共查询到20条相似文献,搜索用时 23 毫秒
1.
J. Hegseth A. Oprisan Y. Garrabos C. Lecoutre-Chabot V. S. Nikolayev D. Beysens 《The European physical journal. E, Soft matter》2008,26(4):345-353
The heating of coexisting gas and liquid phases of pure fluid through its critical point makes the fluid extremely compressible,
expandable, slows the diffusive transport, and decreases the contact angle to zero (perfect wetting by the liquid phase).
We have performed experiments on near-critical fluids in a variable volume cell in the weightlessness of an orbiting space
vehicle, to suppress buoyancy-driven flows and gravitational constraints on the liquid-gas interface. The high compressibility,
high thermal expansion, and low thermal diffusivity lead to a pronounced adiabatic heating called the piston effect. We have
directly visualized the near-critical fluid’s boundary layer response to a volume quench when the external temperature is
held constant. We have found that when the system’s temperature T is increased at a constant rate past the critical temperature T
c
, the interior of the fluid gains a higher temperature than the hot wall (overheating). This extends previous results in temperature
quenching experiments in a similarly prepared system when the gas is clearly isolated from the wall. Large elliptical wetting
film distortions are also seen during these ramps. By ray tracing through the elliptically shaped wetting film, we find very
thick wetting film on the walls. This wetting film is at least one order of magnitude thicker than films that form in the
Earth’s gravity. The thick wetting film isolates the gas bubble from the wall allowing gas overheating to occur due to the
difference in the piston effect response between gas and liquid. Remarkably, this overheating continues and actually increases
when the fluid is ramped into the single-phase supercritical phase. 相似文献
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3.
The structure of polydisperse hard sphere fluids, in the presence of a wall, is studied by the Rosenfeld density functional theory. Within this approach, the local excess free energy depends on only four combinations of the full set of density fields. The case of continuous polydispersity thereby becomes tractable. We predict, generically, an oscillatory size segregation close to the wall, and connect this, by a perturbation theory for narrow distributions, with the reversible work for changing the size of one particle in a monodisperse reference fluid. 相似文献
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Using density functional theory developed by Rosefeld, a model polydisperse fluid has been studied in contact with a membrane permeable to some components of the fluid. Calculations were carried out for three kinds of polydisperse fluid, each characterized by a different distribution of particle sizes. The structure of fluid has been evaluated on both sides of the membrane, plus the distribution of the particles in bulk fluid and in the surface layers. The adsorption and osmotic pressure in the system have been calculated. 相似文献
6.
The morphology of magnetic fluid droplets on magnetic thin film dots is studied experimentally, including the aspect ratio and the contact angle variation of the droplets. Under a uniform external magnetic field, the droplet's aspect ratio increases with the external field and with the diameter of the magnetic dot due to the concentrated magnetic flux inside the magnetic fluid droplet. Similar to the electrical wetting phenomenon, the induced magnetic dipoles in the magnetic film and in the magnetic fluid near the solid–liquid interface change the solid–liquid interfacial tension, and in consequence reduce the apparent contact angle of the magnetic fluid droplet. 相似文献
7.
流体液滴在固体表面的浸润性对其润滑性能至关重要.本文利用分子动力学方法研究了正癸烷纳米液滴在铜表面上的润湿特性.结果表明:在平坦光滑表面上,壁面的厚度和分子数目对润湿效果影响不大.随着壁面能量势阱参数εs 增大,接触角线性减小.随着温度升高,液滴的接触角减小.在沟槽粗糙表面上,随着粗糙度因子增大,对于疏液表面,接触角增大到一定值后基本保持不变,符合Cassie理论;中性和亲液表面接触角则会减小,为Wenzel润湿模式.当表面分数增大时,疏液与亲液表面接触角整体呈减小的趋势,对中性表面影响不大.当温度升高时,粗糙疏液表面接触角会增大,润湿效果更差,而粗糙中性和亲液表面液滴润湿性会更好. 相似文献
8.
More than two decades ago, in a seminal paper John Cahn proposed scaling arguments for the possibility of a wetting transition in two coexisting fluid phases near the critical point. Since then, Cahn's model has been tested in many fluid systems and further refined by including the real interactions between the fluid and the solid wall. A fascinating consequence of the existence of a wetting transition is the possibility for a transition from weak to strong adsorption in the homogeneous phase. The situation is further enriched in nonstandard geometries having special geometrical constraints. The subject of this review concerns one such situation, where charge-stabilized colloidal particles are suspended in the homogeneous region of a binary liquid mixture. In this case, the preferential adsorption of one of the liquid components on to the colloid surface completely modifies the stability of the particles leading to an aggregation process. Although the exact mechanism underlying the adsorption phenomenon is still debated, it is closely related to the wetting transition. Recent experimental developments concerning the static and dynamic aspects of this phenomenon are reviewed. In addition, the main findings of a theoretical model based on the adsorption-modified electrostatic interactions between the colloidal particles are discussed. 相似文献
9.
RICHARD P. SEAR 《Molecular physics》2013,111(7):1013-1017
It has been shown by Stell (1991, J. statist. Phys., 63, 1203) that at low temperature mono-disperse sticky spheres collapse to form coexisting close-packed solid and infinitely dilute gases. We show that polydisperse sticky spheres also collapse and calculate the collapse temperature. The polydisperse spheres separate into fractions with narrower polydispersities which can then solidify. This is perhaps the first example of a single-peaked polydisperse mixture phase solidifying and separating. It implies that a mixture of polydisperse large hard spheres with much smaller hard spheres does not show fluid—fluid coexistence. 相似文献
10.
Dijkstra M 《Physical review letters》2004,93(10):108303
Extensive simulations of a hard sphere fluid confined between two planar hard walls show the onset of crystalline layers at the walls at about 98.3% of bulk crystallization density rho(f) independent of the wall separations L(z), and is, hence, a single wall phenomenon. As the bulk density far from the wall rho(b) increases, the thickness of the crystalline film appears to increase logarithmically, with (rho(f)-rho(b)) indicating complete wetting by the hard sphere crystal of the wall-fluid interface. Increasing rho(b) further, we observe a jump in the adsorption which depends on L(z) and corresponds to capillary freezing. The formation of crystalline layers below bulk crystallization, the logarithmic growth of the crystalline film, its independence of L(z), and its clear distinction from capillary freezing lend strong evidence for complete wetting by the hard sphere crystal at the wall-fluid interface. 相似文献
11.
W. G> Shin D. Y. H. Pui H. Fissan S. Neumann A. Trampe 《Journal of nanoparticle research》2007,9(1):61-69
TSI Nanoparticle Surface Area Monitor (NSAM) Model 3550 has been developed to measure the nanoparticle surface area deposited
in different regions of the human lung. It makes use of an adjustable ion trap voltage to match the total surface area of
particles, which are below 100 nm, deposited in tracheobronchial (TB) or alveolar (A) regions of the human lung. In this paper,
calibration factors of NSAM were experimentally determined for particles of different materials. Tests were performed using
monodisperse (Ag agglomerates and NaCl, 7–100 nm) and polydisperse particles (Ag agglomerates, number count mean diameter
below 50 nm). Experimental data show that the currents in NSAM have a linear relation with a function of the total deposited
nanoparticle surface area for the different compartments of the lung. No significant dependency of the calibration factors
on particle materials and morphology was observed. Monodisperse nanoparticles in the size range where the response function
is in the desirable range can be used for calibration. Calibration factors of monodisperse and polydisperse Ag particle agglomerates
are in good agreement with each other, which indicates that polydisperse nanoparticles can be used to determine calibration
factors. Using a CFD computer code (Fluent) numerical simulations of fluid flow and particle trajectories inside NSAM were
performed to estimate response function of NSAM for different ion trap voltages. The numerical simulation results agreed well
with experimental results. 相似文献
12.
We introduce a mesoscale technique for simulating the structure and rheology of block-copolymer melts and blends in hydrodynamic flows. The technique couples dynamic self-consistent field theory with continuum hydrodynamics and flow penalization to simulate polymeric fluid flows in channels of arbitrary geometry. We demonstrate the method by studying phase separation of an ABC triblock copolymer melt in a submicron channel with neutral wall wetting conditions. We find that surface wetting effects and shear effects compete, producing wall-perpendicular lamellae in the absence of flow and wall-parallel lamellae in cases where the shear rate exceeds some critical Weissenberg number. 相似文献
13.
MITSUAKI GINOZA 《Molecular physics》2013,111(18):1613-1616
An analytical model of the equation of state is presented for the polydisperse fluid of adhesive colloidal particles. The model is based on the mean-spherical approximation solution of the Ornstein-Zernike equation for a multicomponent hard sphere Yukawa fluid in which the Yukawa tails are sufficiently short range and strong. In particular, assuming that distributions of diameters and ‘charges’ of particles are described by the Schulz function, the analytical expressions for the compressibility and the pressure for the intrinsically polydisperse fluid are given in terms of simple functions of the packing fraction, the adhesion parameter and the Schulz distribution parameter. 相似文献
14.
Analytic expressions for the Laplace transform of the interaction energy and force between two exceedingly large hard spheres at infinite dilution in a polydisperse hard-sphere suspending fluid are presented. The equations are based on the Percus–Yevick approximation for the many-component suspending fluid, supplemented by the hypernetted chain approximation for the correlation function of the suspended spheres. By applying the Derjaguin approximation, the energy and force results for two spheres are related to the energy per unit area and the disjoining pressure between two flat walls suspended in a polydisperse fluid. Numerical results for the representative Schultz distributions of the diameters of the species comprising the suspending fluid are presented and discussed. 相似文献
15.
Equilibrium and nonequilibrium aspects of particle adsorption on the walls of fluid-filled nanochannels are examined via molecular dynamics simulations. The force on the particle and the free energy of the system are found to depend on the particle's history (hysteresis), in addition to its radial position and the wetting properties of the fluid, even when the particle moves quasistatically. The hysteresis is associated with changes in the fluid density in the gap between the particle and the wall, which persist over surprisingly long times. The force and free energy exhibit large oscillations with distance when the lattice of the structured nanoparticle is held in register with that of the tube wall, but not if the particle is allowed to rotate freely. Adsorbed particles are trapped in free-energy minima in equilibrium but can desorb if forced along the channel. 相似文献
16.
《Journal of computational physics》2008,227(1):763-775
This paper reports a new numerical scheme of the lattice Boltzmann method for calculating liquid droplet behaviour on particle wetting surfaces typically for the system of liquid–gas of a large density ratio. The method combines the existing models of Inamuro et al. [T. Inamuro, T. Ogata, S. Tajima, N. Konishi, A lattice Boltzmann method for incompressible two-phase flows with large density differences, J. Comput. Phys. 198 (2004) 628–644] and Briant et al. [A.J. Briant, P. Papatzacos, J.M. Yeomans, Lattice Boltzmann simulations of contact line motion in a liquid–gas system, Philos. Trans. Roy. Soc. London A 360 (2002) 485–495; A.J. Briant, A.J. Wagner, J.M. Yeomans, Lattice Boltzmann simulations of contact line motion: I. Liquid–gas systems. Phys. Rev. E 69 (2004) 031602; A.J. Briant, J.M. Yeomans, Lattice Boltzmann simulations of contact line motion: II. Binary fluids, Phys. Rev. E 69 (2004) 031603] and has developed novel treatment for partial wetting boundaries which involve droplets spreading on a hydrophobic surface combined with the surface of relative low contact angles and strips of relative high contact angles. The interaction between the fluid–fluid interface and the partial wetting wall has been typically considered. Applying the current method, the dynamics of liquid drops on uniform and heterogeneous wetting walls are simulated numerically. The results of the simulation agree well with those of theoretical prediction and show that the present LBM can be used as a reliable way to study fluidic control on heterogeneous surfaces and other wetting related subjects. 相似文献
17.
Patricio P Pham CT Romero-Enrique JM 《The European physical journal. E, Soft matter》2008,26(1-2):97-101
It is known that the wetting behaviour of a fluid is deeply altered by the presence of rough or structured substrates. We first review some simple considerations about isotropic fluids and rough substrates, and then we generalize Wenzel's law, which assigns an effective contact angle to a droplet on a rough substrate, when the wetting layer has an ordered phase, like a nematic. We estimate the conditions for which the wetting behavior of an ordered fluid can be qualitatively different from that usually found in a simple fluid. To support our general considerations, we use the Landau-de Gennes mean field approach to investigate theoretically and numerically the wetting transition of a nematic phase on a periodic triangular structured substrate. 相似文献
18.
ABSTRACTWe present a numerical study of a simple density functional theory model of fluid adsorption occurring on a planar wall decorated with a narrow deep stripe of a weaker adsorbing (relatively solvophobic) material, where wall-fluid and fluid-fluid intermolecular forces are considered to be dispersive. Both the stripe and outer substrate exhibit first-order wetting transitions with the wetting temperature of the stripe lying above that of the outer material. This geometry leads to a rich phase diagram due to the interplay between the pre-wetting transition of the outer substrate and an unbending transition corresponding to the local evaporation of liquid near the stripe. Depending on the width of the stripe, the line of unbending transitions merges with the pre-wetting line inducing a two-dimensional wetting transition occurring across the substrate. In turn, this leads to the continuous pre-drying of the thick pre-wetting film as the pre-wetting line is approached from above. Interestingly we find that the merging of the unbending and pre-wetting lines occurs even for the widest stripes considered. This contrasts markedly with the scenario where the outer material has the higher wetting temperature, for which the merging of the unbending and pre-wetting lines only occurs for very narrow stripes. 相似文献
19.
Grand canonical Monte Carlo simulations are used to study the behaviour of triangle-well (TW) fluids with variable well widths confined inside slit pores. The effect of individual factors influencing the properties of confined fluids such as fluid–fluid interactions, pore size and pore wall–fluid interactions are obtained using simulations as it is difficult to experimentally determine the same. An interesting observation of this study is that inside the narrow pore of slit height h* = 5 at the high-pressure condition of P* = 0.8, for the TW fluid with long-range attraction or for the fluid at a low temperature for even a short-range attraction, the density profiles show layering such that there is a sticking tendency of the particles at centre, while there is a depletion of particles near the wall (as the layers at the centre have higher density peak heights than near the walls). 相似文献
20.
For the problem of the 2D wetting transition near a 1D random wall, we show by a renormalization calculation that the effect of disorder is marginally relevant. It is therefore expected that the nature of the wetting transition and the location of the critical point are modified by any amount of disorder. This is supported by numerical simulations based on transfer matrix calculations. We investigate also the problem of wetting near a random wall on hierarchical lattices and find similar results. 相似文献