Daisuke Okai

Abstract Adhesive layers were prepared using photoreactive polymer liquid crystals, and their application as dismantled adhesives based on the change in thermal properties associated with photoisomerization was investigated. Anisotropy in adhesive strength was successfully achieved by controlling the alignment of the liquid crystal using a polyimide alignment film. Furthermore, anisotropy in the adhesive strength due to photoalignment was investigated using the axis-selective photoreactivity of polymer liquid crystals to linearly polarized light.

Type-B serrations were observed during room-temperature tensile deformation of Al-2.17mass%Mg alloy with an average grain size of 12 μm. Digital image correlation was used to visualize Portevin-Le Chatelier (PLC) bands, and microstructural changes in these bands were observed by in-situ X-ray diffraction measurements using synchrotron radiation at SPring-8. The results indicated that the overall density of dislocations, including both mobile and pinned dislocations inside the PLC bands, increased substantially as the bands formed. This suggests that serration occurs due to an increase in the mobile dislocation density resulting from the formation of new dislocations from sources inside the PLC bands.

Al-Zn-Mg alloys with different precipitate sizes were investigated to determine the influence of the precipitate size on the flow stress and dislocation density change during tensile deformation. The dislocation density was measured using in-situ X-ray diffraction at the SPring-8 synchrotron radiation facility with a time resolution of about 2 s. In region II with rapid dislocation multiplication, from under-aging to peak aging, the dislocation density increased with increasing aging time. Under over-aging conditions, the amount of dislocation multiplication in region II decreased with increasing aging time. Even in region III, the increase in dislocation density with plastic deformation was the largest for the peak aging conditions. However, the amount of work hardening was small and the contribution of dislocation hardening to the strength of the material was minimal. For over-aging conditions, the increase in dislocation density in region III was smaller than for the other regions, but the amount of work hardening was relatively large. It is considered that the influence of the dislocation density on work hardening is determined by the effectiveness of precipitates as obstacles to dislocation motion.

The liquid crystalline N-benzylideneaniline (NBA) polymer acts as an adhesive, and its bonded pieces detach upon exposure to UV light due to the trans-cis photoisomerization of the NBA moieties and subsequent phase transition of NBA from a liquid crystal polymer to an isotropic polymer. We improved the photoresponsive durability of the polymer and explored the effect of light irradiation on its thermal properties and adhesion stress. We observed that the transition points of the polymer's thermophysical properties (glass transition, liquid crystal-isotropic transition, G" slope, tan δ) shifted to lower temperatures under light irradiation.