Mesoporous anodic tin oxide with two-dimensional macroporous network

Journal of Solid State Electrochemistry - Here, we report a single-step anodic oxidation process to form a micron-scale island array of mesoporous tin oxide without any template. The grain boundary...     

Complete set of Hopf bifurcation in an autocatalytic ring network

We investigate the Hopf bifurcation for a five species chemical ring network with an autocatalytic reaction. We show that the bifurcation hypersurface in the rate constants space is the boundary of a simply connected set. We use a numerical method to calculate this hypersurface.     

On-line study of polyelectrolyte network formation by interfacial reaction

A modified synthetic boundary experiment of analytical ultracentrifugation has been employed to examine, on-line, polyelectrolyte complex formation at flat interfaces yielding highly swollen membranes/networks. Systematic experiments with sodium alginate as a polyanion and chitosan and poly(l-lysine) as polycations identified the influence of concentration, pH, molar mass, and polycation type on the membrane characteristics and the formation process. The membranes have been evaluated by five characteristics defined herein: total thickness, compactness, heterogeneity, symmetry, and growth. The results confirm the sensitivity of the method suited to elaborate general relationships for polyelectrolyte membrane design.     

Simulation of non-stationary electrodiffusion processes in charged membranes by the network approach

Single techniques of network approach have been used to obtain the numerical solution for a boundary value problem involving the Nernst-Planck and Poisson equations system. A network model has been proposed for a particular physical situation, namely, ionic transport in charged membranes including the Donnan equilibrium relations at the membrane/solution interfaces. With this network model and using the electrical circuit simulation program PSPICE, the ionic concentration profiles as well as electric potentials and ionic fluxes have been simulated as a function of time for the ternary systems HClKCl and NaClKCl.     

Recent advances in polymer network liquid crystal spatial light modulators

Polymer network liquid crystal (PNLC) spatial light modulators are attractive for display and photonic applications because they can achieve submillisecond response time while keeping a large phase change. However, their on-state scattering caused by the grain boundary of LC multidomains hinders their applications. In this article, we review recent progress on the development of scattering-free PNLCs extending from short-wavelength infrared to visible region by reducing the domain sizes to ∼200 nm through low temperature curing process. To reduce operation voltage, both transmissive and reflective modes, LC material properties (birefringence and dielectric anisotropy), polymer composition and concentration, and pretilt angle effect are analyzed. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 183–192     

Effects of phase separation on network and viscoelastic properties in SBS thermoplastic elastomers

Stress relaxation of poly(styrene-b-butadiene-b-styrene) thermoplastic elastomers is studied in dependence of molecular weight and degree of hydrogenation in the temperature range between ?30° and +80 °C. The influence of these parameters on the structure of the physical network and the degree of partial mixing in the domain boundary is investigated by separating the stress-relaxation modulus into a viscoelastic term and an equilibrium network modulus calculated from the relaxation-time spectrum. The temperature dependence of the one-second relaxation modulus is quantitatively described by use of a modified Kerner model for the simulation of the viscoelastic term. The modification allows the estimation of the volume fraction of interfacial material and its correlation to the parameters which govern phase separation.     

Electronic structures and hydrogen bond network of high-density and very high-density amorphous ices

Electronic structures of hexagonal ice (ice Ih), high-density amorphous ice (HDA), and very high-density amorphous ice (VHDA) are investigated using ab initio density functional theory (DFT) at 77 K under a pressure of 0.1 MPa, focusing on band structure, density of states (DOS), partial density of states (PDOS), and electron density. It is found that the integration intensity of the O-2p bonding band in HDA is 1.53 eV wider than that in the VHDA. Because more 2p electrons in HDA participate the 2p-1s hybridization of O-H. The classical molecular dynamics (MD) method has further been carried out to analyze the hydrogen bond network of HDA and VHDA with larger numbers of water molecules under the same temperature, pressure, and boundary conditions used as those during the DFT calculation. MD results show that there exists some water molecules with five hydrogen bonds in both HDA (4.1 +/- 0.1%) and VHDA (2.8 +/- 0.1%), as compared with the LDA, being consistent with the integration intensity results of PDOS. This result can be used to interpret the physical nature of the similar transition temperature of HDA and VHDA to LDA with different heating rates.     

Phase separation in the interpenetrating polymeric network on the basis of polyurethane and polyurethane acrylates

Interpenetrating polymer networks (IPN) of polyurethane and polyurethane acrylate were obtained. A small-angle x-ray scattering technique was used to study the character of the microheterogeneities in IPN and their variation with composition. It was shown that IPN formation is accompanied by phase separation of constituent components. On the basis of experimental data, which involved the mean square of fluctuations of electron densities in IPN, scattering intensity extrapolated to the zero angle, thickness of the transition layer between two phases, degrees of component segregation and diffuseness of phase boundary, degree of miscibility of components on the molecular level, specific inner surface, and the extent of the heterogeneous regions and their mean radius were determined. Parameters that characterize the intensity of microphase separation are dependent on composition: at a higher content of PUA the segregation degree is higher than that of low content. The dimensions of the heterogeneous regions, which extend from one network to the matrix of the other, depend on the composition of IPN and changes most sharply in the range of mean composition due to phase inversion. Thickness of the transition layer ranges from 20 to 40 Å.     

Extracting the underlying effective free energy landscape from single-molecule time series--local equilibrium states and their network

We present a new self-consistent procedure to construct a multidimensional effective free energy landscape from a scalar single molecule time series, when single molecules experience the landscape within a given timescale of "observation." The theory is based on a framework we recently developed to extract a set of local equilibrium states (LESs) and their network from a scalar time series, such as distance between dye molecules tagged in a biomolecule. We scrutinize the appropriateness of the assumptions of local equilibration and local detailed balance among LESs at the single molecule level within the given timescale, rather than postulating them a priori. The self-consistent procedure in this article incorporates the effect of local correlation of the system dynamics inside potential basins, and the effect of finiteness of the sampled data points in assigning the boundary between different LESs. We propose a new simple scheme to assign the dimensionality of the energy landscape from a single molecule time series. We also address the question of what the molecules actually "feel" from the underlying landscape at the single molecule level.     

In situ control of surface molecular order in liquid crystals using a localised polymer network and its application to electro-optical devices

A liquid crystal (LC) alignment technique has been developed that allows local control of the polar pretilt angle over the range of 0–90°. This was achieved through the formation of a polymer network localised in the vicinity of the LC cell substrates. The network was formed as a result of in situ UV-induced polymerisation of a photo-reactive monomer added at concentrations of 0.5–1%. Localisation of the polymer network at the LC–substrate boundary was achieved by the application of a high voltage before polymerisation. The resultant pretilt angle was determined by the voltage applied during the polymerisation and/or the duration of the voltage application before the polymerisation step. The desired pretilt angle could be set over a small area of the sample, which allows the fabrication of LC devices with spatially variable optical retardation. Using this method we fabricated a converging lens, a bi-prism, and a phase diffraction grating with resolution greater than 50 lines mm^?1.     

The study of network formation as a cluster-cluster diffusion-limited aggregation process: Modelling of the curing of an epoxy-resin using the Monte Carlo method

The study of network formation during the curing of an epoxy-resin with anhydride and tertiary amine has been carried out by the Monte Carlo method. Both dynamical and structural properties are studied. The model resembles the well known cluster-cluster aggregation: the reaction is modelled as a “geometrical” phenomenon and neglects attractive and repulsive energies except for an excluded volume condition. A reaction occurs always when two active sites are in the vicinity to each other, meaning that the “chemical” processes are taken to be much faster than diffusion (as in diffusion-limited aggregation). Results are presented of two-dimensional square lattice simulations with periodic boundary conditions and are discussed with respect to the proposed mechanism of the curing reaction and to the assumptions of the diffusion-limited nature of the processes. The scope and limitations of such two-dimensional simulations are discussed.     

正离子的边界半径

本文建议和讨论了离子的边界半径, 给出了一价正离子的边界半径的周期表以及某些常见正离子的边界半径。正离子的边界半径与SP半径、Pauling离子半径、晶体离子半径等有一定的关联, 显示了其合理性和可应用性。由这些关联性质, 还可以预言某些元素的难以测定的电离能。     

Aqueous boundary lubrication: Molecular mechanisms,design strategy,and terra incognita

The molecular mechanisms for aqueous boundary lubrication are very different from those in the classic boundary lubrication, originating from the fluidity of the hydration shells surrounding the surfactant and lipid headgroups. We discuss the important molecular and structural criteria for effective aqueous boundary lubricants, and highlight the strategy for reinforcing the interfacial structure for aqueous boundary lubrication via synergistic interactions between amphiphilic polymers and lipids/surfactants. It is proposed that the energetic considerations of different molecular elastic deformations in the stalk model of cell membrane fusion can be applied to guide our design of molecular architectures for surfactants and lipids to implement structural integrity in aqueous boundary lubrication. We discuss a controversy associated with the quiescent bilayer structure in the context of boundary lubricant interfacial structures. We also highlight other effective aqueous boundary lubrication systems, including hydrated ions and biomimetic hierarchical constructs inspired by the enigmatic and extremely efficient biological lubrication. Finally, we suggest that the Stribeck curve might be re-considered in light of recent advances in aqueous boundary lubrication, although the exact scope of this new aqueous boundary lubrication regime remains terra incognita.     

Elastic bag model for molecular dynamics simulations of solvated systems: application to liquid water and solvated peptides

The fluctuating elastic boundary (FEB) model for molecular dynamics has recently been developed and validated through simulations of liquid argon. In the FEB model, a flexible boundary which consists of particles connected by springs is used to confine the solvated system, thereby eliminating the need for periodic boundary conditions. In this study, we extend this model to the simulation of bulk water and solvated alanine dipeptide. Both the confining potential and boundary particle interaction functions are modified to preserve the structural integrity of the boundary and prevent the leakage of the solute-solvent system through the boundary. A broad spectrum of structural and dynamic properties of liquid water are computed and compared with those obtained from conventional periodic boundary condition simulations. The applicability of the model to biomolecular simulations is investigated through the analysis of conformational population distribution of solvated alanine dipeptide. In most cases we find remarkable agreement between the two simulation approaches.     

Large deformation in filled networks of different architecture and its interpretation in terms of the van der Waals network model

The first quasi-static stretch of the two limiting systems of filler loaded rubber have been investigated. One of them is found by filler to matrix contacts only, the other by crosslinking permanently the matrix. In this case filler-matrix contacts are made by adhesion. The experimental results were described in terms of an extended van der Waals approach. It is illuminated that different filler to matrix contact (permanent bonds or adhesion) lead to different deformation mechanism, substantially affecting the reinforcement. Moreover, filler induced local field-modifications due to the boundary value problem can be understood with the Einstein-Smallwood approach independent of the kind of the filler to matrix contacts.     

An empirical boundary potential for water droplet simulations

An empirical modified boundary potential has been derived to correct the structural perturbations arising from the presence of the vacuum boundary in the simulation of spherical TIP4P water systems. The potential is parameterized for a 12.0-Å sphere of TIP4P water and gives improved number density and orientational sampling behavior. It is also transferable to both larger and smaller simulation systems with only a moderate degradation in performance. Free-energy calculations have been conducted for the perturbation of a TIP4P water molecule to methane under aqueous conditions, and the modified boundary potential gives results consistent with those from simulations using periodic boundary conditions. However, simple half-harmonic boundary potentials give unsatisfactory number density, orientational sampling, and free-energy results. Moreover, use of the modified boundary potential results in a negligible increase in simulation time. It is envisaged that the modified boundary potential will find use in free-energy perturbation calculations on proteins with a solvent sphere centered on the active site. © 1995 by John Wiley & Sons, Inc.     

A simple and effective boundary model in nonequilibrium molecular dynamics method

We propose a simple and effective boundary model in a nonequilibrium molecular dynamics (NEMD) simulation to study the out-of-equilibrium dynamics of polymer fluids. The present boundary model can effectively weaken the depletion effect and the slip effect near the boundary, and remove the unwanted heat instantly. The validity of the boundary model is checked by investigating the flow behavior of dilute polymer solution driven by an external force. Reasonable density distributions of both polymer and solvent particles, velocity profiles of the solvent and temperature profiles of the system are obtained. Furthermore, the studied polymer chain shows a cross-streaming migration towards center of the tube, which is consistent with that predicted in previous literatures. These numerical results give powerful evidences for the validity of the present boundary model. Besides, the boundary model can also be used in other flows in addition to the Poiseuille flow.     

Diffusion boundary layers during electrodialysis

A laser interferometry method for direct measurements of thicknesses of diffusion boundary layers is described. The method is employed to explore electromembrane processes. Thicknesses of diffusion boundary layers at below and above limiting diffusion current densities are measured and compared with theoretical values. It is shown that the diffusion boundary layers in narrow channels of electrodialyzer sections overlap one another at high current densities. This radically alters traditional notions concerning the diffusion boundary layer. An interpretation for variations in the thickness of a diffusion boundary layer at current densities in excess of the limiting diffusion current density is given.     

Lipids and lipid mixtures in boundary layers: From hydration lubrication to osteoarthritis

The hydration layer surrounding the phosphocholine headgroups of single-component phosphatidylcholine lipids, or of lipid-mixtures, assembled at an interface greatly modifies the interfacial properties and interactions. As water molecules within the hydration layer are held tightly by the headgroup but are nonetheless very fluid on shear, the boundary lipid layers, exposing the highly hydrated headgroup arrays, can provide efficient boundary lubrication when sliding against an opposing surface, at physiologically high contact pressures. In addition, any free lipids in the surrounding liquid can heal defects which may form during sliding on the boundary phosphatidylcholine layer. Similar boundary lipid layers contribute to the lubricating, pressure-bearing, and wear-protection functions of healthy articular joints. This review presents a survey of the relationship between the molecular composition of the interfacial complex and the lubrication behavior of the lipid-based boundary layers, which could be beneficial for designing boundary lubricants for intra-articular injection for the treatment of early osteoarthritis.     

Prediction of daytime variations of HO2 radical concentrations in the marine boundary layer using BP network

A Back-Propagation Neural Network (BPNN) was established to predict the daytime variations of HO₂ radical concentration observed in the field campaign RISFEX 2003 (RIShiri Fall Experiment 2003) conducted in September 2003 at Rishiri Island (45.07 N, 141.12 E, and 35m asl) in the Sea of Japan. The initial weight matrices and bias vectors for the network were optimized by a bee evolutionary genetic algorithm (BEGA). It was found that the input variables sensitive to HO₂ variation were photolysis frequency of O₃ to O(¹D) (J(O¹D)), a composite parameter defined as the ratio of HC to NO _x reactivity towards OH radicals (Φ), and the total aerosol surface area (A). The predicted results are closely correlated with the experimental data with the coefficient of determination (R ²) close to 1. In addition, the means and ranges of the predicted HO₂ concentration agree with the observed data with the correlation coefficient (R), the index of agreement (IA) and the fractional bias (FB) in the range of 0.84–0.93, 0.88–0.95 and ?14%–7%, respectively. This study demonstrates that BPNN is a potential tool to predict the daytime variations of HO₂ radical concentrations in the marine boundary layer (MBL).