Shunichi Kawanishi

Laser induced molecular transfer using ablation of a triazeno-polymer

Abstract We report on the laser induced transfer of molecular dopants between thin polymer films. Pulsed UV laser radiation (355 nm) of moderate intensity, is directed through a transparent polymer film and absorbed by a photolabile triazeno-polymer (TP) doped with pyrene at low concentration. The explosive photodecomposition of TP results in the transfer of intact pyrene molecules to a tightly contacted neat polymer film of either poly(ethyl methacrylate) (PEMA) or poly(butyl methacrylate) (PBMA). Fluorometry of the receiving polymer surface indicated that the pyrene emission intensity grows as the laser pulse number increases but reduces with rising laser fluence. Surface examination suggests that most of the transferred dopant is implanted beneath the receiving polymer surface and the efficiency of this process is enhanced with lowering of its glass transition temperature T g . A mechanism is discussed to explain the current experimental results.

Proton irradiation effects on several organic polymers

Abstract High-energy (8 MeV) proton irradiation effects on the mechanical properties of polymers (about 100 μm thickness) with various constituents and chemical structures were studied by tensile tests and compared with those caused by 2 MeV electrons. In the aliphatic polymers studied (PE, PP, EVA, PVDF, ETFE and nylon 6), there is scarcely any difference in the absorbed dose dependence of the tensile strength and ultimate elongation between proton and electron irradiation. In the aromatic polymers studied (PET, PES, U-PS and U-polymer), however, the decrements in the tensile strength and ultimate elongation against proton dose are less than that in electron irradiation. In this manner, linear energy transfer effects were scarcely observed in the aliphatic polymers but were clearly observed in the aromatic polymers.

Laser implantation of photochromic molecules into polymer films: a new approach towards molecular device fabrication

Laser molecular implantation enables us to dope space-selectively a surface layer of a polymer film with intact organic molecules. Thus it is applicable towards building various kinds of devices utilizing functional organic molecules. This paper presents that photochromic molecules can be implanted in polymer surfaces by using 351 nm or 355 nm nanosecond lasers and the implanted molecules can be switched repetitively by the alternate irradiation of UV and visible lights. As an example of the space selectivity, the fabrication of gratings by laser implantation is demonstrated and evaluated from an application view point.

U.v.-irradiation of thin films of polystyrene derivatives : formation of carboxylic group and crosslinking from 4-trimethylsilylmethyl substituent

Abstract Photoirradiation of thin films of poly(4-trimethylsilylmethylstyrene) (PTMSMS), poly(4-methylstyrene) (P4MS), and polystyrene (PS) at 254 nm with a low-pressure Hg lamp in air made the surfaces hydrophilic through oxygenation. The hydrophilicity estimated from the contact angle with water was in the order of PTMSMS ≈ P4MS > PS. Formation of carboxylic acid group on the surface and crosslinking in the bulk were demonstrated for PTMSMS, whereas the photoirradiation of PS and P4MS was accompanied by degradation of the polymer main chain. The chemical behaviour of the polymers reflected selectivities in the cleavage of the benzylic CSi or CH bond of the 4-substituents toward that of the benzylic CH bond on the main chain.

Mechanical properties of organic composite materials irradiated with 2 MeV electrons

Abstract Four kinds of cloth-filled organic composites (filler: glass or carbon fiber; matrix: epoxy or polyimide resin) were irradiated with 2 MeV electrons at room temperature, and were examined with regard to the mechanical properties. Following irradiation the Youngs (tensile) modulus of these composites remains practically unchanged even after irradiation up to 15000 Mrad. The shear modulus and the ultimate strength, on the other hand, begin to decrease after the absorbed dose reaches about 2000 Mrad for the glass/epoxy composite and about 5000–10000 Mrad for the other composites. This result is ascribed to the decrease in the capacity of load transfer from the matrix to the fiber due to the radiation damage at the interface, and the dose dependence is interpreted and formulated based on the mechanics of composite materials and the target theory used in radiation biology. As to the fracture behavior, the propagation energy increases from the beginning of irradiation. This result is attributed to the radiation-induced decrease in the bonding energy at the interface.

Time-resolved surface scattering imaging of organic liquids under femtosecond KrF laser pulse excitation

Time-resolved surface scattering imaging was performed for liquid benzyl chloride and liquid toluene under femtosecond KrF laser ablation conditions. No scattering image was obtained until 1 ns, while scattering started from 2 ns when the laser fluence exceeded 25 mJ/cm2, and its intensity increased with the passage of time. The higher the laser fluence was, the steeper the increasing slope was. The scattering is due to surface roughness, which is the initial stage of macroscopic morphological changes. Root-mean-square surface roughness was estimated from the scattering intensity by using frosted fused-silica plates as reference samples. The induced surface roughness increases to a few hundred nm in 10 ns.

Laser implantation of dicyanoanthracene in poly(methyl methacrylate) from a 100-nm aperture micropipette

Implantation into poly(methyl methacrylate) films has been achieved using a dicyanoanthracene (DCNA) doped 100-nm aperture micropipette excited with a pulsed laser. The distribution of implanted DCNA was observed on the film surface using a fluorescence microscope. The measured implanted area had a diameter of less than 600 nm demonstrating that organic molecular implantation into the surface of a polymer film with spatial resolution in the submicrometer range is now possible.

Effects of ion irradiation on the mechanical properties of several polymers

Abstract The effects of high-energy ion irradiation (8 MeV protons, 30 MeV He2+, 80 MeV C4+, and N4+) on the tensile properties of polymers were studied under conditions in which ions should pass completely through the specimen and the results were compared with 2 MeV electron irradiation effects. Experiments were carried out on polymers having various constituents and molecular structures, i.e. eight aliphatic polymers and four aromatic polymers. In the aliphatic polymers studied (PE, PP, PVdF, ETFE, EVA, nylon-6, EPDM, and PE-TPE), there was scarcely any difference in the dose dependence of the tensile strength and ultimate elongation between proton and electron irradiation. In aromatic polymers (PET, PES, U-PS, and U-polymer), however, the decrements in the tensile strength and ultimate elongation vs proton dose were less than those for electron irradiation. In heavy-ion irradiation, the radiation damage of PE (an aliphatic polymer) decreased with increase of LET, but no obvious LET effects were observed in PES (an aromatic polymer).

Electron irradiation effects on interlaminar shear strength of glass or carbon cloth reinforced epoxy composites

Interlaminar tensile shear tests are conducted to study the degradation mechanisms of electron irradiated glass or carbon cloth reinforced epoxy laminates. Interlaminar shear strength decreases significantly after the dose exceeds 3000 Mrad for glass/epoxy, but remains constant up to 12 000 Mrad for carbon/epoxy. SEM photos reveal that debonding of glass fibres and epoxy matrix (or degradation of silane coupling agents) plays an important role in the dose-dependent strength reduction of glass/epoxy laminates. The decrease in the interlaminar shear strength corresponds to that in the three-point bending strength. On the other hand, the SEM fracture appearance is almost dose-independent for carbon/epoxy laminates. In addition, some preliminary irradiation tests are conducted at −120° C to observe the effects of irradiation temperatures.

Energy transfer quenching of a fluorescent excited radical cation by counter radical anion: dissipation of radical ions generated by photoinduced electron transfer

Abstract Fluorescence from the excited 1,3,5-trimethoxybenzene radical cation (TMB⋅+*) coexsisting with 1,4-dicyanonaphthalene radical anion (DCN⋅−) in acetonitrile was studied by the two-step two-laser excitation technique. The fluorescence intensity observed as a function of the delay time of the excitation pulse relative to generation pulse for TMB⋅+ indicated the quenching by DCN⋅− at ⩽220 ns. From the analysis of the fluorescence behavior by the Forster-type energy transfer theory, the distance between TMB⋅+* and DCN⋅− during their dissipation after the initial photoinduced electron transfer was estimated as a function of time.