Crystal Theory Research Articles

Electro-optical properties of nematic lyotropic chromonic liquid crystals

The electro-optical properties of liquid crystals play an important role in liquid crystal displays. Lyotropic liquid chromonic crystals are attracting the interest of researchers because of its extending application in areas of chemistry, medicine, and biology. An experimental apparatus is constructed based on nematic lyotropic chromonic liquid crystal sunset yellow filled in the twisted nematic liquid crystal cell to obtain two primary parameters of the electro-optical properties, the threshold voltage and relaxation time. The threshold voltage and relaxation time of nematic lyotropic chromonic liquid crystals decrease with the increase of temperature or the decrease of concentration. The concentration of neutral ionic dopants like sodium chloride and magnesium sulfate is positively correlated with the threshold voltage and relaxation time of nematic lyotropic chromonic liquid crystals, while the concentration of alkaline ionic dopants like sodium hydroxide exhibits a negative correlation. The changes of the electro-optical properties with respect to the temperature, solute concentration, and dopant concentration are analyzed based on the alteration of the molecular self-assembly behaviors of lyotropic chromonic liquid crystals. In addition, the viscoelastic theory of nematic thermotropic liquid crystals is proved to be also applicable on nematic lyotropic chromonic liquid crystals for the first time.

Verification of thermodynamic theories of strain-induced polymer crystallization.

We studied the crystallization of nearly "homogeneous" polyethylene glycol (PEG) networks prepared by end-crosslinking of tetra-armed PEG. The influence of stretching ratio and strand length on the melting and crystallization temperature was investigated. The relation of melting temperature and elongation ratio verifies the thermodynamic theories of strain-induced polymer crystallization.

Numerical analysis of subgrain formation during metal cutting and rolling based on the crystal plasticity theory

The grain refinement technology is important in improving the metallic material properties without the requirement of additional alloy elements. Previously, we developed an efficient method for producing ultrafine-grained steel strips using a combination of cutting and heat treatment. However, the effect of cutting on recrystallization was not apparent. The objective of this study is to investigate the effects of metal cutting on static recrystallization and outline its advantages in grain refinement using numerical simulations based on the crystal plasticity theory. Simulation results show that shear deformation in metal cutting activates more slip systems than plane strain compression via rolling, even when considering the same equivalent plastic strain. The geometrically necessary dislocations are assumed to accumulate in the crystal because many slip systems are activated in shear deformation and improve grain refinement via static recrystallization in the subsequent heat treatment. This result indicates that the deformation type plays an important role in the recrystallization process. Thus, cutting is more efficient than rolling for the production of ultrafine-grained steel.

Recent analytic development of the dynamic $ Q $-tensor theory for nematic liquid crystals

<abstract><p>Liquid crystals are a typical type of soft matter that are intermediate between conventional crystalline solids and isotropic fluids. The nematic phase is the simplest liquid crystal phase, and has been studied the most in the mathematical community. There are various continuum models to describe liquid crystals of nematic type, and $ Q $-tensor theory is one among them. The aim of this paper is to give a brief review of recent PDE results regarding the $ Q $-tensor theory in dynamic configurations.</p></abstract>

First-principles investigations of tricarbon: From the isolated C3 molecule to a novel ultra-hard anisotropic solid

Based on crystal chemistry considerations and quantum density functional theory ground state calculations, rhombohedral rh-C3 and hexagonal h-C6 carbon allotropes are proposed and energetically calculated as new stable ultra-hard phases likewise lonsdaleite. Along the two kinds of carbon in linear C2-C1-C2 lattice, distorted tetrahedra C2(sp3) with an angle of 106.17{\deg} (smaller than ideal 109.4{\deg}) and C1(sp)-like hybridizations are inferred from charge density projections. The calculated elastic constants point to a strong anisotropy of mechanical properties of rh-C3 and h-C6 with an exceptionally large C33 values (1636 GPa and 1610 GPa, respectively), exceeding that of lonsdaleite (1380 GPa), due to the presence of aligned tricarbon units along the hexagonal c-axis. Both phases are characterized by large bulk moduli and high hardness values that are slightly less than those of lonsdaleite and diamond. Weak metallic behavior of both new phases is identified from electronic band structure calculations.

Synthesis, crystal structure, spectroscopic, quantum chemical investigation, molecular docking and ADMET prediction of 2(E)-3-(anthracen-9-yl)-1-(1-methyl-1H-pyrrol-2-yl) prop-2-en-1-one

In the present study, 2(E)-3-(anthracen-9-yl)-1-(1-methyl-1H-pyrrol-2-yl) prop-2-en-1-one (3AMP) crystal was grown by slow evaporation method. The single crystal X-ray diffraction analysis and density functional theory (DFT) calculations were carried out for 3AMP crystal. The 3AMP crystallizes in orthorhombic space group Pbca with a = 14.818 (8) Å, b = 9.796 (5) Å, c = 23.239 (11) Å. Hirshfeld surface and finger print plots were analyzed to confirm the existence of intra-, inter-molecular and other weak interactions using Crystal Explorer. The optimized molecular structure and harmonic wavenumbers were calculated by DFT method using B3LYP functional with 6-31G(d,p) basis set. The FT-IR, 1H, 13C NMR and UV–Vis spectra of 3AMP were recorded and analyzed. The optimized geometrical parameters, calculated wavenumbers by DFT method were compared with the experimental results. Natural bond orbital (NBO) analysis was carried out to evaluate the intra- and inter-molecular interactions in the crystal. The energy gap for 3AMP was calculated as 3.156 eV. Molecular electrostatic potential (MEP), Mulliken atomic charges and non-linear optical (NLO) properties for the title crystal were calculated. In addition, gauge invariant atomic orbital (GIAO) method was used to calculate the 1H and 13C NMR chemical shifts in the ground state. To obtain the electronic transitions in UV–Vis spectra of the title molecule in DMSO and ethanol solvents, TD-DFT calculations were performed on the optimized geometry. Furthermore, the compound was subjected to in silico ADMET evaluation. Molecular docking study was carried out to determine the interactions of ligand with the protein Hyaluronidase (PDB ID: 1FCQ).

Physical Basis of Functioning of Antifreeze Protein

Antifreeze proteins, expressed in cold-blooded organisms, prevent ice formation in their bodies, and thus help them to survive in extremely cold winter temperatures. However, the mechanism of action of these proteins is still not clear. In any case, it is not simply a decrease in the temperature of normal ice formation. In this work, investigating the ice-binding protein (a mutant form of the antifreeze protein cfAFP from the spruce budworm Choristoneura fumiferana, which overwinters in needles), we showed that this antifreeze protein does not at all lower the freezing point of water and, paradoxically, increases the melting point of ice. On the other hand, calculations based on the theory of crystallization show that at temperatures of 0° to -30°C ice can only appear on surfaces that contact water, but not in the body of water. These facts suggest a new perspective on the role of antifreeze proteins: their task is not (as it is commonly believed) to bind with nascent ice crystals already formed in the organism and stop their growth, but to bind to those surfaces, on which ice nuclei can appear, and thus completely inhibit the ice formation in supercooled water or biological fluid.

Variational theory of crystal growth and its application for analysis of forming processes for metastable phases in overcooled metallic melts with eutectic composition

The new crystallization theory for overcooled metastable melt is developed; it is based on variational mechanical principles and takes into account regularities of forming and diffusion growth of equilibrium crystals as well as diffusion-free growth of metastable crystals. Calculations for the melt Fe83B17 were conducted on the model; they displayed that simultaneous nucleation and growth of Fe and Fe2B with metastable phase Fe3B are observed in overcooled melt, and growth speed of near-critical dimensional crystals of Fe3B exceeds crystal growth speed of Fe and Fe2B. The effect of diffusion-free growth is observed for Fe3B crystals, when quickly growing Fe3B crystal surface catches boron atoms. Quasi-equilibrium phase diagram for overcooled Fe-B melt was built on the base of the developed theory; it takes into account both equilibrium crystal growth and metastable phase growth. The obtained diagram allows to predict the values of components concentration near the surface of growing crystals both for Fe and Fe2B crystals meeting the requirements of local equi-librium condition on their surface and for Fe3B metastable crystals which are characterized by diffusion-free growth stipulated by high motion speed of crystal surface.

Polycrystal plasticity with grain boundary evolution: a numerically efficient dislocation-based diffuse-interface model

Grain structure plays a key role in the mechanical properties of alloy materials. Engineering the grain structure requires a comprehensive understanding of the evolution of grain boundaries (GBs) when a material is subjected to various manufacturing processes. To this end, we present a computationally efficient framework to describe the co-evolution of bulk plasticity and GBs. We represent GBs as diffused geometrically necessary dislocations, whose evolution describes GB plasticity. Under this representation, the evolution of GBs and bulk plasticity is described in unison using the evolution equation for the plastic deformation gradient, an equation central to classical crystal plasticity theories. To reduce the number of degrees of freedom, we present a procedure which combines the governing equations for each slip rates into a set of governing equations for the plastic deformation gradient. Finally, we outline a method to introduce a synthetic potential to drive migration of a flat GB. Three numerical examples are presented to demonstrate the model. First, a scaling test is used to demonstrate the computational efficiency of our framework. Second, we study the evolution of a tricrystal, formed by embedding a circular grain into a bicrystal, and demonstrate qualitative agreement between the predictions of our model and those of molecular dynamics simulations by Trautt and Mishin (2014 Acta Mater. 65 19–31). Finally, we demonstrate the effect of applied loading in texture evolution by simulating the evolution of a synthetic polycrystal under applied displacements.

The role of dissipation regarding the concept of purely mechanical theories in plasticity

The concept of a purely mechanical theory is revisited within the framework of continuum thermodynamics. It is based on three assumptions: (i) the additive split of the specific free energy into a mechanical contribution not depending on the temperature and a contribution that depends on the temperature only, (ii) a homogeneous and stationary temperature field, and (iii) a negligible heat supply. The consequences of these three assumptions on the dissipation inequality in form of the Clausius–Duhem inequality are discussed. It is shown, that these three assumption yield a vanishing dissipation. This result is valid for the classical Cauchy–Boltzmann continuum as well as for extended continua. Many plasticity theories consider the first two assumptions tacitly, however the role of the heat supply is not discussed. Here, the consequences of a vanishing dissipation with respect to a local crystal plasticity theory are discussed, exemplarily. The paper does not favor a purely mechanical theory but highlights the implications of such an approach.

Active forces modulate collective behaviour and cellular organization.

Biological tissues are composed of various cell types working cooperatively to perform their respective function within organs and the whole body. During development, embryogenesis followed by histogenesis relies on orchestrated division, death, differentiation and collective movements of cellular constituents. These cells are anchored to each other and/or the underlying substrate through adhesion complexes and they regulate force generation by active cytoskeleton remodeling. The resulting changes in contractility at the level of each single cell impact tissue architecture and remodeling by triggering changes in cell shape, cell movement and remodeling of the surrounding environment. These out of equilibrium processes occur through cellular energy consumption, allowing biological systems to be described by active matter physics. Cytoskeleton filaments, bacterial and eukaryotic cells can be considered as a sub-class of active matter termed "active nematics". These biological objects can be modelled as rod-like elements to which nematic liquid crystal theories can be applied. In this work, using an analogy from liquid crystal physics, we show that cell sorting and boundary formation can be explained using differences in nematic activity. This difference in nematic activity arises from a balance of inter- and intra-cellular activity.

The Charge Transfer Band as a Key to Study the Site Selection Preference of Eu3+ in Inorganic Crystals.

On account of the strong oxidizing property of the europium(III) ion, its charge transfer band (CTB) can be easily formed in many inorganic compounds. In this work, the Eu3+ ions were singly doped into the K3LuSi2O7 compound with a hexagonal structure, and two kinds of Eu3+-O2- CTBs were detected by monitoring at specific wavelengths. The qualitative analysis of Eu3+ ion site occupation was illuminated by combining Eu3+-O2- CTBs with the corresponding cell volume. Furthermore, the two kinds of Eu3+ sites are eventually assigned to the K(2) and Lu sites, which means that Eu3+ ions selectively occupy the site with a low coordination number, according to the calculated CT energy by the dielectric theory of complex crystals and the magnitude of CT energy in the excitation spectra. Meanwhile, at high temperatures, the CTB does not show the traditional thermal quenching like f-f transitions but demonstrates thermal enhancement; thus, by using this opposite variation in excitation spectra, a noninvasive optical thermometer is presented, and this opposite variation tendency is thought to be the difference of thermal stability of disparate excited energy states. When new luminescent phosphors are designed with interesting spectral properties, this work will give us an alternative approach to determine the site occupation preference of Eu3+, especially when there are more than two different sites in the compound.

Effect of Fluid Flow on Crystallization in a Segmented Flow Microchannel

Segmented flow crystallization has attracted the attention of engineers in the development of drug substance processes, because the crystallization behavior is different from that observed in conventional stirred tanks. Under segmented flow conditions, the crystal size distribution is narrower, and the crystallization rate is higher than that of batch crystallization. However, the phenomenological theory of segmented flow crystallization has not been clarified. The purpose of this study was to gain more insights into segmented flow crystallization phenomena. We focused on the influence of fluid behavior on crystallization. First, we analyzed the motion of crystals in a segmented flow using computational fluid dynamics. Under the assumption that the mass transfer is the rate-determining step of crystal growth, we evaluated how particle and flow conditions contribute to the mass transfer. The shear rate under segmented flow was found to be approximately 16 times greater than that in a stirred tank. The high shear rate induced a high mass transfer rate, which is often observed under segmented flow conditions.

Thermodynamics of strain-induced crystallization in filled natural rubber under uni- and biaxial loadings, Part II: Physically-based constitutive theory

To understand thoroughly the strain-induced crystallization in natural rubbers, conventional mechanical measurements are inadequate because they only provide a macroscopic relation between stress and strain. In this second part, a physically-based constitutive model for filled natural rubbers is coupled with the infrared thermography-based quantitative surface calorimetry (Part I) to shed new light on multiaxiality of strain-induced crystallization. In contrast to previous works, the kinetics of phase transition outside thermodynamic equilibrium is discussed. By introducing only two additional parameters (compared to the equilibrium crystallization theory), underlying mechanisms of nonequilibrium strain-induced crystallization can be well interpreted. To capture multiaxiality of strain-induced crystallinity, the analytical network-averaging is utilized for the calculation of kinematic internal variables. Model predictions are then compared with comprehensive testing data (Part I) and demonstrate good agreement with these experiments.

A Novel 3D Node Deployment Inspired by Dusty Plasma Crystallization in UAV-Assisted Wireless Sensor Network Applications.

With the rapid progress of hardware and software, a wireless sensor network has been widely used in many applications in various fields. However, most discussions for the WSN node deployment mainly concentrated on the two-dimensional plane. In such a case, some large scale applications, such as information detection in deep space or deep sea, will require a good three dimensional (3D) sensor deployment scenario and also attract most scientists’ interests. Excellent deployment algorithms enable sensors to be quickly deployed in designated areas with the help of unmanned aerial vehicles (UAVs). In this paper, for the first time, we present a three dimensional network deployment algorithm inspired by physical dusty plasma crystallization theory in large-scale WSN applications. Four kinds of performance evaluation methods in 3D space, such as the moving distance, the spatial distribution diversion, system coverage rate, and the system utilization are introduced and have been carefully tested.Furthermore, in order to improve the performance of the final deployment, we integrated the system coverage rate and the system utilization to analyze the parameter effects of the Debye length and the node sensing radius. This criterion attempts to find the optimal sensing radius with a fixed Debye length to maximize the sensing range of the sensor network while reducing the system redundancy. The results suggest that our 3D algorithm can quickly complete an overall 3D network deployment and then dynamically adjust parameters to achieve a better distribution. In practical applications, engineers may choose appropriate parameters based on the sensor’s hardware capabilities to achieve a better 3D sensor network deployment. It may be significantly used in some large-scale 3D WSN applications in the near future.

Analysis on vibration characteristics of large-size rectangular piezoelectric composite plate based on quasi-periodic phononic crystal structure

Based on the theory of composite materials and phononic crystals (PCs), a large-size rectangular piezoelectric composite plate with the quasi-periodic PC structure composed of PZT-4 and epoxy is proposed in this paper. This PC structure can suppress the transverse vibration of the piezoelectric composite plate so that the thickness mode is purer and the thickness vibration amplitude is more uniform. Firstly, the vibration of the model is analyzed theoretically, the electromechanical equivalent circuit diagram of three-dimensional coupled vibration is established, and the resonance frequency equation is derived. The effects of the length, width, and thickness of the piezoelectric composite plate at the resonant frequency are obtained by the analytical method and the finite element method, the effective electromechanical coupling coefficient is also analyzed. The results show that the resonant frequency can be changed regularly and the electromechanical conversion can be improved by adjusting the size of the rectangular piezoelectric plate. The effect of the volume fraction of the scatterer on the resonant frequency in the thickness direction is studied by the finite element method. The band gap in X and Y directions of large-size rectangular piezoelectric plate with quasi-periodic PC structures are calculated. The results show that the theoretical results are in good agreement with the simulation results. When the resonance frequency is in the band gap, the decoupling phenomenon occurs, and then the vibration mode in the thickness direction is purer.

Atomic scale crystal field mapping of polar vortices in oxide superlattices

Polar vortices in oxide superlattices exhibit complex polarization topologies. Using a combination of electron energy loss near-edge structure analysis, crystal field multiplet theory, and first-principles calculations, we probe the electronic structure within such polar vortices in [(PbTiO3)16/(SrTiO3)16] superlattices at the atomic scale. The peaks in Ti L-edge spectra shift systematically depending on the position of the Ti4+ cations within the vortices i.e., the direction and magnitude of the local dipole. First-principles computation of the local projected density of states on the Ti 3d orbitals, together with the simulated crystal field multiplet spectra derived from first principles are in good agreement with the experiments.

Probing the Local Coordination of Hexavalent Uranium and the Splitting of 5f Orbitals Induced by Chemical Bonding

We report here a detailed experimental and theoretical investigation of hexavalent uranium in various local configurations with a high-energy-resolution fluorescence-detected X-ray absorption near-edge structure at the U M4 edge. We show the pronounced sensitivity of the technique to the arrangement of atoms around the absorber and provide a detailed theoretical interpretation revealing the nature of spectral features. Calculations based on density functional theory and on crystal field multiplet theory indicate that for all local configurations analyzed, the main peak corresponds to nonbonding 5f orbitals, and the highest energy peak corresponds to antibonding 5f orbitals. Our findings agree with the accepted interpretation of uranyl spectral features and embed the latter in a broader field of view, which interprets the spectra of a large variety of U6+-containing samples on a common theoretical ground.

A microcontinuum model of nematoacoustics

A micromorphic model of compressible nematic liquid crystals is here proposed in order to revise and extend the micropolar approach which, as here shown, is compatible with incompressible fluid dynamics. On the basis of an expansion of mass density in terms of microdensity, we introduce a density contribution of the free energy which agrees with some constitutive laws pertaining extensions of the classical ”director” theory of liquid crystals. Compressibility is described by a microstretch model which allows to write a set of balance laws comparable with the micropolar approach. Nematoacoustic effects due to the orientation of the wave vector with respect to the nematic configuration are analyzed evidentiating the expected dispersive and dissipative behavior of the admitted wave modes.

Optical activities of helical polymers: a crystal orbital theory based on Wannier functions

Optical activities of helical polymers: a crystal orbital theory based on Wannier functions