In-plane and out-of-plane defectivity in thin films of lamellar block copolymers

Journal Article · Thu Oct 29 00:00:00 EDT 2015 · Journal of Polymer Science. Part B, Polymer Physics

DOI:https://doi.org/10.1002/polb.23937· OSTI ID:1339952

Mahadevapuram, Nikhila ^[1]; Mitra, Indranil ^[1]; Bozhchenko, Alona ^[1]; Strzalka, Joseph ^[2]; Stein, Gila E.  ^[1]

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1. Univ. of Houston, Houston, TX (United States)
2. Argonne National Lab. (ANL), Argonne, IL (United States)

We investigate the ordering of poly(styrene-b-methyl methacrylate) (PS-PMMA) lamellar copolymers (periodicity L₀ = 46 nm) confined between a free surface and brushed poly(styrene-r-methyl methacrylate) silicon substrate. The processing temperature was selected to eliminate wetting layers at the top and bottom interfaces, producing approximately neutral boundaries that stabilize perpendicular domain orientations. The PS-PMMA film thickness (t = 0.5L₀–2.5L₀) and brush grafting density (Σ = 0.2–0.6 nm^–2) were systematically varied to examine their impacts on in-plane and out-of-plane ordering. Samples were characterized with a combination of high-resolution microscopy, X-ray reflectivity, and grazing-incidence small-angle X-ray scattering. In-plane order at the top of the film (quantified through calculation of orientational correlation lengths) improved with tⁿ, where the exponent n increased from 0.75 to 1 as Σ decreased from 0.6 to 0.2 nm^–2. Out-of-plane defects such as tilted domains were detected in all films, and the distribution of domain tilt angles was nearly independent of t and Σ. These studies demonstrate that defectivity in perpendicular lamellar phases is three-dimensional, comprised of in-plane topological defects and out-of-plane domain tilt, with little or no correlation between these two types of disorder. As a result, strong interactions between the block copolymer and underlying substrate may trap both kinds of thermally generated defects.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC02-06CH11357
• OSTI ID: 1339952
• Journal Information: Journal of Polymer Science. Part B, Polymer Physics, Vol. 54, Issue 2; ISSN 0887-6266
• Publisher: Wiley
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
block copolymers
defectivity
directed self-assembly
grazing-incidence small angle X-ray scattering
thin films