高分子超構造の考え方を変える新理論が登場(New Theory Promises to Reshape How We Think About Polymer Superstructures)

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UMass Amherstの科学者たちは、ダブルジャイロイドネットワークがどのように形成されるかを正確に予測。 Scientists at UMass Amherst can now accurately predict how double-gyroid networks form

2022-05-16 マサチューセッツ大学アマースト校

マサチューセッツ大学アマースト校の高分子科学者はこのほど、「Nature Communications」誌において、分子の集合体であるダブルジャイロイドと呼ばれるナノスケール構造に関する長年の謎を解いたと発表した。この形状は、材料科学者にとって最も望ましい形状の1つであり、幅広い応用が期待されている。しかし、これまで、この形状がどのようにして形成されるのか、予測可能な理解が得られていなかった。

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ブロック共重合体のダブルジャイロイドを安定化させる内側パッキングと弾性非対称性 Medial packing and elastic asymmetry stabilize the double-gyroid in block copolymers

Abhiram Reddy,Michael S. Dimitriyev & Gregory M. Grason
Nature Communications  Published: 12 May 2022
DOI:https://doi.org/10.1038/s41467-022-30343-2

Abstract

Triply-periodic networks are among the most complex and functionally valuable self-assembled morphologies, yet they form in nearly every class of biological and synthetic soft matter building blocks. In contrast to simpler assembly motifs – spheres, cylinders, layers – networks require molecules to occupy variable local environments, confounding attempts to understand their formation. Here, we examine the double-gyroid network phase by using a geometric formulation of the strong stretching theory of block copolymer melts, a prototypical soft self-assembly system. The theory establishes the direct link between molecular packing, assembly thermodynamics and the medial map, a generic measure of the geometric center of complex shapes. We show that “medial packing” is essential for stability of double-gyroid in strongly-segregated melts, reconciling a long-standing contradiction between infinite- and finite-segregation theories. Additionally, we find a previously unrecognized non-monotonic dependence of network stability on the relative entropic elastic stiffness of matrix-forming to tubular-network forming blocks. The composition window of stable double-gyroid widens for both large and small elastic asymmetry, contradicting intuitive notions that packing frustration is localized to the tubular domains. This study demonstrates the utility of optimized medial tessellations for understanding soft-molecular assembly and packing frustration via an approach that is readily generalizable far beyond gyroids in neat block copolymers.

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