Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 143, Issue 35, Pages 14106-14114Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.1c03647
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Funding
- National Science Foundation through the Materials Research Science and Engineering Center (MRSEC) Program [DMR-1720256, DMR-1844987]
- Australian Research Council [CE140100036]
- National Health and Medical Research Council [APP1157440]
- UC Santa Barbara MRSEC a member of the Materials Research Facilities Network [NSF DMR-1720256]
- National Science Foundation [CNS1725797]
- California NanoSystems Institute
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-76SF00515]
- DOE Office of Biological and Environmental Research
- National Institutes of Health, National Institute of General Medical Sciences [P41GM103393]
- MRSEC at UC Santa Barbara [NSF DMR-1720256]
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The study reveals the presence of pure HCP sphere phase in specific linear block copolymer melts, challenging the conventional belief that pure HCP is difficult to access without complex processing techniques.
The hexagonally close-packed (HCP) sphere phase is predicted to be stable across a narrow region of linear block copolymer phase space, but the small free energy difference separating it from face-centered cubic spheres usually results in phase coexistence. Here, we report the discovery of pure HCP spheres in linear block copolymer melts with A = poly(2,2,2-trifluoroethyl acrylate) (F) and B = poly(2-dodecyl acrylate) (2D) or poly(4-dodecyl acrylate) (4D). In 4DF diblocks and F4DF triblocks, the HCP phase emerges across a substantial range of A-block volume fractions (circa f(A) = 0.25-0.30), and in F4DF, it forms reversibly when subjected to various processing conditions which suggests an equilibrium state. The time scale associated with forming pure HCP upon quenching from a disordered liquid is intermediate to the ordering kinetics of the Frank-Kasper sigma and A15 phases. However, unlike sigma and A15, HCP nucleates directly from a supercooled liquid or soft solid without proceeding through an intermediate quasicrystal. Self-consistent field theory calculations indicate the stability of HCP is intimately tied to small amounts of molar mass dispersity (D); for example, an HCP-forming F4DF sample with f(A) = 0.27 has an experimentally measured D = 1.04. These insights challenge the conventional wisdom that pure HCP is difficult to access in linear block copolymer melts without the use of blending or other complex processing techniques.
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