Surface morphology evolution of poly(styrene-block-4-vinylpyridine) (PS-b-P4VP)(H) and poly(methyl methacrylate)-dibenzo-18-crown-6-poly(methyl methacrylate) (PMCMA) supramolecular film

Well-ordered nanostructured polymeric supramolecular thin films were fabricated from the supramolecular assembly of poly(styrene-block-4-vinylpyridine) (PS-b-P4VP)(H⁺) and poly(methyl methacrylate)-dibenzo-18-crown-6-poly(methyl methacrylate) (PMCMA). A depression of cylindrical nanodomains was formed by the block of P4VP(H⁺) and PMCMA associates surrounded by PS. The repulsive force aroused from the incompatibility between the block of P4VP(H⁺) and PMCMA was varied through changing the molecule weight (M_w) of PMCMA, the volume fraction of the block of P4VP(H⁺), and annealing the film at high temperature. Increasing the repulsive force led to a change of overall morphology from ordered nanoporous to featureless structures. The effects of solvent nature and evaporation rate on the film morphology were also investigated. Further evolution of surface morphologies from nanoporous to featureless to nanoporous structures was observed upon exposure to carbon bisulfide vapors for different treatment periods. The wettability of the film surface was changed from hydrophilicity to hydrophobicity due to the changes of the film surface microscopic composition.     

Study of the time evolution of the surface morphology of thin asymmetric diblock copolymer films under solvent vapor

The time development of the surface morphology of asymmetric polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) thin films ‘annealing’ in methanol vapor, a selective solvent for minority P4VP block, was investigated by atomic force microscopy(AFM). For PS-b-P4VP with cylindrical structure in bulk, as annealing time progressed, the surface morphology underwent structural transitions from featureless topography to hybrid morphology of cylindrical and spherical pits, to cylinders, to nanoscale depressions, back to cylinders again. The different film thickness made the number of the transitions observed, at any given annealing time, different. The thicker the film is the more transitions at a given annealing time can be observed. If the film was not thick enough, depressions appeared. For PS-b-P4VP with spherical structure in bulk, it displayed nanoscale depressions with the annealing time increasing. A possible mechanism of the transition of morphologies during solvent annealing was proposed.     

Transition behavior and ionic conductivity of lithium perchlorate-doped polystyrene-b-poly(2-vinylpyridine)

We report the transition behavior and the ionic conductivity of ion-doped amorphous block copolymer, based on two compositionally different polystyrene-block-poly(2-vinylpyridine) copolymers (PS-b-P2VPs) that can self-assemble into nanostructures, where P2VP block is ionophilic to lithium perchlorate (LiClO₄). The transition temperatures of LiClO₄-doped PS-b-P2VP, like the order-to-disorder transition (T_ODT), were measured by small-angle X-ray scattering (SAXS) and depolarized light scattering (DPLS). The selective ionic coordination to the nitrogen units of P2VP block leads to the increase of the repulsive interactions between two block components from weak- to strong-segregation regime with increasing amount of LiClO₄, which results subsequently in the increased T_ODT. However, for a compositionally asymmetric PS-b-P2VP under lamellar morphology, the ionic conductivity by the addition of LiClO₄ was remarkably increased at higher temperatures, representing that the effective ionic coordination at the greater volume fraction of P2VP block component improves the ionic conductivity as the temperature approaches to a rubbery phase.     

A facile preparative method for gold-containing vesicles from poly(styrene-block-2-vinylpyridine) block copolymer/HAuCl4 complexes

It is found that the complexes of PS-b-P2VP and HAuCl₄ in THF can form a compound vesicle when the THF solution is treated at 40 °C. The compound vesicle is composed of an insoluble wall formed by P2VP/HAuCl₄ complexes and a soluble PS shell. The vesicular character of the aggregates was investigated by dynamic light scattering (DLS) and transmission electron microscope (TEM). The decrease of the solubility of P2VP blocks in THF drives the PS-b-P2VP/HAuCl₄ complexes to aggregate into vesicles, which are stable upon dilution or crosslinking. Based on this study, the vesicles decorated with gold nanoparticles can be produced, which hold potential for the facile organization of the vesicle-supported precious metal catalysts.     

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.     

Shell-core-corona aggregates formed from poly(styrene)-poly(4-vinylpyridine) block copolymer induced by added homopolymer via interpolymer hydrogen-bonding

The solution behavior of poly(styrene)-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer with added poly(4,4′-oxydiphenylenepyromellitamic acid) (POAA) homopolymer in DMF is studied by dynamic light scattering (DLS), nuclear magnetic resonance (NMR), and transmission electron microscopy (TEM). It is found that coaggregation takes place when mixing PS-b-P4VP block copolymer and POAA homopolymer in DMF due to the strong interpolymer hydrogen-bonding between POAA chains and P4VP blocks. The coaggregation is a diffusion-controlled process and the complexation-induced aggregates are very stable. NMR measurements demonstrate that the resultant aggregates are much more swollen compared with typical amphiphilic block copolymer core-shell micelles. DLS measurements with Eu³⁺ as a probe combined with TEM observation, are employed to study the structure of the aggregates. Results reveal that the formed aggregates are core-shell spheres with the P4VP/POAA complexes as core and the PS blocks as shell when the weight ratio of POAA to PS-b-P4VP is lower. However, a core-shell-corona structure forms with a thin layer of POAA chains adsorbed on the initial core-shell aggregates with increasing weight content of POAA to 60%. Finally, possible mechanisms of the structural transitions are proposed.     

Synthesis, properties, and electrical memory characteristics of new diblock copolymers of polystyrene-block-poly(styrene-pyrene)

In this study, we report the synthesis, properties, and electrical memory characteristics of new diblock copolymers, polystyrene-block-poly(styrene-pyrene) (PS-b-P(St-Py)), prepared by combining atom transfer radical polymerization and Suzuki coupling reaction. The effects of the St?CPy block chain length on the electronic energy level, photophysical properties, and memory characteristics were explored. The PS₄₂-b-P(St-Py)₁₀₈ and PS₆₆-b-P(St-Py)₆₇ devices exhibited a dynamic random access memory characteristics with different turn-on threshold voltages of ?2.7 and ?3.1?V, respectively. Moreover, these memory devices showed a high ON/OFF current ratio of 10⁹ and were electrically stable for at least 10⁴?s in both ON and OFF states. However, the PS₁₁₃-b-P(St-Py)₄₅-based device displayed an insulating state in a low current variation of 10^?12 to 10^?14?A, which had a short St?CPy block length. The mechanism of the switching behavior was explained by the charge hopping conduction between the pyrene units with coexisting charge-trapping environment. The volatility of the memory effect was depended on the ability of charge trapping/back transferring of trapped charge. The present study suggested that the electrical memory characteristics could be efficiently tuned through the block ratio between insulating segment and pendant-conjugated segment of the diblock polymers.     

Morphology of polystyrene/polystyrene-block-poly(methyl methacrylate)/poly(methyl methacrylate) composite particles

Polystyrene/polystyrene-block-poly(methyl methacrylate)/poly(methyl methacrylate) (PS/PS-b-PMMA/PMMA) composite particles were prepared by releasing toluene from PS/PS-b-PMMA/PMMA/toluene droplets dispersed in a sodium dodecyl sulfate aqueous solution. The morphology of the composite particles was affected by release rate of toluene, the molecular weight of PS-b-PMMA, droplet size, and polymer composition. ‘Onion-like’ multilayered composite particles were prepared from toluene droplets of PS-b-PMMA and of PS/PS-b-PMMA/PMMA, in which the weights of PS and PMMA were the same. The layer thicknesses of the latter multilayered composite particles increased with an increase in the amount of the homopolymers. PS-b-PMMA/PS composite particles had a sea-islands structure, in which PMMA domains were dispersed in a PS matrix. On the other hand, PS-b-PMMA/PMMA composite particles had a cylinder-like structure consisting of a PMMA matrix and PS domains.     

Dynamic study of polystyrene-block-poly(4-vinylpyridine) copolymer in bulk and confined in cylindrical nanopores

AAO template is highly recommended to nanostructure polymers and to study polymer properties under confinement. The dynamic properties of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) under confinement using broadband dielectric spectroscopy are investigated in this work and the results compared to those of the bulk. Anodized aluminum oxide (AAO) membranes, having pore diameters from tens to hundreds of nanometers in size, were used to confine PS-b-P4VP. Moreover, the influence of gold nanoparticles (AuNPs) in the copolymer matrix was also studied. The morphology and structure of the bulk copolymer and the copolymer confined in the AAO templates were characterized by transmission electron microscopy, scanning electron microscopy and Small Angle X-Ray Scattering. For PS-b-P4VP in bulk, dielectric relaxation techniques allowed studying selectively the P4VP segmental dynamics within the diblock. At high temperature this copolymer presents a dominant peak (MWS relaxation), most likely originated by the relatively high conductivity combined with the presence of interfaces emerging in the nanostructured samples. Moreover, a pronounced β-relaxation is observed for the copolymer compared with that of pure P4VP. This is likely due to a non-negligible contribution from the α-relaxation of the PS component. The γ-relaxation is markedly different in the copolymer, which is evidenced by a distinct temperature dependence of the resulting relaxation times. When the copolymer is embedded in alumina nanopores with small pore diameters (25 and 35 nm) there are significant changes, where the tendency is going to a faster dynamics when the pore diameter decreases more likely related to the relevance of surface effects. The presence of the AuNPs in the system enhances this effect. These results are in agreement with segregated structures found in the block copolymer by TEM and SAXS.     

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.     

Crystallization behavior of PEO in blends of poly(ethylene oxide)/poly(2‐vinyl pyridine)‐b‐(ethylene oxide) block copolymer

The crystallization behavior of two molecular weight poly(ethylene oxide)s (PEO) and their blends with the block copolymer poly(2‐vinyl pyridine)‐b‐poly(ethylene oxide) (P2VP‐b‐PEO) was investigated by polarized optical microscopy, thermogravimetric analysis, differential scanning calorimetry, and atomic force microscopy (AFM). A sharp decreasing of the spherulite growth rate was observed with the increasing of the copolymer content in the blend. The addition of P2VP‐b‐PEO to PEO increases the degradation temperature becoming the thermal stability of the blend very similar to that of the block copolymer P2VP‐b‐PEO. Glass transition temperatures, T_g, for PEO/P2VP‐b‐PEO blends were intermediate between those of the pure components and the value increased as the content of PEO homopolymer decreased in the blend. AFM images showed spherulites with lamellar crystal morphology for the homopolymer PEO. Lamellar crystal morphology with sheaf‐like lamellar arrangement was observed for 80 wt% PEO(200M) and a lamellar crystal morphology with grain aggregation was observed for 50 and 20 wt% blends. The isothermal crystallization kinetics of PEO was progressively retarded as the copolymer content in the blend increased, since the copolymer hinders the molecular mobility in the miscible amorphous phase. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Effects of additives on the morphologies of thin titania films from self-assembly of a block copolymer

The effects of additives of poly(methyl methacrylate) (PMMA) and HAuCl₄ on the morphologies of hybrid titania films formed via co-assembly of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymers, titania sol-gel precursor in a selective solvent were investigated. The results show that addition of PMMA or HAuCl₄ has an important influence on the morphologies of hybrid titania films. Addition of PMMA or HAuCl₄ can induce the morphology transition of the PS-b-PEO/titania sol-gel mixture from spherical micelles to vesicles. Therefore, the morphologies of the hybrid films formed on silicon substrate surfaces by spin-coating can be controlled by the addition of homopolymer (PMMA) or inorganic precursor (HAuCl₄) into the PS-b-PEO/titania sol-gel mixtures, allowing access to nanoparticles or nanoporous films. After removing the polymer matrix, nanoparticle aggregates or nanobowl-like structures are left behind on the substrate surfaces.     

Sodium Dodecyl Sulfate (SDS)-Loaded Nanoporous Polymer as Anti-Biofilm Surface Coating Material

Biofilms cause extensive damage to industrial settings. Thus, it is important to improve the existing techniques and develop new strategies to prevent bacterial biofilm formation. In the present study, we have prepared nanoporous polymer films from a self-assembled 1,2-polybutadiene-b-polydimethylsiloxane (1,2-PB-b-PDMS) block copolymer via chemical cross-linking of the 1,2-PB block followed by quantitative removal of the PDMS block. Sodium dodecyl sulfate (SDS) was loaded into the nanoporous 1,2-PB from aqueous solution. The SDS-loaded nanoporous polymer films were shown to block bacterial attachment in short-term (3 h) and significantly reduce biofilm formation in long-term (1 week) by gram-negative bacterium Escherichia coli. Tuning the thickness or surface morphology of the nanoporous polymer films allowed to extent the anti-biofilm capability.     

Selective hydrogen bonding and hierarchical nanostructures in poly(hydroxyether of bisphenol A)/poly(?-caprolactone)-block-poly(2-vinyl pyridine) blends

The phase behavior, hydrogen bonding interactions and morphology of poly(hydroxyether of bisphenol A) (phenoxy) and poly(?-caprolactone)-block-poly(2-vinyl pyridine) (PCL-b-P2VP) were investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, optical microscopy and atomic force microscopy (AFM). In this A-b-B/C type block copolymer/homopolymer system, both P2VP and PCL blocks have favorable intermolecular interaction towards phenoxy via hydrogen bonding. However, the hydrogen bonding between P2VP and phenoxy is significantly stronger than that between PCL and phenoxy. Selective hydrogen bonding between phenoxy/P2VP pair at lower phenoxy contents and co-existence of two competitive hydrogen bonding interactions between phenoxy/P2VP and phenoxy/PCL pairs at higher phenoxy contents were observed in the blends. This leads to the formation of a variety of composition dependent nanostructures including wormlike, hierarchical and core-shell morphologies. The blends became homogeneous at 95 wt% phenoxy where both blocks of the PCL-b-P2VP were miscible with phenoxy due to hydrogen bonding. In the end, a model was proposed to explain the microphase morphology of blends based on the experimental results obtained. The swelling of the PCL-b-P2VP block copolymer by phenoxy due to selective hydrogen bonding causes formation of different microphases.     

Nanostructure and hydrogen bonding in interpolyelectrolyte complexes of poly(?-caprolactone)-block-poly(2-vinyl pyridine) and poly(acrylic acid)

Nanostructured poly(?-caprolactone)-block-poly(2-vinyl pyridine) (PCL-b-P2VP)/poly(acrylic acid) (PAA) interpolyelectrolyte complexes (IPECs) were prepared by casting from THF/ethanol solution. The morphological behaviour of this amphiphilic block copolymer/polyelectrolyte complexes with respect to the composition was investigated in a solvent mixture. The phase behaviour, specific interactions and morphology were investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, optical microscopy (OM), dynamic light scattering (DLS) and atomic force microscopy (AFM). Micelle formation occurred due to the aggregation of hydrogen bonded P2VP block and polyelectrolyte (PAA) from non-interacted PCL blocks. It was observed that the hydrodynamic diameter (D_h) of the micelles in solution decreased with increasing PAA content up to 40 wt%. After 50 wt% PAA content, D_h again increased. The micelle formation in PCL-b-P2VP/PAA IPECs was due to the strong intermolecular hydrogen bonding between PAA homopolymer units and P2VP blocks of the block copolymer. The penetration of PAA homopolymers into the shell of the PCL-b-P2VP block copolymer micelles resulted in the folding of the P2VP chains, which in turn reduced the hydrodynamic size of the micelles. After the saturation of the shell with PAA homopolymers, the size of the micelles increased due to the absorption of added PAA onto the surface of the micelles.     

Block copolymers containing pyridine moieties: Precise synthesis and applications

This review highlights the precise synthesis and application of various well-defined rod–coil and coil–coil block copolymers composed of poly(2-(or 4-)vinylpyridine) (P2VP or P4VP) block(s) with pyridine moieties. These polymers were synthesized by means of living anionic polymerization. Poly(hexyl isocyanate) (PHIC) was used as the rod-like segment, because hexyl isocyanate undergoes living anionic polymerization under carefully selected conditions. This review describes the syntheses of the block copolymers, polystyrene-b-P2VP, polystyrene-b-P4VP, polyisoprene-b-P2VP, P2VP-b-poly(methyl methacrylate), P2VP-b-poly(ethylene oxide), P2VP-b-poly(2-(N-carbazolyl)ethyl methacrylate), P2VP-b-PHIC, P2VP-b-PHIC-b-P2VP, and PHIC-b-P2VP-b-PHIC. The formation of self-organized nanostructured materials and molecular assemblies by such block copolymers and their possible applications are also described. These assemblies include monolayers, microphase-separated periodic-ordered nanostructures, micelles, polymer–metal complexes, nanoparticles, inorganic and metal layers, and nanoporous films with nanoparticles.     

Optical, dielectric and thermal properties of nanoscaled films of polyalkylsilsesquioxane composites with star-shaped poly(ε-caprolactone) and their derived nanoporous analogues

Nanoscaled films of poly(methylsilsesquioxane-co-ethylenylsilsesquioxane) (PMSSQ-BTMSE) and polymethylsilsesquioxane (PMSSQ) were prepared from the respective soluble prepolymers, and their thermal, optical, and dielectric properties were characterized. The PMSSQ-BTMSE nanofilm containing an ethylenyl bridge comonomer unit BTMSE was found to be thermally more stable than the nanofilm of PMSSQ, a representative polyalkylsilsesquioxane. Further, in comparison to the PMSSQ film the PMSSQ-BTMSE film exhibits a larger refractive index and a larger dielectric constant but a smaller out-of-plane thermal expansion coefficient, when both prepolymers are cured under the same conditions. These characteristics of PMSSQ-BTMSE films are due to the ethylenyl bridge provided by the BTMSE comonomer unit, which promotes the formation of a tighter, more perfect network structure in cured PMSSQ-BTMSE films. Composite films were prepared by solution-blending the pore generator (referred to as the porogen), a star-shaped poly(ε-caprolactone), with the soluble prepolymers then drying the resulting solution, and the nature of their curing reactions and extent of porogen calcination were investigated. It was found that the thermal curing and calcination processes of the composite films successfully produce PMSSQ-BTMSE and PMSSQ films containing pores that are about 400 nm in diameter. It was confirmed that the presence of these generated nanopores significantly reduces the refractive indices and the dielectric constants of the dielectric films but increases their out-of-plane thermal expansivity, depending on the initial porogen loading. The porosities of the nanoporous dielectric films were estimated from the measured refractive indices. The surface topographies of these films were also investigated, giving information about the sizes of the pores generated in the films. It was also found that prior to calcination the presence of the porogen increases the refractive index and dielectric constant of the composite dielectric films because of its inherent high polarizability, and also increases the thermal expansivity of MSSQ-BTMSE composite films but very slightly decreases the thermal expansivity of MSSQ composite films. It is demonstrated that PMSSQ-BTMSE films and the related nanometer scale nanoporous films are candidates for use as low and ultra-low dielectric interlayers in the fabrication of advanced microelectronic devices.     

Block copolymer photonic mesogels exhibiting dual volume phase transitions

Photonic mesogel films exhibiting brilliant photonic colors were prepared by selective swelling of polystyrene-b-quaternized poly(2-vinyl pyridine) (PS-b-QP2VP) block copolymers, and their volume phase transition behaviors were investigated in various solvent mixtures. The swollen PS-b-QP2VP lamellae segregate into mesophased gels where the highly swollen QP2VP gel layers are alternating with the glassy PS layers and exhibit strong responsive photonic colors in visible regime. Utilizing the changes of photonic stop bands, the swelling behaviors of the photonic mesogels were able to be monitored with sub-nanometer accuracy. Unusual dual volume phase transitions were observed at certain conditions where hydrogen bonding became significantly strong.     

Stabilization of nano-TiO2 aqueous dispersions with poly(ethylene glycol)-b-poly(4-vinyl pyridine) block copolymer and their incorporation in photocatalytic acrylic varnishes

In this work, TiO₂ nanoparticles were dispersed and stabilized in water using a novel type of dispersant based on tailor-made amphiphilic block copolymers of poly(ethylene glycol)-block-poly(4-vinyl pyridine) (mPEG-b-P4VP) prepared by atom transfer radical polymerization (ATRP). The performance of this new block copolymer as dispersant was compared to a polyelectrolyte dispersant commonly used for TiO₂, sodium salt of polyacrylic acid (Na-PAA). The effect of dispersion technique and type and amount of dispersant on deagglomeration and stability of the TiO₂ aqueous suspensions were studied. After incorporation in a standard waterborne acrylic varnish formulation, dry film transparency, photocatalytic activity, and nanoparticle cluster size were also evaluated. The results show that mPEG-b-P4VP copolymer with appropriate block lengths can have a better performance than Na-PAA in terms of aqueous dispersion stabilization and cluster size reduction in the acrylic matrix. This translates into higher film transparency and photocatalytic performance.     

Fabrication of fibril like aggregates by self-assembly of block copolymer mixtures via interpolymer hydrogen bonding

This paper describes the formation of fibril like aggregates from the self-assembly of block copolymer mixture (polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) and polystyrene-b-poly(acrylic acid) (PS-b-PAA)) via interpolymer hydrogen bonding in nonselective solvent. The hydrogen bonding between P4VP and PAA in chloroform leads to the formation of complex. When all the pyridine units in P4VP were all hydrogen bonded to acrylic acid in PAA, the formed complex is insoluble, resulting in the formation of spherical micellar aggregates and nanorods. However, two kinds of supramolecules with insoluble or soluble complex are formed in the solution when PS-b-P4VP and PS-b-PAA are mixed with equal mole ratio. The fibril like aggregates can be formed from the self-assembly of supramolecule with soluble complex during spin-coating process. The effects of evaporation rate of solvent and solution concentrations on the formation of fibril like aggregates were investigated. The results prove that the kinetic factors play an important role in the formation of the fibril like aggregates.