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We investigate the effect of topology on the equilibrium behavior of singly tethered ring polymers adsorbed on an attractive surface. We focus on the change of square radius of gyration R²g, the perpendicular component R²g⊥ and the parallel component R²g ‖ to the adsorbing surface, the mean contacting number of monomers with the surface {M}, and the monomer distribution along z-direction during transition from desorption to adsorption. We find that both of the critical point of adsorption ec and the crossover exponent f depend on the knot type when the chain length of ring ranges from 48 to 400. The behaviors of R²g, R²g⊥, and R²g ‖ are found to be dependent on the topology and the monomer-surface attractive strength. At weak adsorption, the polymer chains with more complex topology are more adsorbable than those with simple topology. However, at strong adsorption, the polymer chains with complex topology are less adsorbable. By analyzing the distribution of monomer along z-direction, we give a possible mechanism for the effect of topology on the adsorption behavior. [ABSTRACT FROM AUTHOR]

We perform lattice Monte Carlo simulation using the bond-fluctuation model to examine the conformation and dynamic properties of a single small flexible ring polymer in the matrix of linear chains as functions of the degree of polymerization of the linear chains. The average conformation properties as gauged by the mean-square radius of gyration and asphericity parameter are insensitive to the chain length for all the chain lengths examined (30, 100, 300, and 1000). However, in the longer chain (300 and 1000) samples, there is an increased spread in the distribution of the value of these quantities, suggesting structural heterogeneity. The center-of-mass diffusion of the ring shows a rapid decrease with increasing chain length followed by a more gradual change for the two longer chain systems. In these longer chain systems, a wide spread in the value of the apparent self-diffusion coefficient is also observed, as well as qualitatively different square displacement trajectories among the different samples, suggesting heterogeneity in the dynamics. A primitive path analysis reveals that in these long chain systems, the ring can exist in topologically distinct states with respect to threading by the linear chains. Threading by the linear chain can dramatically slow down and in some cases stall the diffusive motion of the ring. We argue that the life times for these topological conformers can be longer than the disentanglement time of the linear chain matrix, so that the ring exhibits nonergodic behavior on time scales less or comparable to the life time of these conformers. Our results suggest a picture of the ring diffusion as one where the diffusion path consists of distinctive segments, each corresponding to a different conformer, with slow interconversion between the different conformers. [ABSTRACT FROM AUTHOR]

We report a numerical investigation of the crystallization of monodisperse hard spheres on different patterned substrates. We find that the duration of a metastable fluid state, which may last for relatively long time in the homogeneous crystallization, can be deeply reduced or almost eliminated when a substrate is used as the seed of crystallization. In the presence of the square patterned substrate, which has the basic character of the body-centered cubic (bcc) crystal structure, a transient bcc crystal phase was observed, suggesting that the bcc structure could be possible to be stabilized by the square patterned substrates. The process of crystallization becomes complicated when the patterned substrate is incommensurate with the bulk crystal. Furthermore, a purely face-centered cubic or hexagonal close packed crystal phase with stacking faults can be generated by using a certain patterned substrate without other factors such as gravity. [ABSTRACT FROM AUTHOR]

The effects of hydrodynamic interactions on the lamellar ordering process for two-dimensional quenched block copolymers in the presence of extended defects and the topological defect evolutions in lamellar ordering process are numerically investigated by means of a model based on lattice Boltzmann method and self-consistent field theory. By observing the evolution of the average size of domains, it is found that the domain growth is faster with stronger hydrodynamic effects. The morphological patterns formed also appear different. To study the defect evolution, a defect density is defined and is used to explore the defect evolutions in lamellar ordering process. Our simulation results show that the hydrodynamics effects can reduce the density of defects. With our model, the relations between the Flory–Huggins interaction parameter χ, the length of the polymer chains N, and the defect evolutions are studied. It is found that χN is an important parameter for defect evolutions. Furthermore, the evolution behavior of the defect densities and the average size of domains are compared and the differences are discussed. [ABSTRACT FROM AUTHOR]

The phase behaviors of comblike block copolymer Am+1Bm/homopolymer A mixtures are studied by using the random phase approximation method and real-space self-consistent field theory. From the spinodals of macrophase separation and microphase separation, we can find that the number of graft and the length of the homopolymer A have great effects on the phase behavior of the blend. For a given composition of comblike block copolymer, increasing the number of graft does not change the macrophase separation spinodal curve but decreases the microphase separation region. The addition of a small quantity of long-chain homopolymer A increases the microphase separation of comblike block copolymer/homopolymer A mixture. However, the addition of short-chain homopolymer A will decrease the phase separation region of comblike block copolymer/homopolymer A mixture. It is also found that the microstructure formed by diblock copolymer is easier to be swelled by homopolymer than that formed by comblike block copolymer. This can be attributed to the architecture difference between the comblike block copolymer and linear block copolymer. [ABSTRACT FROM AUTHOR]

Self-assembled behavior of symmetric ABA rod-coil-rod triblock copolymer melts is studied by applying self-consistent-field lattice techniques in three-dimensional space. The phase diagram is constructed to understand the effects of the chain architecture on the self-assembled behavior. Four stable structures are observed for the ABA rod-coil-rod triblock, i.e., spherelike, lamellar, gyroidlike, and cylindrical structures. Different from AB rod-coil diblock and BAB coil-rod-coil triblock copolymers, the lamellar structure observed in ABA rod-coil-rod triblock copolymer melts is not stable for high volume fraction of the rod component (frod=0.8), which is attributed to the intramolecular interactions between the two rod blocks of the polymer chain. When 0.3≤frod≤0.7, the intramolecular interactions between the two rigid blocks of the polymer chain are decrease, which results in the occurrence of some interesting metastable mixed structures. These structures have not been observed in polymers containing only one rod block, such as a lamellar-alt-lamellar structure. The results are expected to provide guidance for the design of microstructures in experiments. [ABSTRACT FROM AUTHOR]

A high magnetic field magneto-optical spectrum is utilized to study the A exciton of bulk 2H-MoTe2 single crystal. A clear Zeeman splitting of the A exciton is observed under high magnetic fields up to 41.68T, and the g-factor (-2.09±.08) is deduced. Moreover, a high magnetic field enables us to obtain the quadratic diamagnetic shifts of the A exciton (0.486 μeV T-2). Accordingly, the binding energy, reduced mass, and radius of the A exciton were obtained by using both two and three dimensional models. Compared with other transition metal dichalcogenides (TMDs), the A exciton of bulk 2H-MoTe2 has a relatively small binding energy and larger exciton radius, which provide fundamental parameters for comprehensive understanding of excitons in TMDs as well as their future applications. [ABSTRACT FROM AUTHOR]

The characteristics of magnetized electron sheath near a positively biased conducting wall parallel to magnetic field formed between two permanent magnetic plates were experimentally investigated in a double plasma device. The magnetic field strength between the magnetic plates is about 1200G which is sufficient to magnetize the plasma such that the ion gyroradius is comparable to the electron Debye length. A virtual cathode (or potential dip) structure was found between the electron-rich sheath and bulk plasma. For a given neutral gas pressure, the potential minimum (dip position) remains almost the same for different positive biases on the wall. For a given bias on the wall, however, the electron sheath thickness and the potential drop from the bulk plasma to the dip decrease with the increase of the neutral gas pressure. In addition, the electron sheath and potential dip appear to be wider and deeper in the downstream side of the wall. [ABSTRACT FROM AUTHOR]

As the wafer size increases, dual frequency (DF) inductively coupled plasma (ICP) sources have been proposed as an effective method to achieve large-area uniform plasma processing. A twodimensional (2D) self-consistent fluid model, combined with an electromagnetic module, has been employed to investigate the influence of the low frequency (LF) source on the plasma radial uniformity in an argon DF discharge. When the DF antenna current is fixed at 10 A, the bulk plasma density decreases significantly with the LF due to the less efficient heating, and the best radial uniformity is obtained at 3.39MHz. As the LF decreases to 2.26 MHz, the plasma density is characterized by an edge-high profile, and meanwhile the maximum of the electron temperature appears below the outer two-turn coil. Moreover, the axial ion flux at 3.39MHz is rather uniform in the center region except at the radial edge of the substrate, where a higher ion flux is observed. When the inner five-turn coil frequency is fixed at 2.26 MHz, the plasma density profiles shift from edge-high over uniform to center-high as the LF coil current increases from 6A to 18 A, and the best plasma uniformity is obtained at 14 A. In addition, the maximum of the electron temperature becomes lower with a second peak appears at the radial position of r=9 cm at 18A. [ABSTRACT FROM AUTHOR]

With the aim of enhancing the efficiency with which plastic scintillators detect high-energy X-rays, hafnium-doped organic-inorganic hybrid scintillators were fabricated via a sol-gel method. Transmission electron microscopy of sampled material reveals the presence of HfxSi1-xO2 nanoparticles, dispersed in a polymer matrix that constitutes the active material of the X-ray detector. With HfxSi1-xO2 nanoparticles incorporated in the polymer matrix, the absorption edge and the luminescence wavelength is shifted, which we attribute to Mie scattering. The detection efficiency for 67.4-keV X-rays in a 0.6-mm-thick piece of this material is two times better than the same thickness of a commercial plastic scintillator-NE142. [ABSTRACT FROM AUTHOR]

Although multiple overstretched DNA states were identified in experiments, the mechanism of the emergence of distinct states is still unclear. Molecular dynamics simulation is an ideal tool to clarify the mechanism, but the force loading rates in stretching achieved by conventional all-atom DNAmodels are much faster, which essentially affect overstretching states. We employed a modified coarse-grained DNAmodel with an unprecedented low loading rate in simulations to study the overstretching transitions of end-opened double-stranded DNA. We observed two-strand peeling off for DNA with low stability and the S-DNA with high stability under tension. By introducing a melting-forbidden model which prevents base-pair breaking, we still observed the overstretching transition induced by the formation of S-DNA due to the change of dihedral angle. Hence, we confirmed that the competition between the two strain-softening manners, i.e., base-pair breaking and dihedral angle variation, results in the emergence of distinct overstretched DNA states. [ABSTRACT FROM AUTHOR]

We present an event-driven molecular dynamics study of glass formation in two-dimensional binary mixtures composed of hard disks and hard ellipses, where both types of particles have the same area. We demonstrate that characteristic glass-formation behavior appears upon compression under appropriate conditions in such systems. In particular, while a rotational glass transition occurs only for the ellipses, both types of particles undergo a kinetic arrest in the translational degrees of freedom at a single density. The translational dynamics for the ellipses is found to be faster than that for the disks within the same system, indicating that shape anisotropy promotes the translational motion of particles. We further examine the influence of mixture's composition and aspect ratio on the glass formation. For the mixtures with an ellipse aspect ratio of k = 2, both translational and rotational glass transition densities decrease with increasing the disk concentration at a similar rate, and hence, the two glass transitions remain close to each other at all concentrations investigated. By elevating k, however, the rotational glass transition density diminishes at a faster rate than the translational one, leading to the formation of an orientational glass for the ellipses between the two transitions. Our simulations imply that mixtures of particles with different shapes emerge as a promising model for probing the role of particle shape in determining the properties of glass-forming liquids. Furthermore, our work illustrates the potential of using knowledge concerning the dependence of glass-formation properties on mixture's composition and particle shape to assist in the rational design of amorphous materials. [ABSTRACT FROM AUTHOR]

We investigate numerically the relaxation and diffusion dynamics in three-dimensional Kob-Andersen glass-forming liquids in which part of the particles are randomly chosen and pinned permanently. We find that both the relaxation dynamics and diffusion dynamics slow down as increasing the pinning concentration (cpin) at fixed temperatures that we study. For higher temperature and lower cpin, the α relaxation time τ and the diffusion coefficient D have the scaling relationship D ~ τ-1. However, this coupling behavior breaks down if cpin is further increased, and the scaling relationship is replaced by D ~ τ-ν with ν < 1. At temperatures around the onset temperature of the bulk system, a transition from ν ~ 0.75 to ν ~ 0.61 with increasing cpin is found. However, at lower temperatures, ν ~ 0.67 holds in the whole studied cpin range. By fitting the relaxation time as a function of cpin with Vogel-Fulcher-Tamman equation, we find that the change of scaling exponent ν is accompanied with the change of fragility parameter K at higher temperatures. However, at lower temperatures, pinning particles have little effect on the system's qualitative properties. Moreover, we investigate three measures of heterogeneity of dynamics and find that the relaxation and the diffusion motion of particles show different responses to the pinned particles, which may lead to the slower relaxation than diffusion and the decoupling of relaxation and diffusion. The string-like motion is found to saturate at the mode-coupling theory (MCT) crossover point, which indicates that other relaxation modes may exist below the MCT transition point. [ABSTRACT FROM AUTHOR]

We study the point-to-set length scales and dynamics in three-dimensional Kob-Andersen glass-forming liquids with amorphous boundary conditions by using molecular dynamics simulation, where a set of particles in an equilibrium configuration are pinned while other particles move as before. We consider three different geometries, i.e., spherical cavity, cubic cavity, and walls, for the pinning set of particles. We present the growing static and dynamic point-to-set correlation length scales in the temperature range higher than the ideal mode-coupling theory transition temperature of the bulk. Our results reveal that the two-point static spatial correlations are almost the same for these three geometries at the same temperature, which implies weak geometry dependence on the structure of such glass-forming liquids. By analyzing z (the distance from the wall) dependent point-to-set overlaps, we find that the particles in the layers near the pinning wall relax slower than those far away from the wall. Associated with the dynamical slowdown, the static length scale increases modestly while the dynamic length scale increases dramatically as the temperature is lowered. Compared with the two cavities, the "Walls" system relaxes faster at the same temperature and the same distance from the wall and has smaller length scales. Moreover, the relation between time scale and static length scales depends on the degree of supercooling and the type of geometries. We did not see any clear evidence for the one-to-one correspondence between static and dynamic point-to-set length scales, and also for the one-to-one correspondence between static length scales and relaxation time in the deep supercooled regime. Our results provide clues for the existence of multi-relaxation modes in the supercooled regime in three-dimensional Kob-Andersen glass-forming liquids. [ABSTRACT FROM AUTHOR]

By incorporating self-consistent field theory with lattice Boltzmann method, a model for polymer melts is proposed. Compared with models based on Ginzburg–Landau free energy, our model does not employ phenomenological free energies to describe systems and can consider the chain topological details of polymers. We use this model to study the effects of hydrodynamic interactions on the dynamics of microphase separation for block copolymers. In the early stage of phase separation, an exponential growth predicted by Cahn–Hilliard treatment is found. Simulation results also show that the effect of hydrodynamic interactions can be neglected in the early stage. For the late stage of phase separation, it is easy to see the effects of hydrodynamic interactions on the ordering process of lamellae phase. From the analysis of structure factor curves, we find that the growth of domains is faster if hydrodynamic interactions are introduced. Furthermore, the scaling of the pattern dynamics is investigated for the late stage at zero thermal noise. By studying the behavior of scaling exponents of the structure factor and the nematic order-parameter correlation function Cnn, we can see that the effects of hydrodynamic interactions lead to bigger growth exponent for both functions. [ABSTRACT FROM AUTHOR]

The self-assembly of symmetric coil-rod-coil ABA-type triblock copolymer melts is studied by applying self-consistent field lattice techniques in a three-dimensional space. The self-assembled ordered structures differ significantly with the variation of the volume fraction of the rod component, which include lamellar, wave lamellar, gyroid, perforated lamellar, cylindrical, and spherical-like phases. To understand the physical essence of these phases and the regimes of occurrence, we construct the phase diagram, which matches qualitatively with the existing experimental results. Compared with the coil-rod AB diblock copolymer, our results revealed that the interfacial grafting density of the separating rod and coil segments shows important influence on the self-assembly behaviors of symmetric coil-rod-coil ABA triblock copolymer melts. We found that the order-disorder transition point changes from frod=0.5 for AB diblock copolymers to frod=0.6 for ABA triblock copolymers. Our results also show that the spherical-like and cylindrical phases occupy most of the region in the phase diagram, and the lamellar phase is found stable only at the high volume fraction of the rod. [ABSTRACT FROM AUTHOR]

We develop a self-consistent-field lattice model for block copolymers and propose a novel and general method to solve the self-consistent-field equations. The approach involves describing the polymer chains in a lattice and employing a two-stage relaxation procedure to evolve a system as rapidly as possible to a free-energy minimum. In order to test the validity of this approach, we use the method to study the microphases of rod-coil diblock copolymers. In addition to the lamellar and cylindrical morphologies, micellar, perforated lamellar, gyroid, and zigzag structures have been identified without any prior assumption of the microphase symmetry. Furthermore, this approach can also give the possible orientation of the rods in different structures. [ABSTRACT FROM AUTHOR]

The tunable multimode electromagnetically induced absorption (EIA)-like transmission was investigated in a two-ring system. In this system, by introducing asymmetry factor δi = λr - λr', we provided several ways to modulate the EIA-like transmission spectra. An off-to-on EIA-like response could be realized by changing the radius or the refractive index of the rings. During the off-to-on process, we found the red shift and blue shift effects in the spectra are appeared and the widths of EIA-like dips are broadened. Numerical simulation by finite element method was conducted to verify our discussion. We believe all these would provide guidelines to design the useful EIA-like devices. [ABSTRACT FROM AUTHOR]

We study the influence of shape of Janus particles on their orientation and surface activity at fluidfluid interfaces via molecular dynamics simulations. The Janus particles are characterized by two regions with different wettability divided along their major axes. Three types of Janus particles are considered: Janus spheres, Janus rods, and Janus disks. We find that Janus spheres and Janus rods prefer one orientation at the interface, regardless of the surface property. In contrast, Janus disks can adopt one of two orientations when adhered to a fluid-fluid interface: one orientation corresponds to the equilibrium state and the other is a kinetically trapped metastable state. The orientation of Janus disks strongly depends on the disk characteristics, such as their size, aspect ratio, and surface property. Furthermore, we find that changes in the shape of Janus particles strongly influence the interfacial tension at the fluid-fluid interface. According to the time evolution of the interfacial tension, the adsorption of Janus particles is characterized by three adsorption stages based on different surface activities and adsorption kinetics depending on the particle shape. [ABSTRACT FROM AUTHOR]

The particle-transfer molecular-dynamics technique is adopted to construct the Lennard-Jones fluid gas-liquid phase diagram. Detailed study of the dependence of the simulation results on the system size and the cutoff distance is performed to test the validity of the simulation technique. Both the traditional cutoff plus long-range correction (CPC) and Ewald summation methods are used in the simulations to calculate the interactions. In the intermediate range of temperatures, the results with the Ewald summation method are almost the same as those with the CPC method. However, in the range close to the critical point, the results with the CPC method deviate from those with the Ewald summation. Compared with the results obtained via the Ewald summation in a smaller system, simply increasing the system size in the CPC scheme may not give better results. [ABSTRACT FROM AUTHOR]

By means of standard and hybrid density functional theory, we analyzed the electronic, optical, and mechanical properties of the two discovered superhard orthorhombic (W) and monoclinic (M) phases of carbon, synthesized by cold compression. We demonstrated that both phases exhibit a transparent insulating behaviour with indirect band gaps of about 5.4 eV (W) and 4.5 eV (M), and highly isotropic optical spectra, substantially different to those of the related body centered tetragonal C4 phase. The analysis of the elastic constants and Vickers hardness confirmed that these phases are as hard as the second hardest material c-BC2N. [ABSTRACT FROM AUTHOR]