Biomedical subjects

VB Fainerman

Publications and source records attributed to VB Fainerman.

6 recordsLinked to original sources

PubMed2000

Phase Transition Processes in Surfactant Adsorption Layers.

Adsorption data in the form of surface tension vs bulk concentration isotherms having strong changes in the slope have often been discussed in the literature in terms of phase transitions in the adsorption layer. It will be shown thermodynamically that these apparent kink points in the isotherms are unreal. A phase transition would cause a completely opposite change in the isotherm. Experimental surface tension data for sodium octanoate and dodecyl ammonium chloride obtained from the literature are reinterpreted on the basis of the Frumkin and reorientation isotherms. Copyright 2000 Academic Press.

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PubMed2000

Effect of the Nonstationary Viscous Flow in the Capillary on Oscillating Bubble and Oscillating Drop Measurements.

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.

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PubMed2000

Bubble Oscillations in a Closed Cell.

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.

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PubMed2000

Resonance Behavior of Oscillating Bubbles.

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.

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PubMed1998

Lifetime Calculations Relative to Maximum Bubble Pressure Measurements

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

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PubMed1997

Dynamic Adsorption Behavior of Polyethylene Glycol Octylphenyl Ethers at the Water/Oil Interface Studied by a Dynamic Drop Volume Technique

The dynamic drop volume technique has been used to measure the dynamic interfacial tensions of nonionic surfactants (Triton X-45, X-100, X-165, and X-405) at the water/nonane and water/butylbenzene interface. The measurements were performed under the conditions of equilibrium distribution of the surfactant between the two liquid phases established after a sufficiently high number of aqueous solution drops have been formed within a small volume of the oil phase under study. The diffusion kinetics model for the description of the adsorption at the surface of growing drops involves equilibrium surfactant distribution and adsorption from both adjacent phases. Two orientational states of adsorbed surfactant molecule at the interface were assumed in agreement with recently published results at the water/air interface. Good agreement between this theory and the experimental data was obtained.

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