Nanoscale 3D ordered polymer networks

High-resolution three-dimensional imaging of topological textures in nanoscale single-diamond networks

Topological defects-extended lattice deformations that are robust against local defects and annealing-have been exploited to engineer novel properties in both hard and soft materials. Yet, their formation kinetics and nanoscale three-dimensional structure are poorly understood, impeding their benefits for nanofabrication. We describe the fabrication of a pair of topological defects in the volume of a single-diamond network (space group Fd3 ¯ m) templated into gold from a triblock terpolymer crystal. Using X-ray nanotomography, we resolve the three-dimensional structure of nearly 70,000 individual single-diamond unit cells with a spatial resolution of 11.2 nm, allowing analysis of the long-range order of the network. The defects observed morphologically resemble the comet and trefoil patterns of equal and opposite half-integer topological charges observed in liquid crystals. Yet our analysis of strain in the network suggests typical hard matter behaviour. Our analysis approach does not require a priori knowledge of the expected positions of the nodes in three-dimensional nanostructured systems, allowing the identification of distorted morphologies and defects in large samples.

Fe3O4-doped mesoporous carbon cathode with a plumber's nightmare structure for high-performance Li-S batteries

Shuttling of lithium polysulfides and slow redox kinetics seriously limit the rate and cycling performance of lithium-sulfur batteries. In this study, Fe3O4-dopped carbon cubosomes with a plumber's nightmare structure (SP-Fe3O4-C) are prepared as sulfur hosts to construct cathodes with high rate capability and long cycling life for Li-S batteries. Their three-dimensional continuous mesochannels and carbon frameworks, along with the uniformly distributed Fe3O4 particles, enable smooth mass/electron transport, strong polysulfides capture capability, and fast catalytic conversion of the sulfur species. Impressively, the SP-Fe3O4-C cathode exhibits top-level comprehensive performance, with high specific capacity (1303.4 mAh g-1 at 0.2 C), high rate capability (691.8 mAh gFe3O41 at 5 C), and long cycling life (over 1200 cycles). This study demonstrates a unique structure for high-performance Li-S batteries and opens a distinctive avenue for developing multifunctional electrode materials for next-generation energy storage devices.

Formation of Perpendicular Three-Dimensional Network Nanostructures in ABC-Star Copolymers

Perpendicular arrangements in hierarchical nanostructures show superior mechanical properties and provide great opportunities for the development of advanced membranes because different channels are connected by the perpendicular blocks. To obtain these perpendicular hierarchical nanostructures, we use a simple ABC-star terpolymer because of the existence of a conjunction point by using the A block as a polymer network template, which guides the BC phase separation accordingly. When χ_BC is 10, the formed phase and the corresponding phase diagram of ABC-star are similar to those of the AB₂ triblock because of the mixture between the B and C blocks. Interestingly, at increased χ_BC, the B and C blocks phase separate, leading to the formation of a series of perpendicular nanostructures, including perpendicular lamellae-in-lamellae (L_⊥), perpendicular lamellae-in-cylinder (C_⊥), and even perpendicular three-dimensional polymer networks (G_⊥). The corresponding stability regime of each phase is identified through the dedicated comparison of free energy, which can well explain the missing phases in Monte Carlo simulations. Our proposed design route according to the target structures and the calculated phase diagram can provide useful guidance for the experimental observation of these perpendicular nanostructures.

Enlarged Phase Regions of Multi-Continuous 3D Network Nanostructures in ABC Triblock Copolymers

Aiming to increase the stability region of three-dimensional (3D) multi-continuous morphologies due to great potential application in smart sensors, gas separation membranes, and photonic materials, in this paper, we control the block ratio of different channels of an ABC triblock copolymer according to the curvature of these multi-continuous nanostructures. In the small A volume fraction region, the multi-continuous gyroid nanostructure is stable when f_B/f_C equals 1/3, while two-domain lamellae (L_B/C) and three-layer lamellae (L₃) are obtained when B and C blocks have comparable volume fractions, suggesting that changing the f_B/f_C ratio is an effective way of forming multi-continuous polymer network nanostructures. Interestingly, a large phase region of the core-shell gyroid and O⁷⁰ are found under the condition of f_B/f_C = 4. The mechanism of changing the ratio to enlarge the phase regimes of multi-continuous nanostructures can be ascribed to the existence of curvature in gyroid and O⁷⁰ nanostructures. Therefore, the formed thin layer must be consistent with these curvatures, which can be tuned by the adjustment of the block ratio. The proposed mechanism and the calculated phase diagram can effectively guide the experimental observation of these multi-continuous nanostructures.

Visualizing the double-gyroid twin

Periodic gyroid network materials have many interesting properties (band gaps, topologically protected modes, superior charge and mass transport, and outstanding mechanical properties) due to the space-group symmetries and their multichannel triply continuous morphology. The three-dimensional structure of a twin boundary in a self-assembled polystyrene-b-polydimethylsiloxane (PS-PDMS) double-gyroid (DG) forming diblock copolymer is directly visualized using dual-beam scanning microscopy. The reconstruction clearly shows that the intermaterial dividing surface (IMDS) is smooth and continuous across the boundary plane as the pairs of chiral PDMS networks suddenly change their handedness. The boundary plane therefore acts as a topological mirror. The morphology of the normally chiral nodes and strut loops within the networks is altered in the twin-boundary plane with the formation of three new types of achiral nodes and the appearance of two new classes of achiral loops. The boundary region shares a very similar surface/volume ratio and distribution of the mean and Gaussian curvatures of the IMDS as the adjacent ordered DG grain regions, suggesting the twin is a low-energy boundary.

Controlling Mirror Symmetry Breaking and Network Formation in Liquid Crystalline Cubic, Isotropic Liquid and Crystalline Phases of Benzil-Based Polycatenars

Spontaneous development of chirality in systems composed of achiral molecules is important for new routes to asymmetric synthesis, chiral superstructures and materials, as well as for the understanding of the mechanisms of emergence of prebiotic chirality. Herein, it is shown that the 4,4'-diphenylbenzil unit is a universal transiently chiral bent building block for the design of multi-chained (polycatenar) rod-like molecules capable of forming a wide variety of helically twisted network structures in the liquid, the liquid crystalline (LC) and the crystalline state. Single polar substituents at the apex of tricatenar molecules support the formation of the achiral (racemic) cubic double network phase with Ia 3 ‾ d symmetry and relatively small twist along the networks. The combination of an alkyl chain with fluorine substitution leads to the homogeneously chiral triple network phase with I23 space group, and in addition, provides a mirror symmetry broken liquid. Replacing F by Cl or Br further increases the twist, leading to a short pitch double gyroid Ia 3 ‾ d phase, which is achiral again. The effects of the structural variations on the network structures, either leading to achiral phases or chiral conglomerates are analyzed.

Formation of Multicontinuous 3D Network Nanostructures with Increased Complexity in ABC-Type Block Copolymers

The multicontinuous network nature of polymer nanostructures provides them with many opportunities to fabricate multifunctional materials with specific mechanical, transport, optical, and other novel properties. In this paper, we generate an effective design principle to craft a series of multicontinuous network structures with controllable channels, including multicontinuous gyroid and O⁷⁰ network morphologies via the self-assembly of ABC-type block copolymers. Importantly, we achieve a much wider (∼25%) compositional range than that of AB diblock copolymers (∼3%), which would increase the widespread application of these multicontinuous polymer networks. Even for the simplest ABC linear system, this method is valid for generating multicontinuous network structures, where gyroids and O⁷⁰ are found to possess large phase regions. This finding can theoretically explain the experimental observation of gyroid and O⁷⁰ phases. We believe that our proposed design principle along with the calculated phase diagram provides a compelling panacea for the fabrication of multicontinuous 3D network nanostructures.

Self-Assembly of Ultrathin Nanocrystals to Multidimensional Superstructures

The self-assembly of ultrathin nanocrystals (UTNCs) into well-organized multidimensional superstructures is one of the key topics in material chemistry and physics. Highly ordered nanocrystal assemblies also known as superstructures or synthetic structures have remained a focus for researchers over the past few years due to synergy in their properties as compared to their components. Here, we aim to present the recent progress being made in this field with highlights of our research group endeavors in the engineering of self-assembled complex multidimensional superstructures of various inorganic materials, including polyoxometalates. The driving forces for the assembly process and its kinetics along with the potential applications associated with these unique ordered and spatially complex superstructures are also discussed.