Microscopic Dynamic Properties Research Articles

Solid surface structure affects liquid order at the polystyrene–self-assembled-monolayer interface

We present a combined x-ray and neutron reflectivity study characterizing the interface between polystyrene (PS) and silanized surfaces. Motivated by the large difference in slip velocity of PS on top of dodecyl-trichlorosilane (DTS) and octadecyl-trichlorosilane (OTS) found in previous studies, these two systems were chosen for the present investigation. The results reveal the molecular conformation of PS on silanized silicon. Differences in the molecular tilt of OTS and DTS are replicated by the adjacent phenyl rings of the PS. We discuss our findings in terms of a potential link between the microscopic interfacial structure and dynamic properties of polymeric liquids at interfaces.

Microscopic simulation on the dynamic failure of metal Al under triangular wave loading

Employing an embedded-atom-method potential and molecular dynamics simulations, we have simulated the microscopic process and dynamical properties of the dynamic failure of metal Al specimens under triangular wave loading. The microstructure evolution of the sample is analyzed using the central symmetry parameter, while the difference of morphology between non molten and molten states is also explained. The pressure profiles were calculated based on the virial theorem, and the results show that the tensile strength of the material is decreased considerably in its molten state. Using the simulation results for different impact velocities, we discuss the variation of morphology and density distribution, from which the change of damage depth in the process from non molten to molten states is obtained. Our simulations also suggest that: the tensile strength of material derived from acoustic approximation is distinctively higher than the peak of internal stress from virial theorem for the melted state.

Microscopic Structural and Dynamical Properties of Amorphous Metallic Alloy Ni33Zr67 at the Temperature T=300K

We study the structural properties and the collective microscopic dynamics of atoms in the amorphous metallic alloy Ni33Zr67 at the temperature T=300K by molecular dynamics simulations. The calculated equilibrium structural and dynamical characteristics are compared with the experimental data on neutron diffraction and on inelastic X-ray scattering. We present the interpretation of observed structural relaxation of the microscopic density fluctuations of particles for amorphous metallic alloy in the framework of the recurrent relation approach. The results of theoretical calculations of the intensity of scattering I(k,ω) for amorphous Ni33Zr67 are in a good agreement with the results of computer simulation as well as with the experimental data on inelastic X-ray scattering.

Microscopic simulation on shock-induced micro-jet ejection from metal Al surface

Via molecular dynamics simulations employing an embedded-atom-method potential, we investigate the microscopic process and dynamical properties of shock-induced micro-jet from a grooved aluminum surface. For a large range of shock pressure, we obtain the micro-jet morphology variation, its mass spatial distribution and mass-velocity distribution. The amorphous state and release melting during the jetting are both analyzed using the central symmetry parameter, where the effect law of release melting on the micro-jet is obtained. It is found that the micro-jet mass keeps a linear increase with the piston velocity prior to release melting; the micro-jet mass is enhanced evidently after release melting; while the velocity of release melting is above a threshold, the jetting mass shows a linear increase with the piston velocity again, where the strength of material can be neglected.

Investigation of the Microscopic Viscoelastic Property for Cross-linked Polymer Network by Molecular Dynamics Simulation

Abstract The purpose of this work is to develop a new analytical method for simulating the microscopic mechanical property of the cross-linked polymer system using the coarse-grained molecular dynamics simulation. This new analytical method will be utilized for the molecular designing of the tire rubber compound to improve the tire performances such as rolling resistance and wet traction. First, we evaluate the microscopic dynamic viscoelastic properties of the cross-linked polymer using coarse-grained molecular dynamics simulation. This simulation has been conducted by the coarse-grained molecular dynamics program in the OCTA) (http://octa.jp/). To simplify the problem, we employ the bead-spring model, in which a sequence of beads connected by springs denotes a polymer chain. The linear polymer chains that are cross-linked by the cross-linking agents express the three-dimensional cross-linked polymer network. In order to obtain the microscopic dynamic viscoelastic properties, oscillatory deformation is applied to the simulation cell. By applying the time-temperature reduction law to this simulation result, we can evaluate the dynamic viscoelastic properties in the wide deformational frequency range including the rubbery state. Then, the stress is separated into the nonbonding stress and the bonding stress. We confirm that the contribution of the nonbonding stress is larger at lower temperatures. On the other hand, the contribution of the bonding stress is larger at higher temperatures. Finally, analyzing a change of microscopic structure in dynamic oscillatory deformation, we determine that the temperature/frequency dependence of bond stress response to a dynamic oscillatory deformation depends on the temperature dependence of the average bond length in the equilibrium structure and the temperature/frequency dependence of bond orientation. We show that our simulation is a useful tool for studying the microscopic properties of a cross-linked polymer.

Theoretical Processing in Understanding the Structures and Properties of Layered Double Hydroxides

We review the techniques,applications,characteristics,and insights gained from the use of theoretical calculations that were applied to the study of layer double hydroxides (LDHs) materials by using a series of typical case studies. The advantages and shortcomings of different theoretical calculation methods (quantum mechanics,molecular mechanics,geometric model,and electrostatic potential energy model) for the study of the properties of LDHs minerals are compared. Based on quantum mechanics calculations,we obtained information about template effects on the construction of layered double hydroxides,super molecular interactions in LDHs containing simple anions,electronic properties,and reaction pathways etc. Compared with quantum mechanics,molecular mechanics is quicker in obtaining information about the interlayer structure,arrangement,orientation,hydration,and the swelling trajectory as well as elastic constants etc of LDHs intercalated with various anions. The geometric model and electrostatic potential energy model offer a more intuitive and visual mathematical model of LDHs minerals. The calculations were done on the verge of full size LDHs,which may allow the prediction of the crystal structure. Along with the development of theoretical methods and computer techniques,computational simulation method has become an effective adjust to experimental techniques for obtaining the microscopic structures,electronic and dynamic properties of LDHs minerals.

Subfemtosecond dynamics of structural protons in silica xerogels

to the silanol groups, when precursors are such as to modify the structural morphology. This paper is also intended to present a complementary experimental technique for the characterization of the microscopic dynamical properties of these materials. The mean kinetic energy Ek and the momentum distribution np of the protons of the structural silanol groups in the two different systems are derived and compared at the same thermodynamic conditions. The results show that Ek is different for the two systems, reflecting the differences in the pore morphology. Indeed, Ek is higher for the system with an average pore diameter of 24 A, as compared to that of 82 A.

The Structural Properties and Diffusion of a Three-Dimensional Isotropic Core-Softened Model Fluid in Disordered Porous Media. Molecular Dynamics Simulation

The microscopic structure and dynamic properties of an isotropic three-dimensional core-softened model fluid in disordered matrices of Lennard-Jones particles have been studied. Molecular dynamics computer simulations in Grand Canonical ensemble were used as the methodological tools. It was shown that the microscopic structure of the fluid is characterized by anomalies similar to those found in a bulk model, but that it is affected by the fluid-matrix interactions. The dynamic properties also exhibit anomalous dependence on fluid density, but the magnitude of these anomalies is suppressed in comparison to the bulk fluid model. The anomalous behaviour of the diffusion coefficient is attributed to structural changes in the first coordination shell of a given fluid particle. It seems that the anomalies can only be suppressed at matrix densities which are higher than those studied in the present work.

Structure and dynamic properties of liquids confined in MCM-41 mesopores

The microscopic structure and dynamic properties of water, methanol, and acetonitrile confined in mesoporous MCM-41 materials have been investigated under monolayer and capillary-condensation conditions as a function of pore size and temperature by in situ FTIR and X-ray diffraction and quasi-elastic neutron scattering techniques. Both interfacial and confinement effects on the structure and dynamics of the liquids in hydrophilic pores are discussed at the molecular level.

Elastic vibrations in seamless microtubules

Parameters characterizing elastic properties of microtubules, measured in several recent experiments, reflect an anisotropic character. We describe the microscopic dynamical properties of microtubules using a discrete model based on an appropriate lattice of dimers. Adopting a harmonic approximation for the dimer-dimer interactions and estimating the lattice elastic constants, we make predictions regarding vibration dispersion relations and vibration propagation velocities. Vibration frequencies and velocities are expressed as functions of the elastic constants and of the geometrical characteristics of the microtubules. We show that vibrations which propagate along the protofilament do so significantly faster than those along the helix.

A Microscopic Description of Concentrated Potassium Fluoride Aqueous Solutions by Molecular Dynamics Simulation

We describe the microscopic structure and dynamical properties of potassium fluoride aqueous solutions at T = 298 K as a function of concentration up to 11.9 M. All calculations are made using constant temperature and pressure as well as microcanonical molecular dynamics simulations on the basis of an optimized pair potential model which is a mix of Coulomb plus standard Lennard-Jones short-range terms for water and ion-water interactions and Tosi-Fumi potential for ion-ion interactions. In particular we propose a modified ion-water interaction that successfully reproduces the experimental behavior of the density and water self-diffusion of the solutions as a function of concentration. Finally, we analyze hydrogen-bonding in solutions looking at pair distribution energies and residence times. We find strong evidence for K + -F - pairing in solutions at the higher concentrations.

Spectroscopic Study of Modified Polytetrafluoroethylene

The effect of thermal gas dynamic destruction of polytetrafluoroethylene on its microscopic and supramolecular structure and dynamic properties is investigated by IR and 19F NMR spectroscopy. It is demonstrated that thermal gas dynamic dispersing changes the structure of polytetrafluoroethylene molecules. One of the possible mechanisms of PTFE depolymerization is the formation of oligomers with terminal –CF3 and –C=CF2 groups. This forms macromolecular packing with higher ordering and with dynamic characteristics other than those inherent in standard PTFE.

Structure and dynamics of 1,4-dioxane-water binary solutions studied by X-ray diffraction, mass spectrometry, and NMR relaxation

The structure of clusters formed in 1,4-dioxane-water binary solutions has been investigated at ambient temperature as a function of 1,4-dioxane concentration by X-ray diffraction for the corresponding solutions and by mass spectroscopy for liquid droplets formed in vacuum from the liquid mixtures by an adiabatic expansion method. The 2H spin-lattice relaxation times of D2O and 1,4-dioxane-d8 molecules in 1,4-dioxane-water binary solutions have also been measured at 30 °C over a whole range of 1,4-dioxane mole fraction. It has been found from the analysis of X-ray radial distribution functions that the number of hydrogen bonds per water and 1,4-dioxane oxygen atom decreases with increasing 1,4-dioxane mole fraction Xdio accompanied by two inflection points at Xdio = ∼-0.1 and ∼0.3: at Xdio ≤ 0.1 the hydrogen-bonded network of water is predominant in the binary solutions, at Xdio ≥ 0.3 the inherent structure of 1,4-dioxane is mostly observed, water molecules probably involved in the structure by hydrogen bonding, and at 0.15 ≤ Xdio ≤ 0.2 both structures of water and 1,4-dioxane are ruptured to form small binary clusters of one or two dioxane and several water molecules. The mass spectra have revealed that at Xdio = 0.01 water clusters Wn (W = water, n = 6 2- 43) are mostly formed, but with increasing Xdio to 0.4 the water clusters are reduced with evolving 1,4-dioxane clusters DmWn (D = 1,4-dioxane, m = 1 – 3, n = 1 – 16). The 2H spin-lattice relaxation data of D2O molecules in the mixtures showed that the rotation of water molecules is gradually retarded with increasing Xdio to −0.3, where the rotation is the slowest, and is then gradually accelerated with further increase in Xdio. The corresponding data of 1,4-dioxane-d8 molecules showed a similar tendency, but the slowest motion observed at Xdio = −0.2. The present microscopic cluster structure and dynamic properties of the mixtures are discussed in connection with the heat of mixing, viscosity, hydrophobic hydration, and clathrate hydrate.

Free volume from the positron annihilation lifetime spectroscopy method and its relationships with the various microscopic and macroscopic dynamic properties of ortho-terphenyl

A phenomenological model linking the macroscopic volumetric behaviour found from dilatometry to the microscopic free-volume hole properties found from positron annihilation lifetime spectroscopy is applied to a set of dynamic properties of a fragile low-molecular-weight glass former: ortho-terphenyl. A number of correlations between the free-volume hole fractions derived from this model and the various dynamic properties such as viscosity, self-rotational diffusion, and tracer translational diffusion can be established over the temperature range from the glass-liquid transition temperature up to via a Williams-Landel-Ferry (WLF)-Doolittle-type equation.

Dynamics of Glasses and Glass-Forming Liquids Studied by Inelastic X-ray Scattering

The development of inelastic x-ray scattering with millielectron volt energy resolution at the European Synchrotron Radiation Facility in Grenoble, France, provides a method for studying high-frequency collective dynamics in disordered systems. This has led to the observation of propagating acoustic phonon-like excitations in glasses and glass-forming liquids down to wavelengths comparable to the interparticle distance. Using the inelastic x-ray scattering results on glycerol as a representative example, it is shown that the microscopic dynamic properties are related to the excess of vibrational states in glasses and to the consequences at the microscopic level of the liquid-glass transition. Moreover, they allow derivation of the infinite frequency sound velocity, a quantity related to the structural relaxation times and to the change of ergodicity at the liquid-glass transition.

Dynamics of Complex Phthalate Liquids. 1. Structural Effects of Molecular Framework

The motional behavior of complex phthalates and structurally related liquids has been investigated in order to study the structural effect of molecular framework on the macroscopic and microscopic dynamic properties. 13C NMR spin−lattice relaxation times and nuclear Overhauser enhancements (NOE) of individual carbon nuclei of bis(2-ethylhexyl) cyclohexane-1,2-dicarboxylate (DEHHP), bis(2-ethylhexyl) isophthalate (DEHIP), bis(2-ethylhexyl) terephthalate (DEHTP), and tris(2-ethylhexyl) trimellitate (TOTM) have been measured as a function of temperature from −40 to 90 °C. Individual 13C peaks were unambiguously assigned by using 2D hydrogen−carbon chemical shift correlation spectra. In addition, the density and viscosity of these compounds as a function of temperature have been measured. The results were also compared with those of 2-ethylhexyl benzoate (EHB), 2-ethylhexyl cyclohexanecarboxylate (EHC), and bis(2-ethylhexyl) phthalate (DEHP), complex liquids studied earlier in our laboratory. Both the macrosc...

Macroscopic glassy relaxations and microscopic motions in a frustrated lattice gas

We study microscopic and macroscopic dynamical properties of a frustrated lattice gas, strictly related to usual spin glasses, showing the violation of Stokes-Einstein law. The glassy behaviors are analyzed and related with experimental results in glass former systems.

Solid-state carbon-13 nuclear magnetic resonance of the lecithin gel to liquid-crystalline phase transition

The temperature dependence of the 13C NMR spectra of dipalmitoylphosphatidylcholine (DPPC) which has been 13C labeled at the carbonyl position of the sn-2 chain, 2-[1-13C]DPPC, is reported. In the L beta' phase an axially symmetric spectrum of 112-ppm breadth is observed, and this transforms to an isotropic-like line ((delta sigma) approximately 7 ppm) in the L alpha phase. In the intermediate P beta phase a temperature-dependent superposition of these spectra is observed, which suggests that this phase exhibits microscopic structural and dynamical properties of both the L beta' and L alpha phases. An analysis of the spectral line shapes leads to the conclusion that the appearance of the isotropic-like line in the P beta' phase is primarily due to a conformational change at the sn-2 carbonyl which is complete at the main transition. Increased rates of axial diffusion in the P beta' phase may contribute to the narrowing.

What is "liquid"? Understanding the states of matter

Liquids exist in a relatively small part of the enormous range of temperatures and pressures existing in the universe. Nevertheless, they are of vital importance for physics and chemistry, for technology, and for life itself. A century of effort since the pioneering work of van der Waals has led to a fairly complete basic understanding of the static and dynamic physicochemical properties of liquids. Advances in statistical mechanics (the fundamental formulations of Gibbs and Boltzmann, integral equations and perturbation theories, computer simulations), in knowledge of intermolecular forces, and in experimental techniques; have all contributed to this. Thirty years ago the very existence of liquids seemed a little mysterious; today one can make fairly precise predictions of the solid-liquid-gas phase diagram and of the microscopic and macroscopic static and dynamic properties of liquids. This paper is a survey, with particular emphasis on equilibrium properties, of the theory which underlies that basic understanding, which is now at least comparable with our understanding of the physics of solids.