Visualization of ripples on the surface of a rising bubble through an immiscible oil/water interface

Abstract  

This paper visually demonstrates instantaneous behavior of ripples propagating on the surface of a rising bubble through an oil/water interface. This experiment uses potassium iodide (KI) 31 wt% as refractive index matching material which makes the water phase invisible. As a result, the generated micro droplets, which are shown in the preceding paper (Uemura et al. in Europhys Lett 92:34004, 2010), cannot be visible in the present results, and therefore the droplets are positively confirmed to be made of water.     

Focusing of an oscillating shock wave emitted by a toroidal bubble cloud

An analysis of pressure-field dynamics is performed for an axially symmetric problem of interaction between a shock wave and a “free” bubble system (toroidal cluster) giving rise to a steady oscillating shock wave. The results of a numerical study of near-axis wave structure are presented for a focusing shock wave emitted by a bubble cluster. It is shown that the wave reflected from the axis has irregular structure. The Mach disk developing on the axis has a core of finite thickness with a nonuniform radial pressure distribution. The evolution of the Mach-disk core is analyzed, and the maximum pressure in the core is computed as a function of the gas volume fraction in the cluster. The effect of geometric parameters of the toroidal bubble cloud on the cumulative effect is examined.     

Formation of dispersive hybrid bands at an organic-metal interface

An electronic band with quasi-one-dimensional dispersion is found at the interface between a monolayer of a charge-transfer complex (TTF-TCNQ) and a Au(111) surface. Combined local spectroscopy and numerical calculations show that the band results from a complex mixing of metal and molecular states. The molecular layer folds the underlying metal states and mixes with them selectively, through the TTF component, giving rise to anisotropic hybrid bands. Our results suggest that, by tuning the components of such molecular layers, the dimensionality and dispersion of organic-metal interface states can be engineered.     

Ionic liquids at the air/water interface

We present molecular dynamics experiments of Langmuir monolayers of iodide and chloride salts of 1-octyl-3-methylimidazolium adsorbed at water/air interfaces, covering a concentration range that spans from a dilute regime up to the experimental surface saturation for both systems. For the chloride case we observed a propensity to form monolayers with nearly equal surface concentration of both cations and anions; whereas for the iodide system, the more marked propensity to surface solvation of the anionic species leads to the appearance of quasi-double-layered structures. At the surface, the imidazolium rings remain in contact with the aqueous substrate, with a wide variety of orientations with respect to the surface normal direction. The global tilt of the hydrophobic tail of the cations was found to be θ_tl ~ 40°and 50°, for the chloride and iodide salts, respectively. Polarization fluctuations of the interface are analyzed in terms of those describing charge distributions of the adsorbed species and the electrical response of the solvent as well. The characteristics of the local densities for the ionic species at the interface provide arguments for the microscopic interpretation of the differences observed in scattering experiments on the dependence of the surface tension with the surfactant concentration.     

Structure of monolayers at the air/water interface

A perturbation theory based on the random phase approximation with a hard disc reference fluid is used to generate substantially analytic results for the form of the small angle scattering from model two dimensional monolayer systems. When applied to systems with a conventional 12-6 Lennard-Jones interaction potential the theory yields results in good agreement with more sophisticated theories and computer simulation. The method is also used for the 12-5 Lennard-Jones interaction potential that characterizes the in-plane interactions of lipid molecules at the air/water interface and gives qualitative agreement with experimental studies. The inclusion of weak dipolar interactions between the monolayer particles is seen to supress any liquid-vapour phase transition.     

Formation of a honeycomb texture for multicrystalline silicon solar cells using an inkjetted mask

An effective way to reduce the reflection of a multicrystalline solar cell is the use of a honeycomb structure, which can be generated by etching a mask isotropically. In this Letter, a directly printed hexagonal inkjet mask is presented. It results in a honeycomb texture with well developed and defined etch pits at an average distance of 50.1 μm and a weighted reflection of 18.4%. The major advantage of this mask is that the masking process is simple and that it has the potential of being fast and having low costs.

     

Ferrocene partition calculation in a biodiesel/water interface using electrochemical methods

This work is a continuation of previous studies concerning the behaviour of ferrocene in a mixture of two insoluble liquids. In this paper, the system reached partition equilibrium after approximately 175 min. Electroanalytical studies were executed, and a high reproducibility was observed in a range of concentrations from 2 to 14?×?10^?5 mol L^?1 of ferrocene that escaped from the oil to the aqueous phase. Because ferrocene most likely occurs only in the monomeric form in both the oil and aqueous phases, it was possible to predict a partition coefficient (log P_(oil/water)) of ferrocene of approximately 2.4.     

Influence of an interface layer on the effective coupling at a ferromagnet/antiferromagnet interface

We examine the exchange anisotropy induced at a ferromagnetic/antiferromagnetic interface when an antiferromagnetic interface layer exists. We show that competition between exchange couplings in the interface layer can result in a ferrimagnetic-like compensation point. This leads to a reversal of the effective field acting on the ferromagnet, and a consequent sign change of the exchange bias for temperatures near the Néel temperature of the antiferromagnet. A surprising result is the sensitive dependence of the compensation point on exchange interactions. Even minute modifications of the exchange interactions near the interface can result in a reversal of the effective field, provided certain conditions are met.     

Rheology of self-assembled monolayers on solid-liquid interface oscillating at MHz frequency

The rheology properties (viscosity and elasticity) of chemisorbed soft matters on a solid-liquid interface oscillating at MHz were investigated using a quartz crystal microbalance (QCM). As a chemisorbed soft matter, we employed the self-assembled monolayers (SAMs) of mercapto oligo(ethylene oxide) methyl ethers, HS(CH₂CH₂O)_nCH₃ (n?=?5, 11, 12, 19, 27, 35 and 43), where those molecular weights had unity. The systematical analyses on the basis of the Voight model revealed the relationships of $\eta \propto M_n^{0.180}$ and $\mu \propto M_n^{0.344}$, where η and μ are the viscosity and elasticity of the SAM, and M_n is the molecular weight of HS(CH₂CH₂O)_nCH₃. As a result, we found that the SAM consisting of the oligomer followed the formula of polymer.     

Transformation of detonation waves at the interface between bubble media

The passage of detonation waves through the interface between bubble media is studied experimentally. Data are obtained for the structure, velocity, and pressure of an incident detonation wave and a wave transmitted through the interface.     

Following transient phases at the air/water interface

A fast pixel array detector, the Pilatus 100 K, has been used in studies of organic monolayers at the air-water interface. The area sensitivity and large dynamic range of the detector, in combination with a “one dimensional pinhole” geometry, make it possible to observe surface processes which were inaccessible to the previous generation of experimental techniques. Especially, time dependent phenomena acting on time scales ranging from seconds to minutes can be observed and analyzed.     

Theoretical analysis of interaction between a particle and an oscillating bubble driven by ultrasound waves in liquid

A theoretical model is developed to describe the interaction of a particle and an oscillating bubble at arbitrary separation between them. The derivation of the model is based on the multipole expansion of the particle and bubble velocity potentials and the use of Lagrangian mechanics. The model consists of three coupled ordinary differential equations. One of them accounts for the pulsation of the bubble and the other two describe the translation of the bubble and particle in an infinite, incompressible liquid. The model here is accurate to order 1/d~(10), where d is the distance between the centers of the particle and bubble. The effects of the size and density of the particle are investigated, namely, the interaction between the particle and bubble changes from repulsion to attraction with the increment of the particle density, and the increment of the particle size makes the interaction between the particle and bubble stronger. It is demonstrated that the driving frequency and acoustic pressure amplitude can affect the interaction of the particle and bubble. It is shown that the correct modeling of the translational dynamics of the bubble and particle at small separation distances requires terms accurate up to the tenth order.     

Formation of a passivating film at the lithium-PEO-LiCF3SO3 interface

The formation of a passivating film on lithium electrodes is demonstrated using ac impedance analysis. The film is formed by an electrochemical reaction between the lithium electrode and the electrolyte, which consists of poly (ethylene oxide) and LiCF₃SO₃. Effects of the salt concentration in the electrolyte and temperature on the nature and conductivity of such films are described. Data obtained from the literature for equivalent systems was interpreted according to the proposed film formation mechanism. The rate-determining step in the dissolution or deposition process of the lithium may, in some cases, be defined by the interphase film.     

Equation of state for a coarse-grained DPPC monolayer at the air/water interface

Pulmonary surfactant, a complex mixture of phospholipids and proteins, secreted by the type II epithelial cells in the lungs, is crucial to reducing the effort required for breathing. A lack of adequate amounts of pulmonary surfactant in underdeveloped lungs of premature infants results in infant respiratory distress syndrome (RDS). Surfactant replacement therapy (SRT) is the approved method of mitigating the effects of RDS. The development of new SRT regimens requires a fundamental understanding of the links between surfactant biochemistry and functionality. We use a coarse-grained (CG) model to predict the surface pressure–surface concentration relationship (equation of state) for pure DPPC, which is a major component of endogenous and synthetic pulmonary surfactant mixtures. We show that the model can be efficiently used to predict the equation of state in excellent agreement with experimental results. We also study the structure of the monolayer as a function of the surface tension of the system. We show that a decrease in the applied surface tension results in an increase in order in the head group region and a decrease in order in the tail region of DPPC. This technique may be useful in the prediction of equations of state for surfactant replacements.     

On Rayleigh's model of a freely oscillating bubble. III. Limits

In the paper the range of bubble sizes for which the effects of gravity, surface tension, viscosity, and heat conduction can be neglected is determined. The equations of motion for macrobubbles and microbubbles are also presented.