Dynamics Of Binary Mixtures Research Articles

Coupled dynamics in binary mixtures of model colloidal Yukawa systems.

The dynamical behavior of binary mixtures consisting of highly charged colloidal particles is studied by means of Brownian dynamics simulations. We investigate differently sized, but identically charged particles with nearly identical interactions between all species in highly dilute suspensions. Different short-time self-diffusion coefficients induce, mediated by electrostatic interactions, a coupling of both self and collective dynamics of differently sized particles: the long-time self-diffusion coefficients of a larger species are increased by the presence of a more mobile, smaller species and vice versa. Similar coupling effects are observed in collective dynamics where both time constant and functional form of intermediate scattering functions' initial decay are influenced by the presence of a differently sized species. We provide a systematic analysis of coupling effects in dependence on the ratio of sizes, number densities, and the strength of electrostatic interactions.

Lattice Boltzmann simulation for phase separation with chemical reaction controlled by thermal diffusion.

This study investigates phase separation behavior and pattern formation in a binary fluid with chemical reaction controlled by thermal diffusion. By incorporating the Arrhenius equation into the lattice Boltzmann method (LBM), the coupling effects of the pre-exponential factor K, viscosity [Formula: see text], and thermal diffusion D on phase separation were successfully evaluated. The effect of the competition between thermal diffusion and concentration on the phase separation morphology and dynamics of binary mixtures under a chemically reacting controlled by slow cooling is assessed based on the extended LBM. The calculations indicated that increases in viscosity and thermal diffusion can obtain interconnected structures (ISs) and lamellar structures (LSs) for cases with small K. However, concentric phase-separated structures (CSs) were observed in cases with large K. The increase in the degree and efficiency of phase separation were significantly greater in cases with decreased viscosity and increased thermal diffusion.

Binary mixtures of locally coupled mobile oscillators.

Synchronized behavior in a system of coupled dynamic objects is a fascinating example of an emerged cooperative phenomena which has been observed in systems as diverse as a group of insects, neural networks, or networks of computers. In many instances, however, the synchronization is undesired because it may lead to system malfunctioning, as in the case of Alzheimer's and Parkinson's diseases, for example. Recent studies of static networks of oscillators have shown that the presence of a small fraction of so-called contrarian oscillators can suppress the undesired network synchronization. On the other hand, it is also known that the mobility of the oscillators can significantly impact their synchronization dynamics. Here, we combine these two ideas-the oscillator mobility and the presence of heterogeneous interactions-and study numerically binary mixtures of phase oscillators performing two-dimensional random walks. Within the framework of a generalized Kuramoto model, we introduce two phase-coupling schemes. The first one is invariant when the types of any two oscillators are swapped, while the second model is not. We demonstrate that the symmetric model does not allow for a complete suppression of the synchronized state. However, it provides means for a robust control of the synchronization timescale by varying the overall number density and the composition of the mixture and the strength of the off-diagonal Kuramoto coupling constant. Instead, the asymmetric model predicts that the coherent state can be eliminated within a subpopulation of normal oscillators and evoked within a subpopulation of the contrarians.

Molecular velocity auto-correlations in glycerol/water mixtures studied by NMR MGSE method

Molecular dynamics in binary mixtures of water and glycerol was studied by measuring the spectrum of water velocity auto-correlation in the frequency range from 0.05−10 kHz by using the NMR method of modulated gradient spin echo. The method shows that the diversity of diffusion signature in the short spin trajectories provides information about heterogeneity of molecular motion due to the motion in the micro-vortexes of hydrodynamic fluctuation, which is especially pronounced for the mixtures with low glycerol content. As concentration of glycerol increases above 10vol%, a new feature of spectrum appears due to interaction of water molecules with the clusters formed around hydrophilic glycerol molecules. New spectrum exposes a rate thickening of molecular friction, according to Einstein–Smoluchowski–Kubo formula, which inhibits rapid molecular motions and creates the conditions for a slow process of spontaneously folding of disordered poly-peptides into biologically active protein molecules when immersed in such a mixture.

Theory for the single-particle dynamics in glassy mixtures with particle size swaps

We present a theory for the single-particle dynamics in binary mixtures with particle size swaps. The general structure of the theory follows that of the theory for the collective dynamics in binary mixtures with particle size swaps, which we developed previously (Szamel 2018 Phys. Rev. E 98 050601). Particle size swaps open up an additional relaxation channel, which speeds up both the collective dynamics and the single-particle dynamics. To make explicit predictions, we resort to a factorization approximation similar to that employed in the mode-coupling theory of glassy dynamics. We show that, like in the standard mode-coupling theory, the single-particle motion becomes arrested at the dynamic glass transition predicted by the theory for the collective dynamics. We compare the non-ergodicity parameters predicted by our mode-coupling-like approach for an equimolar binary hard sphere mixture with particle size swaps with the non-ergodicity parameters predicted by the standard mode-coupling theory for the same system without swaps. Our theory predicts that the ‘cage size’ is bigger in the system with particle size swaps.

Phase separation dynamics in binary systems containing mobile particles with variable Brownian motion

This study investigates the spinodal decomposition dynamics in binary mixtures containing mobile particles by combining the Cahn–Hilliard equation with Langevin dynamics for particles with Brownian motion changes proportional to their mobility. We solve the Cahn–Hilliard equation numerically using a semi-implicit Fourier spectral method, and show that the domain growth rate first increases with the increase in particle mobility, and then decreases. The effect of filler particle concentration on the domain growth depends on its mobility: when the particle mobility is low, the domain growth rate decreases with the increase in particle concentration; whereas when the particle mobility is high, the domain growth rate decreases and then increases and finally decreases again with the increase in particle concentration. The proposed model suggests the possibility of controlling macroscopic behaviour of binary alloys by altering filler particle properties.

On hydrodynamic phase field models for binary fluid mixtures

Two classes of thermodynamically consistent hydrodynamic phase field models have been developed for binary fluid mixtures of incompressible viscous fluids of possibly different densities and viscosities. One is quasi-incompressible, while the other is incompressible. For the same binary fluid mixture of two incompressible viscous fluid components, which one is more appropriate? To answer this question, we conduct a comparative study in this paper. First, we visit their derivation, conservation and energy dissipation properties and show that the quasi-incompressible model conserves both mass and linear momentum, while the incompressible one does not. We then show that the quasi-incompressible model is sensitive to the density deviation of the fluid components, while the incompressible model is not in a linear stability analysis. Second, we conduct a numerical investigation on coarsening or coalescent dynamics of protuberances using the two models. We find that they can predict quite different transient dynamics depending on the initial conditions and the density difference although they predict essentially the same quasi-steady results in some cases. This study thus cast a doubt on the applicability of the incompressible model to describe dynamics of binary mixtures of two incompressible viscous fluids especially when the two fluid components have a large density deviation.

Structure and component dynamics in binary mixtures of poly(2-(dimethylamino)ethyl methacrylate) with water and tetrahydrofuran: A diffraction, calorimetric, and dielectric spectroscopy study.

We have combined X-ray diffraction, neutron diffraction with polarization analysis, small angle neutron scattering,differential scanning calorimetry, and broad band dielectric spectroscopy to investigate the structure and dynamics of binary mixtures of poly(2-(dimethylamino)ethyl methacrylate) with either water or tetrahydrofuran (THF) at different concentrations. Aqueous mixtures are characterized by a highly heterogeneous structure where water clusters coexist with an underlying nano-segregation of main chains and side groups of the polymeric matrix. THF molecules are homogeneously distributed among the polymeric nano-domains for concentrations of one THF molecule/monomer or lower. A more heterogeneous situation is found for higher THF amounts, but without evidences for solvent clusters. In THF-mixtures, we observe a remarkable reduction of the glass-transition temperature which is enhanced with increasing amount of solvent but seems to reach saturation at high THF concentrations. Adding THF markedly reduces the activation energy of the polymer β-relaxation. The presence of THF molecules seemingly hinders a slow component of this process which is active in the dry state. The aqueous mixtures present a strikingly broad glass-transition feature, revealing a highly heterogeneous behavior in agreement with the structural study. Regarding the solvent dynamics, deep in the glassy state all data can be described by an Arrhenius temperature dependence with a rather similar activation energy. However, the values of the characteristic times are about three orders of magnitude smaller for THF than for water. Water dynamics display a crossover toward increasingly higher apparent activation energies in the region of the onset of the glass transition, supporting its interpretation as a consequence of the freezing of the structuralrelaxation of the surrounding matrix. The absence of such a crossover (at least in the wide dynamic window here accessed) in THF is attributed to the lack of cooperativity effects in the relaxation of these molecules within the polymeric matrix.

Ultrafast 2D-IR and simulation investigations of preferential solvation and cosolvent exchange dynamics.

Using a derivative of the vitamin biotin labeled with a transition-metal carbonyl vibrational probe in a series of aqueous N,N-dimethylformamide (DMF) solutions, we observe a striking slowdown in spectral diffusion dynamics with decreased DMF concentration. Equilibrium solvation dynamics, measured with the rapidly acquired spectral diffusion (RASD) technique, a variant of heterodyne-detected photon-echo peak shift experiments, range from 1 ps in neat DMF to ∼3 ps in 0.07 mole fraction DMF/water solution. Molecular dynamics simulations of the biotin-metal carbonyl solute in explicit aqueous DMF solutions show marked preferential solvation by DMF, which becomes more pronounced at lower DMF concentrations. The simulations and the experimental data are consistent with an interpretation where the slowdown in spectral diffusion is due to solvent exchange involving distinct cosolvent species. A simple two-component model reproduces the observed spectral dynamics as well as the DMF concentration dependence, enabling the extraction of the solvent exchange time scale of 8 ps. This time scale corresponds to the diffusive motion of a few Å, consistent with a solvent-exchange mechanism. Unlike most previous studies of solvation dynamics in binary mixtures of polar solvents, our work highlights the ability of vibrational probes to sense solvent exchange as a new, slow component in the spectral diffusion dynamics.

Non-classical gas dynamics of vapour mixtures

AbstractThe non-classical gas dynamics of binary mixtures of organic fluids in the vapour phase is investigated for the first time. A predictive thermodynamic model is used to compute the relevant mixture properties, including its critical point coordinates and the local value of the fundamental derivative of gas dynamics $\Gamma $. The considered model is the improved Peng–Robinson Stryjek–Vera cubic equation of state, complemented by the Wong–Sandler mixing rules. A finite thermodynamic region is found where the nonlinearity parameter $\Gamma $ is negative and therefore non-classical gas dynamics phenomena are admissible. A non-monotone dependence of $\Gamma $ on the mixture composition is observed in the case of binary mixtures of siloxane and perfluorocarbon fluids, with the minimum value of $\Gamma $ in the mixture being always larger than that of its more complex component. The observed dependence indicates that non-ideal mixing has a strong influence on the gas dynamics behaviour, either classical or non-classical, of the mixture. Numerical experiments of the supersonic expansion of a mixture flow around a sharp corner show the transition from the classical configuration, exhibiting an isentropic rarefaction fan centred at the expansion corner, to non-classical ones, including mixed expansion waves and rarefaction shock waves, if the mixture composition is changed.

Composition Dependent Stokes Shift Dynamics in Binary Mixtures of 1-Butyl-3-methylimidazolium Tetrafluoroborate with Water and Acetonitrile: Quantitative Comparison between Theory and Complete Measurements

Here we predict, using a semimolecular theory, the Stokes shift dynamics of a dipolar solute in binary mixtures of an ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), with water (H2O) and acetonitrile (CH3CN), and compare with the experimental results. The latter are from the recent measurements that combined broad-band fluorescence up-conversion (FLUPS) with time-correlated single photon counting (TCSPC) techniques and used coumarin 153 (C153) as a solute probe. Nine different compositions of ([Bmim][BF4] + H2O) and ([Bmim][BF4] + CH3CN) binary mixtures are considered for the extensive comparison between theory and experiments. Two separate model calculations have been performed using the available experimental frequency dependent dielectric function, ε(ω). These calculations semiquantitatively reproduce the experimentally observed (i) IL mole fraction dependence of dynamic Stokes shifts in these mixtures, (ii) composition dependence of average fast, slow, and solvation times, (iii) viscosity dependence of slow times, and (iv) the nonlinear dependence of average solvation times on experimental inverse conductivity. Variations of the calculated dynamics on water dipole moment values (gas phase or liquid phase) and sensitivity to different measurements of ε(ω) for ([Bmim][BF4] + H2O) mixtures are examined. In addition, the importance of the missing contribution to experimental ε(ω) from high frequency collective solvent intermolecular modes for generating the experimentally observed sub-picosecond solvation response in these (IL + polar solvent) binary mixtures has been explored.

Segregation dynamics in dense polydisperse gas-fluidized beds

Abstract New fluidization experiments have been carried out with: a binary mixture containing 2.5 and 3.5 mm particles in equal proportions, some binary mixtures containing 1.5 and 2.5 mm particles in several proportions, and a ternary mixture containing 1.5, 2.5 and 3.5 mm particles in equal proportions. The segregation behavior of the mixtures of spherical glass particles was studied in a pseudo two-dimensional laboratory scale gas-fluidized bed with the aid of a newly developed non-intrusive Digital Image Analysis technique. The segregation index introduced by Goldschmidt et al. [1] has been used to quantify the segregation dynamics in binary mixtures, and two adapted forms of it have been used to study the segregation dynamics of the ternary mixture. Furthermore, a (mean) height index was introduced to provide more details about the dynamics of the ternary system. Our experiments reveal that while the binary systems could segregate slightly at fluidization velocities exceeding the incipient velocities of the individual components, the ternary mixture becomes well mixed at velocities even well below the incipient fluidization velocity of the large, 3.5 mm particle.

Re-entrant behavior in dynamics of binary mixtures of soft hybrid nanocolloids and homopolymers

We present results of measurements of temperature and wavevector dependent dynamics in binary mixtures of soft polymer grafted nanoparticles and linear homopolymers. We find evidence of melting of the dynamically arrested state of the soft nanocolloids with addition of linear polymers followed by a re-entrant slowing down of the dynamics with further increase in polymer density, depending on the size ratio, δ, of the polymers and the nanocolloids. For higher δ the re-entrant behavior is not observed, even for the highest added polymer density, explored here. Possible explanation of the observed dynamics in terms of the presence of a double-glass phase is provided.

Understanding Dynamics in Binary Mixtures of Entangled cis-1,4-Polybutadiene Melts at the Level of Primitive Path Segments by Mapping Atomistic Simulation Data onto the Tube Model

We study dynamics in bidisperse melts of linear cis-1,4-polybutadiene composed of probe and matrix chains at the level of the segment survival probability function ψ(s,t) which is computed directly...

Halothane Solvation in Water and Organic Solvents from Molecular Simulations with New Polarizable Potential Function

The partitioning of a substrate from one phase into another is a complex process with widespread applications: from chemical technology to the pharmaceutical industry. One particularly well-known and well-studied example is 2-bromo-2-chloro-1,1,1-trifluoroethane (halothane) trafficking through the lipid bilayer. Halothane is a model volatile anesthetic known to impact functions of model lipid bilayers, altering the structure and thickness upon its partitioning from the bulk phase. A number of theoretical and experimental investigations suggest the importance of electronic polarizability, determining a preference for halothane to partition in the interfacial systems as in lipid bilayers or binary solvents. The recently published protocol for the development of polarizable force fields based on the classical Drude model has provided fresh impetus to efforts directed at understanding the molecular principles governing complex thermodynamics of the hydrophobic hydration. Here, molecular simulations were combined with free energy simulations to study solvation of halothane in polarizable water and methanol. The absolute free energy of halothane solvation in different solvents (water, methanol, and n-hexane) has been evaluated for additive and polarizable models. It was found that both additive and polarizable models provide an adequate description of the halothane solvation in high-dielectric (polar) solvents such as water, but explicit accounting for electronic polarization is imperative for a correct description of the solvation thermodynamics in nonpolar systems. To study halothane dynamics in binary mixtures, all-atom molecular dynamics (MD) simulations for halothane-methanol mixtures in a wide range of concentrations were performed alongside an analysis of structural organization, dynamics, and thermodynamic properties to dissect the molecular determinants of the halothane solvation in polar and amphiphilic liquids such as methanol. Additionally, a theoretical test of the hypothesis on the weak hydrogen bonding of halothane and methanol in the condensed phase is provided, which was presented on the basis of spectroscopic analysis of the C-H vibrations in different gas-phase complexes. The simulations performed in the condensed phase suggest that hydrophobic interactions between halothane and methanol play a dominant role in preferential solvation.

Dynamics of binary mixtures with ions: dynamic structure factor and mesophaseformation

Dynamic equations are presented for polar binary mixtures containing ions in the presenceof preferential solvation. In one-phase states, we calculate the dynamic structure factor ofthe composition accounting for ion motion. Microphase separation can take place forsufficiently large solvation asymmetry of the cations and the anions. We showtwo-dimensional simulation results of the mesophase formation with an antagonistic salt,where the cations are hydrophilic and the anions are hydrophobic. The structure factorS(q) in the resultant mesophase has a sharp peak at an intermediate wavenumber of theorder of the Debye–Hückel wavenumber. As the quench depth is increased, thesurface tension nearly vanishes in mesophases due to an electric double layer.

Universal three-body dynamics in binary mixtures of ultra-cold atoms

The universal three-body dynamics in ultra-cold binary Fermi and Fermi-Bose mixtures is studied. A comprehensive universal description of the rotational-vibrational spectrum for two identical particles of mass m and the third particle of mass m 1 in the zero-range limit of the interaction between different particles is given for arbitrary values of the mass ratio m/m 1 and the total angular momentum L. For those L and m/m 1, which correspond to the finite number of vibrational states, all the binding energies are described by the universal function depending on two scaled variables. The detailed study is performed for L = 1; in particular, it is shown that a two-hump structure in the mass-ratio dependencies of the elastic scattering cross section and the three-body recombination rate are connected with arising of the bound states.

Thermal Conductivity of Mixtures of Carbon Dioxide and Ethane in the Critical Region

Experimental data are presented for the thermal conductivity of mixtures of carbon dioxide and ethane. The thermal conductivity has been measured with a parallel-plate instrument, as a function of temperature along isochores, so as to obtain detailed information on the behavior of the thermal conductivity of a mixture near the locus of vapor–liquid critical points. The experimental results are in agreement with theoretical predictions from the mode-coupling theory for critical dynamics in binary mixtures.

Dynamics of binary mixtures in inhomogeneous temperatures

A dynamical description for fluid binary mixtures with variable temperature and concentration gradient contributions to entropy and internal energy is given. By using mass, momentum and energy balance equations together with the standard expression for entropy production, a generalized Gibbs–Duhem relation is obtained which takes into account thermal and concentration gradient contributions. Then an expression for the pressure tensor is derived. As examples of applications, interface behavior and phase separation have been numerically studied in two dimensions neglecting the contributions of the velocity field. In the simplest case with a constant thermal gradient, the growth exponent for the averaged size of domains is found to have the usual value z = 1/3 and the domains appear elongated in the direction of the thermal gradient. When the system is quenched by contact with external walls, the evolution of temperature profiles in the system is shown and the domain morphology is characterized by interfaces perpendicular to the thermal gradient.

An Investigation of Water Dynamics in Binary Mixtures of Water and Dimethyl Sulfoxide

The motion of water molecules in mixtures of water and d6-dimethyl sulfoxide (DMSO) has been explored through molecular dynamics (MD) simulations using the SPC/E water model (J. Chem. Phys. 1987, 91, 6269) and the P2 DMSO model (J. Chem. Phys. 1993, 98, 8160). We evaluate the self-intermediate scattering functions, FS(Q,t), which are related by a Fourier transform to the incoherent structure factors, S(Q,omega), measured in quasielastic neutron scattering (QNS) experiments. We compare our results to recent QNS experiments on these mixtures reported by Bordallo et al. (J. Chem. Phys. 2004, 121, 12457). In addition to comparing the MD data to the experimental signals, which correspond to a convolution of S(Q,omega) with a resolution function, we examine the rotational and translational components of FS(Q,t) and investigate to what extent simulation results for the single-molecule dynamics follow the dynamical models that are used in the analysis of the experimental data. We find that the agreement between the experimental signal and the MD data is quite good and that the portion of FS(Q,t) due to translational dynamics is well represented by the jump-diffusion model. The model parameters and their composition dependence are in reasonable agreement with experiment, exhibiting similar trends in water mobility with composition. Specifically, we find that water motion is less hindered in water-rich and water-poor mixtures than it is near equimolar composition. We find that the extent of coupling between rotational and translational motion contributing to FS(Q,t) increases as the equimolar composition of the mixture is approached. Thus, the decoupling approximation, which is used to extract information on rotational relaxation from QNS spectra at higher momentum transfer (Q) values, becomes less accurate than that in water-rich or DMSO-rich mixtures. We also find that rotational relaxation deviates quite strongly from the isotropic rotational diffusion model. We explore this issue further by investigating the behavior of orientational time correlations for different unit vectors and corresponding to Legendre polynomials of orders 1-4. We find that the rotational time correlations of water molecules behave in a way that is more consistent with the extended jump rotation model recently proposed by Laage and Hynes (Science 2006, 311, 832).