Creation of Highly Ordered "Nano-Mille-Feuille" Hard/Soft Nanoparticle Multilayers with Interparticle Cross-Linking by Diacetylene-Containing Chains.

In this study, we attempted to create a precise nanostructure in which hard and soft layers were alternately stacked with a period of 5 nm. Such a periodically stacked structure can be used as a model material to elucidate the origin of the innovative mechanical property improvement proposed for Mg alloy systems. The soft layer was a single layer of nanoparticles made of a ternary copolymer containing a carbazole ring and both hydrocarbon and fluorocarbon chains. The hard layer was a single-particle layer made of magnetite nanoparticles; the surface of these particles was modified with long-chain diynoic acid. The multilayers of each single-particle layer were 54% crystalline and ordered with a D001 crystallite size of approximately 20 nm. The nano-mille-feuille structure, in which the hard and soft layers are repeated in a single-digit nanoperiod, was 56% crystalline and ordered with a D001 crystallite size of approximately 15 nm. Infrared absorption spectroscopy and X-ray photoelectron spectroscopy did not show any loss of both hard and soft layers. Even when the thickness/number of layers was changed variously, no remarkable decrease was observed in the order. Cross-linking between particles by ultraviolet irradiation polymerization was performed for the direct evaluation of the mechanical properties of this structure in the future. Even after topochemical polymerization between the modified chains, the order of the particle stacking structure was maintained.