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Topological insulators constitute one of the most intriguing phenomena in modern condensed matter theory. The unique and exotic properties of topological states of matter allow for unidirectional gapless electron transport and extremely accurate measurements of the Hall conductivity. Recently, new topological effects occurring at Dirac/Weyl points have been better understood and demonstrated using artificial materials such as photonic and phononic crystals, metamaterials and electrical circuits. In comparison, the topological properties of nodal lines, which are one-dimensional degeneracies in momentum space, remain less explored. Here, we explain the theoretical concept of topological nodal lines and review recent and ongoing progress using artificial materials. The review includes recent demonstrations of non-Abelian topological charges of nodal lines in momentum space and examples of nodal lines realized in photonic and other systems. Finally, we will address the challenges involved in both experimental demonstration and theoretical understanding of topological nodal lines., Comment: 21 pages, 11 figures

Although a large class of topological materials have uniformly been identified using symmetry properties of wave functions, the past two years have seen the rise of multi-gap topologies beyond this paradigm. Given recent reports of unexplored features of such phases, platforms that are readily implementable to realize them are therefore desirable. Here, we demonstrate that multi-gap topological phase transitions of non-Abelian charged nodal lines arise in classical phonon waves. By adopting a simple spring-mass system, we construct nodal lines of a three-band system. The braiding process of the nodal lines is readily performed by adjusting the spring constants. The generation and annihilation of the nodal lines are then analyzed using Euler class. Finally, we retrieve topological transitions from trivial nodal lines to a nodal link. Our work provides a simple platform that can offer diverse insights to not only theoretical but also experimental studies on multi-gap topology.

Easy-to-craft photonic crystals enabling frequency-isolated Weyl points, especially at visible wavelengths, are yet to be developed. To this end, we exploited double gyroid (DG) crystals with Parit...

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.

A nodal link is a special form of a line degeneracy (a nodal line) between adjacent bands in the momentum space of a three-dimensional topological crystal. Unlike nodal chains or knots, a nodal link consists of two or more mutually-linked rings that do not touch each other. Recent studies on non-Abelian band topology revealed that the topological charges of the nodal links can have the properties of quaternions. However, a photonic crystal that has a nodal link with non-Abelian charges has not been reported. Here, we propose dielectric photonic crystals in forms of double diamond structures which realize the nodal links in the momentum space. By examining the evolution of the eigenstate correlations along the closed loops which enclose the nodal line(s) of the links, their non-Abelian topological charges are also analyzed. The proposed design scheme and theoretical approach in this work will allow for experimental observation of photonic non-Abelian charges in purely dielectric materials and facilitate the control of the degeneracy in complex photonic structures., 35 pages, 12 figures

We show linked nodal rings in momentum space with a dielectric photonic crystal. From evolutions of the eigenstates polarizations along the loops which enclose the nodal line(s) of the rings, their non-Abelian topological charges are also analyzed.

The topological nature of nodal lines in three-band systems can be described by non-abelian topological charges called quaternion numbers. Due to the gauge freedom of the eigenstates, the sign of quaternion numbers can be flipped by performing a gauge transformation, i.e., choosing a different basis of eigenstates. However, the sign flipping has not been explicitly shown in realistic systems such as phononic and photonic topological semimetals. Here, we elaborate on the sign freedom of non-abelian topological charges by visualizing numerically calculated topological charges in phononic and photonic topological semimetals. For this, we employ a common reference point method for multiple nodal lines and thus confirm that the sign flipping does not cause any inconsistency in building the quaternion group.

Plasmonic polymers consisting of metallic nanoparticles (NPs) are able to squeeze light into the deep-subwavelength space and transfer along a highly confined nanoscale path in long range. DNA nanotechnology, particularly benefiting from the molecular programmability of DNA origami, has provided otherwise nearly impossible platforms for constructing plasmonic nanoparticle polymers with designer configurations and nanoscale gaps. Here, we design and assemble a DNA origami hashtag tile that is able to polymerize into one-dimensional chains with high rigidity. The DNA origami hashtag chains are used as frames to enable robust, versatile, and precise arrangement of metallic NPs into micrometer-long chiral and magnetic plasmonic polymers, which are capable of efficiently transporting plasmonic angular momentum and magnetic surface plasmonic polaritons at the deep-subwavelength scale. Our work provides a molecular platform for the fabrication of long, straight, and structurally complex nanoparticle polymers with emerging plasmonic properties that are appealing to a variety of fields.

Manufacturing, processing, use, and disposal of nanoclay-enabled composites potentially lead to the release of nanoclay particles from the polymer matrix in which they are embedded; however, exposures to airborne particles are poorly understood. The present study was conducted to characterize airborne particles released during sanding of nanoclay-enabled thermoplastic composites. Two types of nanoclay, Cloisite® 25A and Cloisite® 93A, were dispersed in polypropylene at 0%, 1%, and 4% loading by weight. Zirconium aluminum oxide (P100/P180 grits) and silicon carbide (P120/P320 grits) sandpapers were used to abrade composites in controlled experiments followed by real-time and offline particle analyses. Overall, sanding the virgin polypropylene with zirconium aluminum oxide sandpaper released more particles compared to silicon carbide sandpaper, with the later exhibiting similar or lower concentrations than that of polypropylene. Thus, a further investigation was performed for the samples collected using the zirconium aluminum oxide sandpaper. The 1% 25A, 1% 93A, and 4% 93A composites generated substantially higher particle number concentrations (1.3–2.6 times) and respirable mass concentrations (1.2–2.3 times) relative to the virgin polypropylene, while the 4% 25A composite produced comparable results, regardless of sandpaper type. It was observed that the majority of the inhalable particles were originated from composite materials with a significant number of protrusions of nanoclay (18–59%). These findings indicate that the percent loading and dispersion of nanoclay in the polypropylene modified the mechanical properties and thus, along with sandpaper type, affected the number of particles released during sanding, implicating the cause of potential adverse health effects.

Personal accessories such as glasses and watches that we usually carry in our daily life can yield useful information from the human body, yet most of them are limited to exercise-related parameters or simple heart rates. Since these restricted characteristics might arise from interfaces between the body and items as one of the main reasons, an interface design considering such a factor can provide us with biologically meaningful data. Here, we describe three-dimensional-printed, personalized, multifunctional electronic eyeglasses (E-glasses), not only to monitor various biological phenomena but also to propose a strategy to coordinate the recorded data for active commands and game operations for human-machine interaction (HMI) applications. Soft, highly conductive composite electrodes embedded in the E-glasses enable us to achieve reliable, continuous recordings of physiological activities. UV-responsive, color-tunable lenses using an electrochromic ionic gel offer the functionality of both eyeglass and sunglass modes, and accelerometers provide the capability of tracking precise human postures and behaviors. Detailed studies of electrophysiological signals including electroencephalogram and electrooculogram demonstrate the feasibility of smart electronic glasses for practical use as a platform for future HMI systems.

Since the 1990s, applications of holography and Fourier optics have been significantly expanded from the spatial modulation of light propagation to the nanofabrication of superlattices. Holographic mixing of multiple beams is found to be highly compatible with unprecedented engineering of 1D, 2D, and 3D superlattices, particularly at the nanoscales. This is essential for the development of champion photonic crystals working at optical frequencies. However, these extensive efforts toward holographic photonic crystals have declined with the failure to obtain a champion photonic crystal and the rapid rise of other important classes of optical modes in the 2010s such as Weyl points, bound state in continuum (BIC), and exceptional points (EPs). To obtain photonic crystals, the symmetric modulations of the sinusoidally distributed real part of permittivity (Re(ε)), that can be considered as waves of matter from the viewpoint of Fourier optics, are sufficient. However, Weyl points, BIC, and EPs demand more complicated and advanced modulation of such as asymmetrically distributed wave of Re(ε) and the coupled Re(ε) and imaginary ε (Im(ε)). It is, therefore, important to determine whether holographic fabrications can be an efficient solution to Weyl points, BIC, and EPs. In this review, a comprehensive overview of holography, Fourier optical surface/volume gratings, and their implementations for Weyl points, BIC, and EPs is presented.

Self-assembled photonic crystals have proven to be a fascinating class of photonic materials for non-absorbing structural colorizations over large areas and in diverse relevant applications, including tools for on-chip spectrometers and biosensors, platforms for reflective displays, and templates for energy devices. The most prevalent building blocks for the self-assembly of photonic crystals are spherical colloids and block copolymers (BCPs) due to the generic appeal of these materials, which can be crafted into large-area 3D lattices. However, due to the intrinsic limitations of these structures, these two building blocks are difficult to assemble into a direct rod-connected diamond lattice, which is considered to be a champion photonic crystal. Here, we present a DNA origami-route for a direct rod-connected diamond photonic crystal exhibiting a complete photonic bandgap (PBG) in the visible regime. Using a combination of electromagnetic, phononic, and mechanical numerical analyses, we identify (i) the structural constraints of the 50 megadalton-scale giant DNA origami building blocks that could self-assemble into a direct rod-connected diamond lattice with high accuracy, and (ii) the elastic moduli that are essentials for maintaining lattice integrity in a buffer solution. A solution molding process could enable the transformation of the as-assembled DNA origami lattice into a porous silicon- or germanium-coated composite crystal with enhanced refractive index contrast, in that a champion relative bandwidth for the photonic bandgap (i.e., 0.29) could become possible even for a relatively low volume fraction (i.e., 16 vol%).

Single-atom catalysts are heterogeneous catalysts with atomistically dispersed atoms acting as a catalytically active center, and have recently attracted much attention owing to the minimal use of noble metals. However, a scalable and inexpensive support that can stably anchor isolated atoms remains a challenge due to high surface energy. Here, copper-halide polymer nanowires with sub-nanometer pores are proposed as a versatile support for single-atom catalysts. The synthesis of the nanowires is straightforward and completed in a few minutes. Well-defined sub-nanometer pores and a large free volume of the nanowires are advantageous over any other support material. The nanowires can anchor various atomistically dispersed metal atoms into the sub-nanometer pores up to ≈3 at% via a simple solution process, and this value is at least twice as big as previously reported data. The hydrogen evolution reaction activity of -18.0 A mgPt-1 at -0.2 V overpotential shows its potential for single-atom catalysts support.

Soft-matter bicontinuous networks find a double gyroid structure from block copolymer (BCP) self-assembly. A gyroid structure composed of dissimilar blocks has proven its potential as a soft crystal capable of tuning structural periodicity and symmetry, of which the lattice dimension is variable with molecular weight of the polymer. Using an asymmetric polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA), here we show that the self-assembled gyroid films formed via a solvent vapor annealing (SVA) process undergo unique structural distortion due to directional deformation immediately upon deswelling. During the SVA process with PS-b-PMMA films, transient cylinders developed from the as-cast morphology transform into a cubic gyroid structure in a swollen state. Rapid and spontaneous deswelling processes the manners in which the films contract along the z-direction while retaining an enlarged lateral dimension of the cubic form lead to triclinic gyroid structures with z-directional contraction ratios (Cz) of 2.5 and 2.0, respectively. Our X-ray analysis reveals that the deswelling process of the swollen gyroid films produces a notable symmetry-breaking in non-affine gyroid structure that elicits several forbidden reflections such as {110} and {200} reflections. For further characterization of the symmetry-breaking, we delineate the structural features of noncubic gyroid films by computing electron-density difference maps assisted with X-ray measurements. Level-set approach is accordingly developed to quantitate the structural characteristics of the maps in terms of inversion symmetry-breaking, suggesting its possible application to optical Weyl photonic crystals.

The temperature-rate dependent thermomechanical behavior of shape-memory polymers (SMPs) is challenging to study, because the microstructure of SMPs cannot rearrange instantaneously to an equilibrium configuration in response to temperature changes. Herein, we report a temperature-rate dependent three-dimensional constitutive model for SMPs based on a two-phase model consisting of rubbery and glassy phases. To describe the effect of temperature rate on SMPs, the variation of the volume fraction of each phase affected by temperature was considered under different temperature-rate conditions. Additionally, the temperature-rate dependent thermal strain was incorporated into the two-phase model. The developed constitutive model was validated by simulating the shape-memory behavior of SMPs, and by comparing the simulation and experimental results under different temperature-rate conditions.

Correction for ‘Characterization of aerosolized particles from nanoclay-enabled composites during manipulation processes’ by Eun Gyung Lee et al., Environ. Sci.: Nano, 2020, DOI: 10.1039/c9en01211g.

Enormous efforts have been made to harness nanoparticles showing extravasation around tumors for tumor-targeted drug carriers. Owing to the complexity of in vivo environments, however, it is very difficult to rationally design a nanoconstruct showing high tumor specificity. Here, we show an approach to develop tumor-specific drug carriers by screening a library of self-assembled nucleic acid cages in vivo. After preparation of a library of 16 nucleic acid cages by combining the sugar backbone and the shape of cages, we screened the biodistribution of the cages intravenously injected into tumor-bearing mice, to discover the cages with high tumor-specificity. This tumor specificity was found to be closely related with serum stability, cancer cell uptake efficiency, and macrophage evasion rate. We further utilized the cages showing high tumor specificity as carriers for the delivery of not only a cytotoxic small molecule drug but also a macromolecular apoptotic protein exclusively into the tumor tissue to induce tumor-specific damage. The results demonstrate that our library-based strategy to discover tumor-targeted carriers can be an efficient way to develop anti-cancer nanomedicines with tumor specificity and enhanced potency.

A hydrogel of covalently crosslinked chains and ionically crosslinked chains has exhibited high toughness. Under deformation, the covalently crosslinked network remains intact, and the ionically crosslinked network dissipates energy by breaking the ionic bonds. Because the broken ionic bonds can reform spontaneously, the damaged hydrogel can recover its initial state. However, the healing process of dissociated ionic bonds is slow. This paper shows that the healing process of dissociated ionic bonds accelerates under ultrasound radiation. Ultrasound enhanced the mobility of the dissociated chains, resulting in fast recovery of the mechanical properties. While a damaged gel thermally recovered 5 % of its energy density at room temperature in an hour, 37 % of the energy density was recovered using ultrasound in the same period. Molecular dynamic simulations were also included in this study to reveal the effect of ultrasound.

The mechanical modeling and simulation of woven fabric-reinforced shape-memory polymer composites (wf-SMPCs) are quite complex tasks because a temperature change introduces thermal stress that dramatically affects the interaction between the matrix and fiber. This study aimed to develop a new homogenized constitutive model for wf-SMPCs considering the thermally induced residual stress. The orthotropic properties of the wf-SMPC due to the woven fabric reinforcement were modeled using classical anisotropic hyperelasticity theorems. The stress generated in the hyperelastic model was then complemented by combining with the stress generated in the SMP constitutive equation and the thermal residual stress according to Eshelby's inclusion theorem. The prediction capability of the proposed model was verified by three-point bending tests of the wf-SMPC having various fiber volume fractions. Finally, the unique features of the proposed constitutive model were investigated by experiments and simulation of a self-deployable antenna made of a wf-SMPC.

Using a two-phase (rubbery and glassy) phenomenological model and shape memory strains, a three-dimensional constitutive model for shape memory polymers (SMPs) was developed that can simulate multi-axial and large deformation behavior (up to 200% of strain) of SMPs. To derive a constitutive equation, the total deformation gradient was multiplicatively decomposed into hyperelastic, viscoelastic, viscoplastic, and shape memory strains using Helmholtz free energy and the Clausius–Duhem inequality. The shape memory strain was determined from the total deformation by assuming proportionality to the total deformation. The developed constitutive model was validated by simulating the shape memory behavior of SMPs using a finite element method and comparing the simulation results with experiments. Finally, the capabilities of the constitutive equation were demonstrated by simulating constrained shape recovery behavior of SMPs.

Purpose To estimate annual health care and productivity loss costs attributable to overweight or obesity in working asthmatic patients. Materials and methods This study was conducted using the 2003-2013 Medical Expenditure Panel Survey (MEPS) in the United States. Patients aged 18 to 64 years with asthma were identified via self-reported diagnosis, a Clinical Classification Code of 128, or a ICD-9-CM code of 493.xx. All-cause health care costs were estimated using a generalized linear model with a log function and a gamma distribution. Productivity loss costs were estimated in relation to hourly wages and missed work days, and a two-part model was used to adjust for patients with zero costs. To estimate the costs attributable to overweight or obesity in asthma patients, costs were estimated by the recycled prediction method. Results Among 11670 working patients with a diagnosis of asthma, 4428 (35.2%) were obese and 3761 (33.0%) were overweight. The health care costs attributable to obesity and overweight in working asthma patients were estimated to be $878 [95% confidence interval (CI): $861-$895] and $257 (95% CI: $251-$262) per person per year, respectively, from 2003 to 2013. The productivity loss costs attributable to obesity and overweight among working asthma patients were $256 (95% CI: $253-$260) and $26 (95% CI: $26-$27) per person per year, respectively. Conclusion Health care and productivity loss costs attributable to overweight and obesity in asthma patients are substantial. This study's results highlight the importance of effective public health and educational initiatives targeted at reducing overweight and obesity among patients with asthma, which may help lower the economic burden of asthma.