AB-type Block Copolymers Research Articles

Understand the Relative Stability of Single-Gyroid to Double-Gyroid in AB-Type Block Copolymer: Chain Packing and Geometric Analysis

Understand the Relative Stability of Single-Gyroid to Double-Gyroid in AB-Type Block Copolymer: Chain Packing and Geometric Analysis

Stabilizing DG, DD, and DP Bicontinuous Network Phases in Pure AB-Type Block Copolymers beyond Relieving Packing Frustration

Stabilizing DG, DD, and DP Bicontinuous Network Phases in Pure AB-Type Block Copolymers beyond Relieving Packing Frustration

Useful strategy for assuming complex ordered phases possibly formed by ABC-type block copolymers

Block copolymers (BCPs) provide a versatile platform for the formation of various nanostructures. Among them, ABC-type BCPs have great potential to form complex structures, which may have promising applications in nanotechnology. However, the self-assembly behavior of ABC-type BCPs is still not well understood because of its complexity, especially about the formation of complex structures that are difficult to be assumed from AB-type BCPs. In this paper, we propose a useful rule to systematically assume ordered structures possibly formed by ABC-type BCPs. We hypothetically change an AB-type BCP to an ABC-type architecture by replacing the ending portion of each free B block with a C block, to see how the C blocks separate from the ordered structure preformed by the AB-type BCP. We propose that the C domains firstly aggregate at the vertices of the Voronoi cell of the precursory AB-type structures to form spheres, then along the edges to form struts, and finally on the faces to form layers. Accordingly, we have obtained a large number of ABC-type structures, some of which are very complex and have not been reported before. The validity of the assumption rule is testified by using self-consistent field theory to determine the stability of some assumed structures. This rule can serve as a useful guide for the exploration of interesting novel structures in ABC-type BCPs. Published by the American Physical Society 2024

Fabrication of Hierarchical Assemblies through Temperature-Triggered Liquid Crystallization Driven Self-Assembly.

Functional hierarchy is prevalent in biological systems owing to natural evolution. Efforts to replicate these structures in artificial materials have gained traction in materials science. Although artificial hierarchical structures are fabricated at different scales based on site-specific interactions using ABC-type block copolymers (BCPs), the fabrication of such hierarchical structures using AB-type BCPs via a simple and efficient method remains challenging. Herein, a class of amphiphilic BCPs (PDenm -b-PACholn ) is reported comprising dendronized oligoethylene glycol (Den) and cholesterol (AChol) as hydrophilic and hydrophobic moieties, respectively. By employing the collapse of PDenm blocks at a specific temperature, the fabrication of bundled fibers and multilayer vesicles is achieved with an obvious hierarchy. Different from common reversible aggregation-disaggregation processes of thermal-responsive polymers, the ordering of the core-forming block with liquid crystalline (LC) properties provides robustly physical cross-linking, coupled with epitaxial growth and the lateral fusion of LC blocks, guiding the formation of stable hierarchical micellar structures. It is highlighted that the combination of temperature-sensitive properties and LC ordering alignment offers a novel approach for constructing hierarchical structures using AB-type BCPs via an efficient one-step assembly method.

Macromolecular architectural effects on solution self-assembly of amphiphilic AB-type block copolymers

This review discusses the self-assembly of amphiphilic linear and various non-linear polymers such as star and cyclic architectures, highlighting how polymer architecture impacts self-assembly behavior.

Reexamine the emergence and stability of the square cylinder phase in block copolymers.

Recently, a few AB-type multiblock copolymers have been successfully designed to form stable square cylinder phase based on self-consistent field theory (SCFT) calculations. The previous works only identify the stability region of the square phase but not analyzing its stability, which is closely related to the free-energy landscape. In this work, we have reexamined the stability of the square phase in $\mathrm{B_1 A_1 B_2 A_2 B_3}$ linear pentablock and $\mathrm{(B_1AB_2)_5}$ star triblock copolymers by drawing the free-energy landscape with respect to the two dimensions of a rectangular unit cell. Our results demonstrate that the square phase continuously transfers to the rectangular phase as the degree of packing frustration is gradually released. Moreover, the prolate contour lines of the free-energy landscape indicate the weak stability of the square phase in the $\mathrm{B_1 A_1 B_2 A_2 B_3}$ copolymer. In contrast, the stability of the square phase is notably improved in the $\mathrm{(B_1AB_2)_5}$ copolymer due to its enhanced concentration of bridging configurations. Our work sheds light on the understanding of the stability of the square cylinder phase in block copolymers. Accordingly, we propose some possible strategies for further designing new AB-type block copolymer systems to obtain more stable square phase.

Theoretical Study of Phase Behaviors of Symmetric Linear B1A1B2A2B3 Pentablock Copolymer.

The nanostructures that are self-assembled from block copolymer systems have attracted interest. Generally, it is believed that the dominating stable spherical phase is body-centered cubic (BCC) in linear AB-type block copolymer systems. The question of how to obtain spherical phases with other arrangements, such as the face-centered cubic (FCC) phase, has become a very interesting scientific problem. In this work, the phase behaviors of a symmetric linear B1A1B2A2B3 (fA1 = fA2, fB1 = fB3) pentablock copolymer are studied using the self-consistent field theory (SCFT), from which the influence of the relative length of the bridging B2-block on the formation of ordered nanostructures is revealed. By calculating the free energy of the candidate ordered phases, we determine that the stability regime of the BCC phase can be replaced by the FCC phase completely by tuning the length ratio of the middle bridging B2-block, demonstrating the key role of B2-block in stabilizing the spherical packing phase. More interestingly, the unusual phase transitions between the BCC and FCC spherical phases, i.e., BCC → FCC → BCC → FCC → BCC, are observed as the length of the bridging B2-block increases. Even though the topology of the phase diagrams is less affected, the phase windows of the several ordered nanostructures are dramatically changed. Specifically, the changing of the bridging B2-block can significantly adjust the asymmetrical phase regime of the Fddd network phase.

Single Gyroid Self-Assembled by Linear BABAB Pentablock Copolymer.

Although the double-gyroid (DG) structure has been commonly formed from the self-assembly of block copolymers, the single-gyroid (SG) structure is rarely reported. Moreover, the SG structure even shows better performance than DG in some optical applications. How to prepare the SG structure has become an attractive but challenging topic. We speculate that the SG structure can be stabilized by the synergistic effect of released packing frustration and stretched bridging block in AB-type block copolymers. Accordingly, we propose the minimum conditions for the design of architecture that enables the two mechanisms simultaneously. Following these conditions, a simple linear BABAB pentablock copolymer is successfully devised. SCFT calculations confirm that the SG phase can be stabilized by tailoring the architecture. Our work is hopeful to promote relevant experimental studies for engineering the unusual SG structure.

Effect of branching architecture on the self-assembly of symmetric ABC-type block terpolymers

It has been well known that the phase boundaries of AB-type block copolymers can be largely deflected by designing their asymmetric architectures to regulate the stable regions of various ordered phases in a large range. One of the simplest asymmetric architecture is ABn miktoarm star, of which the spherical and cylindrical regions are significantly enlarged by the deflections of the phase boundaries toward large volume fraction of A-block. Accordingly, we design a symmetric ABC-type pentablock terpolymer by branching B-blocks, i.e. connecting one of the B-arms of a pair of miktoarm star copolymers AB2 and CB2 together. This symmetric pentablock terpolymer is composed of two equal A and C blocks tethered on a B-chain. We investigate the self-assembly behaviors of this terpolymer using self-consistent field theory, focusing on the control of the length ratio of the middle B-block to the total B-blocks on the regions of alternating spherical, cylindrical and gyroid phases. It is predicted that the three phase regions are successfully regulated in a large range by the architectural parameter, which are accompanied by a lot of interesting phase behaviors. For instance, an unusual order-order transition from the spherical phase to the gyroid phase with the absence of the cylindrical phase is determined. Our results reveal that these interesting phase behaviors result from three sophisticated effects including the branching effect on the spontaneous curvature, the released packing frustration from different B-blocks and the stretched bridging middle B-block.

Scattering Function and Spinodal Transition of Linear and Nonlinear Block Copolymers Based on a Unified Molecular Model

This work uses a block copolymer architecture [(A′B)nA2]m to unify the scattering function and spinodal transition of typical AB-type block copolymers. The key roles of block number, junction points and asymmetry ratios of block length are (1) to determine the form factor of each block copolymer at the molecular scale; (2) to affect the entropy loss across the spinodal transition and may result in deflection of spinodal curves. The common features are validated in typical linear and nonlinear block copolymers, including AB diblock, asymmetric A′BA triblock, miktoarm stars of ABn, AnBn, (AB)n, (A′B)nA, A′BAm, and multi-graft combs of (BnA2)m and [(A′B)nA2]m. The explicit scattering functions and form factors of various block copolymers can be directly applied in radiation experiments (i.e. neutron or X-ray scattering) to unravel the effect of molecular architecture in solution and microphase separation in disordered melt. The molecular model used in this study is also helpful to guide the chemical synthesis to explore more potentially interesting block copolymers.

Square patterns formed from the directed self-assembly of block copolymers

Incorporation the design of AB-type block copolymers into the strategy of directed self-assembly should provide a promising perspective for the formation of large-scale ordered square patterns..

Largely Tunable Asymmetry of Phase Diagrams of A(AB)n Miktoarm Star Copolymer

Topological asymmetry is an important factor to change the phase diagram of AB-type block copolymer with respect to the volume fraction of A-blocks from symmetric to asymmetric. However, many topol...

Stabilizing Phases of Block Copolymers with Gigantic Spheres via Designed Chain Architectures.

It is generally believed that the spherical domains self-assembled from AB-type block copolymers are composed of the minority A blocks with a volume fraction of fA < 1/2. Breaking this generic rule so that the spherical domains are formed by the majority A blocks (fA > 1/2) requires mechanisms to drastically expand the stable region of spherical packing phases. Self-consistent field theory predicts that dendron-like AB-type block copolymers, composed of G - 1 generations of A blocks connected with the outermost generation of B blocks, exhibit a stable region of spherical packing phases extending to fA ∼ 0.7. The extremely expanded spherical regions shed light on the mechanisms governing the self-assembly of amphiphilic macromolecules, as well as provide opportunities to engineer complex spherical packing phases.

High‐Fidelity, Sub‐5 nm Patterns from High‐χ Block Copolymer Films with Vapor‐Deposited Ultrathin, Cross‐Linked Surface‐Modification Layers

Front Cover: In article 1900514 by Joona Bang, Sung Gap Im, and co-workers, a robust neutralization methodology is developed to neutralize the two interfaces in a block copolymer film via initiated chemical vapor deposition. A highly uniform film of crosslinked AB-type random copolymers, sandwich an AB-type block copolymer film to produce perpendicular sub-5 nm nanodomains.

Lattice self-consistent field calculations of confined symmetric block copolymers of various chain architectures.

The effects of chain architecture and confinement on the structure and orientation of lamellae formed by incompressible and symmetric AB-type block copolymer melts confined between two parallel and identical surfaces are investigated using self-consistent field calculations on a simple cubic lattice. Five systems of various chain architectures (linear, ring, and star) and lengths are studied, with their bulk lamellar period L0 chosen such that they have comparable L0/Rg, where Rg denotes the ideal-chain radius of gyration. For thin films of thickness D = L0 confined between two neutral surfaces, we define the rescaled volume fraction profiles of A, B, chain end, and joint segments in the parallel and perpendicular lamellae such that these profiles can be directly compared among the five systems to quantitatively reveal the interplay between the chain-end enrichment near confining surfaces and the surface-induced A-B compatibilization, and how such interplay is affected by the chain architectures (for example, the chain-crowding effects in the star block copolymers). The effects of D and surface preference for one of the blocks are also investigated.

Light-responsive block copolymers with a spiropyran located at the block junction

Block copolymers with a functional group between their blocks are relatively little explored even though this molecular architecture can reduce the aggregation of the functional groups, promote the phase separation in nanophase-separated materials, and has other interesting effects. Spiropyrans are well-known for their ability to switch to their polar merocyanine form in response to light, force and other stimuli. The synthesis of stimuli-responsive AB-type block copolymers with spiropyran moieties located at the junction of the blocks is presented here. A homopolymer is synthesized from a trimethylindolenine-based atom transfer radical polymerization (ATRP) initiator, followed by its modification to a spiropyran end-functionalized polymer. The spiropyran functionalized polymer is then used as a macro-initiator for the synthesis of a second polymer block by ring opening polymerization (ROP). Alternatively, spiropyran homopolymers are conjugated to other preformed polymers by esterification. The resulting block copolymers reversibly switch under UV and white light irradiation over multiple cycles, and a block copolymer reduced the tendency of the merocyanine to aggregate during switching. The stimuli-responsive block copolymer could be useful for a range of applications, e.g. for bioinspired polymersome nanoreactors, or in membranes with switchable permeability.

Shape control of nanostructured cone-shaped particles by tuning the blend morphology of A-b-B diblock copolymers and C-type copolymers within emulsion droplets

An approach to blend AB-type block copolymers and C-type copolymers within the emulsion droplet is an efficient particle shape-engineering strategy.

Effects of Chain Topology on the Self-Assembly of AB-Type Block Copolymers

The effects of chain topology on the self-assembly of block copolymers are examined using an ABAT block copolymer, composed of an AB diblock copolymer with an extra A block tethered onto the B block, as a model system. The topology of the ABAT block copolymer is regulated by the tethering point, such that the block copolymer changes continuously from linear ABA triblock copolymer to A2B miktoarm star copolymer as the tethering position moves from the B end to the AB junction. The phase diagrams of ABAT copolymers of different tethering positions are constructed using the self-consistent field theory. The theoretical results reveal that the phase behavior of the system depends sensitively on the topology of the ABAT copolymers. In particular, a considerably wide stable region of the perforated lamellar (PL) phase is predicted for ABAT with proper tethering positions. The PL phase could even completely replaces the gyroid phase at relatively strong segregation. Furthermore, a large window of the hexagonally...

Metallic Nanodot Patterns with Unique Symmetries Templated from ABC Triblock Terpolymer Networks.

Nanotemplates derived from the self-assembly of AB-type block copolymers provide an elegant route to achieve well-defined metallic dot arrays, even if the variety of pattern symmetries is restricted due to the limited number of structures offered by microphase separated diblock copolymers. A strategy that relies on the use of complex network structures accessible through the self-assembly of linear ABC-type terpolymers is presented for the formation of metallic nanodots arrays with "outside-the-box" symmetries. Patterned templates formed by the cubic Q214 and orthorhombic O70 network structures are used as excellent platforms to build well-ordered gold nanodot arrays with unique p3m1 and p2 symmetries, respectively. A simple yet efficient blending strategy is used to tune the critical dimensions of the p3m1 pattern while laterally ordered gold nanodot arrays are also demonstrated through a directed self-assembly approach. Such highly ordered gold nanodots with tunable particle dimensions and array periods, enabling the control of their plasmonic responses, are attractive probes for biological imaging.

Nonclassical Spherical Packing Phases Self-Assembled from AB-Type Block Copolymers.

Among the various ordered morphologies self-assembled from block copolymers, the spherical packing phases are particularly interesting because they resemble the familiar atomic crystals. The commonly observed spherical morphology of block copolymers is the body-centered-cubic phase. Recently, a number of novel spherical packing phases, i.e., the complex Frank-Kasper phases originally obtained in metallic alloys, have been observed in block copolymer melts. Theoretical studies have revealed that conformational asymmetry of the different blocks provides a key mechanism to stabilize the Frank-Kasper phases. Furthermore, local segregation of different copolymers in blends of diblock copolymers and copolymer architectures provides additional mechanisms to enhance the stability of the complex ordered phases. In this Viewpoint we summarize recent advances in our understanding of the formation of the nonclassical spherical packing phases in AB-type block copolymers, emphasizing the formation mechanisms of these fascinating complex ordered structures.