Effective Polarizability Research Articles

The effect of monomer polarizability on the stability and salt partitioning in model coacervates.

Coacervation of charged polymer chains has been a topic of major interest in both polymer and biological sciences, as it is a subset of a phenomenon called liquid-liquid phase separation (LLPS). In this process the polymer-rich phase separates from the polymer-lean supernatant while still maintaining its liquid-like properties. LLPS has been shown to play a crucial role in cellular homeostasis by driving the formation of membraneless organelles. It also has the potential to be harnessed to aid in novel therapeutical applications. Recent studies have demonstrated that there is no one simple mechanism which drives LLPS, which is instead a result of the combined effect of electrostatic, dipolar, hydrophobic, and other weak interactions. Using coarse-grained polymer simulations we investigate the relatively unexplored effects of monomer polarizability and spatially varying dielectric constant on LLPS propensity, and these factors affect the properties of the resulting condensates. In order to produce spatial variations in the dielectric constant, all our simulations include explicit solvent and counterions. We demonstrate that polarizability has only a minor effect on the bulk behaviour of the condensates but plays a major role when ion partitioning and microstructure are considered. We observe that the major contribution comes from the nature of the neutral blocks as endowing them with an induced dipole changes their character from hydrophobic to hydrophilic. We hypothesize that the results of this work can aid in guiding future studies concerned with LLPS by providing a general framework and by highlighting important factors which influence LLPS.

Reflectarray Design Using a Discrete Dipole Framework

We propose and numerically validate a patch reflectarray modeling approach suitable for small patches that describes each patch as a pair of polarizable magnetic dipoles. We introduce an extraction technique to obtain the effective polarizability of the patch dipoles via full-wave simulations on individual patches, followed by a beamforming design routine valid under weakly scattering configurations. This dipole framework serves as an alternative to the ray tracing model often used in reflectarray designs, in which rays are drawn from the feed point and scattered off of the patch elements. Whereas the ray tracing method solves the design problem in terms of phase delays, the dipole framework presented here has the potential to accurately design and predict beam patterns using a fully dipolar treatment of empirically characterized patches. We illustrate this technique by applying it to two modulation strategies: a variable patch size reflectarray in which the phase can be continuously tuned (grayscale patch response), and a fixed patch size (binary patch response) in which on/off modulation is achieved through selective patch electrical shorting. Methods for incorporating these cases into the dipole design framework are discussed and the results compared to those from full wave simulation.

The effect of immediate environment on bond strength of different bond types-A valence bond study.

The ability to design catalysis largely depends on our understanding of the electrostatic effect of the surrounding on the bonds participating in the reaction. Here, we used a simplistic model of point charges (PCs) to determine a set of rules guiding how to construct PC-bond arrangement that can strengthen or weaken different chemical bonds. Using valence bond theory to calculate the in situ bond energies, we show that the effect of the PC mainly depends on the bond's dipole moment irrespective of its type (being covalent or charge shift). That is, polar bonds are getting stronger or weaker depending on the signand location of the PC, whereas non- or weakly polar bonds become stronger or weaker depending only on the location of the PC and to a smaller extent compared with polar bonds. We also show that for polar bonds, the maximal bond strengthening and weakening effect can be achieved when the PC is placed along the bond axis, as close as possible to the more and less polarizable atom/fragment, respectively. Finally, due to the stabilizing effects of polarizability, we show that, overall, it is easier to cause bond strengthening compared with bond weakening. Particularly, for polar bonds, bond strengthening is larger than bond weakening obtained by an oppositely signed PC. These rules should be useful in the future design of catalysis in, e.g., enzyme active sites.

Lattice dynamical and thermodynamic properties study of ceria using density functional theory and Hubbard correction

In this study, the lattice dynamical and thermodynamic properties of CeO2 were investigated with first principles density functional theories LDA, PBE and DFT + U approximations. The phonon dispersion relation, phonon density of states, Brillion Zone-center phonon frequencies, Born effective charge and polarizability of CeO2 were calculated to investigate the lattice dynamical properties. The value of acoustic phonon frequency TA (Γ) , TO1(Γ) and TO2(Γ) calculated with DFT + U approximation is in better agreement with experimental value as compared to LDA and PBE calculations. The polarizability of CeO2 decreases with increasing frequency and approaches zero with further increase in frequency. Moreover, the temperature dependence of Helmholtz free energy, internal energy, entropy, chemical potential and specific heat capacity at constant volume were analyzed to investigate the thermodynamic properties of CeO2. The lattice dynamical and thermodynamic properties of CeO2 calculated with density functional theories are in agreement with both experimental values and theoretical findings.

Effect of Rod-like Nanoparticles on the Dielectric Susceptibility of Nematic Nano-Composites: A Molecular Theory

The effect of rod-like nanoparticles on the high-frequency dielectric susceptibility of the nematic nano-composites has been investigated in the framework of a molecular theory. Analytical expressions for the components of the effective polarizability of a rod-like nanoparticle in the nematic host have been obtained and used in the calculations of the dielectric susceptibility of the composites as functions of the nanoparticle volume fraction. Numerical calculations of the susceptibility have been undertaken using the nematic liquid crystal 5CB as a host doped with either gold or silver particles for different values of the concentration of nanoparticles. It has been shown that the rod-like nanoparticles have a much stronger effect on the components of the dielectric susceptibility of the nano-composites including, in particular, the one with gold nanoparticles in the vicinity of the plasmon resonance. The main conclusion is that at sufficiently large concentration of nanoparticles, the anisotropy of the dielectric susceptibility of the nano-composites may even change the sign with an increasing concentration which may be important for various applications.

Optical Trapping of a Single Molecule of Length Sub-1 nm in Solution

Optical Trapping of a Single Molecule of Length Sub-1 nm in Solution

Global Full-Dimensional Potential Energy Surface for the Reaction 23Na87Rb + 23Na87Rb → 23Na2 + 87Rb2 and the Formation Rate and Lifetime of the 23Na287Rb2 Collision Complex.

A full-dimensional global potential energy surface (PES) for the reaction 23Na87Rb + 23Na87Rb → 23Na2 + 87Rb2 was constructed based on high-level ab initio calculations. The short-range part was expressed as a permutation invariant polynomial-neural network (PIP-NN) fit of 22 003 ab initio points calculated using a coupled cluster method with the one-electron basis 5s5p5d2f plus effective core potentials and core polarizability potentials, while the long-range part was represented in an asymptotically correct form based on multipole expansion. The formation rate of the 23Na287Rb2 complex calculated using a quantum statistical method is in good agreement with experiment, while the estimated 19.20 μs lifetime of the complex from Rice-Ramsperger-Kassel-Marcus (RRKM) theory is significantly shorter than the measured millisecond decay rate, signaling either the inadequacy of RRKM theory or a yet unresolved loss mechanism.

High Dielectric Nonpolar Interfacial Layers Derived from Nanocellulose for Electrowetting Devices

AbstractA dielectric material is a particular type of insulator that does not conduct electricity but gets polarized when subjected to electricity, which is a crucial part of electronics such as cables, capacitors, displays, transformers, etc. Currently, synthesizing a nonpolar dielectric remains challenging. In this study, a method to make a high dielectric and nonpolar fluoropolymer and its nanocomposites based on cellulose nanocrystals (CNCs) by grafting it with nonpolar polymer 2,2,2‐trifluoroethyl methacrylate is reported. A high dielectric constant but nonpolar nanocellulose material is obtained for the first time. This material has an anisotropic arrangement of dipoles with a high polarizability effect, thereby displaying excellent dielectric properties (e.g., dielectric constant and loss: 8.59 and 0.017 at 10 kHz) and high stability (dielectric constant at 8.21 at 1 MHz). The dielectric material is miscible as an additive with other commercial fluoropolymer plastic, which demonstrates a high breakage voltage ranging from 4.6 to 9.2 kV/0.1 mm. When it is used as an interfacial layer in electrowetting display devices, it also demonstrated a low voltage driven and fast‐response effect. The excellent dielectric performances allow to develop more high‐performance dielectrics and electronics such as memories, sensors, actuators, wires, and film capacitors.

Molecular simulation of the structural and thermodynamic properties of n-alkane/brine interfacial systems with nonionic surfactants

All-atom molecular dynamics (MD) simulations are used to study the structural and thermodynamic properties of water + n-heptane interfacial systems in the presence of salinity (NaCl, NaI, KCl, and KI) and two different nonionic surfactants. Excellent qualitative and quantitative agreement with interfacial tension experimental data is obtained, but this requires applying a charge scaling factor to the ionic species, suggesting the likely role of polarizability effects. Tensoactive behavior is observed for the NaI and KI systems, coinciding with layering of the iodide species near the interface. There are significant interaction differences between the surfactants and the different ionic species, but the structural and thermodynamic behavior of the surfactant molecules is relatively unaffected by the specific salt species. Our analysis suggest that the surfactant-surfactant interactions play a critical role in determining the interfacial behavior, with a much smaller impact associated with the composition of the brine phase.

Fast Polarizable Water Model for Atomistic Simulations.

Simulating water accurately has been a major challenge in atomistic simulations for decades. Inclusion of electronic polarizability effects holds considerable promise, yet existing approaches suffer from significant computational overheads compared to the widely used nonpolarizable water models. We have developed a globally optimal polarizable water model, OPC3-pol, that explicitly accounts for electronic polarizability with minimal impact on the computational efficiency. OPC3-pol reproduces five key bulk water properties at room temperature with an average relative error of 0.6%. In atomistic simulations, OPC3-pol's computational efficiency is in between that of 3- and 4-point nonpolarizable models; the model supports increased (4 fs) integration time step. OPC3-pol is tested in simulations of globular protein ubiquitin and a B-DNA dodecamer with several AMBER force fields, ff99SB, ff14SB, ff19SB, and OL15, demonstrating structure stability close to reference on multi-microsecond time scale. Simulation of an intrinsically disordered amyloid β-peptide yields an ensemble with the radius of gyration of a random coil. The proposed water model can be trivially adopted by any package that supports standard nonpolarizable force fields and water models; its intended use is in long classical atomistic simulations where water polarization effects are expected to be important.

Featuring a new computational protocol for the estimation of intensity and overall quantum yield in lanthanide chelates with applications to Eu(III) mercapto-triazole Schiff base ligands

Computational studies on luminescent properties of lanthanides chelates are important for the pre-synthetic design of new luminescent materials. However, the development of suited computational methods and protocols is still in its infancy. Here we present a new computational protocol for a systematic description and analysis of luminescent properties of Ln(III) chelates. The new methodologies herein presented are divided in three major categories: (1) Utilization of local vibrational mode theory for obtaining local Ln–ligand force constants; (2) Calculation of ligand effective polarizabilities through complex localized molecular orbitals; and (3) Extended formulation of excited state donor–acceptor RL distances accounting for excited molecular orbitals weights. The protocol was applied to understand the underlying photophysical processes in two Eu(III) complexes with mercapto-triazole Schiff bases as main ligands, utilizing time-dependent density functional theory (ωB97X-D/MWB52(Eu)/Def2-TZVP). The introduction of local force constants into lanthanide spectroscopy led to a unique explanation of the inverse relationship between the Ln–ligand strength and ligand effective polarizability. This new protocol will contribute to a better understanding of Ln–ligand bond properties, to more accurate results in terms of Judd–Ofelt intensity parameters and overall quantum yield, and will bridge the current gap between available theoretical results and experimental data.

Effective Chiral Interactions between Nonchiral Rigid Macromolecules in a Chiral Solvent and the Induced Cholesteric Liquid Crystal Phase

It has been shown that a nonchiral anisotropic macromolecule embedded in a chiral dielectric solvent possesses an effective optical activity proportional to the optical activity of the solvent. As a result, there exists an effective chiral interaction between the macromolecules, which creates a torque acting on the primary axes of the two interacting molecules. A general expression for the effective chiral interaction potential has been derived in terms of the effective polarizability and the effective gyration tensor of the macromolecule in the chiral solvent. Explicit expressions for the components of the effective polarizability and the gyration have been obtained using the model of a hard rod filled with anisotropic dielectric and embedded into the isotropic chiral dielectric medium. The theory predicts the formation of the cholesteric helical structure in the nematic polymer liquid crystal phase induced by a chiral solvent.

Bayesian analysis of nuclear polarizability corrections to the Lamb shift of muonic H-atoms and He-ions

The extraction of nuclear charge radii from spectroscopy experiments in muonic atoms is currently limited by the large uncertainties associated with the theoretical evaluation of the nuclear polarizability effects. To facilitate calculations, these polarizability corrections are conventionally expressed as an expansion in a dimensionless parameter η, which has been argued in previous literature to hold an approximate value of 0.33 in light-nuclear systems. In this work, we check this claim by doing a Bayesian analysis of the nuclear-polarizability corrections to the Lamb shift in μ 2H and μ 3H atoms and in μ 3He+ and μ 4He+ ions at various orders in the η-expansion. Our analysis supports the claim that η ≪ 1 in these systems and finds truncation uncertainties that are similar to the previous estimate, the only exception being the truncation uncertainties in the μ 3He+ ion, which are found to be larger.

Negative differential thermal conductance between Weyl semimetals nanoparticles through vacuum

In this work, the near-field radiative heat transfer (NFRHT) between two Weyl semimetal (WSM) nanoparticles (NPs) is investigated. The numerical results show that negative differential thermal conductance (NDTC) effect can be obtained in this system, i.e., when the temperature of the emitter is fixed, the heat flux does not decrease monotonically with the increase of the temperature of the receiver. Specifically, when the temperature of the emitter is 300 K, the heat flux is identical when the temperature of the receiver is 50 K or 280 K. The NDTC effect is attributed to the fact that the permittivity of the WSMs changes with the temperature. The coupling effects of polarizability of two WSM NPs have been further identified at different temperature to reveal the physical mechanism of the NDTC effect. In addition, the NFRHT between two WSM NPs can be greatly enhanced by exciting the localized plasmon and circular modes. This work indicates that the WSMs maybe promising candidate materials for manipulating NFRHT.

Influence of 5-Halogenation on the Base-Pairing Energies of Protonated Cytidine Nucleoside Analogue Base Pairs: Implications for the Stabilities of Synthetic i-Motif Structures for DNA Nanotechnology Applications.

DNA nanotechnology has been employed to develop devices based on i-motif structures. The protonated cytosine-cytosine base pairs that stabilize i-motif conformations are favored under slightly acidic conditions. This unique property has enabled development of the first DNA molecular motor driven by pH changes. The ability to alter the stability and pH transition range of such DNA molecular motors is desirable. Understanding how i-motif structures are influenced by modifications, and which modifications enhance stability and/or affect the pH characteristics, are therefore of great interest. Here, the influence of 5-halogenation of the cytosine nucleobases on the base pairing of protonated cytidine nucleoside analogue base pairs is examined using complementary threshold collision-induced dissociation techniques and computational methods. The nucleoside analogues examined here include the 5-halogenated forms of the canonical DNA and RNA cytidine nucleosides. Comparisons among these systems and to the analogous canonical base pairs previously examined enable the influence of 5-halogenation and the 2'-hydroxy substituent on the base pairing to be elucidated. 5-Halogenation of the cytosine nucleobases is found to enhance the strength of base pairing of DNA base pairs and generally weakens the base pairing for RNA base pairs. Trends in the strength of base pairing indicate that both inductive and polarizability effects influence the strength of base pairing. Overall, the present results suggest that 5-halogenation, and in particular, 5-fluorination and 5-iodination, provide effective means of stabilizing DNA i-motif conformations for applications in nanotechnology, whereas only 5-iodination is effective for stabilizing RNA i-motif conformations but the enhancement in stability is less significant.

Thermal, optical, and volumetric studies on mixing properties of binary nematic mixtures of 9CHBT/11CHBT

• Phase diagrams of a series of binary nematic mixtures (9CHBT/11CHBT) were studied by DSC method. • The modified four-parameter model was used by fitting the experimental data. • The temperature dependence of refractive indices, birefringence and order parameters in nematic phase was investigated. • Quantum chemical calculations on the nematogens provide supportive picture of the optical measurements. Phase diagrams and optical properties of a series of nematic binary mixtures composed of 4-(trans-4′-n-nonylcyclohexyl) isothiocyanatobenzen (9CHBT) and 4-(trans-4′-n-undecylcyclohexyl) isothiocyanatobenzen (11CHBT) were established in the entire range of molar fraction by differential scanning calorimetry method, refractometry as well as density measurements. In this research the thermodynamic, optical, and volumetric properties of the eutectic mixture ( E 9 , 11 ) composed of 9CHBT and 11CHBT ( x 11 C H B T = 0.4 ) were studied and interpreted. The binary phase diagram is in comparable with that predicted from Schroder–van Laar equation. The excess functions were determined using the calculated activity coefficients of the eutectic mixture. Moreover, the temperature dependence of refractive indices, birefringence, and order parameters of the pure nematogens and the binary eutectic mixture was investigated. In contrast to the individual nematogens, the eutectic mixture ( E 9 , 11 ) displays a crossover temperature ( T CO ) based on the four-parameter model. Finally, results from quantum chemical calculations on the studied nematogens provide an overall supportive and coherent picture of the thermal, optical measurements. All calculations were performed using the Turbomole software package. The used methodology allows for an acceptable approximation of effective polarizabilities.

Quasitrapped modes in metasurfaces of anisotropic MoS2 nanoparticles for absorption and polarization control in the telecom wavelength range

We investigate the resonant optical response of single material-anisotropic nanoparticles (NPs) of molybdenum disulfide (MoS$_2$) and their two-dimensional arrays (metasurfaces) irradiated by plane waves of the telecomunication optical range. Nanoparticles in the form of a disk with centered and shifted hole are considered. Using the recently experimental measured the MoS$_2$ dielectric permittivity and numerical calculations with analytical multipole analysis, we show that the material-anisotropy of NPs can lead to specific nonlocal contributions in their magnetic and electric dipole response and affect the effective dipole polarizabilities. Applying a special procedure we determine the period of the MoS$_2$ metasurfaces supporting the quasi-trapped mode (QTM) resonance around the tellecom wavelength of 1550 nm. It is shown that regardless extremely weak absorption of the single nanoparticles, the excitation of the QTM leads to effective narrowband absorption in the metasurfaces. Influences of the linear polarization direction of normally incident waves on the QTM implementation and the reflection and transmission spectra are studied. It is found and demonstrated, for the first time, that a metasurface, composed of the MoS$_2$ disks with their anisotropy perpendicularto the metasurface plane, has the properties of a continuous birefringent medium. Due to these properties, normally incident and linear-polarized waves can be transformed in the transmitted and reflected waves with changed polarizations.

Correlation analysis of the solubility of organic compounds: influence of the polarizability effect

Correlation analysis of the solubility of organic compounds: influence of the polarizability effect

Analysis of inhomogeneous meta-surfaces under oblique incidents

A semi-analytical method for analyzing inhomogeneous meta-surfaces under oblique incidence based on the polarizabilities of constituent particles and interaction constants is presented. The inhomogeneity is proposed in which a meta-surface is considered as a periodic array of repetitive super-cells. Our proposed method provides effective polarizabilities and therefore it gives a comprehensive view of meta-surface behavior. To validate our proposed method, several examples are illustrated, which include different cases of isotropic and bi-anisotropic arrays. In the first example, an array of different sizes of Gold spherical Nano-particles is considered. In the second example, a combined array of Gold (Plasmonic) and Si (dielectric) particles is analyzed and the third example includes an array of different sizes of mutually coupled Gold Nano-disks. The effective polarizabilities of all these arrays are computed under the illumination of oblique incident waves with different incident angles. The accuracy of this method is verified by comparing the computed reflection and transmission coefficients to the results produced by the HFSS software.

Flexoelectric nanostructure design using explicit topology optimization

Flexoelectricity is the coupling between polarization and strain gradient. As the large strain gradient leads to a strong flexoelectric effect, the design of flexoelectric nano-structure via topology optimization has seen growing attentions. In the present work, an explicit topology optimization framework is proposed for flexoelectric structures design. To achieve this purpose, the Moving Morphable Void (MMV)-based approach is employed in the context of Isogeometric Analysis (IGA) combined with the Trimming Surface Analysis (TSA). Energy conversion factor and effective electric polarizability are respectively optimized to improve the flexoelectric performance of the nanostructure. Performing design under the explicit framework coupled with IGA can bring several advantages. Due to the use of NURBS basis functions of IGA, the required continuity in the approximation of the PDEs of flexoelectricity can be satisfied straightforwardly. Furthermore, with the use of the TSA technique, the occurrence of weak/gray material, which may cause numerical instability in flexoelectricity design, can be avoided. Also due to the explicit geometry description in MMV, the optimized result can be imported to the CAD system directly, which is significant for nanoscale structure from manufacturing perspective. Several representative numerical examples for topology optimization of flexoelectric structures are presented to demonstrate the effectiveness and advantages of the proposed approach.