Orientational Preference in Multilayer Block Copolymer Nanomeshes with Respect to Layer-to-Layer Commensurability

Reactive Multilayer Coating As Versatile Nanoarchitectonics for Customizing Various Bioinspired Liquid Wettabilities

In last few decades, multilayer coatings have achieved enormous attention owing to their unique ability to tune thickness, topography, and chemical composition for developing various functional materials. Such multilayer coatings were mostly and conventionally derived by following a simple layer-by-layer (LbL) deposition process through the strategic use of electrostatic interactions, hydrogen bonding, host-guest interactions, covalent bonding, etc. In the conventional design of multilayer coatings, the chemical composition and morphology of coatings are modulated during the process of multilayer constructions. In such an approach, the postmodulations of the porous multilayers with different and desired chemistries are challenging to achieve due to the lack of availability of readily and selectively reactive moieties. Recently, the design of readily and selectively reactive multilayer coatings (RMLCs) provided a facile basis for postmodulating the prepared coating with various desired chemistries. In fact, by taking advantage of the inherent ability of co-optimizing the topography and various chemistries in porous RMLCs, different durable bioinspired liquid wettabilities (i.e., superhydrophobicity, underwater superoleophobicity, underwater superoleophilicity, slippery property, etc.) were successfully derived. Such interfaces have enormous potential in various prospective applications. In this review, we intend to give an overview of the evolution of LbL multilayer coatings and their synthetic strategies and discuss the key advantages of porous RMLCs in terms of achieving and controlling wettability properties. Recent attempts toward various applications of such multilayer coatings that are strategically embedded with different desired liquid wettabilities will be emphasized.

Priming self-assembly pathways by stacking block copolymers

Block copolymers spontaneously self-assemble into well-defined nanoscale morphologies. Yet equilibrium assembly gives rise to a limited set of structures. Non-equilibrium strategies can, in principle, expand diversity by exploiting self-assembly's responsive nature. In this vein, we developed a pathway priming strategy combining control of thin film initial configurations and ordering history. We sequentially coat distinct materials to form prescribed initial states, and use thermal annealing to evolve these manifestly non-equilibrium states through the assembly landscape, traversing normally inaccessible transient structures. We explore the enormous associated hyperspace, spanning processing (annealing temperature and time), material (composition and molecular weight), and layering (thickness and order) dimensions. We demonstrate a library of exotic non-native morphologies, including vertically-oriented perforated lamellae, aqueduct structures (vertical lamellar walls with substrate-pinned perforations), parapets (crenellated lamellae), and networks of crisscrossing lamellae. This enhanced structural control can be used to modify functional properties, including accessing regimes that surpass their equilibrium analogs.

Rectangular Cylinders Formed by Compositionally Bidisperse ABC Triblock Terpolymer Blends: A Self-Consistent Field Theory Study

Compared with traditional cylinders that have circular cross-sections, cylinders with rectangular cross-sections can endow nanomaterials with various novel optical properties and functions. In this work, the formation of the rectangular cylinders self-assembled by compositionally bidisperse ABC triblock terpolymer blends has been investigated via numerical simulations based on self-consistent field theory. The specially designed blending systems are composed of two types of linear ABC triblock terpolymers that have the same total chain lengths and the middle B block chain lengths, but different chain lengths of the side A/C blocks. By tuning the chain length fractions and the interactions between different blocks, rectangular cylinders with a fourfold symmetry pattern were successfully obtained in our simulations. Each rectangular phase domain is self-assembled together by the short and long side blocks of the same species. The simulation results indicate that the selective aggregation of the short side blocks determines the formation of the rectangular cylindrical phase, i.e., the short side blocks prefer to aggregate at the four corners within a rectangular cylindrical phase domain. This simulation result reveals a formation mechanism that is different from the mechanism proposed in previous experiments [Asai ACS Macro Lett., 2014, 3, 166-169]. Moreover, under different middle B block chain length fractions, phase diagrams as a function of the interaction parameter between different blocks and the short side block chain length fraction have been constructed. The phase diagrams show that the parameter window of the rectangular cylinders is considerably expanded by increasing the chain length fraction of the middle B blocks. Our simulation works can provide a theoretical basis for molecular design to regulate and fabricate nanomaterials with nontraditional phase domains in future experiments.

Templating Functional Materials Using Self-Assembled Block Copolymer Thin-Film for Nanodevices

The nanomorphologies and nanoarchitectures that can be synthesized using block copolymer (BCP) thin-film self-assembly have inspired a variety of new applications, which offer various advantages, such as, small device footprint, low operational power and enhanced device performance. Imperative for these applications, however, is the ability to transform these small polymeric patterns into useful inorganic structures. BCP-templated inorganic nanostructures have shown the potential for use as active materials in various electronic device applications, including, field-effect transistors, photodetectors, gas sensors and many more. This article reviews various strategies that have been implemented in the past decade to fabricate devices at nanoscale using block copolymer thin films.

Wafer-Scale Unidirectional Alignment of Supramolecular Columns on Faceted Surfaces

The long-range alignment of supramolecular structures must be engineered as a first step toward advanced nanopatterning processes aimed at miniaturizing features to dimensions below 5 nm. This study introduces a facile method of directing the orientation of supramolecular columns over wafer-scale areas using faceted surfaces. Supramolecular columns with features on the sub-5 nm scale were highly aligned in a direction orthogonal to that of the facet patterning on unidirectional and nanoscopic faceted surface patterns. This unidirectional alignment of supramolecular columns is also observed by varying the thickness of the supramolecular film or by altering the dimensions of the facet pattern. The ordering behavior of the supramolecular columns can be attributed to the triangular depth profile of the bottom facet pattern. Furthermore, this directed self-assembly principle allows for the continuous alignment of supramolecular structures across ultralarge distances on flexible patterned substrates.

Self-template-assisted micro-phase segregation in blended liquid-crystalline block copolymers films toward three-dimensional structures

In-plane mesopatterns derived from block-copolymer (BCP) micro-phase segregation in thin films have attracted much interest in practical applications as well as fundamental research programs. However, phase segregation along the film-normal direction has been less studied. Here, we describe a strategy to concurrently, yet independently, control in-plane micro-phase and out-of-plane macro-phase segregation in multiblended films composed of liquid-crystalline BCPs (LCBCPs), affording spontaneously layered three-dimensional (3D) mesostructures. This strategy relies on sequential liquid crystallization during the cooling process in thermal annealing as follows. The constituent LCBCP with the highest isotropic-transition temperature (T _iso) first liquid-crystallizes and segregates from the other LCBCP mixture remaining in isotropic states to form a noncontaminated layer at the top surface. This preformed LCBCP layer preserves its inherent in-plane pattern and acts as a template guiding the subsequent micro-phase segregations of the other low-T _iso LCBCPs underneath. This self-template-assisted micro-phase segregation (STAMPS) readily provides 3D mesostructures, the potential toward rational material design of which is also demonstrated in water-separation applications.

Hybrid patterns from directed self-assembly of diblock copolymers by chemical patterns

The surface affinity is a critical factor for controlling the formation of monolayer nanostructures in block copolymer thin films. In general, strong surface affinity tends to induce the formation of domains with low spontaneous curvature. Abiding by this principle, we propose a facile chemoepitaxial scheme for producing large-scale ordered hybrid patterns by the directed self-assembly of diblock copolymers. The guiding chemical pattern is designed as periodic stripes with alternately changing surface affinities. As a consequence, two different geometries of domains are formed on the stripes with different affinities. The self-assembly process of block copolymers guided by the stripe patterns is investigated using cell dynamics simulations based on time-dependent Ginzburg-Landau theory, and the kinetic stability diagram is estimated. Hybrid patterns are successfully achieved with both cylinder-forming and sphere-forming diblock copolymers. In the cylinder-forming system, the major hybrid pattern exhibiting a considerable stability window is composed of parallel cylinders and perforated lamellae, while it is composed of monolayer spheres and parallel cylinders in the other system. Encouragingly, the chemoepitaxial method is valid till the period of the guiding pattern is a large multiple of the domain spacing. The chemoepitaxial scheme demonstrated in this work serves as a nice supplement to the graphoepitaxial one proposed in our previous work.

Three-dimensional electroactive ZnO nanomesh directly derived from hierarchically self-assembled block copolymer thin films

Three-dimensional (3D) nanoarchitectures can offer enhanced material properties, such as large surface areas that amplify the structures' interaction with environments making them useful for various sensing applications. Self-assembled block copolymers (BCPs) can readily generate various 3D nanomorphologies, but their conversion to useful inorganic materials remains one of the critical challenges against the practical application of self-assembled BCPs. This work reports the vapor-phase infiltration synthesis of optoelectrically active, 3D ZnO nanomesh architectures by combining hierarchical successive stacking of self-assembled, lamellar-phase polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) BCP thin films and a modified block-selective vapor-phase material infiltration protocol. The 3D ZnO nanomesh exhibits optoelectrical functionality, featuring stack-layer-number-dependent electrical conductance resembling the percolative transport originating from the intrinsic morphological network connectivity of the lamellar BCP pattern with symmetric block ratio. The results not only illustrate the first demonstration of electrical functionality based on the ZnO nanoarchitecture directly generated by the infiltration synthesis in self-assembled BCP thin films but also present a new, large-area scalable, metal oxide thin film nanoarchitecture fabrication method utilizing industry-compatible polymer solution coating and atomic layer deposition. Given the large surface area, three-dimensional porosity, and readily scalable fabrication procedures, the generated ZnO nanomesh promises potential applications as an efficient active medium in chemical and optical sensors.