Band gap of shear horizontal waves for one-dimensional phononic crystals with chiral materials.

Extensive applications of chiral lattice structures in the field of acoustic wave manipulation and vibration modulation show the effectiveness of chirality route to the design of phononic crystals. However, how and to what extent the material chirality affects the band gap properties of phononic crystals remains unclear. In this study, one-dimensional phononic crystals made of chiral materials is proposed, and a theoretical model of shear horizontal (SH) wave propagation in the chiral phononic crystals is developed based on the noncentrosymmetric micropolar elasticity theory. Through the transfer matrix method, the dispersion relationship of SH wave propagation is obtained and the effects of material chirality on the band-gap properties are investigated. Our work demonstrates that the change of material chirality can significantly affect the dispersion relationship of phononic crystals, leading to the wide band gap and low frequency. In a unit cell, when the chiral coefficients of the two parts have opposite signs but the same magnitude and the chiral directions are consistent with the vibrational direction, it is the most favorable for the phononic crystals to achieve the lowest frequency and widest band gap. This study suggests that the material chirality can be harnessed to effectively tune the band-gap properties of phononic crystals. The present study provides insight for the chirality route to the design of phononic crystals.

Passive white light cavities with metal coatings.

White light cavities with broadband resonance are usually filled with negative dispersion medium, which inevitably leads to gain. In this article, pure passive white light cavities are designed, in which negative dispersion medium is no longer necessary. Theoretically, if the reflection phase of the cavity wall can exhibit a negative dispersion slope, then it can also satisfy white light cavities conditions without medium. In practice, the negative dispersion property of the cavity wall can be realized by two metal coatings with different reflection coefficients. Therefore, our white light cavities are composite cavities, in which the main cavity provides resonance while the auxiliary cavity forms the cavity wall, providing negative dispersion reflection phase. Further, atomic gas can be employed to improve the performance of the white light cavities. Atomic gas exploits effects such as Electromagnetic Induced Transparency (EIT), enabling the white light cavities to be controlled by coherent driving field. With the passive characters, our design can be realized and implemented much more easily.

Interaction of two quantum dots mediated by edge modes of coupled-cavity arrays.

Topological photonics is a hot topic in recent years. We combine it with the quantum optics and explore the dynamics of two quantum dots (QDs) separated by the finite coupled-cavity arrays (CCAs). The finite CCAs possessing the alternating hopping strengths will lead to the existence of the topological protected edge modes, also called zero energy modes, when the boundaries leave the weak hopping at two ends. Due to the two edge modes, i.e., symmetric and antisymmetric, with nearly degenerate frequencies, the dynamics of two QDs coupled to the cavities at both ends exhibit complicated behaviors. When the CCAs are composed of a large number of cavities, there are two kinds of phenomena: if the coupling between QDs and cavity is weak, two edge modes will cancel each other out and isolate two QDs deeply; if the coupling between QDs and cavities is large compared with hopping strength, the edge mode disappears and two QDs can be connected through extend modes. Importantly, when the CCAs are formed by a small number of cavities, energy can be transferred to each other between two QDs through the edge modes. Such energy transfer is topologically protected, and the period is long and easily controlled. We also investigate the effects of topologically protected quantum entangled states on such system and find that the quantum entanglement can be well kept or generated for appropriate choices of system parameters and initial states. The investigations enrich the manifestation of topological physics and are helpful to apply the topological protection to quantum computation and quantum communication.

Formation of chiral morphologies of biological materials induced by chirality.

Chiral growth exists prevalently in natural materials. The mechanism underlying the formation of chiral morphologies in biological and man-made materials has been an important issue of both theoretical and technological interest. In this paper, an elastic rod model taking into account chiral microstructures is developed to investigate the formation of chiral morphologies of biological materials. The curvature and twist of chiral shapes are investigated with this model using the variational method of energy. The result shows the misfit of chirality of two-layer structured biological materials may induce various chiral morphologies, such as helices and twisting belts. Furthermore, it was found that cooperative or competitive interactions between anisotropic elasticity and chirality can also lead to the formation of chiral morphologies, and the fibre orientation angles and chiral parameters are the determining factors to the shape, size and handedness of chiral morphologies. This work is expected to shed new light on the physical mechanisms of the formation of various chiral morphologies in the biological world and provide useful guidance for the design of deformation driving and shape control of soft robots and machines.

Chiral interaction of an atom in a sandwiched waveguide.

The chiral interaction between light and matter is mainly caused by the spin-momentum locking and makes the chiral quantum optics enter a vigorous development stage. Here, we explore the condition of the perfect chiral interaction between an atom possessing circular dipole and the surface plasmon polariton (SPP) mode. The realization of the perfect chiral interaction must satisfy the following two conditions at the same time. First, the SPP mode should possess the transverse circular polarization; and second, the atom decays mainly into the SPP mode, while the decay through other channel can be ignored. In this paper, we adopt a simple but effective structure to satisfy both of requirements, which is the sandwiched waveguide made of metal. We found that the transverse circular polarization of SPP mode might be achieved within the structure possessing multiple interfaces instead of the interface separating two semi-infinite materials. In our model, the decay rate into SPP mode overwhelms that through traveling wave, which provides higher quantum efficiency. What's more, we found that only the symmetric TM-polarized SPP mode might get the transverse circular polarization. For the sandwiched structure containing metal, the existence of two SPP modes weakens the overall chiral interaction. However, the structure containing left-handed materials (LHMs), which can only support one symmetric TM-polarized SPP mode, can get the nearly perfect chiral interaction. We measure the chiral interaction through the decay rate, radiation field distribution and the unidirectional rate through the energy flux. Our work provides a reference for exploring the perfect chiral interaction in more complex structures and has potential and wide applicability to other optical processes.

Preparation of Core-Shell Silica Microspheres with Controllable Shell Thickness for Fast High Performance Liquid Chromatography Separation of Alkyl Benzenes and Intact Proteins.

As it is difficult to prevent secondary nucleation and agglomeration during the preparation of core-shell silica microspheres, these issues have been successfully resolved in this study using template-dissolution-induced redeposition. The non-porous particles are transformed into core-shell silica microspheres (CSSMs) in the presence of cetyltrimethylammonium bromide and octyltrimethylammonium bromide under basic conditions. The shell thickness and pore sizes of the CSSMs are controlled by adjusting the etching time and molar ratio of the template, respectively. The CSSMs are modified using octadecyltrimethylammonium chloride to separate the mixture of alkyl benzenes, and a high column separation efficiency is achieved within two minutes. The CSSMs are used for the separation and analysis of proteins and the digests of bovine serum albumin. The chromatographic column packed with core-shell particles affords a significantly higher separation efficiency than the commercial column. Therefore, as a chromatographic stationary phase, these core-shell particles can potentially be used for the fast separation of proteins, small solutes, and complex samples.

pH-dependent selective separation of acidic and basic proteins using quaternary ammoniation functionalized cysteine-zwitterionic stationary phase with RPLC/IEC mixed-mode chromatography.

In this paper, a cysteine-functionalized zwitterionic stationary phase (Cys-silica) was prepared based on the "thiol-ene" click chemistry between cysteine and vinyl-functionalized silica, and was further modified with bromoethane, 1-bromooctane and 1-bromooctadecane, respectively, to obtain a series of quaternary ammoniation-functionalized stationary phases (Cys-silica-Cn, n = 2, 8 and 18). These zwitterionic stationary phases were regarded as reversed-phase/ion-exchange (RP/IEC) mixed-mode chromatography (MMC) stationary phases for protein separation. The retention behaviors of proteins on these zwitterionic stationary phases were carefully investigated. The results indicated that the retentions of acidic and basic proteins on these zwitterinonic stationary phases were significantly influenced by the acetonitrile and salt concentrations, pH of mobile phase as well as the hydrophobicity of the ligand. The separation selectivity of proteins on these zwitterionic stationary phases strongly depended on the pH value of mobile phase. The baseline separation of 6 kinds of basic proteins can be achieved at pH 8.0 using Cys-silica-C2 or Cys-silica-C8 column, and 5 kinds of acidic proteins can also be separated completely at pH 4.0 with Cys-silica-C2 column. Moreover, owing to the quaternary ammoniation-functionalization on Cys-silica by using appropriately hydrophobic bromoalkanes, the selectivity and separation efficiency of proteins can be enhanced greatly. As a result, the acidic and basic proteins can be separated completely step by step from the complex sample by adjusting pH of mobile phase using a single Cys-silica-C2 column, which illustrates that the cysteine-functionalized zwitterionic stationary phase has a great potential for protein separation.

Polar Superhelices in Ferroelectric Chiral Nanosprings.

Topological objects of nontrivial spin or dipolar field textures, such as skyrmions, merons, and vortices, interacting with applied external fields in ferroic materials are of great scientific interest as an intriguing playground of unique physical phenomena and novel technological paradigms. The quest for new topological configurations of such swirling field textures has primarily been done for magnets with Dzyaloshinskii-Moriya interactions, while the absence of such intrinsic chiral interactions among electric dipoles left ferroelectrics aside in this quest. Here, we demonstrate that a helical polarization coiled into another helix, namely a polar superhelix, can be extrinsically stabilized in ferroelectric nanosprings. The interplay between dipolar interactions confined in the chiral geometry and the complex strain field of mixed bending and twisting induces the superhelical configuration of electric polarization. The geometrical structure of the polar superhelix gives rise to electric chiralities at two different length scales and the coexistence of three order parameters, i.e., polarization, toroidization, and hypertoroidization, both of which can be manipulated by homogeneous electric and/or mechanical fields. Our work therefore provides a new geometrical configuration of swirling dipolar fields, which offers the possibility of multiple order-parameters, and electromechanically controllable dipolar chiralities and associated electro-optical responses.

Hollow Au-Cu2O Core-Shell Nanoparticles with Geometry-Dependent Optical Properties as Efficient Plasmonic Photocatalysts under Visible Light.

Hollow Au-Cu2O core-shell nanoparticles were synthesized by using hollow gold nanoparticles (HGNs) as the plasmon-tailorable cores to direct epitaxial growth of Cu2O nanoshells. The effective geometry control of hollow Au-Cu2O core-shell nanoparticles was achieved through adjusting the HGN core sizes, Cu2O shell thicknesses, and morphologies related to structure-directing agents. The morphology-dependent plasmonic band red-shifts across the visible and near-infrared spectral regions were observed from experimental extinction spectra and theoretical simulation based on the finite-difference time-domain method. Moreover, the hollow Au-Cu2O core-shell nanoparticles with synergistic optical properties exhibited higher photocatalytic performance in the photodegradation of methyl orange when compared to pristine Cu2O and solid Au-Cu2O core-shell nanoparticles under visible-light irradiation due to the efficient photoinduced charge separation, which could mainly be attributed to the Schottky barrier and plasmon-induced resonant energy transfer. Such optical tunability achieved through the hollow cores and structure-directed shells is of benefit to the performance optimization of metal-semiconductor nanoparticles for photonic, electronic, and photocatalytic applications.

Hierarchical chirality transfer in the growth of Towel Gourd tendrils.

Chirality plays a significant role in the physical properties and biological functions of many biological materials, e.g., climbing tendrils and twisted leaves, which exhibit chiral growth. However, the mechanisms underlying the chiral growth of biological materials remain unclear. In this paper, we investigate how the Towel Gourd tendrils achieve their chiral growth. Our experiments reveal that the tendrils have a hierarchy of chirality, which transfers from the lower levels to the higher. The change in the helical angle of cellulose fibrils at the subcellular level induces an intrinsic torsion of tendrils, leading to the formation of the helical morphology of tendril filaments. A chirality transfer model is presented to elucidate the chiral growth of tendrils. This present study may help understand various chiral phenomena observed in biological materials. It also suggests that chirality transfer can be utilized in the development of hierarchically chiral materials having unique properties.

Preparation and characterization of a novel dual-retention mechanism mixed-mode stationary phase with PEG 400 and succinic anhydride as ligand for protein separation in WCX and HIC modes.

A novel dual-retention mechanism mixed-mode stationary phase based on silica gel functionalized with PEG 400 and succinic anhydride as the ligand was prepared and characterized by infrared spectra and elemental analysis. Because of the ligand containing PEG 400 and carboxyl function groups, it displayed hydrophobic interaction chromatography (HIC) characteristic in a high-salt-concentration mobile phase, and weak cation exchange chromatography (WCX) characteristic in a low-salt-concentration mobile phase. As a result, it can be employed to separate proteins with both WCX and HIC modes. The resolution and selectivity of the stationary phase was evaluated under both HIC and WCX modes with protein standards, and its performance was comparable to that of conventional ion-exchange chromatography and HIC columns. The results indicated that the novel dual-retention mechanism column, in many cases, could replace two individual WCX and HIC columns as a '2D column'. In addition, the mixed retention mechanism of proteins on this '2D column' was investigated with stoichiometric displacement theory for retention of solute in liquid chromatography in detail in order to understand why the dual-retention mechanism column has high resolution and selectivity for protein separation under WCX and HIC modes, respectively. Based on this '2D column', a new 2DLC technology with a single column was developed. It is very important in proteome research and recombinant protein drug production to save column expense and simplify the processes in biotechnology.

Surface effects on the superelasticity of nanohelices.

Helical nanomaterials with superelasticity have a wide range of promising applications in micro-/nanoelectromechanical systems. Based on the theory of surface elasticity, we present a nonlinear rod model to investigate the superelasticity of nanohelices. Our results demonstrate that the superelasticity of nanohelices exhibits a distinct size dependence due to the increased ratio of surface area to volume. The superelasticity can effectively enhance the efficiency of energy storage and retrieval of nanohelices. This study is helpful for the characterization of the mechanical properties of nanosized helical materials and the optimal design of nanohelix-based devices.