Creating Aligned Nanopores by Magnetic Field Processing of Block Copolymer/Homopolymer Blends

Highly Ordered Porous Inorganic Structures via Block Copolymer Lithography: An Application of the Versatile and Selective Infiltration of the "Inverse" P2VP-b-PS System

A facile and versatile strategy was developed to produce highly ordered porous metal oxide structures via block copolymer (BCP) lithography. Phase separation of poly(2-vinylpyridine)-b-polystyrene (P2VP-b-PS) was induced by solvent vapor annealing in a nonselective solvent environment to fabricate cylindrical arrays. In this work, we thoroughly analyzed the effects of the film thickness, solvent annealing time, and temperature on the ordering of a P2VP-majority system for the first time, resulting in "inverse" structures. Reflectometry, atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy were used to characterize the formation of the highly ordered BCP morphology and the subsequently produced metal oxide film. At 40 min solvent annealing time, hexagonally close packed structures were produced with cylinder diameters ∼40 nm. Subsequently, the BCP films were infiltrated with different metal cations. Metal ions (Cr, Fe, Ni, and Ga) selectively infiltrated the P2VP domain, while the PS did not retain any detectable amount of metal precursor. This gave rise to a metal oxide porous structure after a UV/ozone (UVO) treatment. The results showed that the metal oxide structures demonstrated high fidelity compared to the BCP template and cylindrical domains presented a similar size to the previous PS structure. Moreover, XPS analyses revealed the complete elimination of the BCP template and confirmed the presence of the metal oxides. These metal oxides were used as hard masks for pattern transfer via dry etching as a further application. Silicon nanopores were fabricated mimicking the BCP template and demonstrated a pore depth of ∼50 nm. Ultimately, this strategy can be applied to create different inorganic nanostructures for a diverse range of applications, for example, solar cells, diodes, and integrated circuits. Furthermore, by optimizing the etching parameters, deeper structures can be obtained via ICP/RIE processes, leading to many potential applications.

Versatile strategies to tailor the glass transition temperatures of bottlebrush polymers

The glass transition temperature (Tg) of bottlebrush polymers can be controlled via side-chain length, blend composition and brush topology. Elucidating interactions between these parameters and their design rules enables accurate targeting of Tg at arbitrary molecular weights.

Ordered Mesoporous Microcapsules from Double Emulsion Confined Block Copolymer Self-Assembly

Polymeric microcapsules with shells containing homogeneous pores with uniform diameter on the nanometer scale are reported. The mesoporous microcapsules are obtained from confined self-assembly of amphiphilic block copolymers with a selective porogen in the shell of water-in-oil-in-water double emulsion drops. The use of double emulsion drops as a liquid template enables the formation of homogeneous capsules of 100s of microns in diameter, with aqueous cores encapsulated in a shell membrane with a tunable thickness of 100s of nanometers to 10s of microns. Microcapsules with shells that exhibit an ordered gyroidal morphology and three-dimensionally connected mesopores are obtained from the triblock terpolymer poly(isoprene)-block-poly(styrene)-block-poly(4-vinylpyridine) coassembled with pentadecylphenol as a porogen. The bicontinuous shell morphology yields nanoporous paths connecting the inside to the outside of the microcapsule after porogen removal; by contrast, one-dimensional hexagonally packed cylindrical pores, obtained from a traditional diblock copolymer system with parallel alignment to the surface, would block transport through the shell. To enable the mesoporous microcapsules to withstand harsh conditions, such as exposure to organic solvents, without rupture of the shell, we develop a cross-linking method of the nanostructured triblock terpolymer shell after its self-assembly. The microcapsules exhibit pH-responsive permeability to polymeric solutes, demonstrating their potential as a filtration medium for actively tunable macromolecular separation and purification. Furthermore, we report a tunable dual-phase separation method to fabricate microcapsules with hierarchically porous shells that exhibit ordered mesoporous membrane walls within sponge-like micron-sized macropores to further control shell permeability.

Towards Macroscopically Anisotropic Functionality: Oriented Metallo-supramolecular Polymeric Materials Induced by Magnetic Fields

Based on the predesigned self-selective complexation, metallo-supramolecular P3HT-b-PEO diblock copolymers with varying block ratios were synthesized, and their oriented polymer films generated during solvent evaporation in a 9 T magnetic field were investigated. An anisotropic, ordered layer structure was achieved using [P3HT₂₀ -Zn-PEO₁₀₇ ] and carefully characterized by polarized optical microscopy (POM), AFM, polarized UV/Vis spectroscopy, and GI-SAXS/WAXS. The PEO-removed [P3HT₂₀ -Zn-PEO₁₀₇ ] film was obtained after decomplexation with TEA-EDTA under mild conditions, and the selective removal of PEO domains was evidenced by UV/Vis and ATR-FTIR spectroscopy. Anisotropic photoconductivity of the magnetically aligned film was evaluated by flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements. The results indicated that the presence of insulating crystalline PEO segments diminished the photoconductivity along the P3HT backbone direction.

High-throughput morphology mapping of self-assembling ternary polymer blends

Multicomponent blending is a convenient yet powerful approach to rationally control the material structure, morphology, and functional properties in solution-deposited films of block copolymers and other self-assembling nanomaterials. However, progress in understanding the structural and morphological dependencies on blend composition is hampered by the time and labor required to synthesize and characterize a large number of discrete samples. Here, we report a new method to systematically explore a wide composition space in ternary blends. Specifically, the blend composition space is divided into gradient segments deposited sequentially on a single wafer by a new gradient electrospray deposition tool, and characterized using high-throughput grazing-incidence small-angle X-ray scattering. This method is applied to the creation of a ternary morphology diagram for a cylinder-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) block copolymer blended with PS and PMMA homopolymers. Using “wet brush” homopolymers of very low molecular weight (∼1 kg mol⁻¹), we identify well-demarcated composition regions comprising highly ordered cylinder, lamellae, and sphere morphologies, as well as a disordered phase at high homopolymer mass fractions. The exquisite granularity afforded by this approach also helps to uncover systematic dependencies among self-assembled morphology, topological grain size, and domain period as functions of homopolymer mass fraction and PS : PMMA ratio. These results highlight the significant advantages afforded by blending low molecular weight homopolymers for block copolymer self-assembly. Meanwhile, the high-throughput, combinatorial approach to investigating nanomaterial blends introduced here dramatically reduces the time required to explore complex process parameter spaces and is a natural complement to recent advances in autonomous X-ray characterization.

Compositionally graded electrospray deposition combined with grazing incidence small angle X-ray scattering forms a high-throughput approach for mapping phase behavior in ternary mixtures as demonstrated here using block copolymer blends.

Oriented thick films of block copolymer made by multiple successive coatings: perforated lamellae versus oriented lamellae

Building 3D ordered nanostructures by copolymer deposition on a substrate implies a full control beyond the thin film regime. We have used here block copolymers (BCPs) forming bulk lamellar phases to form thick, i.e. much thicker than the lamellar period, structured films on a substrate. Films are formed by a simple method of multiple successive coatings. The film structure is controlled using the combined action of surface templating and annealing time. Sections of the thick layers were characterized by scanning electron microscopy (SEM) after etching of one of the BCP moieties. We show that perfect hexagonally perforated films (HPL) with lamellae parallel to the substrate are formed for a wide thickness range up to 300 nm. Grazing incidence small angle X-ray scattering (GISAXS) confirms such an organization by revealing that perforations sit on a hexagonal lattice. A lamellar organization perpendicular to the substrate is shown to take over for thicker films. A scenario consistent with our observations is proposed, where the sequence of phases results from the balance between surface and stretching energy effects.

Kinetic Monitoring of Block Copolymer Self-Assembly Using In Situ Spectroscopic Ellipsometry

Understanding the kinetic pathways of self-assembly in block copolymers (BCPs) has been a long-standing challenge, mostly due to limitations of in situ monitoring techniques. Here, we demonstrate an approach that uses optical birefringence, determined by spectroscopic ellipsometry (SE), as a measure of domain formation in cylinder- and lamellae-forming BCP films. The rapid experimental acquisition time in SE (ca. 1 sec) enables monitoring of the assembly/disassembly kinetics of BCP films during solvent-vapor annealing (SVA). We demonstrate that upon SVA, BCP films form ordered domains that are stable in the swollen state, but disorder upon rapid drying. Surprisingly, the disassembly during drying strongly depends on the duration of solvent exposure in the swollen state, explaining previous observations of loss of order in SVA processes. SE thus allows for decoupling of BCP self-assembly and disordering that occurs during solvent annealing and solvent evaporation, which is difficult to probe using other, slower techniques.