A variety of sub‐10 nm nanoparticles are successfully prepared by crosslinking of polystyrene‐b‐poly(1,3‐butadiene) (PS‐b‐PB) and polystyrene‐b‐poly(4‐vinyl pyridine) (PS‐b‐P4VP) block copolymer micelles and inverse micelles. Among them, the core‐crosslinked PS‐b‐PB micelles can self‐assemble into ultrathin (< 10 nm) macroporous (pore size <1 µm) membranes in a facile way, i.e., by simply drop‐coating the particle solution onto a mica surface. No continuous/porous membranes are produced from shell‐crosslinked PS‐b‐PB micelles and both forms of PS‐b‐P4VP micelles. This suggests that the unique structure of the block copolymer precursor, including the very flexible core‐forming block and the glassy corona‐forming block and the specific block length ratio, directly determines the formation of the macroporous membrane.
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.
Summary: We report the multiple morphologies and their transformation of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) in low‐alkanol solvents. In order to improve the solubility of polystyrene block in alcohol solvents, the solution of block copolymer sample was treated at a higher temperature, and then the influence of rate of decreasing temperature on multiple morphologies (including spheres, rods, vesicles, porous vesicles, large compound vesicles, and large compound micelles) was observed. The transformation of spheres to rods, to tyre‐shaped large compound micelles, and to sphere‐shaped large compound micelles was also realized. The formation mechanisms of the multiple morphologies and their transformation are discussed briefly.
Aggregates of PS‐P4VP formed in butanol by quenching from 110 °C to room temperature. 相似文献
We report that the nanostructures of poly(styrene‐block‐4‐vinylpyridine) block copolymer (PS‐b‐P4VP) thin film on a wafer substrate can be re‐assembled by sequential vapor treatment using selected solvents. Metal or other inorganic nanoparticles that were randomly pre‐loaded inside or on the surface of PS‐b‐P4VP thin film could be pulled to the rim of PS and P4VP along with the movements of PS and P4VP blocks during the treatment. As a result, the patterned polymeric or inorganic/polymer composite nanoisland and nanoring arrays were fabricated.
Hierarchical nanoporous structures are fabricated by adsorption of micelles of diblock copolymer‐templated Au‐nanoparticles onto a hydrophilic solid substrate. Gold nanoparticles are prepared using micelles (19 nm) of polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) as nanoreactors. Deposition of thin films of the micellar solution, modified with a non‐selective solvent (THF), on hydrophilic surfaces leads to the formation of hierarchical nanoporous morphologies. The thin films exhibit two different pore diameters and a total pore density of 15 × 108 holes per cm2. The structure was analyzed in terms of topography and chemical composition using AFM, TEM and XPS measurements. The PS‐b‐P4VP template was subsequently removed by oxygen plasma etching, to leave behind metallic nanopores that mimic the original thin film morphology.
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.
Complex micelles were obtained from PS‐b‐PNIPAM‐b‐PAA micelles and PEG‐b‐P4VP block copolymers via the strong electrostatic interaction and hydrogen bonding between PAA and P4VP blocks in water. The PS block formed the core and the PAA/P4VP complex shell functioned as a semi‐permeable membrane which could control the permeation of small molecules. Between the core and shell, the large fluid‐filled space that was formed with the thermoresponsive PNIPAM gel could retain the loaded drug for a long period of time. With increasing temperature, the shrinkage of the PNIPAM coils pumped the drug out of the complex micelles. The complex micelles functioned as a contractive “nanopump”, which could potentially be applied as a thermosensitive controlled release system.
This paper describes a new approach towards preparing self‐assembled hydrogen‐bonded complexes that have vesicle and patched spherical structures from two species of block copolymer in non‐selective solvents. The assembly of vesicles from the intermolecular complex formed after mixing polystyrene‐block‐poly(4‐vinyl phenol) (PS‐b‐PVPh) with poly(methyl methacrylate)‐block‐poly(4‐vinylpyridine) (PMMA‐b‐P4VP) in tetrahydrofuran (THF) is driven by strong hydrogen bonding between the complementary binding sites on the PVPh and P4VP blocks. In contrast, well‐defined patched spherical micelles form after blending PS‐b‐PVPh with PMMA‐b‐P4VP in N,N‐dimethylformamide (DMF): weaker hydrogen bonds form between the PVPh and P4VP blocks in DMF, relative to those in THF, which results in the formation of spherical micelles that have compartmentalized coronas that consist of PS and PMMA blocks.
PS‐b‐PAA spherical micelles with a liquid core and a PAA shell are prepared with the assistance of 1,2‐dichloroethane. During the process of adding a mixture of PNIPAM‐b‐P4VP and PEG‐b‐P4VP, multi‐layered micelles with a mixed corona that consists of both PNIPAM and PEG chains are constructed through the electrostatic interaction and hydrogen bonding between the PAA block and the P4VP block. When heating above the LCST, the PNIPAM chains collapse onto the PAA/P4VP complex layer while the PEG chains still stretch into the solution through the collapsed PNIPAM layer, which leads to the formation of hydrophilic channels around the PEG chains. The ibuprofen encapsulated in the hollow space can diffuse through the channels and its release rate can be controlled by changing the ratio of PEG chains to PNIPAM chains in the corona.
The mixed Langmuir monolayers and Langmuir–Blodgett (LB) films of homo‐polystyrene (h‐PS) and the diblock copolymer polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) have been characterized by the Langmuir monolayer technique and tapping mode atomic force microscopy (AFM), respectively. When the content of h‐PS is below 80 wt.‐%, the mixed LB films of h‐PS/PS‐b‐P2VP mainly exhibit isolated circular nanoaggregates. With a further increase of the h‐PS content (80–95%), however, highly uniform and stable necklace‐network structures are observed in the mixed LB films.
A route has been developed to disperse metal‐containing phthalocyanine dyes in a non‐polar medium based on amphiphilic block copolymer micelles of poly[styrene‐block‐(4‐vinylpyridine)] (PS‐b‐P4VP) and poly[styrene‐block‐(acrylic acid)] (PS‐b‐PAA) copolymers. Polar P4VP and PAA efficiently encapsulate cobalt(II ), manganese(II ), and nickel(II ) phthalocyanine dyes by axial coordination of nitrogen and µ‐oxo bridged dimerization with the transition metals, respectively. Good dispersion of the dyes is confirmed by the linear enhancement of Q‐bands in UV–vis absorption spectra with dye concentration. A thin monolayered PS‐b‐P4VP micelle film that contained a nickel(II ) phthalocyanine dye which efficiently adsorbs a laser beam on a localized area to generate a local heat higher than the glass transition temperatures of both blocks. One‐dimensional laser writing on the dye‐containing film allows the fabrication of a few submicrometer wide line patterns in which the self‐assembled nanostructure of the block copolymer is modified by the directional heat arising from laser scanning.
Layer‐by‐layer (LbL) assembly was conducted on CaCO3 microparticles pre‐doped with polystyrene‐block‐poly(acrylic acid) (PS‐b‐PAA) micelles, and resulted in micelles encapsulation in the microcapsules after core removal. Distribution of the micelles in the templates and capsules was characterized by transmission electron microscopy and confocal laser scanning microscopy. The micelles inside the capsules connected with each other to form a chain and network‐like structure with a higher density near the capsule walls. The hydrophobic PS cores were then able to load small uncharged hydrophobic drugs while the negatively charged PAA corona could induce spontaneous deposition of water‐soluble positively charged drugs such as doxorubicin.
Micelles made from linear polystyrene‐block‐polyisoprene (PS/PI) in decane are spherical. The differences in the structure of micelles made from linear and cyclic PS/PI were investigated using small‐angle X‐ray scattering at rest and under shear flow. The effect of shear revealed that micelles made from cyclic copolymer chains have an elongated shape, which was confirmed by transmission electron microscopy. The cyclization of diblock copolymer chains is thus a new method to control the micellar morphology.
Summary: A simple route to an ordered array of metal/semiconductor oxide composite nanodots is presented. Micellar monolayer films of polystyrene‐block‐poly(2‐vinyl pyridine) (PS‐b‐P2VP) loaded with HAuCl4 in the P2VP nanodomains are used as templates. TiO2 is generated selectively within the polar P2VP domains of PS‐b‐P2VP/HAuCl4 films by chemical vapor deposition of TiCl4. Subsequent removal of the organic matrix by oxygen plasma or UV light leads to an array of Au/TiO2 composite nanoparticles on the substrate surface.
Schematic illustration of the process to fabricate an array of Au/titania composite nanodots. 相似文献
Functionalizing and controlling nanostructures resulting from block copolymer self‐assembly are key factors in defining their application. In this work, a simple but quite general route to achieve both goals simultaneously is discussed. In thin films of polystyrene‐block‐poly(vinyl pyridine) (PS‐b‐PVP) with small concentrations of a gold salt, the salt is found to complex with the PVP block which leads to an orientation of the microdomains normal to the surface after solvent annealing together with functionalization. By increasing the amount of gold salt, on the other hand, micelles are found to form in solutions leading to a range of different morphologies in the thin films.
Summary: A polymeric supramolecule consisting of symmetric polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP), dodecylbenzenesulfonic acid (DBSA), and 3‐pentadecylphenol (PDP) was formed by proton transfer and hydrogen bonding. The surface morphology of a thin film of the polymeric supramolecule has been investigated. The spherical PS microdomains embedded in a P4VP(DBSA)1.0(PDP)1.0 matrix are observed for the as‐cast film because the weight fraction, fcomb, of the P4VP(DBSA)1.0(PDP)1.0 blocks is much higher than that of PS as a result of the non‐covalent interactions of P4VP and DBSA and DBSA and PDP. Upon annealing the PS‐b‐P4VP(1:1)(DBSA)1.0(PDP)1.0 film at high temperatures, the hydrogen bonding between the DBSA and PDP diminishes, which leads to a change of overall morphology from an ordered sphere to a pitted structure.
AFM topographic image of a PS‐b‐P4VP(1:1)(DBSA)1.0(PDP)1.0 thin film. 相似文献
Blends of polystyrene/poly(methyl methacrylate) (PS/PMMA) (30/70) prepared by simple melt mixing form a droplet (PS) in‐matrix (PMMA) morphology. It is found that addition of a carefully designed copolymer PS‐b‐P(S‐ran‐MMA) (SSM) compatibilizer could convert the morphology into a co‐continuous system. Indeed, the continuity of the dispersed PS phase increased with an increase in PS‐b‐P(S‐ran‐MMA) content, and a fully co‐continuous morphology (continuity = 100%) was obtained at 20% SSM fraction with a characteristic size of 100 nm.
DUV interferometric lithography and diblock copolymer self‐organization have successfully been combined to provide a simple and highly collective nanopatterning technique enabling the organization of nanoparticles over several orders of magnitude, from nanometre to millimetre. The nanostructural changes at the surface of the polymer film after thermal annealing have been monitored by AFM and the process parameters optimized for obtaining a long‐range organization of the lamellar domains. In particular, the impact of the annealing conditions and geometric parameters of the substrate patterns have been investigated. The nanopatterns resulting from the lamellar demixion of (PS‐b‐MMA) were used for a controlled deposition of nanoparticles. The affinity of the hydrophobic particles for the PS block was demonstrated, opening new doors towards the preparation of high‐density arrays of nanoparticles with potential applications in data storage.
A chiral polymeric micelle is described, formed from the self‐assembly of TPPS and PEG114‐b‐P(4VP)38 in aqueous media based on their electrostatic interaction. The self‐assembly behavior is studied by DLS, SLS, TEM, UV‐vis absorption spectroscopy, and CD spectroscopy. The experimental results indicate that the resultant hybrid spherical micelles with a hybrid P(4VP)/TPPS core and a PEG shell show chiral signatures. In addition, the chiral micelles have a large dimension and biphasic segregated structure because of the formation of H‐aggregates and J‐aggregates in the micellar core.
Poly(vinyl phenol)‐block‐polystyrene (PVPh‐b‐PS) diblock copolymers are synthesized by sequential anionic polymerization with sec‐butyl lithium as the initiator. The PVPh‐b‐PS diblock copolymer is cast (on a substrate) from several solvent mixtures that contain tetrahydrofuran/toluene ratios of 1:0.1, 1:1, and 1:2. After solvent evaporation the resulting films are characterized by SEM, TEM, and contact angle measurements. A honeycomb structure is fabricated from the vesicle structure at relatively low toluene contents. On the contrary, at relatively higher toluene contents, a micelle structure with porous microspheres is formed, which possesses higher surface roughness and results in film surface superhydrophobicity. The simple method described here that uses common/selective mixed solvents may be easily extended to prepare honeycomb structures and superhydrophobic surfaces simultaneously from a wide variety of block copolymers by carefully controlling the weight composition of the block copolymer and the selective solvent content.
