Block Copolymer Nanospheres Research Articles

Templated self-assembly of block copolymers and morphology transformation driven by the Rayleigh instability.

In the current study, we investigate the self-assembly of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) confined in the nanopores of the anodic aluminum oxide (AAO) template and the subsequent morphology transformation induced by the Rayleigh instability. PS-b-P4VP nanotubes and nanorods with various internal nanostructures are fabricated by wetting the AAO template with PS-b-P4VP/chloroform solution, and then followed by solvent evaporation. After the removal of AAO template by potassium hydroxide solution, several different solvents (chloroform, toluene, and N,N-dimethylformamide) with different qualities are used to swell and anneal those nanotubes and nanorods suspended in aqueous media. Morphology transformation from nanostructured PS-b-P4VP nanotubes or nanorods to ordered nanospheres is observed by annealing upon chloroform and toluene while the morphology remains unchanged upon N,N-dimethylformamide annealing, indicating that solvent quality is a key factor in tuning the morphology and internal structures. Kinetics study and theoretical analysis for the morphology transition from two-dimensional (2D) block copolymer (BCP) nanotubes and nanorods to three-dimensional (3D) BCP nanospheres are further performed. From the morphological evolution and the quantitative calculation, it is confirmed that this transition is induced by the Rayleigh instability. This study provides a simple but promising method, that is, solvent annealing method, for the fabrication of BCP nanospheres with ordered internal nanostructures, which may have great application in drug delivery and other nanotechnology.

Controllable assembly of two types of metal nanoparticles onto block copolymer nanospheres with ordered spatial distribution

Pd@PS-P2VP @DT–Au core–shell particles are fabricated based on the modified AAO template method and anin situreduction process, showing efficient optical and catalytic properties.

Hierarchically Built Hetero-superstructure Arrays with Structurally Controlled Material Compositions

Hierarchical assemblies are repeatedly encountered in nature, and when replicated in synthetic patterns and materials, can enhance their functionality or impart multifunctionality. In order to assemble a hierarchical superstructure that consists of components made up of multiple nanostructures, control over placement and stoichiometry is desirable. Macroscopic arrays that present up to three levels of hierarchy are demonstrated here and are achieved using the self-assembly of soft, collapsible block copolymer nanospheres for the first two levels, followed by directed self-assembly of metal nanospheres for the third. The fabrication approach combines advantages of soft sphere self-assembly to yield non-close-packed and variable array pitch values, with the inherent chemical functionality presented by the polymer-based soft spheres; these assemblies can then be transformed into a range of different materials, including metal or semiconductor nanostructures, or further tailored with an additional level of complexity. Structural investigation shows the superstructure formation to be governed by generic design rules that can be extended across different material combinations.

The Influences of Cooperative Swelling and Coordination on Patterned Decoration of Gold on Block Copolymer Nanospheres

Ordered nanoring arrays are a new pattern of block copolymer thin films generated by spin‐coating of block copolymer reverse micelles on silicon substrates, which can further direct the formation of gold nanoring arrays on block copolymer thin films. Here, it is reported that the cooperation of swelling and coordination can influence the surface pattern of the block copolymer nanospheres. A hexagonally arranged dot pattern can be transformed into a ring pattern on polystyrene‐block‐poly(2‐vinylpyridine) nanospheres, and the new pattern can further direct the decoration of gold nanoparticles by balancing the swelling of the poly(2‐vinylpyridine) chains and the coordination effect between gold ions and the pyridine units. image

Uniform Graphene Quantum Dots Patterned from Self-Assembled Silica Nanodots

Graphene dots precisely controlled in size are interesting in nanoelectronics due to their quantum optical and electrical properties. However, most graphene quantum dot (GQD) research so far has been performed based on flake-type graphene reduced from graphene oxides. Consequently, it is extremely difficult to isolate the size effect of GQDs from the measured optical properties. Here, we report the size-controlled fabrication of uniform GQDs using self-assembled block copolymer (BCP) as an etch mask on graphene films grown by chemical vapor deposition (CVD). Electron microscope images show that as-prepared GQDs are composed of mono- or bilayer graphene with diameters of 10 and 20 nm, corresponding to the size of BCP nanospheres. In the measured photoluminescence (PL) spectra, the emission peak of the GQDs on the SiO(2) substrate is shown to be at ∼395 nm. The fabrication of GQDs was supported by the analysis of the Raman spectra and the observation of PL spectra after each fabrication step. Additionally, oxygen content in the GQDs is rationally controlled by additional air plasma treatment, which reveals the effect of oxygen content to the PL property.

Mesoporous Block‐Copolymer Nanospheres Prepared by Selective Swelling

Block-copolymer (BCP) nanospheres with hierarchical inner structure are of great interest and importance due to their possible applications in nanotechnology and biomedical engineering. Mesoporous BCP nanospheres with multilayered inner channels are considered as potential drug-delivery systems and templates for multifunctional nanomaterials. Selective swelling is a facile pore-making strategy for BCP materials. Herein, the selective swelling-induced reconstruction of BCP nanospheres is reported. Two poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) samples with different compositions (PS(23600)-b-P2VP(10400) and PS(27700)-b-P2VP(4300)) are used as model systems. The swelling reconstruction of PS-b-P2VP in ethanol, 1-pyrenebutyric acid (PBA)/ethanol, or HCl/ethanol (pH = 2.61) is characterized by scanning electron microscopy and transmission electron microscopy. It is observed that the length of the swellable block in BCP is a critical factor in determining the behavior and nanostructures of mesoporous BCP nanospheres in selective swelling. Moreover, it is demonstrated that the addition of PBA modifies the swelling structure of PS(23600)-b-P2VP(10400) through the interaction between PBA and P2VP blocks, which results in BCP nanospheres with patterned pores of controllable size. The patterned pores can be reversibly closed by annealing the mesoporous BCP nanospheres in different selective solvents. The controllable and reversible open/closed reconstruction of BCP nanospheres can be used to enclose functional nanoparticles or drugs inside the nanospheres. These mesoporous BCP nanospheres are further decorated with gold nanoparticles by UV photoreduction. The enlarged decoration area in mesoporous BCP nanospheres will enhance their activity and sensitivity as a catalyst and electrochemical sensor.

Fabrication of Polymer Nanospheres Based on Rayleigh Instability in Capillary Channels

We report a simple method to produce block copolymer nanospheres by swelling the short rodlike entities generated from Rayleigh instability of polymer nanotubes within the cylindrical nanopores of an anodic aluminum oxide (AAO) membrane. Poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) nanotubes were first allowed to form inside the cylindrical nanopores through solution-wetting of an AAO membrane followed by solvent evaporation. Upon thermal annealing, undulations in the nanotube wall occurred due to Rayleigh instability and finally led to the formation of nanorods containing regular encapsulated holes. The structures were susceptible to ultrasonication and could be cut into short rodlike blocks with uniform size. These PS-b-P2VP entities were suspended in water with the help of a nonionic surfactant and then swollen by a good solvent for both PS and P2VP. The swollen PS-b-P2VP entities were deformable and spontaneously evolved into nanospheres so as to minimize the interfacial energy. The characterization of...

Preparation and characterization of methoxy poly(ethylene glycol)/poly( ε-caprolactone) amphiphilic block copolymeric nanospheres for tumor-specific folate-mediated targeting of anticancer drugs

Biodegradable methoxy poly(ethylene glycol)/poly( ε-caprolactone) (MPEG/PCL) amphiphilic block copolymer nanospheres coupled to folic acid have been designed to target a folate-binding protein that is overexpressed on the surface of many tumoral cells. For this purpose, hydroxy groups terminated on the MPEG/PCL copolymer were converted into primary amino groups, which were used to conjugate with the carboxylic group of folic acid. Nanospheres were prepared by the formation of micelles of the copolymer with or without the anticancer agent paclitaxel. Folate-mediated MPEG/PCL nanospheres were compared with hydroxyl- and amino-terminated nanospheres in terms of their size, surface characteristics, and drug-loading efficiency. Regardless of the type of terminal group, the MPEG/PCL nanospheres showed a narrow size distribution with an average diameter <80 nm without paclitaxel, and an average diameter of 115 nm when loaded with the drug. The results from zeta potential and X-ray photoelectron spectroscopy measurements revealed that the folate molecules were partially exposed, and were expressed on the surface of the nanospheres allowing folate receptor recognition. In in vitro, cytotoxicity tests, the nanospheres loaded with paclitaxel showed a higher cell viability than in cases where paclitaxel was absent. Thus, folate-mediated nanospheres composed of MPEG and PCL are potentially new drug carriers for tumor cell-selective targeting treatments.

Preparation and characterization of methoxy poly(ethylene glycol)/poly($epsiv;-caprolactone) amphiphilic block copolymeric nanospheres for tumor-specific folate-mediated targeting of anticancer drugs

Biodegradable methoxy poly(ethylene glycol)/poly( ε -caprolactone) (MPEG/PCL) amphiphilic block copolymer nanospheres coupled to folic acid have been designed to target a folate-binding protein that is overexpressed on the surface of many tumoral cells. For this purpose, hydroxy groups terminated on the MPEG/PCL copolymer were converted into primary amino groups, which were used to conjugate with the carboxylic group of folic acid. Nanospheres were prepared by the formation of micelles of the copolymer with or without the anticancer agent paclitaxel. Folate-mediated MPEG/PCL nanospheres were compared with hydroxyl- and amino-terminated nanospheres in terms of their size, surface characteristics, and drug-loading efficiency. Regardless of the type of terminal group, the MPEG/PCL nanospheres showed a narrow size distribution with an average diameter <80 nm without paclitaxel, and an average diameter of 115 nm when loaded with the drug. The results from zeta potential and X-ray photoelectron spectroscopy measurements revealed that the folate molecules were partially exposed, and were expressed on the surface of the nanospheres allowing folate receptor recognition. In in vitro, cytotoxicity tests, the nanospheres loaded with paclitaxel showed a higher cell viability than in cases where paclitaxel was absent. Thus, folate-mediated nanospheres composed of MPEG and PCL are potentially new drug carriers for tumor cell-selective targeting treatments.

Taxol-loaded block copolymer nanospheres composed of methoxy poly(ethylene glycol) and poly( ε-caprolactone) as novel anticancer drug carriers

We prepared the methoxy poly(ethylene glycol) (MePEG)/poly( ε-caprolactone) (PCL) amphiphilic block copolymeric nanospheres containing taxol which has promising anticancer activity. MePEG/PCL block copolymeric nanospheres (MEP50) showed a narrow size distribution and an average diameter of less than 100 nm. When the initial weight ratio of taxol to polymer was 0.5 : 1.0, we could obtain the nanospheres having a relatively high drug-loading of more than about 20%. The size of the MePEG/PCL nanospheres also increased according to the taxol loading. However, the nanospheres did not exhibit a significant change in the size distribution and also showed a size of less than 100 nm for even that with drug-loading content (DLC) of about 20%. From the 1H NMR analysis, we identified that the MePEG/PCL nanospheres prepared by dialysis procedure have core-shell structure consisting of the hydrophilic outer shell of MePEG and the hydrophobic inner core of PCL. We confirmed the low toxicity of MePEG/PCL nanospheres (MEP70) in the acute toxicity study using male ICR mice. In addition, considering the extremely lipophilic characteristics of taxol, this MePEG/PCL, nanosphere system with high taxol loading content and suspended properties in water could be useful for the delivery of taxol.

Preparation and Performance of Pd Particles Encapsulated in Block Copolymer Nanospheres as a Hydrogenation Catalyst

Triblock nanospheres with hydroxylated polyisoprene (PHI) coronas, cross-linked poly(2-cinnamoyloxyethyl methacrylate) shells, and poly(acrylic acid) (PAA) cores were prepared following a method described previously. Equilibrating such nanospheres with a PdCl2 solution in methanol enabled the loading of Pd2+ into the PAA cores of the nanospheres. After the excess PdCl2 in the methanol phase was removed, Pd(II) inside the nanosphere cores was reduced with hydrazine to yield Pd nanoparticles. Such encapsulated Pd particles were dispersed in methanol or water, which solubilized PHI. Like Pd black, the nanosphere-encapsulated Pd nanoparticles catalyzed the hydrogenation of alkenes. The need for the reactant(s) to diffuse into and products to diffuse out of the encapsulating nanospheres expectedly slowed the catalytic reactions. The more interesting aspect had been in our ability to modify the activity of the Pd catalyst via changing the pH and thus the conformation of the encapsulating polymer chains.