Sessile organisms cause serious fouling problems on artificial submerged surfaces all around the world. Tributyltin (TBT)-based antifouling paints have been widely used and show high antifouling performance against sessile organisms. However, TBT was banned from use in ship paints globally in 2008 by IMO because of its considerable endocrine disrupting effects in marine organisms. This has created a demand for ecofriendly antifouling materials. Recently, the antifouling properties of specific chemical and physical surface properties have attracted attention for the development of green antifouling technologies. Therefore, we focused on the relationship between surface chemical composition and antifouling activity against the settlement of sessile organisms. In this study, we prepared chemically crosslinked PVA thin films and investigated the antifouling activities against sessile organisms in both laboratory and field conditions. Our results highlight the inhibitory activity of hydroxyl functional groups in PVA against larval settlements with no toxicity detected in laboratory tests. Furthermore, the chemically crosslinked PVA coatings were demonstrated to display easy release activity against settled barnacles in the sea.

In recent years, methods for evaluating various dirt such as air and water have been developed. Techniques have been developed for measuring orbital deviation by image measurement. In this method, the trajectory distortion is measured by measuring the coordinates of the center of gravity of the circle with a digital camera. However, due to repeated train running, the surface of the recursive target for measurement becomes black due to dirt, and the position of the center of gravity of the circle cannot be accurately measured on the image. When the target becomes black, the position of the center of gravity of the circle cannot be accurately measured on the image, so cleaning is required about twice a month. Dirt due to the deposits is an important issue, and a technique for protecting the surface of the target from dirt is desired. By evaluating the contamination of the target numerically, it is possible to more efficiently develop a better arrangement position and an antifouling technology. The developed dirt evaluation device digitizes the degree of dirt using a photo sensor and numerically evaluates the degree of dirt. This paper describes the principle, measurement method, and actual evaluation results of the developed contamination evaluation device.

Techniques have been developed for measuring orbital deviation by image measurement. In this method, the trajectory distortion is measured by measuring the coordinates of the center of gravity of the circle with a digital camera. However, due to the repeated train running, the surface of the recursive target for measurement becomes black due to dirt, and the position of the center of gravity of the circle cannot be accurately measured on the image. When the target becomes black, the center of gravity of the circle cannot be accurately measured on the image, so currently it needs to be cleaned about twice a month. Dirt due to the deposits is an important issue, and a technique for protecting the surface of the target from dirt is desired. In this study, we evaluated the surface effect of hydrophilic, water-repellent and metamaterial sheets on water and muddy water. Prevention is possible due to the oil repellency and dustproof effect, which leads to a reduction in maintenance work. In the near future, it aims to develop an oil-repellent and dust-proof metamaterial sheet for maintenance-free technology.

Measuring residual stress is important for evaluating the long-term quality of assembled products that feature ultraviolet (UV) curable resin as an adhesive. In this study, the residual stress of UV-curable adhesive was evaluated by measuring the normal force acting on UV-cured resin filled between two plates, using a photo-rheometer. The normal force was generated rapidly when the UV curable resin was exposed to UV light. The change in the normal force then became more gradual. Increasing the UV intensity and thickness increased the normal force. The onset time of normal force generation became faster for thinner initial thicknesses and high UV intensity. There were positive correlations between the curing speed and UV intensity, as well as between the residual normal force and gap.

Sports mouthguards (MGs) can reduce the risks of sports-related oral injuries. The aim of this study was to fabricate a composite photopolymer with shock-absorbing properties suitable for use in 3D-printed MGs. By using a commercial, flexible, rubber-like photopolymer as matrix and a commercial rigid simulated polypropylene photopolymer as a reinforcement material, five composites with different Shore A hardness levels were fabricated. Furthermore, four laminated materials were prepared to assess the improvement effects associated with adding a rigid outer layer. The five composites and four laminated materials were evaluated in terms of their shock absorbing capabilities via a steel ball drop impact test along with two types of conventional mouthguard materials. The rubber-like photopolymer composite material compounded with the rigid photopolymer with a Shore A hardness of 50 showed excellent shock absorbing capabilities that were compatible with conventional mouthguard materials, suggesting that this shock absorbing photopolymer composite is a candidate material for 3D-printed sports MGs. If the commercial flexible rubber-like photopolymer is to be applied alone without reinforcement, laminating a rigid photopolymer on the outer surface may be an effective means of improving the shock absorption capabilities of such a MG. We succeeded in fabricating a prototype of a double-layered mouthguard with these composite materials using a 3D digital dental workflow.

A positive-type photosensitive polyimide (PSPI) based on a chain extendable poly(amic acid) (PAA), a thermally degradable cross-linker 1,3,5-tris[(2-vinyloxy)ethoxy]benzene (TVEB), a photoacid generator (PAG) (5-propylsulfonyloxyimino-5H-thiophene-2-ylidene)-(2-methylphenyl)acetonitrile, a chain extender diphenyl isophthalate (DPI) and a thermal base generator (TBG) t-butyl 2,6-dimethylpiperidine-carboxylate has been developed. The PAA prepared from 3,3’,4,4’-biphenyltetracarboxylic dianhydride and 4,4'-oxydianiline was end-capped with di-tert-butyl dicarbonate, and undergoes a chain extending reaction during a curing stage to constitute a linear structure. This advancing PSPI exhibited high resolution of 3 μm, good mechanical properties, low residue content of cross-linker, low imidization temperature (250 ℃) catalyzed by TBG, preventing corrosion of Cu circuits due to neutralization of photogenerated acids with bases from TBG and the extended pot-life by using the chain extender with high hydrolytic stability, inducing a wide-ranging applicability.

The defect states have a prominent role in electrical performance of organic materials including polymers. Stretching flexible organic solar cells introduces new defects that reduce their efficiency notably. We have studied the changes of density and distribution of these defects versus strain in a roll-to-roll printed organic solar cell with P3HT:PCBM active layer. The junction capacitance spectroscopy, including C(V) and C(f) measurements, was employed as a novel and convenient method in solar cells under strain to characterize the density of states distribution over the band gap. C(V) measurements yielded flat-band potential and the total shallow defects density and C(f) spectroscopy resulted in distribution profiles. In both measurements, the junction capacitance increased with strain due to additional states contribution. The results show spreading of the distribution profile over more energy levels and more than 30% increase in total traps density for 50 mε mechanical strain.

A rheological study of visible-light sensitive reworkable photocuring resins was carried out using reworkable monomers. A dimethacrylate monomer containing tertiary ester units in a molecule and a methacrylate monomer, which has both an epoxy moiety and a thermally-cleavable tertiary ester moiety in a molecule, were employed as the reworkable monomers. The reworkable monomers were successfully cured by green light irradiation (530-nm light) using a visible-light sensitive photoradical initiator. When the cured reworkable resins were baked after UV light irradiation (365-nm light) in the presence of a photoacid generator, the storage moduli of the cured resin decreased at elevated temperatures. The decreased storage moduli revealed by rheological studies were due to the acid-catalyzed decomposition of the tertiary ester linkages in the cured reworkable monomers. The effect of the chemical structure on the rheological properties was discussed.

In the case of polymer sustained vertical alignment (PSVA) and polyimide-less (PI-less) alignment technologies, polymer-alignment layers are formed by exposure of ultraviolet (UV) light to a liquid crystal (LC) layer including a LC composition and a reactive monomer. We were able to develop a high reliable fluorinated diluter for the LC composition toward the PSVA and the PI-less technologies. In addition, we also developed the PSVA and the PI-less in-plane switching mode LC cells with both fast response speed and high voltage holding ratio by combining the reactive monomer carrying a polarized UV absorption unit, chalcone.