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ABSTRACT: The dynamic behavior of a bubble or drop oscillating at the tip of a capillary immersed in a surfactant solution is considered. The pressure variation in the cell and the nonstationary flow in the capillary are taken into account. The amplitude- and phase-frequency characteristics of the system are obtained, which contain information about the relaxation processes at the interface and in the bulk phases. Their dependency on the system geometry, the bulk properties of contacting media, and the viscoelastic properties of the interface is analyzed. Copyright 2000 Academic Press.
Journal of Colloid and Interface Science 01/2001; 232(1):25-32. · 3.07 Impact Factor
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ABSTRACT: A theoretical analysis is given to describe the behavior of an oscillating bubble in a closed measuring cell taking into account the finite liquid compressibility and the cell deformation. The results show that the behavior of a closed liquid cell can differ significantly from that of open cells. For example, under the same conditions two stable meniscus positions can be obtained in a closed cell. In a closed cell a meniscus larger than a hemisphere can be stable even when the gas compartment is open, while in an open cell such a meniscus is always unstable. For closed cells the meniscus can jump between the two equilibrium positions either randomly or under the influence of regular factors, such as external pressure, temperature, and surface tension changes. Relationships are obtained for the description of the pressure response on external harmonic perturbations which make it possible to determine the complex dilatational elasticity as a function of frequency. It is shown that the measured signal can depend on the cell properties, which should be taken into account in the interpretation of experimental data. Copyright 2000 Academic Press.
Journal of Colloid and Interface Science 05/2000; 224(2):245-254. · 3.07 Impact Factor
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ABSTRACT: A convolution-type equation has been derived to describe the behavior of a bubble under periodical pressure oscillations. This equation holds for a diffusion-controlled adsorption mechanism and small disturbances of the equilibrium state, and it describes both the established and transition regimes of bubble oscillation. Systems free of any surfactant and in the presence of a surfactant are considered. The results obtained allow all aspects of surfactant influence on the bubble oscillation resonance to be analyzed. The sharp increase in the bubble oscillation amplitude may result in bubble detachments, even at rather low harmonic pressure oscillations. The presence of surfactant can result in a depression of the resonance amplitudes. Copyright 2000 Academic Press.
Journal of Colloid and Interface Science 05/2000; 224(1):47-55. · 3.07 Impact Factor
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ABSTRACT: Acoustic spectroscopy was used to monitor the droplet size distribution in a classic three component system of heptane, water, and aerosol-OT (AOT). The size of the reverse microemulsion drops was varied by changing the molar ratio of water to AOT surfactant. The acoustic results for this transparent microemulsion were found to be in close agreement with literature results obtained with small angle neutron scattering and small angle X-ray scattering. The system was investigated well into the turbid region where microemulsion changes to macroemulsion. The droplet size distribution was found to shift to a bimodal form due to this transition. Copyright 1999 Academic Press.
Journal of Colloid and Interface Science 09/1999; 216(2):303-308. · 3.07 Impact Factor
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ABSTRACT: A relation between the dynamic electrophoretic mobility of spherical colloidal particles in a concentrated suspension and the colloid vibration potential (CVP) generated in the suspension by a sound wave is obtained from the analogy with the corresponding Onsager relation between electrophoretic mobility and sedimentation potential in concentrated suspensions previously derived on the basis of Kuwabara's cell model. The obtained expression for CVP is applicable to the case where the particle zeta potential is low, the particle relative permittivity is very small, and the overlapping of the electrical double layers of adjacent particles is negligible. It is found that CVP shows much stronger dependence on the particle volume fraction φ than predicted from the φ dependence of the dynamic electrophoretic mobility. It is also suggested that the same relation holds between the electrokinetic sonic amplitude of a concentrated suspension of spherical colloidal particles and the dynamic electrophoretic mobility. Copyright 1999 Academic Press.
Journal of Colloid and Interface Science 05/1999; 212(2):449-452. · 3.07 Impact Factor
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ABSTRACT: The theoretical description of maximum bubble pressure experiments needs to consider inertial properties of the gas and liquid. On the basis of an analysis of the time-dependent pressure gradient inside the capillary, bubble lifetime and bubble deadtime are estimated. Numerical calculations of the derived model equations yield different importent dependencies which allow us to better understand bubble pressure experiments at high bubble frequencies: gas flow velocity as function of time, bubble radius as function of time, pressure drop within the capillary as function of time, and bubble lifetime as function of the initial gas velocity. Copyright 1998 Academic Press. Copyright 1998Academic Press
Journal of Colloid and Interface Science 02/1998; 197(2):383-90. · 3.07 Impact Factor
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ABSTRACT: The collection efficiency of single bubbles rising through a very dilute pulp of hydrophobized quartz particles has been determined. Measurements have been performed under conditions in which the bubble surface is mobile, as a function of electrolyte concentration, particle diameter (7 to 70 &mgr;m), bubble diameter (0.77 x 10(-3) to 1.52 x 10(-3) m), and particle advancing water contact angle. Situations in which the product of attachment and stability efficiency is at its maximum value have been identified, permitting a stringent, critical test of collision theory to be performed. A collision theory has been developed which accounts for the influence of positive and negative inertial forces in the case of bubbles with mobile surfaces. The approach considers only long-range hydrodynamic interactions under conditions where short-range interactions are strongly suppressed (i.e., high particle contact angle and high electrolyte concentrations) and attachment occurs at first collision. In this instance, good agreement between theory and experiment is achieved for particle diameters between 7 and 60 &mgr;m and Stokes numbers up to 0.27. The analytical equation developed is termed the generalized Sutherland equation (GSE). Copyright 1998 Academic Press. Copyright 1998Academic Press
Journal of Colloid and Interface Science 01/1998; 197(2):275-92. · 3.07 Impact Factor
