Thermal treatments unlock low-symmetry phases resembling those of metals and alloys
Two polymers that are immiscible would separate on a macroscopic scale—like oil and water—to minimize interfacial ...area. However, when the different polymer chains are linked with a covalent bond to form a linear diblock copolymer, the forced interaction drives a self-assembly into periodic domains at the scale of 10 to 100 nm (
1
). The shapes and arrangements of these domains are often very simple, such as spherical micelles in a body-centered cubic (bcc) lattice. One notable exception was the discovery that spherical micelles can assemble into a Frank-Kasper (FK) σ phase (
2
), a complex low-symmetry structure common in metals and alloys. Many other metallurgical FK structures are known, so if similar principles govern lattice selection in these distinct materials classes, then it is possible that many linear diblock copolymer phases remain undiscovered. On page 520 of this issue, Kim
et al.
(
3
) predict that several FK phases have nearly degenerate free energies, and show how clever thermal treatments can control the ordering pathway to access two of these previously undocumented structures.
Bottlebrush polymers have been used as surface-active additives for chemically-identical linear polymers because they spontaneously accumulate at surfaces through an entropy-mediated process. In this ...work, we design functional bottlebrush polymer additives with mixed side-chain chemistries that can deliver unique surface properties. Bottlebrush polymers with poly(dimethylsiloxane) (PDMS) side-chains and bottlebrush copolymers with PDMS and poly(lactic acid) (PLA) side-chains are synthesized using ring opening metathesis polymerization. Contact angle goniometry, X-ray photoelectron spectroscopy (XPS), and microscopy demonstrate a spontaneous accumulation of these additives at the film surface without lateral phase segregation. Bottlebrush polymers were found to enrich the film surface more strongly than linear block copolymers of PDMS-b-PLA, and the surface contact angle was tunable by varying the composition and quantity of added bottlebrush copolymer. Significantly, bottlebrush additives segregate rapidly, during film casting. This work demonstrates that low-surface energy bottlebrush copolymer additives can be used to introduce new surface properties in polymer films.
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•We prepare bottlebrush polymers with multiple side-chain functionalities.•Functional bottlebrush additives accumulate at film interfaces.•Small amounts of additive produce large changes in surface wettability.•Bottlebrushes segregate rapidly during casting.•Surface-active bottlebrushes represent a versatile approach to tailor thin films.
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