混合流体浸润相变的研究(Ⅱ) 二元系统的三相共存态

本文仍从Sullivan模型出发,发展文献[1]中提出的展开方法,在动力学图象中,就混合系统中最具有代表性的状态——二元三相系的浸润相变性质,进行解析研究。所得结论对已有结果作了补充与修正。     

墙的力程加长有利于一级浸润相变的反例

迄今讨论的浸润相变模型中,墙的力程加长总是有利于一级相变而不利于二级相变。本文提出了一个可以解析地讨论的反例。 关键词：     

混合流体浸润相变的研究(Ⅱ)——二元系统的三相共存态

本文仍从Sullivan模型出发,发展文献[1]中提出的展开方法,在动力学图象中,就混合系统中最具有代表性的状态——二元三相系的浸润相变性质,进行解析研究。所得结论对已有结果作了补充与修正。 关键词：     

混合流体浸润相变的研究(Ⅲ) 二元系统的四相共存态

本文讨论二元Sullivan系统的一个特殊状态——二元四相系的浸润相变性质,该系统的许多性质可以通过对两个二元二相系的讨论而得到。结果表明:这一系统同时存在一级相变和二级相变。     

有序-无序型铁电和反铁电相变的格林函数理论

本文在对称截断近似下,对格林函数在研究有序-无序型铁电和反铁电相变中的应用做了初步探讨。还发现,可以直接利用所得的序参数S随温度T变化关系,同时确定相变的二个临界参数S_c和T_c,从而自然得出相交级数(一级相变或二级相变)的结论。本文较详细地讨论了所得结果,并给出了几种晶体的理论结果与实验的比较。 关键词：     

混合流体浸润相变的研究(Ⅲ)——二元系统的四相共存态

本文讨论二元Sullivan系统的一个特殊状态——二元四相系的浸润相变性质,该系统的许多性质可以通过对两个二元二相系的讨论而得到。结果表明:这一系统同时存在一级相变和二级相变。 关键词：     

浸润相变及有关问题

介绍了浸润和浸润相变的概念，讨论了近年来人们关心的Ｓｕｌｉｖａｎ模型及由于数学表达上的类比而出现的“动力学方法”。     

具有不同作用势的两平行墙间流体的浸润相变

用解析方法讨论了当两平行墙对流体施加不同的作用势时流体的浸润相变。系统的状态很敏感地依赖于两墙的作用势和两墙间距离的大小。即使两墙差别很小,在一定条件下仍可发生浸润一墙而不浸润另一墙的现象。系统中发生的浸润相变可能是一级的,也可能是二级的。 关键词：     

谈谈浸润相变

浸润相变通常指液体在固体表面上所发生的从部分浸润状态到完全浸润状态的转化。简要介绍了与这一现象有关的概念，性质和具体应用，描述了实验上对浸润状态的测量，并说明了与浸润相变有关的一些现象。另外，还介绍了所谓和学方法对Ｓｕｌｌｉｖａｎ流体浸润相变的理研究，即通过数学类比，将变这一热力学问题化成保守势场中经典粒子运动的力学问题来研究。     

二维相变系统Collins模型的统计理论

Kawamura曾利用Collins模型,在忽略4-原子存在的情况下,研究了二维系统的相变。本文进一步考虑4-原子的存在,计算了有空格点存在时系统的吉布斯自由能,研究了4-原子所占百分数对三相点t_t,P_t值以及临界点t_c,p_c值的影响,获得了具有三相点和临界点的完整相图。本文还讨论了相变时各相的面积与温度之间的关系。所得结果与通常的三维物质非常相似。 关键词：     

Evolution of thermodynamic potentials in closed and open nanocrystalline systems: Ge-Si:Si(001) islands

An open (closed) system, in which matter is (not) exchanged through surface diffusion, was realized via growth kinetics. Epitaxially grown Si-Ge:Si (001) islands were annealed in different environments affecting the diffusivity of Si adatoms selectively. The evolution of the driving forces for intermixing while approaching the equilibrium was inferred from Synchrotron x-ray measurements of composition and strain. For the open system, intermixing due to the Si inflow from the wetting layer (reservoir) caused a decrease in the Ge content, leading to a lowering of the elastic energy and an increase in the mixing entropy. In contrast, for the closed system, while keeping the average Ge composition constant, atom rearrangement within the islands led to an increase in both elastic and entropic contributions. The Gibbs free energy decreased in both cases, despite the different evolution paths for the composition profiles.     

Field Emission Electric Propulsion: Emission Site Distribution of Slit Emitters

Field emission electric propulsion is the technological application of the principle of liquid metal ion sources as thrusters in electric space propulsion. Research work sponsored by the European Space Agency (ESA) on a slit-type field ion thruster is reported and discussed. The most significant new features of its emission performance are as follows: For the first time, a slit emitter with a closed propellant supply system was fired in any optional direction, requiring, in principle, no gravitational forces. Quantitative data relating the constituents of the residual gas atmosphere to the wetting behavior of the liquid metal propellant and the emission site distribution were obtained. A homogeneous distribution of equally spaced emission sites was observed; the measured spacing is in good agreement with a simple hydrostatic model of wavelike instabilities on electrically stressed surfaces of fluids.     

Line tension and nanometer drop wettability on solid surfaces

The dimensional dependence of the angle of solid surface wetting by a small drop on the latter’s size R and radius of the wetting outline r is considered. Numerical values of specific linear energy γ?(r) and line tension σ _r (r) of the wetting outline are calculated for a nanometer tin drop-substrate surface-aluminum film system. It is shown that wetting angle θ(R,r) in the drop-substrate surface system increases as the wetting outline’s radius decreases.     

Threshold criterion for wetting at the triple point

Grand canonical simulations are used to calculate adsorption isotherms of various classical gases on alkali metal and Mg surfaces. Ab initio adsorption potentials and Lennard-Jones gas-gas interactions are used. Depending on the system, the resulting behavior can be nonwetting for all temperatures studied, complete wetting, or (in the intermediate case) exhibit a wetting transition. An unusual variety of wetting transitions at the triple point is found in the case of a specific adsorption potential of intermediate strength. The general threshold for wetting near the triple point is found to be close to that predicted with a heuristic model of Cheng et al. This same conclusion was drawn in a recent experimental and simulation study of Ar on CO2 by Mistura et al. These results imply that a dimensionless wetting parameter w is useful for predicting whether wetting behavior is present at and above the triple temperature. The nonwetting/wetting crossover value found here is w approximately 3.3.     

Wetting by solid helium,a model system

This is a review of the wetting properties of solid helium on various solid substrates. Due to its extreme purity and to its very fast growth dynamics, solid helium 4 is often considered as a model system in materials science. Several wetting phenomena have been studied with helium 4 crystals, namely contact angles on solid substrates with variable roughness, wetting on graphite where epitaxial growth takes place, the roughening transition as a function of film thickness, the wetting of grain boundaries by the liquid phase.     

The effect of inclusion size on grain boundary wetting in Al-Sn alloys

The wetting behavior of liquid metal was studied for the Al-Sn system with particular reference to low Sn concentrations. It was shown that for Sn concentrations below 5 wt-%, liquid grain boundary films break up into separate inclusions, the wetting angle of which increases with decreasing inclusion size. Possible explanations for this phenomenon are discussed, and it is concluded that the wetting angle is not a fixed constant according solely to Young's equation, but that a correction factor is required for small inclusions.     

Nonequilibrium wetting transition in a nonthermal 2D Ising model

Nonequilibrium wetting transitions are observed in Monte Carlo simulations of a kinetic spin system in the absence of a detailed balance condition with respect to an energy functional. A nonthermal model is proposed starting from a two-dimensional Ising spin lattice at zero temperature with two boundaries subject to opposing surface fields. Local spin excitations are only allowed by absorbing an energy quantum (photon) below a cutoff energy E _c . Local spin relaxation takes place by emitting a photon which leaves the lattice. Using Monte Carlo simulation nonequilibrium critical wetting transitions are observed as well as nonequilibrium first-order wetting phenomena, respectively in the absence or presence of absorbing states of the spin system. The transitions are identified from the behavior of the probability distribution of a suitably chosen order parameter that was proven useful for studying wetting in the (thermal) Ising model.     

Third-order non-linear susceptibility in a three-level QD system

Third-order non-linear susceptibility is derived for a three-level quantum dot system. Then the total absorption (linear and non-linear) for InGaAsP three-level quantum dot systems is calculated at various parameters (wetting layer composition, pump power, quantum size effect and dephasing linewidth). The spectral hole appears at low power with increasing Ga mole-fraction in the wetting layer.     

The mean-field adsorption on a sinusoidally corrugated substrate revised

The fluid system at the bulk liquid–gas coexistence in a presence of a sinusoidally corrugated substrate exhibits not only the wetting transition, but additionally a first-order, thin–thick transition. The mean-field analysis of this transition based on a simple effective Hamiltonian is valid only in long wavelength limit. In this case the filling transition occurs so close to the wetting temperature, that the behavior of the interface is dominated by fluctuations, therefore the mean-field approach breaks down. We analyze the filling transition with the help of Hamiltonian evaluated from Landau theory. The applicability of our Hamiltonian is not restricted only to the vicinity of the wetting point. We obtain the phase diagram valid beyond the temperature range corresponding to the strong fluctuations regime. It displays more complex dependence on different length scales of the system and includes the old one as a particular case.     

Reversible sphere-to-lamellar wetting transition at the interface of a diblock copolymer system

We use ellipsometry to investigate a transition in the morphology of a sphere-forming diblock copolymer thin-film system. At an interface the diblock morphology may differ from the bulk when the interfacial tension favours wetting of the minority domain, thereby inducing a sphere-to-lamella transition. In a small, favourable window in energetics, one may observe this transition simply by adjusting the temperature. Ellipsometry is ideally suited to the study of the transition because the additional interface created by the wetting layer affects the polarisation of light reflected from the sample. Here we study thin films of poly(butadiene-ethylene oxide) (PB-PEO), which order to form PEO minority spheres in a PB matrix. As temperature is varied, the reversible transition from a partially wetting layer of PEO spheres to a full wetting layer at the substrate is investigated.