Kazushi Yamada

AFM observation of silk fibroin on mica substrates: morphologies reflecting the secondary structures

Bombyx mori silk fibroin was fixed on mica substrates by cast of aqueous fibroin solutions, and the microscopic morphologies of the samples were revealed by means of atomic force microscopy. By adjusting the method used to prepare the solution, we succeeded in forming quasi-2-dimensional thin films in which a network of fibroin molecules developed over the substrate. The film network consisted of fibroin in a random coil structure. The morphology of the network changed after thermal or methanol treatments, which are known to convert the secondary structure of fibroin from the random coil to the β-sheet type. In both of these cases, the network morphology disappeared and characteristic island-like morphologies appeared. On the other hand, temporally evolving gelation occurred in a fibroin solution due to the formation of β-sheet crystals. Such islands were also observable in a specimen prepared by the cast of the gel-containing solution. Based on these results, it was concluded that the islands consist of β-sheet crystals. Of particular interest is the observation that all of the islands had a common thickness value of 1.3 nm. These morphologies are discussed in terms of the secondary structure of fibroin.

Laser Ablation of Silk Protein (Fibroin) Films

Fibroin is the main protein component of silk and is expected to have functional applications in bioelectronics and medicine. We investigated nanosecond (ns) pulsed laser ablation of solid fibroin films with/without a dye as a photosensitizer. Laser lights at 248 nm and 532/355/351 nm excited the peptide bond of fibroin and the dye, respectively. The neat film irradiated at 248 nm was scarcely accessible to etching and swelling, and instead, a microscopic pattern (structure) was formed. In contrast, for ablation of the doped film at 532/355/351 nm, we found marked swelling (height ~500 µm) and deep etching (depth ~10 µm) on the irradiated surfaces. The dye-photosensitized ablation was brought about by a photothermal mechanism, whereas ablation of neat films may be induced by another process, such as a photochemical one. The ablation processes are discussed in terms of the properties of fibroin and the mode of excitation.

Nanohole Processing of Polymer Films Based on the Laser-Induced Superheating of Au Nanoparticles

We present a novel laser processing technique that enables us to form nanoholes (d < 100 nm) on a polymer film. The important feature of the present technique is the utilization of a hybrid target, which contains an organic polymer and metal nanoparticles. The Au nanoparticles were fixed to a glass substrate (avoiding aggregation of the nanoparticles) by a technique involving a self-assembled monolayer of 3-aminopropyltrimethoxysilane. The film was coated with a thin film of poly(methyl acrylate) and then irradiated with a nanosecond 532 nm pulsed laser light. The light excited the resonant plasmon absorption band of the Au nanoparticles. Subsequently, the particles underwent explosive vaporization via a superheated state, resulting in the formation of nanoholes within the film. The relevant aspects of the nanohole formation process and the mechanism underlying the process are presented.

Advanced Copper/Polyimide Hybrid Technology

In the past, a unique hybrid IC processing approach which combines wet-metallized copper, air-fired (ruthenium-based) RuO 2 paste, and photoactive polyimide, was presented by the authors [1], Now, a further improved and advanced new copper/polyimide hybrid technology Mitsubishi Copper Polyimide Hybrid (MCPH) has been developed. The new MCPH was processed using a large (106 x 106 mm) Al 2 O 3 substrate, full copper system (all layers) with 50-µm fine lines. For the first layer, the full-additive process was adopted, while for the other layers, a semiadditive process was employed. The photoactlve polyimide interlayer insulation is screen printed, and after the exposure and development steps, is cured using a conveyor belt furnace. This new process has many excellent features, such as uniform coating thickness, better mass-production capability, etc. The MCPH fundamental processes were evaluated and established using an MCPH Test Element Group (TEG). This TEG has fine lines, small diameter vias and/or pads, matrix lines, etc. To compare characteristics, the same circuit as a conventional hybrid IC was fabricated by applying the MCPH technology. As a result, this functional MCPH (MCPH ES) is a compact size (less than 1/2 the circuit area), has excellent electrical parameters, and high reliability. This MCPH ES uses a flip-chip IC (2.9 mmx 3.4 mm) with 30 small solder bumps (100 µm, min. 170-µm pitch). Important MCPH process factors and/or reliability factors were fully evaluated by using the TEG and functional ES. Through various tests (thermal cycle, voltage loaded, humidity, pressure cooker, break-down or leak, etc.), the MCPH shows excellent reliability characteristics. Consequently, a unique MCPH has been developed using a simple, reliable, cost-effective and excellent massproduction multilayer-hybrid process.

Compression and injection molding techniques for natural fiber composites

Abstract: The forming of a natural fiber composite part, particularly when it involves intricate geometries, is often one of most difficult challenges faced by manufacturers. The intrinsic properties of natural fibers, such as the hygroscopicity and heat sensitivity, further complicate this process. This chapter outlines the challenges faced during compression and injection molding, which are two of the most frequently used techniques for forming natural fiber composites. Several emerging technologies – such as micro-braiding, long fiber pellet and textile insert molding – that are tailored for natural fiber composite forming will be introduced. A strategy to enhance the thermal resistance of natural fibers so that they can be incorporated into high temperature engineering thermoplastics is also discussed.

Position-Selective Arrangement of Nanosized Polymer Microsphere on Diblock Copolymer Film with Sea-Island Microphase Structure

A fluorescent polystyrene microsphere with a diameter of 20 nm whose surface is modified with carboxylic acid groups was arranged selectively on one component of a diblock copolymer film of polystyrene and poly(4-vinylpyridine) (P4VP). Atomic force microscopy (AFM) observations showed that the microsphere was adsorbed only to the island part corresponding to the P4VP phase of the microphase structure of the film due to hydrogen bonding between the carboxylic acid groups of the microsphere and the pyridyl groups of P4VP. When the diameter of the microsphere was 50 nm, the microsphere was rarely adsorbed to the block copolymer film.

Heat seal processing by using various seal bar shape

In this study, oriented polypropylene/cast polypropylene (OPP/CPP) laminated films were heat sealed by various stainless mesh sheets in order to evaluating the effect of heat sealing bar shape on heat sealed properties. The heat sealed conditions were set at heat sealed time of 1.0 s with a pressure of 0.3 MPa at various heat sealed temperatures of 100 to 120 °C. The difference of higher order structure of these films was discussed on the basis of results of micro-Raman spectroscopy, DSC and peel test. From the result, it was found that peel strength was affected by the heat sealing bar surface shape. It can be note that the relationship between the internal structure change and properties of the heat sealed films could be clarified by analyzed at very small area of the heat sealed films on the basis of the results by using micro-Raman spectroscopy imaging.

Effect of surface treatment of cellulose fiber (CF) on durability of PLA/CF bio-composites

Bio-composites made of polylactic acid (PLA) matrix reinforced with cellulose fibers (CF) were prepared using a twin-screw extruder and injection molding. The CFs were coated with epoxy-based surface treatment agents. Accelerated degradation tests were carried out on these PLA/CF composites at high temperatures (60 °C) or at constant temperature and constant humidity (60 °C/70% RH), and the higher-order structure changes and degradation characteristics of the molded products were evaluated. In the accelerated degradation test at 60 °C, the thermal and mechanical properties of PLA/CF composites showed no degradation, whereas at 60 °C and 70% RH, the melting point decreased ca. 25 °C and the storage modulus with increasing elapsed time decreased more than 50%. However, the thermal and mechanical properties of the PLA/CF composites treated with low-molecular-weight epoxy did not degrade, even at the high humidity of 70% RH. These results strongly suggest that the surface treatment agent not only improves interfacial adhesion between CF and PLA but also plays an important role in inhibiting degradation of the PLA matrix.