John C. Berg | PubMed Health

PubMed2001

Diffusion-Controlled Adsorption at the Liquid-Air Interface: The Long-Time Limit.

The applicability of the Hansen and Joos long-time limits for the dynamic surface tension of solutions is investigated by regressing diffusion coefficients from numerical solutions to the Ward and Tordai equation. The Hansen limit is found to correctly describe the dynamic surface tension evolutions at long times. However, both the surfactant concentration and the adsorption time affect the accuracy of the long-time limit. The study also indicates that, because the reduction in surface tension (at long times) may be smaller than can be measured by current tensiometry methods, the application of the Hansen limit to long-time data may not always be feasible. Copyright 2001 Academic Press.

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PubMed2001

Quantitative Analysis of Fluid Interface-Atomic Force Microscopy.

Net repulsive interactions between n-hexadecane and a poly-styrene microsphere in aqueous solutions are measured with atomic force microscopy and interpreted using the augmented Young-Laplace equation. The true separation between probe and fluid interface is implicitly computed from the force-distance data, providing a more accurate description of drop or bubble deformation. Experiments and theoretical arguments demonstrate that a fluid interface stiffens with increasing deformation and is not accurately treated as a Hookean spring. The unexpected stability of the draining aqueous film between hydrophobic bodies in electrolyte solutions is explained primarily by the deformation of the oil drop in response to the applied normal force, as well as the increased hydrodynamic resistance due to the increased drainage area. Copyright 2001 Academic Press.

Journal Article↗