Fabricating Freestanding, Broadband Reflective Cholesteric Liquid-Crystal Networks via Topological Tailoring of the Sm-Ch Phase Transition.

Numerous biological systems in nature provide much inspiration for humanity to master diverse coloration strategies for creating stimuli-responsive materials and display devices, such as to access gorgeous structural colors from well-defined photonic structures. Cholesteric liquid crystals (CLCs) are a fascinating genre of photonic materials displaying iridescent colors responsive to circumstance changes; however, it is still a big challenge to design materials with broadband color variation as well as good flexibility and freestanding capacity. Herein, we report a feasible and flexible strategy to fabricate cholesteric liquid-crystal networks (CLCNs) with precise colors across the entire visible spectrum through molecular structure tailoring and topology engineering and demonstrate their application as smart displays and rewritable photonic paper. Influences of chiral and achiral LC monomers on the thermochromic behaviors of CLC precursors as well as on the topology of the polymerized CLCNs are systematically investigated, demonstrating that the monoacrylate achiral LC facilitated the formation of a smectic phase-chiral phase (Sm-Ch) pretransitional phase in the CLC mixture and improved the flexibility of the photopolymerized CLCNs. High-resolution multicolor patterns in one CLCN film are generated through photomask polymerization. In addition, the freestanding CLCN films show perceivable mechanochromic behaviors and repeated erasing-rewriting performances. This work opens avenues toward the realization of pixelated colorful patterns and rewritable CLCN films promising in technology fields ranging from information storage and smart camouflage to anti-counterfeiting and smart display.

Research progress on ZnSe and ZnTe anodes for rechargeable batteries.

Transition-metal chalcogenides (TMCs) with tunable direct bandgaps and interlayer spacing are attractive for energy-related applications. Semiconducting zinc chalcogenides, especially their selenides (ZnSe) and tellurides (ZnTe), with enhanced conductivity, high theoretical capacity, low operation voltage and abundance, have appeared on the horizon and receive increasing interest in terms of electrochemical energy storage and conversion. Despite the existing typical obstruction owing to the large volume change, relatively low electrical conductivity and sluggish ion diffusion kinetics into the bulk phase, several effective strategies such as compositing, doping, nanostructuring, and electrode/cell design have exhibited promising applications. We herein provide a timely and systematic overview of recent research and significant advances regarding ZnSe, ZnTe and their hybrids/composites, covering synthesis to electrode design and to applications, especially in advanced Li/Na/K-ion batteries, as well as the reaction mechanisms thereof. It is hoped that the overview will shed new light on the development of ZnSe and ZnTe for next-generation rechargeable batteries.

Selective sequential infiltration synthesis of ZnO in the liquid crystalline phase of silicon-containing rod-coil block copolymers.

The combination of block copolymer (BCP) thin film self-assembly and selective infiltration synthesis of inorganic materials into one BCP block provides access to various organic-inorganic hybrids. Here, we apply sequential infiltration synthesis, a vapor-phase hybridization technique, to selectively introduce ZnO into the organic microdomains of silicon-containing rod-coil diblock copolymers and a triblock terpolymer, polydimethylsiloxane (PDMS)-b-poly{2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene} (PDMS-b-PMPCS) and PDMS-b-polystyrene-b-PMPCS (PDMS-b-PS-b-PMPCS), in which the PMPCS rod block is a liquid crystalline polymer. The in-plane cylindrical PDMS-b-PMPCS and core-shell cylindrical and hexagonally perforated lamellar PDMS-b-PS-b-PMPCS films were infiltrated with ZnO with high selectivity to the PMPCS. The etching contrast between PDMS, PS and the ZnO-infused PMPCS enables the fabrication of ZnO/SiOx binary composites by plasma etching and reveals the core-shell morphology of the triblock terpolymer.

Shape-Stable Hydrated Salts/Polyacrylamide Phase-Change Organohydrogels for Smart Temperature Management.

Flexible and environmentally friendly phase-change materials (PCMs) with appropriate phase transition temperatures display great potential in the regulation of environmental temperature. Here, we synthesized a series of room-temperature-use phase-change organohydrogels (PCOHs) comprising phase-change hydrated salts (disodium phosphate dodecahydrate, DPDH) and polyacrylamide (PAM) glycerol hydrogels through a facile photoinitiated one-step in situ polymerization procedure. Incorporating the environmentally friendly cost-effective DPDH hydrated salts PCMs into antidrying three-dimensional (3D) networks of the PAM organohydrogel can overcome the solid rigidity and melting leakage to achieve flexibility for wearable temperature management devices. The microstructures and physical interactions among the components of the PCOHs were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD), which demonstrate that the DPDH were uniformly loaded in the networks of the PAM. Phase-change storage and thermal properties of the PCOHs were characterized by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), and the PCOHs show high energy transition efficiency and shape stability during the long-term storage and thermal cycling. Dynamic rheology and compression tests demonstrate that PCOHs can withstand a certain stress and display flexibility performance even above the melting temperature of DPDH. We also described the smart temperature management capability and the potential application of the PCOHs. This investigation offers a facile method to construct a skin-friendly flexible phase-change glycerol hydrogel and provides an alternative to the traditional melt impregnation or microencapsulation method to prepare phase-change energy storage composites.

Bending Behavior and Directed Self-Assembly of Rod-Coil Block Copolymers.

The formation of zigzags, chevrons, Y-junctions, and line segments is demonstrated in thin films formed from cylindrical morphology silicon-containing conformationally asymmetric rod-coil diblock copolymers and triblock terpolymers under solvent annealing. Directed self-assembly of the block copolymers within trenches yields well-ordered cylindrical microdomains oriented either parallel or transverse to the sidewalls depending on the chemical functionalization of the sidewalls, and the location and structure of concentric bends in the cylinders is determined by the shape of the trenches. The innate etching contrast, the spontaneous sharp bends and junctions, and the range of demonstrated periodicity and line/space ratios make these conformationally asymmetric rod-coil polymers attractive for nanoscale pattern generation.

Transparent Stretchable Dual-Network Ionogel with Temperature Tolerance for High-Performance Flexible Strain Sensors.

A stretchable transparent double network ionogel composed of physically cross-linked poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)) and chemically cross-linked poly(methyl methacrylate-co-butylmethacrylate) (P(MMA-co-BMA)) elastomer networks within [EMIM][TFSI] ionic liquid was fabricated through a facile one-pot thermal polymerization. The dual-network (DN) ionogel presents good mechanical performance (failure tensile stress 2.31 MPa, strain 307%) with a high loading of ionic liquid (70 wt %) for achieving required ionic conductivity (>0.1 S/m at room temperature). The transparent chemical cross-linked P(MMA-co-BMA) elastomer network endows high transparency (>93%) and high stretchability to the DN ionogel. The DN ionogel maintains good toughness, elasticity, and transparency in a wide temperature range (-40 to 80 °C) for the application in a harsh environment. In addition, the sensitivity of the DN ionogel to the change of environment temperature and deformation was detected and described. The practical potential of the DN ionogel in flexible electronic devices is further revealed by fabricating DN ionogel strain sensors to detect the movement of different human limbs including the bending of the finger, wrist, and elbow as well as the slight throat jitter during the swallowing and vocalization, showing fast response, high sensitivity, and good repeatability.

Vertical Lamellae Formed by Two-Step Annealing of a Rod-Coil Liquid Crystalline Block Copolymer Thin Film.

Silicon-containing block copolymer thin films with high interaction parameter and etch contrast are ideal candidates to generate robust nanotemplates for advanced nanofabrication, but they typically form in-plane oriented microdomains as a result of the dissimilar surface energies of the blocks. Here, we describe a two-step annealing method to produce vertically aligned lamellar structures in thin film of a silicon-containing rod-coil thermotropic liquid crystalline block copolymer. The rod-coil block copolymer with the volume fraction of the Si-containing block of 0.22 presents an asymmetrical lamellar structure in which the rod block forms a hexatic columnar nematic liquid crystalline phase. A solvent vapor annealing step first produces well-ordered in-plane cylinders of the Si-containing block, then a subsequent thermal annealing promotes the phase transition from in-plane cylinders to vertical lamellae. The pathways of the order-order transition were examined by microscopy and in situ using grazing incidence small-angle X-ray scattering and wide-angle X-ray scattering.

Core-Shell and Zigzag Nanostructures from a Thin Film Silicon-Containing Conformationally Asymmetric Triblock Terpolymer.

The self-assembly of multiblock copolymers generates diverse hierarchical nanostructures and greatly extends the range of microdomain geometries beyond those produced by diblock copolymers. We report the synthesis of a conformationally asymmetric ABC triblock terpolymer in which the end blocks are a mesogen-jacketed liquid crystalline polymer and poly(dimethylsiloxane), respectively, and its self-assembly under mixed solvent vapor annealing forms a range of sphere, cylinder, and perforated lamellar core-shell morphologies, as well as stacked multilevel structures. Sub-7 nm diameter SiOx nanopatterns were generated by selective plasma etching of the small volume fraction Si-containing core block giving a line/space ratio of ∼1:4. Moreover, the conformational asymmetry of this terpolymer leads to zigzag cylinders on a flat substrate and stable cylinder alignment transverse to template sidewalls within lithographically patterned trenches.

Self-assembly of a silicon-containing side-chain liquid crystalline block copolymer in bulk and in thin films: kinetic pathway of a cylinder to sphere transition.

The self-assembly of a high-χ silicon-containing side-chain liquid crystalline block copolymer (LC BCP) in bulk and in thin films is reported, and the structural transition process from the hexagonally packed cylinder (HEX) to the body-centered cubic structure (BCC) in thin films was examined by both reciprocal and real space experimental methods. The block copolymer, poly(dimethylsiloxane-b-11-(4'-cyanobiphenyl-4-yloxy)undecylmethacrylate) (PDMS-b-P(4CNB11C)MA) with a molecular weight of 19.5 kg mol-1 and a volume fraction of PDMS 27% self-assembled in bulk into a hierarchical nanostructure of sub-20 nm HEX cylinders of PDMS with the P(4CNB11C)MA block exhibiting a smectic LC phase with a 1.61 nm period. The structure remained HEX as the P(4CNB11C)MA block transformed to an isotropic phase at ∼120 °C. In the thin films, the PDMS cylindrical microdomains were oriented in layers parallel to the substrate surface. The LC block formed a smectic LC phase which transformed to an isotropic phase at ∼120 °C, and the microphase-separated nanostructure transformed from HEX to BCC spheres at ∼160 °C. The hierarchical structure as well as the dynamic structural transition of the thin films were characterized using in situ grazing-incidence small-angle X-ray scattering and grazing-incidence wide-angle X-ray scattering. The transient morphologies from the HEX to BCC structure in thin films were captured by scanning electron microscopy and atomic force microscopy, and the transition pathway was described.

Extraordinary boundary morphologies of large-scale ordered domains of spheres in thin films of a narrowly dispersed diblock copolymer via thermodynamic control.

Long-range ordering of body centered cubic (BCC) spheres and various extraordinary morphologies at the boundaries of the adjacent orderly oriented domains are observed in thermally annealed thin films of a series of specific narrowly dispersed diblock copolymers, poly(dimethylsiloxane)-b-poly{2,5-bis[(4-butoxyphenyl)oxycarbonylstyrene} (PDMS-b-PBPCS, DB). The series of asymmetrical DB block copolymers (BCPs) with volume fractions of PDMS (f(PDMS)'s) from 10% to 23% self-assemble into thermodynamically stable body centered cubic (BCC) nanostructures in bulk at ambient temperature after thermal annealing. The thin films of these BCPs with a relatively large film thickness on a carbon-film coated substrate are annealed in a vacuum at 180 °C for 3 days and are characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). For all thin films of these BCPs, micrometer-scale domains with a rectangular unit cell similar to the projection of the BCC lattice along the [110] direction to the substrate are observed. And the XPS results indicate that the surface layers of the thin films are composed of both PDMS and PBPCS blocks. For the thin films of the BCPs with f(PDMS) values of 10% and 13%, the neighboring [110]-oriented BCC domains match well with each other, and the boundaries are defect-free. For the thin film of the BCP with a f(PDMS) value of 23%, the PDMS spheres in the [110]-oriented BCC domains in the TEM micrograph are overlapped with each other, and interesting morphologies including defect-free interfaces, interfaces with line defects, and domains with defects and local ordering are observed at the boundaries of the neighboring [110]-oriented domains.