Grain coarsening on the free surface and in the thickness direction of a sphere-forming triblock copolymer film. Issue 11 (November 2018)

• Record Type: Journal Article
• Authors: Bayomi, Rasha; Honda, Konomi; Wataoka, Isao; Takagi, Hideaki; Shimizu, Nobutaka; Igarashi, Noriyuki; Sasaki, Sono; Sakurai, Shinichi
• Is Part Of: Polymer journal. Volume 50:Issue 11(2018:Nov.)
• Page Start: 1029
• Page End: 1042
• Publication Date: 2018-11
• Subjects: Polymers -- Periodicals; 547.7
• DOI: 10.1038/s41428-018-0094-y
• Languages: English
• ISSNs: 0032-3896

Abstract

Abstract Controlling a block copolymer "grain", in which the microdomains are regularly ordered in a single lattice, is important for developing high-performance polymeric materials. This is because the grains, which are several micrometers in size, can directly affect the properties of the materials. In this regard, we focused on grain coarsening on the free surface and in the thickness direction of a sphere-forming triblock copolymer film. We evaluated the grain size on the free surface using atomic force microscopy combined with image processing, and in the thickness direction, we used small-angle X-ray scattering edge-view measurements. It was found that the grain growth in the direction parallel to the free surface was very slow in the early stage of thermal annealing. Then, the grain growth shifted to a rapid growth mechanism with a power-law relationship (grain size ~t α, withα = 0.7) after ~30 min. Based on the value of the growth exponentα, the grain growth mechanism is considered to fall between the random and deterministic processes. In contrast, for the thickness direction, a much larger value (α = 1.72) was obtained. For such a largeα value, it is impossible to consider the growth mechanism of the grain within the conventional to framework of the growth of domains and droplets. Therefore, our results may require a new framework to explain the behavior of the grain growth in the spherical microdomain system. Another notable finding is that the thickness of the oriented layer near the free surface or near the surface in contact with the substrate can be as thick as 9.5 µm, which is substantially larger than the reported values of the propagation distance of surface-induced orientation of microdomains in block copolymers. Based on the results of the current study, it is speculated that grain growth serves as a propagator for the regular ordering of spherical microdomains and the orientation of the lattice. The grain size was quantitatively evaluated on the free surface, and in the thickness direction. The grain growth on the free surface was very slow in the early stage of thermal annealing, then it shifted to a rapid mode with a power law (~t 0.7 ). While in the thickness direction, the growth followed a power law oft 1.72 until 1180 min, then it shifted to a slow mode witht 0.21 . Furthermore, the oriented layer near the free surface was found to be as thick as 9.5 µm, indicating that grain growth serves as a propagator for the regular ordering of spherical microdomains and orientation of the bcc lattice.