Nano Explorations: Emergence of layered nanoscale mesh networks through bottom-up confinement self-assembly—Jan. 10

Emergence of layered nanoscale mesh networks through bottom-up confinement self-assembly

Tuesday, January 10, 2023
11 a.m. – 11:45 a.m. ET
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Zehao Sun, PhD candidate
Materials Science & Engineering

Classical block copolymer self-assembly enables access to a range of ordered nanostructure geometries—such as spheres, cylinders, gyroids, and lamellae—that are well-known and useful, but also limited. Nevertheless, there remains a large gap between the simple patterns commonly formed by block copolymers and the patterns required for many nanoscale applications. For example, single and multilayer mesh nanostructures are of particular interest in a range of technologies; their fabrication, however, has been a long-standing challenge. State-of-the-art techniques usually require successive alignment of layers of self-assembled line patterns on topographically patterned substrates. Thus far, a simple, straightforward fabrication process through “bottom-up” macromolecular design rather than “top-down” pre- or post-treatments has not been demonstrated.

The challenge arises from the spontaneous nature of block copolymer self-assembly. Without constraints in any direction in space, unconfined microphase separation tends to give cubic-symmetric networks, such as the most frequently observed gyroids. In this talk, Sun will introduce a bottom-up design of triblock bottlebrush copolymers that addresses this challenge.

Two Janus domains are present in these copolymers: one perpendicular and one parallel to the polymer backbone. The former enforces a lamellar superstructure that intrinsically confines the intra-layer self-assembly of the latter, giving rise to a low-symmetry, mesh-like monoclinic (54°) M15 network substructure with excellent long-range order, as well as a tetragonal (90°) T131 mesh. 3D reconstruction from scanning transmission electron microscope tomography was used to confirm the structures that have not been reported before among soft materials. Those layered mesh networks with a sub-10 nm half-pitch can be produced in large scale on flat silicon substrates through a simple solvent annealing step, without the need for specialized substrates or low-throughput templating techniques such as electron-beam lithography.

In addition, numerical simulations show that the spatial constraints exerted on the polymer backbone drive the emergence of M15, and yield T131 in the strong segregation regime. In summary, this work demonstrates that the intrinsic molecular confinement is a viable path to bottom-up assembly of new geometrical phases of soft matter, extending the capabilities of block copolymer nanofabrication.

Attendees can join and participate in the series via Zoom. 

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