Controlling the Orientation of Block Copolymer Thin Films using Thermally-Stable Gold Nanoparticles with Tuned Surface Chemistry

The Effect of Colloidal Nanoparticles on Phase Separation of Block and Heteroarm Star Copolymers Confined between Polymer Brushes

The effect of colloidal nanoparticles on the phase changes of the amphiphilic AB linear diblock, A1A2B, and A2B heteroarm star copolymers confined between two polymer brush substrates was investigated by using a real-space self-consistent field theory. By changing the concentrations of nanoparticles and polymer brushes, the phase structure of the amphiphilic AB copolymer transforms from lamellar to core-shell hexagonal phase to cylinder phase. The pattern of A2B heteroarm star copolymer changes from core-shell hexagonal phases to lamellar phases and the layer decreases when increasing the density of the polymer brushes. The results showed that the phase behavior of the system is strongly influenced by the polymer brush architecture and the colloidal nanoparticle numbers. The colloidal nanoparticles and the soft confined surface of polymer brushes make amphiphilic AB copolymers easier to form ordered structures. The dispersion of the nanoparticles was also investigated in detail. The soft surfaces of polymer brushes and the conformation of the block copolymers work together to force the nanoparticles to disperse evenly. It will give helpful guidance for making some new functional materials by nano etching technology, nano photoresist, and nanoprinting.

Hybrid Time-Dependent Ginzburg–Landau Simulations of Block Copolymer Nanocomposites: Nanoparticle Anisotropy

Block copolymer melts are perfect candidates to template the position of colloidal nanoparticles in the nanoscale, on top of their well-known suitability for lithography applications. This is due to their ability to self-assemble into periodic ordered structures, in which nanoparticles can segregate depending on the polymer–particle interactions, size and shape. The resulting coassembled structure can be highly ordered as a combination of both the polymeric and colloidal properties. The time-dependent Ginzburg–Landau model for the block copolymer was combined with Brownian dynamics for nanoparticles, resulting in an efficient mesoscopic model to study the complex behaviour of block copolymer nanocomposites. This review covers recent developments of the time-dependent Ginzburg–Landau/Brownian dynamics scheme. This includes efforts to parallelise the numerical scheme and applications of the model. The validity of the model is studied by comparing simulation and experimental results for isotropic nanoparticles. Extensions to simulate nonspherical and inhomogeneous nanoparticles are discussed and simulation results are discussed. The time-dependent Ginzburg–Landau/Brownian dynamics scheme is shown to be a flexible method which can account for the relatively large system sizes required to study block copolymer nanocomposite systems, while being easily extensible to simulate nonspherical nanoparticles.

From macromonomers to bottlebrush copolymers with sequence control: synthesis, properties, and applications

Bottlebrush polymers (BBPs) are a type of comb-like macromolecules with densely grafted polymeric sidechains attached to the polymer backbones, and many intriguing properties and applications have been demonstrated due to...

Asymmetric Incorporation of Silver Nanoparticles in Polymeric Assemblies by Coassembly of Tadpole-Like Nanoparticles and Amphiphilic Block Copolymers

A general approach to asymmetrically localize nanoparticles (NPs) in larger polymeric nanostructures is demonstrated by coassembly of tadpole-like silver NPs (AgNPs) and amphiphilic block copolymers (BCPs). The tadpole-like AgNPs are prepared by template synthesis using a tailor-made A(BC)₂₀ star polymer, namely poly(ethylene glycol)[poly(acrylic acid)-block-polystyrene]₂₀ [PEG(PAA-b-PS)₂₀ ], as template resulting in AgNPs decorated with twenty short PS chains and one long PEG chain, named Ag@PEG(PS)₂₀ . The asymmetric distribution of these AgNPs in various polymeric nanostructures, e.g., spherical micelles, cylindrical micelles, vesicles, and sponge phase, is achieved via coassembly of the as-prepared Ag@PEG(PS)₂₀ and PEG-b-PS in solution driven by the anisotropic nature of the Ag@PEG(PS)₂₀ . This report not only provides a new strategy for the fabrication of tadpole-like NPs but also offers opportunity for off-center distributing NPs in hybrid assemblies, which may find applications in, e.g., sensing, catalysis, and diagnostics.

Bottlebrush Copolymer as Surface Neutralizer for Vertical Alignment of Block Copolymer Nanodomains in Thin Films

Herein we designed bottlebrush copolymers for use as a neutral additive to block copolymer (BCP) thin films in which they are segregated to the interfaces via architectural effects and produce nonpreferential interfaces to induce perpendicular orientation of BCP microdomains. Two BCP systems were employed, a conventional poly(styrene-b-methyl methacrylate) (PS-b-PMMA) with relatively low χ and similar surface energies between blocks, and a high χ poly(styrene-b-methacrylic acid) (PS-b-PMAA) with distinct surface energies. The bottlebrushes, with either short side-chains of PS-r-PMMA or PS-r-PMAA random copolymers, were synthesized via ring-opening metathesis polymerization (ROMP). Remarkably, it was observed that the top and bottom interfaces of both BCP films were enriched with bottlebrush copolymers, regardless of the surface energy difference between blocks, hence, vertically oriented microdomains were achieved for both BCP systems. This can be attributed to the screening of polymer interactions by a good solvent during the spin-casting process, allowing architectural effects to play a role in surface segregation of bottlebrush copolymers, as confirmed by contact angle measurements and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). We believe that this concept can be further extended to various applications that require polymer films with functional surfaces.

Ligand-Assisted Direct Photolithography of Perovskite Nanocrystals Encapsulated with Multifunctional Polymer Ligands for Stable, Full-Colored, High-Resolution Displays

Micropatterns with a high stability, definition, and resolution are an absolute requirement in advanced display technology. Herein, patternable perovskite nanocrystals (PNCs) with excellent stability were prepared by exchanging pristine ligands with multifunctional polymer ligands, poly(2-cinnamoyloxyethyl methacrylate). The polymer backbone contains a cinnamoyl group that has been widely employed as a photo-cross-linker under 365 nm UV irradiation. Also, the terminal group is readily adjustable among NH₃Cl, NH₃Br, and NH₃I, allowing us to obtain multicolored PNCs via instant anion exchange. Furthermore, the resulting ligand exchanged PNCs exhibited enhanced stability toward polar solvents without any undesirable influence on the structural or optical properties of the PNCs. Using anion exchanged PNCs, RGB microarrays with a subpixel size of 10 μm × 40 μm were successfully demonstrated. Our results highlight the versatility and feasibility of a simplified patterning strategy for nanomaterials, which can be generally applied in the fabrication of various optoelectronic devices.

High-Fidelity, Sub-5 nm Patterns from High-χ Block Copolymer Films with Vapor-Deposited Ultrathin, Cross-Linked Surface-Modification Layers

Despite their capability, sub-10 nm periodic nano-patterns formed by strongly segregating block copolymer (BCP) thin films cannot be easily oriented perpendicular to the substrate due to the huge surface energy differences of the constituent blocks. To produce perpendicular nano-patterns, the interfacial energies of both the substrate and free interfaces should be controlled precisely to induce non-preferential wetting. Unfortunately, high-performance surface modification layers are challenging to design, and different kinds of surface modification methods must be devised respectively for each neutral layer and top coat. Furthermore, conventional approaches, largely based on spin-coating processes, are highly prone to defect formation and may readily cause dewetting at sub-10 nm thickness. To date, these obstacles have hampered the development of high-fidelity, sub-5 nm BCP patterns. Herein, an all-vapor phase deposition approach initiated chemical vapor deposition is demonstrated to form 9-nm-thick, uniform neutral bottom layer and top coat with exquisite control of composition and thickness. These layers are employed in BCP films to produce perpendicular cylinders with a diameter of ≈4 nm that propagate throughout a BCP thickness of up to ≈60 nm, corresponding to five natural domain spacings of the BCP. Such a robust approach will serve as an advancement for the reliable generation of sub-10 nm nano-patterns.

Well-Ordered Inorganic Nanoparticle Arrays Directed by Block Copolymer Nanosheets

Precise control over the spatial arrangement of inorganic nanoparticles on a large scale is desirable for the design of functional nanomaterials, sensing, and optical/electronic devices. Although great progress has been recently made in controlling the organization of nanoparticles, there still remains a grand challenge to arrange nanoparticles into highly-ordered arrays over multiple length scales. Here, we report the directed arrangement of inorganic nanoparticles into arrayed structures with long-range order, up to tens of microns, by using hexagonally-packed cylindrical patterns of block copolymer nanosheets self-assembled within collapsed emulsion droplets as scaffolds. This technique can be used to generate nanoparticle arrays with various nanoparticle arrangements, including hexagonal honeycomb structures, periodic nanoring structures, and their combinations. This finding provides an effective route to fabricate diverse nanoparticle arrayed structures for the design of functional materials and devices.

Spatial control of the topography of photo-sensitive block copolymer thin films

Spatially controlling self-assembly of block copolymer thin films through photoinduced molecular interactions that significantly impact on the glass transition temperature.

Thermal Approaches to Perpendicular Block Copolymer Microdomains in Thin Films: A Review and Appraisal

Block copolymer thin films are highly versatile and accessible materials capable of producing nanofeatures in the size regime of a few to hundreds of nanometers by a simple spin-coating-and-anneal process. Unfortunately, this simple protocol usually leads to parallel microdomains, which limits the applicability of such nanofeatures. A great deal of effort has been put into achieving perpendicular microdomains, but those that incorporate thermal annealing are arguably the most practical and reproducible in the lab and industry. This review discusses the recent ongoing efforts on various thermal approaches to achieving perpendicular microdomains in order to provide the readers with a toolbox to work with.

Monte Carlo Study of Degenerate Behavior of AB Diblock Copolymer/Nanoparticle under Cylindrical Confinement

Degenerate behavior (i.e., forming different self-assembled structures for a given block copolymer (BCP) under the same confinement) commonly exists in various confined systems. Understanding degenerate behavior is crucial for precise control over the structures formed by self-assembly systems under confinement. In this study, the degenerate behavior of a self-assembled AB diblock copolymer/nanoparticle (NP) mixture in a cylindrical pore is studied using Monte Carlo simulation. We find that the degenerate behavior of such a mixture depends on the introduction of the NP. Under different pore sizes, four typical degenerate structures [i.e., single helices (S-helices), double helices (D-helices), parallel cylinders, and stacked toroids] can be obtained if the NP content is zero. However, when the NP content in the mixture is increased, it is found that the number of degenerate structures decreases, that is, only blocky structures can be obtained in the case of high NP content. Moreover, the probability of forming S-helices decreases, whereas the probability of forming D-helices increases with increase in the NP content. Analysis of the interactive enthalpy densities and the chain conformation of the systems indicates that entropy plays an important role in the degenerate structure formation. This study provides some new insights into the degenerate behavior of a BCP/NP mixture under confinement, which can offer a theoretical reference for further experiments.

Spin-Casting Polymer Brush Films for Stimuli-Responsive and Anti-Fouling Surfaces

Surfaces modified with amphiphilic polymers can dynamically alter their physicochemical properties in response to changes of their environmental conditions; meanwhile, amphiphilic polymer coatings with molecular hydrophilic and hydrophobic patches, which can mitigate biofouling effectively, are being actively explored as advanced coatings for antifouling materials. Herein, a series of well-defined amphiphilic asymmetric polymer brushes containing hetero side chains, hydrophobic polystyrene (PS) and hydrophilic poly(ethylene glycol) (PEG), was employed to prepare uniform thin films by spin-casting. The properties of these films were investigated by water contact angle, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and quartz crystal microbalance (QCM). AFM showed smooth surfaces for all films with the roughness less than 2 nm. The changes in water contact angle and C/O ratio (XPS) evidenced the enrichment of PEG or PS chains at film surface after exposed to selective solvents, indicative of stimuli- responsiveness. The adsorption of proteins on PEG functionalized surface was quantified by QCM and the results verified that amphiphilic polymer brush films bearing PEG chains could lower or eliminate protein-material interactions and resist to protein adsorption. Cell adhesion experiments were performed by using HaCaT cells and it was found that polymer brush films possess good antifouling ability.

Fluorescent gold nanoparticles with chain-end grafted RAFT copolymers: influence of the polymer molecular weight and type of chromophore

Fluorescence of gold nanoparticles functionalized with chain-end grafted RAFT copolymers increases with polymer corona thickness.

Perpendicularly Oriented Block Copolymer Thin Films Induced by Neutral Star Copolymer Nanoparticles

By introducing neutral star copolymers consisting of poly(styrene-r-methyl methacrylate) (PS-r-PMMA) arms, a perpendicular orientation of PS-b-PMMA microdomains in thin films could be achieved without any surface treatment. The star copolymers were synthesized by arm-first method in which short chain arms are cross-linked by employing a multifunctional coupling reagent via atom transfer radical polymerization. To find the optimal neutral composition for the perpendicular orientation, we varied the composition of MMA in PS-r-PMMA arms from 40 mol % to 80 mol %. It was found that the star copolymer having an overall PS and PMMA composition of 59:41 exhibits the well-ordered perpendicular orientation of lamellar structures after thermal annealing. Furthermore, we also prepared the deuterated star copolymers to trace them within PS-b-PMMA films along vertical direction by neutron reflectivity. In this case, it was observed that star copolymers were mainly located at the top surface and bottom interface of the films, thereby effectively neutralizing the surface/interfacial energy differences.

Understanding the microstructure of particle dispersion in confined copolymer nanocomposites

Innovation: confinement enhances the dispersion of particles with weak attraction in copolymers, while the effect can be reversed as the attraction increases.

Directed self-assembly of block copolymers: a tutorial review of strategies for enabling nanotechnology with soft matter

Self-assembly of soft materials is broadly considered an attractive means of generating nanoscale structures and patterns over large areas. However, the spontaneous formation of equilibrium nanostructures in response to temperature and concentration changes, for example, must be guided to yield the long-range order and orientation required for utility in a given scenario. In this review we examine directed self-assembly (DSA) of block copolymers (BCPs) as canonical examples of nanostructured soft matter systems which are additionally compelling for creating functional materials and devices. We survey well established and newly emerging DSA methods from a tutorial perspective. Special emphasis is given to exploring underlying physical phenomena, identifying prototypical BCPs that are compatible with different DSA techniques, describing experimental methods and highlighting the attractive functional properties of block copolymers overall. Finally we offer a brief perspective on some unresolved issues and future opportunities in this field.

Selective confinement of oleylamine capped Au nanoparticles in self-assembled PS-b-PEO diblock copolymer templates

Amphiphilic polystyrene-block-polyethylene oxide (PS-b-PEO) block copolymers (BCPs) have been demonstrated to be effective in directing organization of colloidal Au nanoparticles (NPs). Au NPs have been incorporated into the polymer and the different chemical affinity between the NP surface and the two blocks of the BCP has been used as a driving force of the assembling procedure. The morphology of the nanocomposites, prepared and fabricated as thin films, has been investigated by means of atomic force and scanning electron microscopies as a function of the NP content and BCP molecular weight. NPs have been effectively dispersed in PS-b-PEO hosts at any investigated content (up to 17 wt%) and a clear effect of the BCP properties on the final nanocomposite morphology has been highlighted. Finally, electrostatic force microscopy has demonstrated the conductive properties of the nanocomposite films, showing that the embedded Au NPs effectively convey their conductive properties to the film. The overall investigation has confirmed the selective confinement of the as-prepared surfactant-coated metal NPs in the PS block of PS-b-PEO, thus proposing a very simple and prompt assembling tool for nanopatterning, potentially suitable for optoelectronic, sensing and catalysis applications.

Effect of CdSe nanoparticle addition on nanostructuring of PS-b-P4VP copolymer via solvent vapor exposure

The surface morphology of poly(styrene-b-4 vinyl pyridine) (PS-b-P4VP) diblock copolymer thin films after solvent vapor annealing has been studied. Morphological features can be switched upon exposure to vapors of a solvent selective for one of the blocks. Self-assembled nanostructures such as hexagonal or striped morphologies were obtained varying vapor exposure time. In addition, the effect of the presence of CdSe nanoparticles located in the P4VP block on obtained nanostructures was analyzed. Atomic force microscopy (AFM) was used for morphological characterization of the block copolymer and the nanocomposites. AFM images showed that nanostructuring was different depending on the amount of CdSe nanoparticles, due to the decrease in P4VP chain mobility.

High thermal stability of block copolymer-capped Au and Cu nanoparticles

Pyridine-containing block copolymers (PS-P4VP) can effectively stabilize metal nanoparticles which survive prolonged heating in solutions at high temperatures.

Nanoporous bicontinuous structures via addition of thermally-stable amphiphilic nanoparticles within block copolymer templates

Herein, we fabricated the bicontinuous structures from nanocomposites of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) block copolymer and the shell-cross-linked, thermally stable gold nanoparticles (Au NPs). The surface property of Au NPs was controlled with ligands containing various compositions of PS and PMMA so that the resulting Au NPs were selective to PS or PMMA block or nonselective (i.e., neutral) to both blocks. The amphiphilic Au NPs were also prepared by coating the surface of Au NPs with equimolar mixtures of PS and PMMA selective ligands. Consequently, it was found that the morphological behaviors of thermally annealed nanocomposites containing amphiphilic Au NPs and PS-b-PMMA were dramatically different from the case of neutral Au NPs that were coated with nonselective ligands. With increasing the amount of amphiphilic Au NPs, a transition from lamellar to bicontinuous structures was observed, whereas the neutral Au NPs were aggregated within the PS-b-PMMA lamellae. Furthermore, the nanoporous bicontinuous thin films were fabricated on the silicon substrates and the morphological behaviors were quantitatively investigated by grazing-incidence small-angle X-ray scattering (GISAXS) analysis.

Nanoparticle assemblies in thin films of supramolecular nanocomposites

We demonstrated a versatile approach to obtain layered nanoparticle sheets with in-plane hexagonal order and 3-D ordered arrays of single nanoparticle chains in thin films upon blending nanoparticles with block copolymer (BCP)-based supramolecules. Basic understanding on the thermodynamic and kinetic aspects of the assembly process paved a path to manipulate these assemblies to meet demands in nanoparticle-based device fabrication and understand structure-property correlations.