There is a significant need for new strategies in semiconductor manufacturing that can go beyond current structural limits. Block copolymers, which can self-assemble into various nanostructures, offer a unique advantage in these processes. In the directed self-assembly of block copolymers, a lamella-forming block copolymer can be processed on chemically patterned surfaces, where each pattern preferentially wets one of the polymer blocks. During thermal annealing, if the surface energies of the blocks are balanced, the block copolymer spontaneously self-assembles into precise nanodomains. These domains align with the underlying chemical patterns, enabling highly controlled and scalable nanomanufacturing with reduced roughness.
One of the goals of directed self-assembly is to design block copolymers with the highest possible interaction parameter (χ), to enable the formation of smaller structures. However, increasing χ also increases the difference in surface energies, making self-assembly more difficult under practical processing conditions. Recently, it has been shown that it is possible to decouple the thermodynamic properties from the surface properties by using A-b-(B-r-C) architectures. In these systems, if the surface energy of the A block is intermediate between the components of the copolymer block, the overall surface energy can be tuned by changing the composition of the copolymer block, while still maintaining a sufficiently high χ between the blocks.
In this research, we aim to incorporate nature’s precision into self-assembling A-b-(B-r-C) architectures to create A-b-(B-sq-C) structures, where the A block is a synthetic polymer, and the sequenced block is made of a biomaterial called peptoids. Peptoids are regioisomers of peptides, where the side chains are located on the terminal amine instead of the alpha-carbon. Peptoids are chosen as candidate biomimetic materials due to three main properties. First, they can be synthesized with protein-like precision, allowing the production of block copolymers without dispersity. Second, their vast chemical diversity provides an extensive design library to explore. Third, the precise positioning of each monomer in the peptoid chain enables a new design space for tuning the properties of the block copolymer—not by changing chemical identity or composition, but by organizing each repeat unit with atomic-level precision.
For the design of sequence-specific block copolymers, we employed a co-design approach that integrates computational tools, such as coarse-grained and all-atom simulations, to guide targeted synthesis and high-throughput experimentation. Using coarse-grained simulations, we mapped over 300 different sequences and observed how characteristics such as chemical identity, composition, block length, number, and position affect the interfacial properties of the system.
We found that the chemical identity of the copolymers and their sequence design work synergistically to influence interfacial behavior. The primary mechanism of sequence-specific property tuning appears to be the preferential enrichment of the interface with the more “favorable” component. Moreover, we observed that more “blocky” chains deviate from models derived for random copolymer chains, indicating the need for a new sequence-dependent effective interaction parameter, χ effective.
We synthesized peptoids composed of N-(Methoxyethyl)Glycine and N-(n-Butyl)Glycine with various compositions, sequences, and chain lengths ranging from 6 to 36 repeat units. These were prepared using automated peptide synthesizers via solid-phase submonomer synthesis. Surface energy measurements revealed that several synthetic block candidates exhibited intermediate polarity—one of the key requirements for achieving a high-χ, equal-γ block copolymer design. Additionally, atomic force microscopy measurements of the contact angle between the peptoid and different synthetic polymers demonstrated that interfacial tension is dependent on peptoid composition and the choice of synthetic polymer.
Through this work, we have gained insights into how the sequence-specific properties of peptoids influence interfacial characteristics, which are critical for the design of A-b-(B-sq-C) block copolymer architectures. The extremely low dispersity and precise sequence control of peptoid-based A-b-(B-sq-C) polymers will be vital for the nanomanufacturing of 8 nm process nodes and beyond.