The University of Tokyo · Materials Science
Professor Hideaki Yokoyama's research lab specializes in the design, synthesis, and characterization of advanced block copolymers for creating nanostructured materials with precise control over morphology and dynamics. The lab focuses on self-assembly phenomena in thin films and bulk materials, particularly the formation of ordered microdomains, nanocellular structures, and surface-segregated architectures using stimuli-responsive or selective solvents such as supercritical CO2. A key emphasis is placed on understanding and manipulating diffusion, phase behavior, and interfacial effects in asymmetric diblock copolymers to enable applications in nanofabrication, templating, and functional surface engineering.
Figures are computed from collected data and may differ slightly.
The structure of asymmetric poly(styrene-b-2-vinylpyridine) (PS-PVP) diblock copolymers allowed to order in a thin film is observed by a combination of secondary ion mass spectrometry and scanning force microscopy. The surface/interface-induced ordering persists over a surprisingly long range (more than 1 μm). The 2-D structure in the layer parallel to a surface is mainly a distorted hexagonal structure similar to that of the (110) plane of a body-centered cubic structure. In contrast to the lon
Uniform nanocellular structures are successfully formed within the spherical nanodomains of CO2-philic fluorinated blocks in Poly[styrene-block-4-(perfluorooctylpropyloxy)styrene] (PS−PFS) and Poly[styrene-block-perfluorooctylethyl methacrylate] (PS−PFMA) monoliths using supercritical (SC) carbon dioxide (CO2). The nanocells have a very small surface area, indicative of the closed cell structure. Temperature of depressurization (Td) is the key to the uniform nanocellular formation in the CO2-phi
The temperature and molecular weight dependence of the self-diffusion coefficient of asymmetric diblock copolymers (polystyrene-b-2-vinylpyridine) (PS−PVP) with a spherical PVP domain structure has been measured by forward recoil spectrometry. The self-diffusion coefficient D is decreased by up to a factor of 10-4 by the existence of the ordered spherical microstructure. The normalized diffusion coefficient D/D0, where D0 is the diffusion coefficient of homopolystyrene with same molecular weight
A novel, facile, and reproducible method of fabricating nanocells in thin films (see Figure) has been developed using a fluorinated block copolymer with a supercritical carbon dioxide (scCO2) soluble block as a template. The nanocells have an average spacing of 34 nm and a number density of 9 × 1010 cm–2. The size of nanocellular structures is readily tunable by changing the saturation pressure of scCO2.
A block copolymer of deuterated polystyrene (dPS) and 2-[2-(2-methoxyethoxy)ethoxy]ethyl methacrylate (PME3MA) spontaneously exposes the PME3MA block, which is soluble in water, to the surface in a vacuum. dPS−PME3MA mixed with polystyrene (PS) segregates to the PS surface and changes the hydrophobic PS surface into hydrophilic surface. Neutron reflectivity, X-ray photoelectron spectroscopy, and dynamic secondary ion mass spectrometry probe the surface segregation of dPS−PME3MA to the surface of
The morphology and self-diffusion in thin films of asymmetric polystyrene-b-2-vinylpyridine (PS−PVP) diblock copolymers were investigated by secondary ion mass spectrometry (SIMS). An oscillatory depth profile of the PVP volume fraction is observed, implying a periodic arrangement of layers of PVP spherical domains organized parallel to the silicon substrate that persisted for films as thick as at least 200 nm (6 layers). The period of the PVP volume fraction oscillation is reasonably close to t
Surface structures of asymmetric poly[styrene-block-4-(perfluorooctylpropyloxy)styrene] block copolymers (PS−PF) with the shorter PF block than the PS block have been investigated using X-ray photoelectron spectroscopy (XPS) and dynamic secondary ion mass spectrometry (SIMS). Fluorooctyl side groups (C8F17) of the block copolymers segregate to the surface due to their low surface energy. Asymmetry of the block remarkably influences the structure of the C8F17 side groups and the backbone of PS−PF
Self-diffusion and tracer diffusion (diffusion in a fixed diblock copolymer matrix) of ABA triblock copolymers of styrene and 2-vinylpyridine (PVP-PS-PVP) have been measured in a spherically ordered domain structure and compared to that of diblock copolymers. In most of the cases, the self-diffusion and tracer diffusion of the triblock copolymer is controlled by a “walking” diffusion mechanism in which one PVP end block is activated at a time, giving rise to an exponential decrease in D/D0 as ex
Small capsules: Nanoscale silica capsules can be synthesized by the oxidation of nanoscale bubbles in the poly(dimethylsiloxane) domains of poly(styrene-b-dimethylsiloxane). These nanobubbles are introduced by a process involving supercritical carbon dioxide. The nanocapsules are opened up after dry etching (see AFM image).
This paper reports the appearance of a unique foam structure and pressure-induced order–order transition (OOT) of semifluorinated block copolymers in supercritical carbon dioxide (scCO2). The morphological transition of block copolymers with the fluorinated block in scCO2 is induced by the increasing apparent volume fraction of the fluorinated domain, which is preferentially swollen with CO2. The poly(styrene-b-perfluorooctylethyl methacrylate) (PS-PFMA) and PS-PFMA/homoPS blend were swollen wit
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