Self-Assembly of Hierarchical High-χ Fluorinated Block Copolymers with an Orthogonal Smectic-within-Lamellae 3 nm Sub-Lattice and Vertical Surface Orientation

Published

April 16, 2024

Author(s)

Bijal Patel, Hongbo Feng, Whitney Loo, Chad R. Snyder, Christopher Eom, Julia Murphy, Daniel Sunday, Paul Nealey, Dean DeLongchamp

Abstract

Hierarchical structure-within-structure assemblies offer a route toward increasingly complex and multifunctional materials while pushing the limits of block copolymer self-assembly. We present a detailed study of the self-assembly of a series of fluorinated high-χ block copolymers (BCPs) prepared via postmodification of a single poly(styrene)-block-poly(glycidyl methacrylate) (S-b-G) parent polymer with the fluorinated alkylthiol pendent groups containing 1, 6, or 8 fluorinated carbons (termed trifluoro-ethanethiol (TFET), perfluoro-octylthiol (PFOT), and perfluoro-decylthiol (PFDT), respectively). Bulk X-ray scattering of thermally annealed samples demonstrates hierarchical molecular assembly with phase separation between the two blocks and within the fluorinated block. The degree of ordering within the fluorinated block is highly sensitive to synthetic variation; a lamellar sublattice was formed for S-b-GPFOT and S-b-GPFDT. Thermal analyses of S-b-GPFOT reveal that the fluorinated block exhibits liquid crystal-like ordering. The complex thin-film self-assembly behavior of an S-b-GPFOT polymer was investigated using real-space (atomic force microscopy and scanning electron microscopy) and reciprocal-space (resonant soft X-ray scattering (RSoXS), grazing incidence small- and wide-angle scattering) measurements. After thermal annealing in nitrogen or vacuum, films thicker than 1.5 times the primary lattice spacing exhibit a 90-degree grain boundary, exposing a thin layer of vertical lamellae at the free interface, while exhibiting horizontal lamellae on the preferential (polystyrene brush) substrate. RSoXS measurements reveal the near-perfect orthogonality between the primary and sublattice orientations, demonstrating hierarchical patterning at the nanoscale.

Citation

ACS Nano

Volume

18

Issue

17

Pub Type

Journals

Download Paper

https://doi.org/10.1021/acsnano.4c00664

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Keywords

block copolymer, thin film, hierarchical self-assembly, high-chi, resonant soft X-ray scattering

Citation

Patel, B. , Feng, H. , Loo, W. , Snyder, C. , Eom, C. , Murphy, J. , Sunday, D. , Nealey, P. and DeLongchamp, D. (2024), Self-Assembly of Hierarchical High-χ Fluorinated Block Copolymers with an Orthogonal Smectic-within-Lamellae 3 nm Sub-Lattice and Vertical Surface Orientation, ACS Nano, [online], https://doi.org/10.1021/acsnano.4c00664, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=956219 (Accessed May 29, 2024)