Interlayer-expanded VS2 nanosheet: Fast ion transport, dynamic mechanism and application in Zn2+ and Mg2+/Li+ hybrid batteries systems.

Currently, the development of polyvalent ions battery systems are still restricted by lacking suitable cathode materials with high energy density and long cycle life attributing to sluggish kinetic mechanism and of polyvalent ions. Herein, an effective inter-layer scaling strategy is proposed by using a simple hydrothermal method. The super layer spacing VS2 (∼1 nm) cathode dramatically improves electrochemical performance of zinc-ion batteries (ZIBs) and magnesium/lithium hybrid ion batteries (MLIBs). The specific discharge capacities of ZIBs and MLIBs are 450.7 and 488.8 mA h g-1 at current density of 0.1 A g-1 which are much higher than the same type of battery systems. Finally, the diffusion mechanism and the corresponding theoretical model is established by adopting first principles. In brief, the work provides an effective strategy for the large scale application of multivalent and hybrid batteries systems.

Universal scaling laws of diffusion in two-dimensional granular liquids.

We find, in a two-dimensional air table granular system, that the reduced diffusion constant D* and excess entropy S(2) follow two distinct scaling laws: D*∼e(S(2)*) for dense liquids and D∼e(3S(2)*) for dilute ones. The scaling for dense liquids is very similar to that for three-dimensional liquids proposed previously [M. Dzugutov, Nature (London) 381, 137 (1996); A. Samanta et al., Phys. Rev. Lett. 92, 145901 (2004)]. In the dilute regime, a power law [Y. Rosenfeld, J. Phys.: Condens. Matter 11, 5415 (1999)] also fits our data reasonably well. In our system, particles experience low air drag dissipation and interact with each others through embedded magnets. These near-conservative many-body interactions are responsible for the measured Gaussian velocity distribution functions and the scaling laws. The dominance of cage relaxations in dense liquids leads to the different scaling laws for dense and dilute regimes.

A density functional theory of chiral block copolymer melts.

A density functional theory is developed for the diblock copolymer melt, where one block contains the segment orientation dependent chiral interaction. In addition to the standard (scalar) pair interaction between the two types of monomers, the chiral block has the additional pairwise interaction, which is linear in the tangent vectors of the segments. We construct a density functional, which contains both the scalar density field and the vector chain alignment field. The quadratic part of the density functional comes from the mean field theory of the microscopic model, whereas the fourth order terms are introduced phenomenologically in the spatially local form. From the stability analysis of this model, we find that the additional chiral interaction shifts the order-disorder transition, which is consistent with the behavior of experimental system. Further numerical calculation reveals a new metastable chiral helical cylinder structure, which is similar to the one found experimentally. Another similar metastable structure but with zigzag modulation is also observed. As the helical and zigzag structures disappear when the chiral interaction is switched off, we understand that the chiral effect is the driving force for the formation of these exotic metastable structures.

Dynamics of finite-symmetry and general-shaped objects under shear and shear alignment of uniaxial objects at finite temperatures.

We prove that, for an object with a finitefold rotational symmetry (except for a twofold one) around an axis and mirror symmetries (such as a square rod or pentagonal slab, etc.), dynamics of the symmetry axis in low Reynolds number shear flow exactly follows the same form as that of a uniaxial object (e.g., a circular rod or symmetric ellipsoid) as the so-called Jeffery orbits. We use the formulation in which the dynamics of the rigid body follows first-order ordinary differential equations in time [Phys. Rev. E 84, 056309 (2011)]. Interaction between the object and the shear flow enters through a set of scalar coefficients, and the flow field does not need to be solved dynamically. Results of numerical simulations for general-shaped objects also are discussed. In the second part, Brownian dynamics of a uniaxial object is studied numerically. With D as the rotational diffusion constant, α as a parameter characterizing the aspect ratio, and γ as the shear rate, the object starts to align with the flow when the value of D/(γα) decreases near 1. At large α (the long object limit), the results suggest much lower flow alignment when D/(γα)>1.

Dynamical solutions for migration of chiral DNA-type objects in shear flows.

We present a dynamical analysis of chiral object motions to explain physical mechanisms and give quantitative predictions on the shear-induced drift motions of chiral objects and the chiral separation of enantiomers using shear flows. For objects well represented by the uniaxial approximation, such as DNA and chiral disk hexamers, dynamical motions in low-Reynolds-number shear flows are solved analytically, in terms of steady-state object-flow interacting parameters, which can be calculated numerically by well-established methods. The shear-induced drifting speed of long helices are evaluated. Good agreements are found between our results and those obtained from dynamical simulations [Makino and Doi, Phys. Fluids 17, 103605 (2005)]. We also compare our results with those obtained experimentally [Marcos, Fu, Powers, and Stocker, Phys. Rev. Lett. 102, 158103 (2009)]. The analysis may also be extended to study other important chiral-flow interactions in nature environments and microfluidic devices, such as the particle-wall and interparticle interactions.

Differential adhesion and actomyosin cable collaborate to drive Echinoid-mediated cell sorting.

Cell sorting involves the segregation of two cell populations into `immiscible' adjacent tissues with smooth borders. Echinoid (Ed), a nectin ortholog, is an adherens junction protein in Drosophila, and cells mutant for ed sort out from the surrounding wild-type cells. However, it remains unknown which factors trigger cell sorting. Here, we dissect the sequence of this process and find that cell sorting occurs when differential expression of Ed triggers the assembly of actomyosin cable. Conversely, Ed-mediated cell sorting can be rescued by recruitment of Ed, via homophilic or heterophilic interactions, to the wild-type cell side of the clonal interface, even when differential Ed expression persists. We found, unexpectedly, that when actomyosin cable was largely absent, differential adhesion was sufficient to cause limited cell segregation but with a jagged tissue border (imperfect sorting). We propose that Ed-mediated cell sorting is driven both by differential Ed adhesion that induces cell segregation with a jagged border and by actomyosin cable assembly at the interface that smoothens this border.

Phase separation of thin-film polymer mixtures under in-plane electric fields.

Phase-separation dynamics of polymer thin-film mixtures of polystyrene (PS) and poly(methyl methacrylate) (PMMA) are observed while an in-plane electric field is applied, instead of the out-of-plane fields usually employed previously. The phase separation is accompanied by the formation of PS dewetting holes at zero or weak fields. The dewetting velocity at 0.25 µm/min is a few times slower than that seen in regular bilayer dewetting. With the increasing of the field strength, we observe the formation of PS droplets in PMMA matrix, a reversal from zero- or low-field conditions. The PS dewetting holes are also suppressed. At further increased fields, PS droplets quickly penetrate up to the top of the PMMA matrix, leading to smaller and more irregular final PS droplets. This is manifested in the dramatic decrease in the growth exponent of the droplet size L from L∼t1.5 to L∼t0.1. These morphology changes are explained by the electrostatic energy resulted from the PS and PMMA dielectric contrast.

A statistical simulation approach for early stage thin-film growth from vapor-deposited atoms.

We present a statistical simulation method for the early stage of thin-film growth from vapor-deposited atoms, which simulate evolution of density, size, and spatial distribution of the growing islands on a supported substrate. The method describes surface processes of the deposited atoms by random walks and the Arrhenius form. However, we utilize the statistical behavior of the atomic surface processes over a time scale significantly larger than the typical attempt time (10(-13) s). This novel method saves enormous simulation time and thus overcomes the difficulty resulting from the remarkable gap between the typical experimental deposition rates and the attempt frequency. The statistical approach is verified by comparisons with direct step-by-step (kinetic Monte Carlo) simulations at large deposition rates. Results obtained for low deposition rates matching experimental conditions are also presented.

Field-induced columnar structures in a quasi-two-dimensional system of dipolar particles.

We study the formation of columnar structures of uniaxial dipoles in an external magnetic field both experimentally and theoretically. By applying an external magnetic field parallel to a thin layer of a magnetorheological fluid, we manipulate a single initial cluster of suspended colloidal particles. We find that the cluster breaks up into columns that have approximately uniform widths and intercolumnar spacings. Both the average column width and inter column spacing are observed to vary linearly with column length. The observed linear relationships between column width and spacing versus the column length are interpreted theoretically by computing the potential energy of an ensemble of closed-packed columns of spherical dipolar particles.

Mean-field theory for inhomogeneous electrolytes.

We calculate the free energy density for inhomogeneous electrolytes based on the mean-field Debye-Hückel theory. Derived are the contributions of (1) the differential term for the electrolyte density being slow varying in one direction and (2) the boundary term for an electrolyte confined to one side of a planar interface. These contributions are shown to cause an electrolyte depletion near the air-water interfaces, which makes the surface tension increase, to be significantly larger than those predicted by previous theories. Nonuniform electrolyte densities are also computed near the water-electrolyte and electrolyte-electrolyte interfaces. Finally we calculate the interaction of two uncharged macrospheres due to the electrolyte depletion.

Shear alignments in three-dimensional simulations of lamellar phases.

Experiments studying layer orientation of sheared lamellar phases have consistently observed not only the seemingly obvious parallel orientation (with layers parallel to the shear plane), but also the so called perpendicular orientation (with layer normals along the vorticity direction) at the condition of higher shear frequencies and near the lamellar phase transition. We find that three-dimensional simulations of a deterministic mesoscopic dynamical equation (without thermal fluctuations) under the convection of simple shear flows have shown exactly such a dependence. The simulations show the important role played by the transverse orientation (layer normal along the velocity direction) and highlight the mechanism of the shear alignment being the competition between the shear frequency and the mesoscopic time scale of pattern organization.

Measurement of mean flows of Faraday waves.

We measure the velocities of the mean flows that are driven by curved rolls in a pattern formation system. Curved rolls in Faraday waves are generated in experimental cells consisting of channels with varying widths. The mean flow magnitudes are found to scale linearly with roll curvatures and squares of wave amplitudes, agreeing with the prediction from the analysis of phase dynamics expansion. The effects of the mean flows on reducing roll curvatures are also seen.

Nonlinear wave dynamics in Faraday instabilities.

Nonlinear wave dynamics in parametrically driven surface waves are studied in numerical simulations of the two-dimensional Navier-Stokes equation, with an emphasis on the evolution and interaction between different wave number modes. The dynamics are found to be closely correlated with the single-mode nonlinear saturated wave amplitudes. Modulating behavior of primary wave modes in a particular parameter range and in time scales much longer than the underlining wave periods is observed.