Naoya Torikai

Friction behavior of high-density poly(2-methacryloyloxyethyl phosphorylcholine) brush in aqueous media

Super-hydrophilic polymer brushes were prepared by surface-initiated atom transfer radical polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) on initiator-immobilized silicon wafers. The graft density was estimated to be 0.22 chains nm based on the linear relationship between and the layer thickness. The contact angle against water was very low, and air bubbles in water hardly attached onto the brush surface, indicating a super-hydrophilic surface. Neutron reflectivity measurements of the poly(MPC) brush showed that the grafting polymer chains extended a fair amount in the vertical direction from the substrate in a good solvent such as water, while they shrunk in a poor solvent. Frictional properties of the poly(MPC) brushes were characterized by sliding a glass ball probe in air and various solvents under a load of 0.49 N at a sliding velocity of 90 mm min. An extremely low friction coefficient of the poly(MPC) brush was observed in humid atmosphere because water molecules adsorbed into the brush layer acted as a lubricant.

The neutron reflectometer (C3-1-2) at the JRR-3M reactor at JAERI

Abstract A neutron reflectometer has been installed at the cold neutron guide tube (C3-1-2) of the JRR-3M reactor at JAERI. Incident neutrons for the reflectometer have a long wavelength of 12.6 A, with a wavelength resolution of 3.2%. The reflectometer has the advantage of a large reflection angle which is appropriate for studies of low- q and off-specular phenomena. The neutron intensity reduction due to the long wavelength is substantially compensated by the relatively coarse beam divergence and wavelength resolution. The reflectometer is mounted in vertical geometry to yield a beam of 3 × 40 mm 2 and is applicable to measurements of mirror systems formed on flat substrates. Applications of the reflectometer to neutron optics and polymer studies are demonstrated and discussed.

Advanced Neutron Reflectometer for Investigation on Dynamic/Static Structures of Soft-Interfaces in J-PARC

A novel neutron reflectometer with horizontal geometry will be established at BL16 in Materials and Life Science Experimental Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC) as a successor of a reflectometer ARISA-II. ARISA-II corresponding to a single neutron beam downward at 2.22 deg has achieved off-specular and time-resolved reflectivity measurements. The novel reflectometer is designed so as to receive two tilted neutron beams (2.22 & 5.71 deg), which gives us an opportunity in investigation on a free liquid surface. The reflectometer can provide a micro-sized beam by slit collimation and obtain a fair reflectivity with small sample area. Also, T0 chopper and neutron focusing mirror are newly introduced. The T0 chopper can suppress the background due to fast neutrons. The focusing mirror produces further reduction of measurement time not only for specular reflection by focusing neutrons on a sample, but also grazing incidence small-angle neutron scattering (GISANS) measurements by focusing on a detector.

Studies on the interfaces of microphase-separated structures of block copolymers by neutron reflectivity

Abstract Segment distributions in lamellar microphase-separated structures of three partially deuterium-labeled poly(styrene-b2-vinylpyridine)s were investigated by neutron reflectivity measurement. By fitting the calculated reflectivity profiles to the experimental one, it was clarified that the lamellar microdomains preferentially oriented parallel to the film surface and that the thickness of the lamellar interface was about 35 A. Also, it was found that the segments in the vicinity of the chemical junction points between two blocks were localized strongly near the lamellar interface, while the segments on the free ends were localized at the center of the lamellar microdomains with fairly wide distribution.

Development of Spectroelectrochemical Cells for in situ Neutron Reflectometry

A new spectroelectrochemical cell for in situ neutron reflectometry was developed. Electrochemical reactions were determined using this in situ cell with a LiMn2O4/SrRuO3 multi layer thin film. Changes in interfacial structures on the surface of the thin film are also observed by in situ neutron reflectivity measurements. The performances of this in situ cell were expected the determination of changes on the interface between the electrodes and electrolytes.

Precise Design of Surface Nano-texture and Surface Chemistry of Polymeric Solids

Surface properties of polymeric materials were controlled by fabrication of nano-structure and submicronorder structure of poly(fluoroalkyl acrylate) using the chemical and physical surface modification techniques. The relationship between the ordered structure of fluoroalkyl (R f) groups and water repellency mechanism was precisely investigated by grazing-incidence X-ray diffraction, water contact angle measurements and X-ray photoelectron spectroscopy. It was revealed that poly{2-(perfluorooctyl)ethyl acrylate} (PFA-C8) was crystallized and formed ordered structure to result in high water repellency. Surface nano-texturing onto PFA-C8 film surface was carried out using an anodic aluminum oxide (AAO) membrane as a mold. The nano-texture of AAO mold with a pore diameter of 200 nm was transformed onto the PFA-C8 film surface to fabricate nano-structure, which revealed high water and oil repellency. On the other hand, various types of monomers were grafted on the solid surface through surface-initiated atom transfer radical polymerization to result in high-density polymer brushes. Hydrophobic PFA-C8brush surface revealed a low friction coefficient and a good wear resistance. Water lubrication and low friction were observed on the hydrophilic polymer brush. These polymer brushes were successfully introduced on the commercial fluoropolymer, which has inherent radical initiator functional groups. These results indicated that nano-layer immobilization through surface-initiated polymerization and surface texturing are promising methods to control the surface chemistry and surface structure at dimensions in the nano-meter range.

Profile measurement of a bent neutron mirror using an ultrahigh precision non-contact measurement system with an auto focus laser probe

A bent neutron mirror has been considered as one of the best solutions for focusing neutron beams from the viewpoint of cost-benefit performance. Although the form deviation of the bent profile is expected because of the large spot size, it is difficult to measure due to its geometric limitation. Here, we propose a non-contact measurement system using an auto focus (AF) laser probe on an ultrahigh precision machine tool to precisely evaluate the form deviation of the bent mirror. The AF laser probe is composed of a diode laser, a position sensitive sensor, a charge-coupled device (CCD) camera and a microscope objective lens which is actuated by an electromagnetic motor with 1 nm resolution for position sensing and control. The sensor enables a non-contact profile measurement of a high precision surface without any surface damage in contrast with contact-type ultrahigh precision coordinate measurement machines with ruby styli. In the on-machine measurement system, a personal computer simultaneously acquires a displacement signal from the AF laser probe and 3-axis positional coordinates of the ultrahigh machine tool branched between the linear laser scales and the numerical controller. The acquisition rate of the 4-axis positional data in 1 nm resolution is more than 10 Hz and the simultaneity between the axes is negligible. The profile of a neutron bent mirror was measured from a transparent side using the developed system, and the result proves that the form deviation of the mirror enlarged the the spot size of focused neuron beam.

Depth distribution of different solvents in a phase-separated block copolymer thin film

The structural change induced by the contact with different solvents was investigated for a diblock copolymer thin film, of polystyrene (PS) and poly(2-vinylpyridine) (P2VP), forming a lamellar structure by in-situ neutron reflectometry with a conventional cell for the measurement on solid/liquid interfaces. In the case of methanol, which is a selective solvent for P2VP, the structural change was induced by the penetration of methanol into the film, and the original lamellar structure was almost recovered by drying the film even after the solvent contact. On the other hand, when toluene was used as a selective solvent for PS, the block copolymer thin film was easily dissolved into toluene, and its original state was never recovered after the solvent contact. Further, water induced the structural change in the block copolymer thin film similarly to methanol, though it is a poor solvent common for PS and P2VP.

Development of a Physically Bent Cylindroid Mirror for Beam Focusing for a Pulsed Neutron Reflectometer

To gain in intensity and realize a grazing-incidence small-angle scattering (GISAS) measurement on a pulsed neutron reflectometer, we are now developing focusing devices using a cylindrically bent supermirror coated on a flat float glass substrate. They have been characterized at pulsed neutron sources, and we successfully focused neutron beam into about 1mm width in either vertical or horizontal direction using the bent mirror with the focal distance of about 4 m.

In-Situ Reflectometry Observation on Structural Changes of Thin Self-Assembled Block Copolymer Films

The structural changes induced by solvent contact or heating were observed for thin spin-coated polystyrene-block-poly(2-vinylpyridine) diblock copolymer (PS-P2VP) films using in-situ neutron reflectivity and grazing-incidence small-angle X-ray scattering (GISAXS) techniques. The lamellarly-ordered PS-P2VP film showed some structural changes in contact with water though it is a poor solvent for both the component polymers, while the original structure was recovered after drying the film. When toluene was used as a selectively good solvent for PS, the thin film was dissolved into the solvent. On the other hand, the thin as-prepared PS-P2VP film with spherical microdomains exhibited laterally a pair of scattering spots symmetrical relative to the specular reflection ridge in the GISAXS pattern, indicating the existence of some lateral structural correlation in the film. On a temperature jump up to 200 °C, these two scattering spots started to disappear around the glass transition temperature, and then almost completely vanished at 200 °C unexpectedly though the PS-P2VP used here should be kept in the strong-segregation state. The spherical structure could be completely disordered or kept ordered but with lateral distortion in its orientation. Being cooled down to a room temperature again, the two scattering spots were recovered, and became more intense with their position shifting slightly to lower QY-region than before heating due to the improvement in ordering.