Intradomain Textures in Block Copolymers: Multizone Alignment and Biaxiality

TL;DR

This paper reveals that block copolymer morphologies inherently possess complex, multizone segment orientation patterns, including biaxial order aligned with interface curvature, which influence their structure and properties.

Contribution

It uncovers the generic multizone and biaxial segment orientation textures in BCP morphologies using theoretical and simulation methods, advancing understanding of their internal structure.

Findings

Segments align normal and parallel to interfaces in different regions.

Biaxial order correlates with interface curvature in curved morphologies.

These textures are intrinsic and not dependent on specific alignment-promoting factors.

Abstract

Block copolymer (BCP) melt assembly has been the subject of decades of study, with focus largely on self-organized spatial patterns of periodically-ordered segment density. In this study, we demonstrate that underlying these otherwise well-known composition profiles (i.e. ordered lamella, cylinders, spheres and networks) are generic and heterogeneous patterns of segment orientation that couple strongly to morphology, even in the absence of specific factors that promote intra- or inter-chain segment alignment. We employ a combination of self-consistent field theory and coarse-grained simulation methods to measure polar and nematic order parameters of segments in a freely-jointed chain model of diblock melts. We show that BCP morphologies are generically characterized by a {\it multizone} texture, with segments predominantly aligned normal and parallel to inter-domain interfaces in the respective brush and interfacial regions of the microdomain. Further, morphologies with anisotropically-curved interfaces (i.e. cylinders and networks) exhibit biaxial order that is aligned to the principal curvature axes of the interface. Understanding these generic features of intra-domain texture provide new opportunities for manipulating multi-scale structure and functional properties of BCP assembly.