ABSTRACT:Heat is transported by phonons through dielectric solids such as ceramics and organic insulating resins. Especially in organic insulating resins, phonons scatter intensely mainly by their amorphous structure, which affects their thermal conductivities, usually 1 to 3 orders lower than those of ceramics and metals. Here, we show that by the thermosetting resin system with a crystal-like structure that is microscopic anisotropy, the thermal conductivities of the resin themselves can be improved while keeping their macroscopic isotropy. We studied four kinds of diepoxy monomers with a biphenyl group or two phenyl benzoate groups as mesogens, and cured them thermally with an aromatic diamine curing agent. These thermal conductivities were maximally 5 times higher than that of conventional epoxy resins because mesogens were highly ordered to form crystal-like structures to suppress phonon scattering. We also succeeded in the direct confirmation of the existence of crystal-like structures in the epoxy resins by TEM observation. These results suggest a novel strategy to improve thermal conductivities of insulating resins themselves by controlling the high-order structures.

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A new interfacial-gel copolymerization technique is proposed to prepare steric gradient-index (GRIN) optical waveguides and lens arrays. Since the GRIN profile is obtained from the thin-gel phase formed on the wall of a polymer substrate, many geometrical GRIN materials, such as axial-, radial-, and spherical-GRIN, can be monolithically fabricated. In this paper the principle of GRIN formation is clarified, and a few steric radial -GRIN circuit components are demonstrated.