Research in Interests
- Introduction
- Soft nanomaterials with electronic, photonic, magnetic, and catalytic functionalities
- Polymer nanomaterials with metal, semiconductor, oxide nanoparticles
- Block copolymers and their micelles with magnetic and catalytic nanoparticles
- Hierarchical materials of nanostructures in microstructures
- Biomimetic materials
- Thin films of self-assembling materials for device applications
- Self-assembled polymeric nanotemplates for ultrahigh density arrays
- Nanopatterning with thin films of block copolymers
- Directed self-assembly of nanoparticles on nanostructured templates
- Nanolithography with self-assembled monolayers
- Thin films of block copolymers
- Introduction
- Orientation of block copolymers on self-assembled monolayers
- Synthesis of nanopatterned inorganic materials
- Integration with top-down lithography for directed self-assembly
- Block copolymer micelles
- Introduction
- Array of nanoparticles
- Hierarchical array of nanoparticles
- Graphene nanopatterning
- Supracolloidal chain of diblock copolymer micelles
Our research involves developing novel electronic, photonic, magnetic, and catalytic materials based on soft materials including polymers, colloids, and liquid crystals. We particularly interest in utilizing self-assembling nature and nanostructures of soft materials to make them suitable for device applications.
For example, diblock copolymers spontaneously form nanometer-sized micelles in a selective solvent for one of the blocks. These micelles can be coated on solid substrates to form a self-assembled nanostructure, which can serve as a nanostructured template to direct the synthesis of an ultrahigh density array of magnetic nanoparticles.
We also emphasize thin films of soft materials because functional materials should be in the form of thin films in most device applications. We investigate fabrication strategies of controlled and directed nanostructures by adjusting interfaces and surface of thin films of soft materials, ncluding a biomimetic approach.
The basis of our research is investigation of the relationship between molecular and supramolecular structures and their physical properties. The followings are selected topics in our central interests.
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Block copolymers composed of different covalently bonded polymer chains can spontaneously form a variety of periodic nanometer-sized morphologies such as spherical, cylindrical, and lamellar structures by microphase separation. These nanostructures depend on the molecular weight, the relative volume fraction, and the Flory-Huggins interaction parameter of copolymers. Block copolymers can be spin-coated onto a substrate, followed by thermal or solvent vapor annealing to form nanostructured thin films, which hold a great promise for controlled nanopatterning of diverse materials in large area.
For unconfined films of symmetric diblock copolymers on substrates, the relative interfacial energies between each block and the substrate, and the relative surface energy of each block induce a preferential wetting of one block at an interface. To control interactions between block copolymers and substrates is to employ self-assembled monolayers (SAMs) of alkylsiloxanes on SiO2.
Nanostructures of block copolymers have been intensively used as etching masks and templates, which are created by selectively removing one of the blocks. They were directly utilized as a template for various metal oxide nanostructures produced by the hydrothermal growth and sol-gel procedures, which can be applicable to large area electronic devices and superhydrophobic interfaces.
Self-assembly of block copolymers on a flat substreate normally create fingerprint-like patterns having nanodomains with no long-range order. To fabricate well-aligned nanostructures over a large area, the self-assembly of the block copolymers can be induced in a confined space on the sub-micrometer scale.
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Block copolymers can form nanometer-sized micelles with a soluble corona and an insoluble core in a selective solvent that dissolves only one of the blocks. The size of the copolymer micelles can be determined by the molecular weight of the copolymers and the interactions between the blocks and the solvent. By coating single layer of copolymer micelles on substrates, we can fabricate a hexagonal array of nano-sized micelles in large area which can be applied to prepare nanoarrays of diverse materials.
Block copolymer micelles containing precursors of nanoparticles were coated onto the substrate to form a two-dimensional array of micelles. Then, an array of nanoparticles was fabricated in situ on the substrate by plasma treatment without deteriorating the original arrangement of micelles. Since the plasma treatment removed the copolymers completely, a pure array of nanoparticles was fabricated.
For multiple functionalities with nanoparticles, controlled assembly of several types of nanoparticles on a solid substrate is desirable. A single-layered film consisting of spherical micelles of block copolymers can guide the placement of nanomaterials to generate hierarchical arrangement of nanoarrays.
Block copolymer micelles can be spin-coated onto graphene films to form a single-layered micellar films. Diverse types of arrayed nanoparticles can be synthesized from copolymer micelles on graphene, which can be utilized as an etching mask to transfer their hexagonal pattern onto graphene, a nanotemplate to yield decorating metal nanoparticles, and an etcher to tailor graphene into nanostructured carbon films.
Colloidal nanoparticles such as spherical gold nanoparticles and one-dimensional gold nanorods self-assemble into various superstructures from aggregated clusters to organized superlattices. In particular, directional attraction between nanoparticles with orthogonal repulsion to attraction can produce a chain-like supracolloidal polymer. By controlling the attraction and repulsion of spherical micelles of diblock copolymers composed of a polar block and a non-polar block, hierarchically co-assembled suprachains as well as supracolloidal polymer chains can be generated.
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