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1.
We summarize the main results of our study of the density-density correlation function for Sullivan's model of a gas adsorbed on a solid substrate. In the approach to complete wetting, when a thick film of liquid density is adsorbed at the substrate, long-ranged transverse (parallel to the surface) correlations develop at the edge of the film where the density profile is similar to that of a liquid-gas interface. For a class I wetting situation the range of the transverse correlations increases and ultimately diverges as the bulk gas pressure approaches the saturated vapour pressure. We comment on other situations where long-ranged correlations arise and mention the possibility of observing these in diffraction experiments and in computer simulations. Sullivan's model always predicts a second-order phase transition between class II and class I wetting. By extending his model and allowing the attractive part of the solid-fluid potential to be longer-ranged than the attractive fluid-fluid potential we find that this wetting transition can become a first-order (Cahn) transition.  相似文献   

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We consider two different problems involving the localization of a single polymer chain: (i) a periodic AB copolymer at a selective fluid-fluid interface, with the upper (resp. lower) fluid attracting A (resp. B) monomers (ii) a homopolymer chain attracted to a hard wall (wetting). Self avoidance is neglected in both models, which enables us to study their localization transition in a grand canonical approach. We recover the results obtained in previous studies via transfer matrix methods. Moreover, we calculate in this way the loop length distribution functions in the localized phase. Some finite size effects are also determined and tested numerically. Received 13 April 2000  相似文献   

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The adsorption is studied of a fluid at a structured solid substrate by means of computer simulations on the Delft Molecular Dynamics Processor. Two types of particles are present, 2904 of one type for building a three-layer substrate and about 8500 of another type for composing the fluid. Interactions between like and unlike atoms are modeled by pair potentials of Lennard-Jones form cut off at 2.5. Simulations are performed at constant temperature and variable ratio of substrate-adsorbate to adsorbate-adsorbate attraction. On the basis of measurements of density profiles, coverages, surface tensions, and contact angles, a wetting as well as a drying phase transition have been identified. Both transitions are of first order.  相似文献   

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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.  相似文献   

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This paper is devoted to the study of the Young equation, which gives a connection between surface tensions and contact angle. We derive the generalized form of this equation for anisotropic models using thermodynamic considerations. In two dimensions with SOS-like approximations of the interface, we prove that the surface tension may be computed explicitly as a simple integral, which of course depends upon the orientation of the interface. This allows a complete study of the wetting transition when a constant wall attraction is taken into account within the SOS and Gaussian models. We therefore give a complete analysis of the variation of the contact angle with the temperature for those models. It is found that for certain values of the parameters, two wetting transitions may successively appear, one at low temperature and one at high temperature, giving the following states: film—droplet—film. This study rests upon the generalized Young equation, the validity of which is proved for the Gaussian model with a constant wall attraction, using microscopic considerations.On leave from Faculté des Sciences, Université de l'Etat, 7000-Mons, Belgium.  相似文献   

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When a V2O5 crystallite is placed on an anatase pellet and heated at 823–923 K, vanadium ions migrate over the surface of anatase grains enveloping them in a thin overlayer. XPS, X-ray and EPR studies show that at 823 K a very thin layer is formed, its properties being strongly modified by interaction with the anatase support. At 923 K, on top of this inner layer an outer layer migrates, whose properties are similar to V2O5. As in the same conditions no migration is observed on rutile, it is concluded that this phenomenon is a manifestation of wetting of one oxide by another oxide, the difference in the surface free energy being the driving force of the migration.  相似文献   

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Certain properties of the Bell-type correlations and, in particular, the impossibility of using them to transmit signals faster than light, are investigated from the point of view of the conceptual structure of quantum mechanics and of Whitehead's process philosophy. The collapses of quantum states are shown to correspond to perspectives of different frames of reference on a Whiteheadian process of self-creation of actual entities. The analysis suggests a fundamental limitation on the capacity to describe the propagation of influences among the results of measurements at space-like separation. It is further shown that, if Whitehead's framework is modified in a specific way, it accounts very well for the apparent existence of superluminal influences, and for the impossibility of using them for superluminal communication.This work was supported in part by a grant from the Colgate Research Council.  相似文献   

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The profiles of the concentration and the exchange enthalpy at the solid-fluid interface are investigated with the framework of a layer model (or inhomogeneous cell model). It is shown that for systems consisting of isotropic units, concentration distributions in the interfacial phase obey an exponential law. This is in agreement with results obtained from other theories or computer simulations. Subsequently, a characteristic thickness δ* (or n*d) is defined. This factor, together with the surface characterist scaling factor C* and the value of bulk concentrations, will determine the shape of distribution profiles of the concentration and the exchange energy in the interfacial phase. As a result, it is found that this factor δ* is associated with C*. This is empl estimate C* from δ*. Finally, the connection between the attachment energy Eatt and C* is discussed f crystal.  相似文献   

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For the study of the interaction of a liquid alloy with differently oriented single crystalline sapphire surfaces precise surface tension data of the liquid are fundamental. We measured the surface tension of liquid Al-Cu contactlessly on electromagnetically levitated samples using the oscillating drop technique. Data were obtained for samples covering the entire range of composition and in a broad temperature range. The surface tensions can be described as linear functions of temperature with negative slopes. Moreover, they decrease monotonically with an increase of aluminium concentration. The observed behaviour with respect to both temperature and concentration is in agreement with a thermodynamic model calculation using the regular solution approximation. Surface tensions were used to calculate interfacial energies from the contact angles of liquid Cu droplets, deposited on the C(0001), A(11-20), R(1-102) surfaces of an α-Al2O3 substrate. The contact angles were measured by means of the sessile drop method at 1380?K. In the Cu/α-Al2O3 system, no anisotropy is evident neither for the contact angles nor for the interfacial energies of different surfaces. The work of adhesion of this system is isotropic, too.  相似文献   

14.
The spectral density associated with correlations of relative displacements is calculated in the Toda chain. Strong nonlinear motion activated already at low temperatures gives rise to a shoulder on the high-frequency side of the phonon peak. This secondary structure is a reminiscence of the soliton response obtained with a more refined untraditional approach.  相似文献   

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New phenomena have been reported recently in connection with Gaussian beam interaction with a plane dielectric interface, namely, the deterioration of the reflected and refracted beams from shapes predicted by geometric optics, and the generation of higherorder components that cause angular beam deflection. Any bounded, symmetric beam, which is not necessarily Gaussian, can be comprised in terms of an angular spectrum of plane waves. Utilizing such a modal expansion, a model of the interaction process that seems to point out the generality of the phenomena involved for bounded symmetrical beams with any cross-section is presented. The procedure is applied to a Cauchy profile, and analytical results are given. Comparison with previous results obtained for the Gaussian beam and careful examination of the respective spectral functions demonstrate close correspondence between the results. This adds credence to the general approach presented here which can be applied to bounded symmetrical beams of general shape.  相似文献   

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We use the "wavelet transform microscope" to carry out a comparative statistical analysis of DNA bending profiles and of the corresponding DNA texts. In the three kingdoms, one reveals on both signals a characteristic scale of 100-200 bp that separates two different regimes of power-law correlations (PLC). In the small-scale regime, PLC are observed in eukaryotic, in double-strand DNA viral, and in archaeal genomes, which contrasts with their total absence in the genomes of eubacteria and their viruses. This strongly suggests that small-scale PLC are related to the mechanisms underlying the wrapping of DNA in the nucleosomal structure. We further speculate that the large scale PLC are the signature of the higher-order structure and dynamics of chromatin.  相似文献   

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In this paper we present a condition for thermodynamic equilibrium of gas bubbles of dimensions larger that a few tens of nanometers trapped at a solid–liquid interface. It is defined an intensive adimensional function that relates bubble stability with wettability and surface corrugation related parameters. From it, we deduce that bubbles can be stable on smooth, highly hydrophobic surfaces and that, on weakly hydrophobic surfaces, bubbles may be stabilized by topographical heterogeneities like pores and grooves.  相似文献   

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Self-consistent nuclear-matter calculations are presented which take into account Dahlblom's results for the contribution to the binding energy due to three-body correlations. We propose a justified parametrization of the single-particle potential for particle states, the energy contribution of which cancels approximately the energy from certain three-body correlations. Indications are given of how to fix this particle-state potential for a given two-body interaction. Two nucleon-nucleon potentials are used: the Reid soft-core potential and a fully momentum-dependent one-boson-exchange potential similar to the form proposed by Ingber and Potenza. The mechanism of the increase in the total wound due to three-body correlations is investigated and reasons are given why this does not prevent the saturation densities from moving to higher values. Due to three-body correlations and with self-consistency on the hole spectrum, the increase in nuclear-matter binding energy is 0.60 MeV/A for the Reid soft-core interaction and 0.68 Mev/A for the OBEP. The saturation momentum is shifted from 1.42 fm?1 to 1.44 fm?1 for the Reid potential and from 1.58 fm?1 to 1.62 fm?1 for the OBEP.  相似文献   

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