Chiral Inclusions Research Articles

Poisson's Ratio beyond the Classically Allowable Range in Chiral Isotropic Elastic Materials: Effect of k and Experiment

Poisson's ratio in chiral isotropic elastic solids can be larger or smaller than the classical thermodynamic bounds. The effect of Cosserat coupling constant k is studied. Analysis shows that solids with weak coupling exhibit Poisson's ratio anomalies for larger specimen sizes than corresponding solids with strong coupling. Experiments on a quasi‐isotropic composite with chiral inclusions show Poisson's ratio greater than 0.5.

Recent advances in the field of chiral crystallization.

Crystallization is one of the largest and most economical bulk purification techniques used in industry today. There has been an increase in demand for enantiomerically pure compound production for research, organic synthesis, pharmaceutical drug production, and other applications. Even after asymmetric synthesis, chiral purification will always be necessary. The focus of this review is on recent advances in chiral crystallization for the purification of enantiomers. A comprehensive discussion of three techniques and their mechanisms is provided, namely: attrition-enhanced deracemization, cocrystallization, and inorganic ionic cocrystallization. Several examples of attrition-enhanced deracemization are discussed. The key advantage of this technique is that it eliminates enantiomeric waste and can be used to produce enantiomeric excesses of greater than 99% from racemic mixtures. Chiral cocrystallization is examined, with over 60 cocrystallizing compounds, as an excellent means for enantiomeric enrichment. Selective chiral inclusion complexation was shown to be a novel approach for the formation of cocrystals. Chiral inorganic ionic cocrystallization is a new technique involving the formation of cocrystals between chiral ligands and certain metal salts in order to produce conglomerate crystal behavior in otherwise racemic compounds.

Interaction of electromagnetic wave and metamaterial with inductive type chiral inclusions

The principle of calculation of a plate from a metamaterial with inductive type chiral inclusions is submitted. It is shown that distribution of an electromagnetic wave to such substance can be investigated with the help of introduction of a chiral parameter and on the basis of a detailed method of calculation. By comparison of two methods the dependence of chiral parameter from frequency of electromagnetic radiation falling on a plate is found. With the help of a detailed method the nonlinear differential equation for potential on the chiral plate is found. It is shown that this equation has solutions as traveling solitary and standing waves but not traveling sine waves. The analysis of the received solutions of the nonlinear equation is carried out. Transition from the multiwave solution to the solution as standing waves is graphically shown at reduction ofdistance between the chiral elements.

Emergent chiroptical properties in supramolecular and plasmonic assemblies.

This tutorial provides a comprehensive description of the origin of chiroptical properties of supramolecular and plasmonic assemblies in the UV-visible region of the electromagnetic spectrum. The photophysical concepts essential for understanding chiroptical signatures are presented in the first section. Just as the oscillator strength (a positive quantity) is related to absorption, the rotational strength (either a positive or a negative quantity) defines the emergence of chiroptical signatures in molecular/plasmonic systems. In supramolecular systems, induced circular dichroism (ICD) originates through the off-resonance coupling of transition dipoles in chiral inclusion complexes, while exciton coupled circular dichroism (ECD) originates through the on-resonance exciton coupling of transition dipoles in chiral assemblies resulting in the formation of a bisignated CD signal. In bisignated ECD spectra, the sign of the couplet is determined not only by the handedness of chiral supramolecular assemblies, but also by the sign of the interaction energy between transition dipoles. Plasmonic chirality is briefly addressed in the last section, focusing on inherent chirality, induced chirality, and surface plasmon-coupled circular dichroism (SP-CD). The oscillator strength is of the order of 1 in molecular systems, while it becomes very large (104-105) in plasmonic systems due to the collective plasmonic excitations, resulting in intense CD signals, which can be exploited for the design of plasmonic metamaterial platforms for chiral sensing applications.

Interaction of Electromagnetic Wave and Metamaterial with Inductive Type Chiral Inclusions

The principle of calculation of a plate from a metamaterial with inductive type chiral inclusions is submitted. It is shown that distribution of an electromagnetic wave in such substance can be investigated with the help of using of a chiral parameter and on the basis of a detailed method of calculation. By comparison of two methods the dependence of chiral parameter from frequency of electromagnetic radiation falling on a plate is found. With the help of a detailed method the nonlinear differential equation for potential on the chiral plate is found. It is shown that this equation has solutions as traveling solitary waves and standing waves but not traveling sine waves. The analysis of the received solutions of the nonlinear equation is carried out. Transition from the multiwave solution to the solution as standing waves is graphically shown at reduction of distance between the chiral elements.

Polarization Control with Helical Metasurfaces

The ability to fully control the polarization of light using chiral metadevices has drawn considerable attention in various applications of integrated photonics, communication systems, and life sciences. In this work, we propose a comprehensive approach for the design of metasurfaces with desired polarization properties for reflected and transmitted waves based on the proper spatial arrangement of chiral inclusions in the unit cell. Polarization conversion is achieved by engineering induced electric and magnetic dipole moments of the metasurface inclusions. We show that under a proper arrangement, the same inclusion can be used as a building block of metasurfaces with drastically different wave-transformation functionalities. The horizontally and vertically oriented metallic helices were used as simplest chiral inclusions, which can be manufactured by the established 3D fabrication techniques from THz up to the visible spectral range. The proposed metadevices provide a deep understanding of the light–matter interaction for polarization conversions with helix-based structures and opens the way to new possibilities of electromagnetic polarization control with advanced chiral metadevices in communication and imaging systems.

Chiral sensing with achiral isotropic metasurfaces

Metasurfaces, the two-dimensional analogues of metamaterials, are ideal platforms for sensing molecular chirality at the nanoscale, e.g. of inclusions of natural optically active molecules, as they offer large accessible areas (they are essentially surfaces) and can accommodate the necessary strong resonances for coupling the probing radiation with the chiral inclusions. Here, we examine theoretically achiral isotropic metasurfaces, and we treat them as polarizable surfaces that support resonant electric and magnetic currents, which are coupled via the chiral inclusions. We derive analytically, and verify numerically, expressions that provide insight to the enhancement mechanism of the magneto-electric coupling and explain why circular dichroism signals (difference in absorption between left- and right- circularly polarized waves) can arise from both the real and the imaginary part of the chirality parameter $\kappa$. Our analysis demonstrates distinct chiroptical signals where the contributions from both the real and imaginary part of $\kappa$ can be independently observed and, based on such measurements, we propose a scheme for the unambiguous determination of an unknown chirality.

Erratum to: Homogenization method for one-dimensional photonic crystals with magnetic and chiral inclusions

Erratum to: Homogenization method for one-dimensional photonic crystals with magnetic and chiral inclusions

Homogenization method for one-dimensional photonic crystals with magnetic and chiral inclusions

We have theoretically investigated the electromagnetic properties for one-dimensional (1D) photonic crystals with magnetic and artificial chiral inclusions in the quasi-static limit, that is when the size of the unit cell of the crystal is small with respect to the wavelength of the operating wave. We suggest a homogenization theory to determine the effective tensors of the optical response, to achieve this objective, we apply the Bloch’s plane waves method to describe the electromagnetic modes that can propagate in the periodic structure under consideration. Subsequently, the Maxwell’s “microscopic” equations are homogenized replacing the Bloch waves by plane waves that attenuate the fast oscillations of the electromagnetic fields within the unit cell (macroscopic level), i.e., the average-macroscopic electromagnetic fields are determined by the component corresponding to the null reciprocal lattice vector in the expansion in plane waves. The numerical implementation of our theory of homogenization allow us to study the effective bianisotropic electromagnetic response (effective dielectric permittivity, magnetic permeability and electric-magnetic coupling tensors, this last is described by an effective chiral parameter) for 1D photonic crystals whose constituents in its unit cell are a dielectric layer and another magnetic (both isotropic and anisotropic) or chiral inclusion layer. The results are illustrated and discussed by the effective parameters as a function of the filling fraction of the inclusion and show for each case of homogeneous effective medium different components of anisotropy in the electromagnetic response of permittivity, permeability and chirality with the increase of the filling fraction. Besides, the behaviors of the obtained graphs agree well with Rytov’s formulas of effective medium. The relevant results of this theory will be very useful for the study and better understanding of the nature and design of metamaterials with predetermined anisotropic optical properties.

Interaction of Electromagnetic Wave and Metamaterial with Inductive Type Chiral Inclusions

Издательство Новые технологии выпускает журналы: Инфомационные технологии; Мехатроника, Автоматизация, Управление; Горные машины и автоматика; Микросистемная техника; Безопасность жизнедеятельности. Все журналы входят в перечень изданий, рекомендованных ВАК

Simultaneous Perfect Bending and Polarization Rotation of Electromagnetic Wavefront Using Chiral Gradient Metasurfaces

We introduce chiral gradient metasurfaces that allow perfect transmission of all the incident wave into a desired direction and simultaneous perfect rotation of the polarization of the refracted wave with respect to the incident one. Besides using gradient polarization densities which provide bending of the refracted wave with respect to the incident one, using metasurface inclusions that are chiral allows the polarization of the refracted wave to be rotated. We suggest a possible realization of the proposed device by discretizing the required equivalent surface polarization densities realized by proper helical inclusions at each discretization point. By only using a single optically thin layer of chiral inclusions, we are able to unprecedentedly deflect a normal incident plane wave to a refracted plane wave at $45^{\circ}$ with $72\%$ power efficiency which is accompanied by a $90^{\circ}$ polarization rotation. The proposed concepts and design method may find practical applications in polarization rotation devices at microwaves as well as in optics, especially when the incident power is required to be deflected.

Enhancement of circular dichroism in epsilon-near-zero chiral hyperbolic metamaterials

We are presenting a theoretical study of light transmission through a slab of hyperbolic metamaterial composed of gold rods, with chiral inclusions, thus possessing both hyperbolic and chiral properties. 4 × 4 transfer matrix formalism was used for solution of a wave transmission through a slab of a chiral hyperbolic material. We have shown that circular dichroism (CD) can be enhanced by several orders of magnitude in epsilon-near-zero (ENZ) mode when the diagonal component of the permittivity tensor corresponding to the normal to interface coordinate tends to zero. The necessary condition of the enhancement is a non-zero light incidence angle. This effect results from a considerable wavelength shortening in normal direction that increases the interaction between light and matter. We have shown that the increase of the incidence angle leads to the increase of dichroism in vicinity of ENZ wavelength range and the dichroism can change sign in this resonance area. The dichroism becomes huge at large incidence angles (θ > 30°) and for each incidence angle the maximal enhancement is observed within a certain wavelength range (in vicinity of ϵ-near-zero). In opposite to discussion of the enhancement of the pseudochirality reported previously in the literature, our study relates to the true chirality. We expect these results to be of interest to researchers engaged in chemical composition of organic substances by retrieval of effective parameters from measurements of the CD.

Artificial Chiral Media Using Conical-Coil Wire Inclusions

The electromagnetic response of the electrically small conical wire coil as a chiral inclusion is described. An existing model of the helical coil wire inclusion is extended to model the conical coil wire inclusion, using the Method of Moments (MoM) to determine the dominant resonant circuit impedance of the inclusion. Material parameters are determined using mixing relations with polarizability coefficients expressed for the conical coil inclusion geometry. The polarization conversion of a dielectric slab loaded with conical coil inclusions is predicted and compared to simulated results using a forward scattering technique.

Enantiospecific Detection of Chiral Nanosamples Using Photoinduced Force

We propose a novel high resolution microscopy technique for enantio-specific detection of chiral samples down to sub-100 nm size, based on force measurement. We delve into the differential photo-induced optical force exerted on an achiral probe in the vicinity of a chiral sample, when left and right circularly polarized beams separately excite the sample-probe interactive system. We analytically prove that the differential force is entangled with the enantiomer type of the sample enabling enantio-specific detection of chiral inclusions. Moreover, we demonstrate that the differential force is linearly dependent on both the chiral response of the sample and the electric response of the tip and is inversely related to the quartic power of probe-sample distance. We provide physical insight into the transfer of optical activity from the chiral sample to the achiral tip based on a rigorous analytical approach. We support our theoretical achievements by several numerical examples, highlighting the potential application of the derived analytic properties. Lastly, we demonstrate the sensitivity of our method to enantio-specify nanoscale chiral samples with chirality parameter in the order of 0.01, and discuss how this could be further improved.

Study of the Flow Response of a Chiral Fluid Confined in a Channel in the Presence of the Transverse Magnetic Field

The chiral materials are composed of the chiral molecules or inclusions which have ability to rotate electromagnetic waves or polarized light to a desired angle depending on chirality or handedness of the molecule or inclusions and the length of the medium. Fluids like sugar solution, sugar cane juice, turpentine and most of the body fluids etc are chiral. In recent years considerable attention has been given on the study of effect of chirality of molecules or inclusions on the propagation of electromagnetic waves through chiral medium, fabrication of chiral bio-interface materials, synthesis of chiral drug and chiral polymers. In this regard, present paper is intended to study the flow response of chiral fluid flowing in a vertical channel bounded by rigid permeable boundaries in the presence of applied transverse magnetic field under the influence of viscous dissipation, and convection electric current. The simplified and generalised non-linear momentum and energy equations governing the flow of a chiral fluid confined in a channel are solved for velocity and temperature for various values of dimensionless parameter analytically using the regular perturbation method with buoyancy parameter ‘N’ as perturbation parameter and numerically using finite difference method with Successive Over Relaxation (SOR) technique. The results obtained are depicted graphically and found that the resistance to flow of chiral fluid decreases with increase in the transverse magnetic field and the flow reversal occurs with change in the chirality parameter γ from -1 to 1

A Simple First-Principles Homogenization Theory for Chiral Metamaterials

We discuss a simple first-principles homogenization theory for describing, in the long-wavelength limit, the effective bianisotropic response of a periodic metamaterial composite without intrinsic chiral and magnetic inclusions. In the case where the dielectric contrast is low, we obtain a full analytical description which can be considered the extension of Landau-Lifshitz-Looyenga effective-medium formulation in the context of periodic metamaterials.

On-axis Gaussian beam scattering by an object with a chiral inclusion

A semi-analytical solution to the scattering by an arbitrarily shaped object with a chiral inclusion, for oblique incidence of an on-axis Gaussian beam, is formulated based on the extended boundary condition method. The incident Gaussian beam, scattered fields as well as internal fields are expanded in terms of appropriate spherical vector wave functions, and the unknown expansion coefficients are determined by a system of equations derived from Schelkunoff׳s equivalence theorem and continuous boundary conditions. Numerical results of the normalized differential scattering cross section are presented, and the scattering characteristics are discussed concisely.

Hierarchical organization of chiral rafts in colloidal membranes.

Liquid-liquid phase separation is ubiquitous in suspensions of nanoparticles, proteins and colloids. It has an important role in gel formation, protein crystallization and perhaps even as an organizing principle in cellular biology. With a few notable exceptions, liquid-liquid phase separation in bulk proceeds through the continuous coalescence of droplets until the system undergoes complete phase separation. But when colloids, nanoparticles or proteins are confined to interfaces, surfaces or membranes, their interactions differ fundamentally from those mediated by isotropic solvents, and this results in significantly more complex phase behaviour. Here we show that liquid-liquid phase separation in monolayer membranes composed of two dissimilar chiral colloidal rods gives rise to thermodynamically stable rafts that constantly exchange monomeric rods with the background reservoir to maintain a self-limited size. We visualize and manipulate rafts to quantify their assembly kinetics and to show that membrane distortions arising from the rods' chirality lead to long-range repulsive raft-raft interactions. Rafts assemble into cluster crystals at high densities, but they can also form bonds to yield higher-order structures. Taken together, our observations demonstrate a robust membrane-based pathway for the assembly of monodisperse membrane clusters that is complementary to existing methods for colloid assembly in bulk suspensions. They also reveal that chiral inclusions in membranes can acquire long-range repulsive interactions, which might more generally have a role in stabilizing assemblages of finite size.

Spontaneous resolution versus formation of racemic crystals of indenylpotassium complexes

During a study of stereochemically labile organometallic reagents, we found that crystallisation of [K(ind)(pmdta)]n (ind = indenyl, pmdta = N,N,N',N'',N''-pentamethyldiethylenetriamine) from tetrahydrofuran (THF) gave rise to three different crystalline phases depending on the concentration. The more concentrated solutions gave racemic crystals of the previously known coordination polymer [K(ind)(pmdta)]n, α-1. More dilute solutions gave crystals of a new phase, β-1, which was found to undergo spontaneous resolution. From even more dilute solutions, we were able to isolate a chiral inclusion compound with THF, 2, which also undergoes spontaneous resolution. Crystals of β-1 and 2 were enantiomerically pure, and since β-1 is a reactive organometallic reagent, attempts were made to use the crystals in enantioselective synthesis. Reacting single crystals with N-chlorosuccinimide gave rise to chiral 1-chloroindene, but no enantiomeric excess was observed.

Compact negative‐epsilon stop‐band structures based on double‐layer chiral inclusions

Here the authors propose to use electrically excited compact chiral resonators in microstrip configurations for realisation of weakly-radiating stop-band transmission lines. The fundamental resonant mode of these resonators can be excited by both electric and magnetic fields applied parallel to the spiral axis. The authors propose to use a racemic arrangement of an equal amount of left- and right-handed chiral particles between the ground plane and the signal strip and orient the particles so that they are excited by the electric field of the microstrip line. The advantage of this configuration (in addition to strong coupling and weak radiation from excited particles) is that the ground plane can be preserved from being etched (continuous ground structure). The other advantage is that the size of negative permittivity lines loaded with chiral particles can be made very small compared to previous implementations based on complementary split-ring resonators. The circuit models with properly extracted parameters accurately describe the behaviour of both negative permittivity and double-negative lines loaded with electrically coupled resonators. This parameter extraction technique is based on the comparison between the simulated (or measured) transmission and reflection characteristics of the host line loaded with such resonators and those obtained from its lumped-element equivalent circuit model.