The sound velocity in ideal liquid mixtures from thermal volume fluctuations.

The selection of the correct mixing rule for sound velocity in ideal liquid mixtures determines the interpretation of the sound velocity in real mixtures. This is especially important for the determination of apparent properties of solutes, such as their apparent compressibility. There are different approaches reported in the literature, and this article presents a new derivation of the mixing rule based on statistical mechanics. It is shown that the correlation of volume fluctuations between adjacent components has a crucial influence on the ideal mixing rule.     

The characterization and thermal stability of a cluster grafted on silica surface

Ru₃(CO)₁₂, supported on silica in the absence of oxygen, reacts with silanol groups of the surface to produce a grafted cluster

, which has been characterized by IR and Raman spectroscopy; the molecular formula of this cluster is in agreement with the stoichiometric balance of CO evolved during its formation from Ru₃(CO)₁₂. The grafted cluster is an intermediate step to produce by thermal decomposition small metallic ruthenium particles of 14 Å together with some Ru(II) carbonyl species encapsulated in the silica surface.     

Disjoining pressure and the film-height-dependent surface tension of thin liquid films: New insight from capillary wave fluctuations

In this paper we review simulation and experimental studies of thermal capillary wave fluctuations as an ideal means for probing the underlying disjoining pressure and surface tensions, and more generally, fine details of the Interfacial Hamiltonian Model. We discuss recent simulation results that reveal a film-height-dependent surface tension not accounted for in the classical Interfacial Hamiltonian Model. We show how this observation may be explained bottom-up from sound principles of statistical thermodynamics and discuss some of its implications.     

Space-time scales in the Lagrange theory of thermal hydrodynamic fluctuations

The value and temperature dependence of the Maxwell relaxation time of viscous tensions and the Lagrangian particle radius, which are the main space-time scales in the Lagrange theory of thermal hydrodynamic fluctuations, are discussed. These parameters play the key role in the estimations of the relative value of the collective component of the molecular self-diffusion coefficient. Special attention is paid to the consistency of estimates obtained by different methods.     

On the thermal fluctuations of free charge in the Ershler-Randles circuit

Noise method for the analyzing of thermodynamic second-order fluctuations of the electrical double layer charge in complicated electrochemical systems is developed. The method is based on the joint application of the Nyquist fluctuation-dissipation theorem and Laplace transform. Second-order fluctuations of the free charge in the electrical double layer are studied under the conditions when the weak-signal faradaic impedance of equilibrated electrode is determined by the diffusion impedance, alongside with the slow-discharge resistance. It is shown that, unlike the high-order fluctuations, the level of thermodynamic second-order fluctuations of the free charge does not depend on the mechanism of interaction of the thermodynamic system with thermostat; it fully corresponds to the conceptions of the Gibbs statistical thermodynamics.     

Equilibrium fluctuations in the theory of surface processes on microparticles

The question of the role of equilibrium fluctuations in the adsorption theory and kinetics of surface processes occurring on the particles of the nanometer size range is discussed. Differences are put forward that need to be introduced to the fluctuation theory of surface processes on microparticles and that generalize Hill’s approach to describing the thermodynamic properties of small systems. We show the importance of allowing for the discrete character of adsorption centers on the surfaces and their heterogeneity when describing adsorption isotherms and the rates of adsorption processes.     

Unconventional spinodal surface fluctuations on polymer films

We study the temporal growth pattern of surface fluctuations on a series of spinodally unstable polymer films where the instability can be adjusted with the film thickness, h0. For the most unstable film studied (whose /(h0 - h(sp))/h(sp)/ = 0.988; h(sp) is the thickness where the second derivative of the interfacial potential of the film equals zero), the growth rate function of the surface modes as a function of the wavevector fits well to the mean-field theory. When the film thickness is increased such that /(h0 - h(sp))/h(sp)/ < or = 0.977, the mean-field theory demonstrates marked disagreement with experiment, notwithstanding the provision of the known corrections from nonlinear effects and thermal noise. We show that the deviations arise from large-amplitude fluctuations induced by homogeneous nucleation, which are not considered in the conventional treatments.     

Effective surface tension for capillary fluctuations at the vapor-liquid interface

Thermal fluctuations of the surface of argon-like cluster are considered. Data obtained by molecular dynamics method are used to find effective surface tension for the capillary component of fluctuations, which characterizes the deviation of Fourier spectrum observed in numerical experiment from the spectrum of macroscopic capillary waves. The variational method was used to solve the problem. It is revealed that effective surface tension is close to constant value within a rather wide wavelength range. At the boundary of this range in the region of large wave numbers, the obtained value quickly tends to infinity, while spectral amplitudes decay thus corresponding to the theory proposed previously. The width of damping region is estimated for different temperatures and cluster sizes.     

Predicting the surface tension of liquid metals

The recent availability of more complete and reliable surface tension data for molten metals has led the authors to seek a general surface tension correlation which would include other fundamental properties of the molten metals. The relationship proposed has a thermodynamic basis and relates the surface tension of a molten metal to its heat of vaporiza3ion and ionic radius. Based on data reported by several investigators, the error in the calculated value of surface tension is less than ten per cent in the melting point region.     

Microscopic theory for interface fluctuations in binary liquid mixtures

Thermally excited capillary waves at fluid interfaces in binary liquid mixtures exhibit simultaneously both density and composition fluctuations. Based on a density functional theory for inhomogeneous binary liquid mixtures we derive an effective wavelength dependent Hamiltonian for fluid interfaces in these systems beyond the standard capillary-wave model. Explicit expressions are obtained for the surface tension, the bending rigidities, and the coupling constants of compositional capillary waves in terms of the profiles of the two number densities characterizing the mixture. These results lead to predictions for grazing-incidence x-ray scattering experiments at such interfaces.     

Voltage-expandable liquid crystal surface

Based on dielectrophoretic effect, we report a novel approach which can extensively spread a liquid crystal (LC) interface. With interdigitated striped electrodes, the droplets can be stretched along the striped electrode direction; while with zigzag interdigitated electrodes, the droplets can be further stretched sidewise. In our demonstration, the occupied area of a 1.9-mm-aperture LC droplet doped with 1.2 wt% black dye could be expanded over ～3.5× at 78 V(rms). The spreading and recovering times were measured to be ～0.39 s and ～0.75 s, respectively. The slower response time confirms the extreme expanding of the LC surface. The contrast ratio is over ～120?:?1 in transmissive mode. Color light switch was also demonstrated by spreading colored-dye doped LC droplets. The mechanical stability of the device was also evaluated. Liquid devices based on this cell structure have the advantages of good stability, simple operation and low power consumption. This work opens a new gateway for voltage controllable, polarization-insensitive, and broadband liquid photonic devices which may find numerous applications in switchable windows, variable optical attenuators, and displays.     

离子液体水合物反应液表面张力的研究

表面张力是衡量水合物动力学促进剂促进效果的主要参数,为了探究离子液体应用于水合物生成促进的可行性,实验合成了具有表面活性功能的离子液体[HMIPS]DBSA、[MIMPS]DBSA、[PIPS]DBSA和[PYPS]DBSA,并分别测定了在不同浓度及温度条件下的表面张力。结果表明:四种离子液体的最低表面张力相较于纯水均降低了一半以上,其中[MIMPS]DBSA的降幅最小;各离子液体的表面张力随着浓度的升高而降低并达到一定值,其中[MIMPS]DBSA的CMC浓度为700 ppm左右,其余三种离子液体的CMC浓度则均在900 ppm以上;此外,各离子液体的表面张力随着温度的升高而逐渐降低,但相较于浓度对其的影响,降幅要小得多。这说明浓度是影响水合物反应液表面张力的主要控制因素。可以发现所合成的离子液体与当前最好的促进剂SDS相比,有待于进一步优化。但离子液体的高度可设计性及生物可降解性给水合物促进剂的研发提供了广阔的发展空间,具有很好的发展前景。     

Thermal runaway in the thermal explosion of a liquid

To study the thermal explosion of liquids a low pressure autoclave has been built. The first stage of a thermal explosion, the thermal runaway, has been studied. Evaluation of the temperature-time history results in kinetic data. Comparison with other thermal methods shows that the reliability of the method is better than with DTA.Tertiary butylperoxybenzoate has been investigated in the temperature range of 330 K to 440 K. Decomposition starts with a short period of autocatalysis, up to a conversion of about 0.05. The subsequent decomposition can be described by a second order process in the first instance and by a first order process in the last resort. Induced decomposition occurs up to a conversion of about 0.95.

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Zusammenfassung Zur Untersuchung der thermischen Explosion von Flüssigkeiten wurde ein Niederdruckautoklav konstruiert. Es wurde das erste Stadium der thermischen Explosion, das thermische Durchgehen untersucht. Die Auswertung des Temperatur-Zeit-Geschehens ergibt kinetische Daten. Vergleiche mit anderen thermischen Methoden zeigen, daß diese Methode zuverlässiger als die DTA ist. Tertiär-Butylperoxybenzoat wurde im Temperaturbereich von 330–440 K untersucht. Die Zersetzung verläuft zu Beginn eine kurze Zeit bis zu einer Konversion von etwa 0.05 autokatalytisch. Die folgende Zersetzung kann in erster Linie als ein Prozeß zweiter Ordnung und letztlich als ein nach erster Ordnung verlaufender Prozeß angesehen werden. Eine induzierte Zersetzung erfolgt bis zu einer Konversion von 0.95.

     

Ab initio cluster calculations of silica surface sites

Silica surface sites, which can be formed in cleavage processes, and their hydrolyzed counterparts are investigated with ab initio cluster calculations. Natural Bond Orbital (NBO) theory is used to characterize bonding around silica surface sites. Higher energy lone pairs of electrons on oxygen atoms either hyperconjugate to vicinal silanol/siloxane antibonding orbitals or backdonate electron density via donor–acceptor π-type bonding with participation of pd or p hybrids on silicon atoms. Upon substitution of hydroxyl groups of orthosilicic acid with silica monomers the strength of siloxane and silanol Si–O bonding increases as energies of bonding orbitals and contributions from p-orbitals decrease. Silanone sites and a complementary pair of silyl/siloxy radical sites are found to be the most stable geminal and single non-hydrolyzed sites, respectively. Atomic charges based on natural wavefunctions and on fitting to electrostatic potential, and characteristic bands of IR spectra associated with siloxane and silanol stretching vibrations of silica surface sites are reported.     

Influence of the ionic liquid/gas surface on ionic liquid chemistry

Applications such as gas storage, gas separation, NP synthesis and supported ionic liquid phase catalysis depend upon the interaction of different species with the ionic liquid/gas surface. Consequently, these applications cannot proceed to the full extent of their potential without a profound understanding of the surface structure and properties. As a whole, this perspective contains more questions than answers, which demonstrates the current state of the field. Throughout this perspective, crucial questions are posed and a roadmap is proposed to answer these questions. A critical analysis is made of the field of ionic liquid/gas surface structure and properties, and a number of design rules are mined. The effects of ionic additives on the ionic liquid/gas surface structure are presented. A possible driving force for surface formation is discussed that has, to the best of my knowledge, not been postulated in the literature to date. This driving force suggests that for systems composed solely of ions, the rules for surface formation of dilute electrolytes do not apply. The interaction of neutral additives with the ionic liquid/gas surface is discussed. Particular attention is focussed upon H(2)O and CO(2), vital additives for many applications of ionic liquids. Correlations between ionic liquid/gas surface structure and properties, ionic liquid surfaces plus additives, and ionic liquid applications are given.     

Measurement of the surface tension of liquid marbles

The capillary rise and Wilhelmy plate methods have been used to study the "surface tension" of water marbles encapsulated with polytetrafluoroethylene (PTFE) powders of 1-, 35-, and 100-μm particle size. With the capillary rise technique, a glass capillary tube was inserted into a water marble to measure the capillary rise of the water. The Laplace pressure exerted by the water marble was directly measured by comparing the heights of the capillary rise from the marble and from a flat water surface in a beaker. An equation based on Marmur's model was proposed to calculate the water marble surface tension. This method does not require the water contact angle with the supporting solid surface to be considered; it is therefore a simple but efficient method for determining liquid marble surface tension. The Wilhelmy method was used to measure the surface tension of a flat water surface covered by PTFE powder. This method offers a new angle for investigating liquid marble shell properties. A discussion on the nature and the realistic magnitude of liquid marble surface tension is offered.     

Study of transient thermal surface processes

Summary The method of nanosecond time-resolved photothermal displacement spectroscopy in combination with time-resolved light reflectivity measurements has been used to study aluminum and stainless steel substrates with sputter deposited Au and Sn films. The results show, that this method can be used as a non-contacting surface thermometer. In addition, a strong correlation between signal decay and film thickness could be observed.

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Untersuchung transienter thermischer Oberflächenprozesse