Block copolymer gyroids for nanophotonics: significance of lattice transformations

A gyroid crystal possesses a peculiar structural feature that can be conceptualized as a triply periodic surface with a constant mean curvature of zero. The exotic optical properties such as the photonic bandgap and optical chirality can emerge from this three-dimensional (3D) morphological feature. As such, gyroid crystals have been considered as the promising structures for photonic crystals and optical metamaterials. To date, several methods have been proposed to materialize gyroid crystals, including 3D printing, layer-by-layer stacking, two-photon lithography, interference lithography, and self-assembly. Furthermore, the discovery of Weyl points in gyroid crystals has further stimulated these advancements. Among such methods, the self-assembly of block copolymers (BCPs) is unique, because this soft approach can provide an easy-to-craft gyroid, especially at the nanoscale. The unit-cell scale of a gyroid ranging within 30–300 nm can be effectively addressed by BCP self-assembly, whereas other methods would be challenging to achieve this size range. Therefore, a BCP gyroid has provided a material platform for metamaterials and photonic crystals functioning at optical frequencies. Currently, BCP gyroid nanophotonics is ready to take the next step toward topological photonics beyond the conventional photonic crystals and metamaterials. In particular, the intrinsic lattice transformations occurring during the self-assembly of BCP into a gyroid crystal could promise a compelling advantage for advancing Weyl photonics in the optical regime. Lattice transformations are routinely considered as limitations, but in this review, we argue that it is time to widen the scope of the lattice transformations for the future generation of nanophotonics. Thus, our review provides a comprehensive understanding of the gyroid crystal and its lattice transformations, the relevant optical properties, and the recent progress in BCP gyroid self-assembly

DFT study of carbazole derivatives dehydrogenation on Pd(111) catalyst

The carbazole derivatives such as 9-ethylcarbazole have been studied as a potential hydrogen storage candidate. It is found that these materials can store hydrogen under moderate-to-ambient conditions in liquid state so that the transportation of hydrogen would be convenient. Besides, the reversibility of hydro/dehydrogenation is much better than the existing solid type of hydrogen storage carriers. However, the major problem for carbazole derivatives which contain ethyl and acetyl group is the cleavage between functional group and carbazole. Therefore, the hydrogen carrier must be regenerated cyclically, which lead to an increase in operational cost. In this work, the Density Functional Theory calculations are performed to understand the dehydrogenation reaction mechanism and decomposition of 9-ethy/acetylcarbazole on Pd(111). The secondary alcohol hydrogenated acetyl group distort the hydrogenated form of 9-acetylcarbazole on Pd(111), which lead to reducing activation energy. With respect to decomposition of functional group, 9-ethylcarbazole is slightly more stable than 9-acetylcarbazole. These results suggest the direction of molecular design for hydrogen storage materials

Processing and Evaluation of a Carbon Fiber Reinforced Composite Bar Using a Closed Impregnation Pultrusion System with Improved Production Speed

In this paper, an epoxy resin-based carbon fiber reinforced composite (CFRP) bar pultrusion system using a closed impregnation device which has various advantages in process compared to traditional open bath type pultrusion system was developed, and the fiber impregnation system was improved through the analysis of resin properties for the high-speed production of CFRP bars used to support the mother glass in the display transfer cassettes. To improve the fiber feeder system, fiber guides were switched from perforated plates to roller guides for spreading fibers, which allowed the input fibers to be widened and flattened while reducing the fiber thickness. Additionally, the correlation between resin viscosity and impregnation speed were analyzed to evaluate the resulting mechanical properties at different pultrusion speeds and temperatures. A CFRP bar was produced with resin injection at room temperature and a pultrusion rate of 400 mm/min and compared to a CFRP bar produced with fiber spreading, a resin injection temperature of 40 °C, and a pultrusion rate of 600 mm/min; the latter with a 50% improved production rate showed improvements in mechanical properties, including the cross-sectional void by 98.7%, surface roughness by 75.5%, deflection by 34.9%, and bending strength by 70%

Processing and Evaluation of a Carbon Fiber Reinforced Composite Bar Using a Closed Impregnation Pultrusion System with Improved Production Speed

In this paper, an epoxy resin-based carbon fiber reinforced composite (CFRP) bar pultrusion system using a closed impregnation device which has various advantages in process compared to traditional open bath type pultrusion system was developed, and the fiber impregnation system was improved through the analysis of resin properties for the high-speed production of CFRP bars used to support the mother glass in the display transfer cassettes. To improve the fiber feeder system, fiber guides were switched from perforated plates to roller guides for spreading fibers, which allowed the input fibers to be widened and flattened while reducing the fiber thickness. Additionally, the correlation between resin viscosity and impregnation speed were analyzed to evaluate the resulting mechanical properties at different pultrusion speeds and temperatures. A CFRP bar was produced with resin injection at room temperature and a pultrusion rate of 400 mm/min and compared to a CFRP bar produced with fiber spreading, a resin injection temperature of 40 °C, and a pultrusion rate of 600 mm/min; the latter with a 50% improved production rate showed improvements in mechanical properties, including the cross-sectional void by 98.7%, surface roughness by 75.5%, deflection by 34.9%, and bending strength by 70%

Broadband Modulation of Terahertz Waves With Non-Resonant Graphene Meta-Devices

Single-layer graphene absorbs a small fraction of incident terahertz waves by intraband transition of Dirac fermions. The amounts of absorption, reflection, and transmission of terahertz waves depend on the doping level of graphene, i.e., the Fermi level, and they exhibit relatively weak frequency dependency at terahertz frequencies. By hybridizing gated single-layer graphene with a non-resonant meta-atom structure, we show that the effective surface conductivity of meta-atom hybridized graphene can be significantly enhanced, and large intensity modulation of transmitted terahertz waves can be achieved without sacrificing the broadband modulation feature of single-layer graphene. For a frequency insensitive response, the meta-atoms are designed so that their resonance is positioned outside the frequencies of interest. Exploiting the enhanced effective surface conductivity with a non-resonant feature, larger modulation was possible over broad operating frequency from 0.3 to 2.3 THz. We anticipate that this electrically controlled graphene meta-device may play an important role in the realization of practical terahertz modulators

Transition-Metal-Free Synthesis of 2‑Substituted Methyl Benzo[<i>b</i>]furan-3-carboxylates

A concise and highly efficient synthetic pathway was developed for 2-substituted methyl benzo­[<i>b</i>]­furan-3-carboxylates. This method provides convenient and cost-effective access for 2-substituted methyl benzo­[<i>b</i>]­furan-3-carboxylates without the use of a transition metal catalyst for synthesis. Furthermore, in most cases, this method gives excellent yields and conventional flash column chromatography is not needed for purification

Transition-Metal-Free Synthesis of 2‑Substituted Methyl Benzo[<i>b</i>]furan-3-carboxylates

A concise and highly efficient synthetic pathway was developed for 2-substituted methyl benzo­[<i>b</i>]­furan-3-carboxylates. This method provides convenient and cost-effective access for 2-substituted methyl benzo­[<i>b</i>]­furan-3-carboxylates without the use of a transition metal catalyst for synthesis. Furthermore, in most cases, this method gives excellent yields and conventional flash column chromatography is not needed for purification