluded that the effect of immobilization of nanoparticles on the substrate, together with entropy effect to minimize the energetically unfavorable chain stretching contributes to the most effective alignment between each layer.

     

Self‐assembled complexes of poly(acrylic acid) and poly(styrene)‐block‐poly(4‐vinyl pyridine)

Polymer complexes were prepared from high molecular weight poly(acrylic acid) (PAA) and poly(styrene)‐block‐poly(4‐vinyl pyridine) (PS‐b‐P4VP) in dimethyl formamide (DMF). The hydrogen bonding interactions, phase behavior, and morphology of the complexes were investigated using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). In this A‐b‐B/C type block copolymer/homopolymer system, P4VP block of the block copolymer has strong intermolecular interaction with PAA which led to the formation of nanostructured micelles at various PAA concentrations. The pure PS‐b‐P4VP block copolymer showed a cylindrical rodlike morphology. Spherical micelles were observed in the complexes and the size of the micelles increased with increasing PAA concentration. The micelles are composed of hydrogen‐bonded PAA/P4VP core and non‐bonded PS corona. Finally, a model was proposed to explain the microphase morphology of complex based on the experimental results obtained. The selective swelling of the PS‐b‐P4VP block copolymer by PAA resulted in the formation of different micelles. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1192–1202, 2009