Commensurability effect in diblock copolymer lamellar phase under d-dimensional nanoconfinement

Self-assembly of colloids with competing interactions confined in spheres

At low temperatures, colloidal particles with short-range attractive and long-range repulsive interactions can form various periodic microphases in bulk. In this paper, we investigate the self-assembly behaviour of colloids with competing interactions under spherical confinement by conducting molecular dynamics simulations. We find that the cluster, mixture, cylindrical, perforated lamellar and lamellar structures can be obtained, but the details of the ordered structures are different from those in bulk systems. Interestingly, the system tends to form more perforated structures when confined in smaller spheres. The mechanism behind this phenomenon is driven by the relationship between the energy of the ordered structures and the bending of the confinement wall, which is different from the mechanism in copolymer systems.

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

Despite their capability, sub-10 nm periodic nano-patterns formed by strongly segregating block copolymer (BCP) thin films cannot be easily oriented perpendicular to the substrate due to the huge surface energy differences of the constituent blocks. To produce perpendicular nano-patterns, the interfacial energies of both the substrate and free interfaces should be controlled precisely to induce non-preferential wetting. Unfortunately, high-performance surface modification layers are challenging to design, and different kinds of surface modification methods must be devised respectively for each neutral layer and top coat. Furthermore, conventional approaches, largely based on spin-coating processes, are highly prone to defect formation and may readily cause dewetting at sub-10 nm thickness. To date, these obstacles have hampered the development of high-fidelity, sub-5 nm BCP patterns. Herein, an all-vapor phase deposition approach initiated chemical vapor deposition is demonstrated to form 9-nm-thick, uniform neutral bottom layer and top coat with exquisite control of composition and thickness. These layers are employed in BCP films to produce perpendicular cylinders with a diameter of ≈4 nm that propagate throughout a BCP thickness of up to ≈60 nm, corresponding to five natural domain spacings of the BCP. Such a robust approach will serve as an advancement for the reliable generation of sub-10 nm nano-patterns.

Supramolecular Modification of ABC Triblock Terpolymers in Confinement Assembly

The self-assembly of AB diblock copolymers in three-dimensional (3D) soft confinement of nanoemulsions has recently become an attractive bottom up route to prepare colloids with controlled inner morphologies. In that regard, ABC triblock terpolymers show a more complex morphological behavior and could thus give access to extensive libraries of multicompartment microparticles. However, knowledge about their self-assembly in confinement is very limited thus far. Here, we investigated the confinement assembly of polystyrene-block-poly(4-vinylpyridine)-block-poly(tert-butyl methacrylate) (PS-b-P4VP-b-PT or SVT) triblock terpolymers in nanoemulsion droplets. Depending on the block weight fractions, we found spherical microparticles with concentric lamella⁻sphere (ls) morphology, i.e., PS/PT lamella intercalated with P4VP spheres, or unusual conic microparticles with concentric lamella⁻cylinder (lc) morphology. We further described how these morphologies can be modified through supramolecular additives, such as hydrogen bond (HB) and halogen bond (XB) donors. We bound donors to the 4VP units and analyzed changes in the morphology depending on the binding strength and the length of the alkyl tail. The interaction with the weaker donors resulted in an increase in volume of the P4VP domains, which depends upon the molar fraction of the added donor. For donors with a high tendency of intermolecular packing, a visible change in the morphology was observed. This ultimately caused a shape change in the microparticle. Knowledge about how to control inner morphologies of multicompartment microparticles could lead to novel carbon supports for catalysis, nanoparticles with unprecedented topologies, and potentially, reversible shape changes by light actuation.

Thermal Approaches to Perpendicular Block Copolymer Microdomains in Thin Films: A Review and Appraisal

Block copolymer thin films are highly versatile and accessible materials capable of producing nanofeatures in the size regime of a few to hundreds of nanometers by a simple spin-coating-and-anneal process. Unfortunately, this simple protocol usually leads to parallel microdomains, which limits the applicability of such nanofeatures. A great deal of effort has been put into achieving perpendicular microdomains, but those that incorporate thermal annealing are arguably the most practical and reproducible in the lab and industry. This review discusses the recent ongoing efforts on various thermal approaches to achieving perpendicular microdomains in order to provide the readers with a toolbox to work with.

Semicrystalline Block Copolymers in Rigid Confining Nanopores

We have investigated PLLA crystallization in lamellae-forming PS-b-PLLA confined to straight cylindrical nanopores under weak confinement (nanopore diameter D/equilibrium PS-b-PLLA period L0 ≥ 4.8). Molten PS-b-PLLA predominantly forms concentric lamellae along the nanopores, but intertwined helices occur even for D/L0 ≈ 7.3. Quenching PS-b-PLLA melts below TG(PS) results in PLLA cold crystallization strictly confined by the vitrified PS domains. Above TG(PS), PLLA crystallization is templated by the PS-b-PLLA melt domain structure in the nanopore centers, while adsorption on the nanopore walls stabilizes the outermost cylindrical PS-b-PLLA shell. In between, the nanoscopic PS-b-PLLA melt domain structure apparently ripens to reduce frustrations transmitted from the outermost immobilized PS-b-PLLA layer. The onset of PLLA crystallization catalyzes the ripening while transient ripening states are arrested by advancing PLLA crystallization. Certain helical structure motifs persist PLLA crystallization even if PS is soft. The direction of fastest PLLA crystal growth is preferentially aligned with the nanopore axes to the same degree as for PLLA homopolymer, independent of whether PS is vitreous or soft.

Self-assembly of nanostructured block copolymer nanoparticles

In this highlight, we discuss the self-assembly of block copolymer (BCP) nanoparticles. We first review the state-of-art of hierarchical structural features of BCP nanoparticles due to 3D geometric confinement, both theory and experiments. Simultaneously, we highlight the applications based on these structural features: the generation of multifunctional hybrid nanoparticles, the fabrication of mesoporous BCP nanoparticles, and applications of using BCP nanoparticles as nanocontainers or nanocargos. Finally, we discuss the challenge in the fabrication and potential applications of nanostructured BCP nanoparticles.

Phase segregation of a symmetric diblock copolymer in constrained space with a square-pillar array

In this study, we apply a self-consistent field theory of polymers to study the structures of a symmetric diblock copolymer in parallel substrates filled with square-pillar arrays in which the substrates and pillars exhibit a weak preference for one block of the copolymer. Three classes of structures, i.e., lamellae, perpendicular cylinders, and bicontinuous structures, are achieved by varying the polymer film thickness, the pillar pitch (the distance between two centers of the nearest neighboring pillars), the gap and rotation of the pillars. Because of the confinement along horizontal directions imposed by the pillar array, eight novel types of perpendicular lamellar structures and eight novel types of cylindrical structures with various shapes and distributions occur. In the hybridization states of the parallel and perpendicular lamellar structures, several novel bicontinuous structures such as the double-cylinder network, pseudo-lamellae, and perforated lamellar structure are also found. By comparing the free energies of the various possible structures, the antisymmetric parallel lamellae are observed to be stable with the larger pillar gap at a certain film thickness. The structural transformations between the alternating cylindrical structures (alternating cross-shaped, square-shaped, and octagonal perpendicular cylinders) and parallel lamellae with increasing film thickness or pillar gap are well explained by the modified strong separation theory. Our results indicate that array confinement can be an effective method to prepare novel polymeric nanopattern structures.

Phase behavior of binary blends of diblock copolymer/homopolymer confined in spherical nanopores

Binary blends of a diblock copolymer (AB) and an incompatible homopolymer (C) confined in spherical cavities are studied using a simulated annealing technique. The phase behavior of the blends is examined for four typical cases, representing the different selectivity of the pore surface to the A, B, and C species. The internal morphology of the spherical polymeric particles is controlled by the homopolymer volume fraction, the degree of confinement, and the composition of the copolymer. Inside a particle, the homopolymers segregate to form one or, under some conditions, two domains; thus, the homopolymers may act as an additional controlling parameter of the shape and symmetry of the copolymer domain. A rich array of confinement-induced novel diblock copolymer morphologies is predicted. In particular, core-shell particles with the copolymers as the shell wrapping around a homopolymer core or a copolymer-homopolymer combined core and Janus-like particles with the copolymers and the homopolymers on different sides are obtained.

Confined Self-Assembly of Asymmetric Diblock Copolymers within Silica Nanobowl Arrays

The confined self-assembly of asymmetric diblock copolymer polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) within an array of silica nanobowls prepared using a colloidal spheres templating technique is investigated. By manipulation of the nanobowl size, block copolymer (BCP) thickness, and interfacial interaction, a rich variety of ordered BCP nanostructures not accessible in the bulk system or under other confinements are obtained, resulting in hierarchically ordered nanostructures.