Biomedical subjects
Publications and source records attributed to Gerard H Wegdam.
This special issue of Applied Optics contains research papers on photon correlation and scattering, many of which were presented at the OSA Topical Meeting that was held 16-18 August 2004.
Measuring the surface response function of a fluid allows us to ascertain many of its properties. Simplified surface response functions are presented for several interface conditions, including (a) a thin-film between two fluids of infinite extent, (b) the newly derived fluid-fluid interface between finite boundaries, and (c) the traditional fluid-fluid interface between infinite boundaries. The finite-boundary derivation indicates that wall effects are very short range. This portends that the effects of external vibrations, which traditionally make this measurement challenging, can be mitigated by scattering from thin fluid layers.
We study droplet coalescence in a molecular system with a variable viscosity and a colloid-polymer mixture with an ultralow surface tension. When either the viscosity is large or the surface tension is small enough, we observe that the opening of the liquid bridge initially proceeds at a constant speed set by the capillary velocity. In the first system we show that inertial effects become dominant at a Reynolds number of about 1.5+/- 0.5 and the neck then grows as the square root of time. In the second system we show that decreasing the surface tension by a factor of 10(5) opens the way to a more complete understanding of the hydrodynamics involved.
We study the thickness of wetting layers in the binary-liquid mixture cyclohexane methanol. Far from the bulk critical point, the wetting layer thickness is independent of temperature, resulting from the competition between van der Waals and gravitational forces. Upon approaching the bulk critical temperature [t=(T(c)-T)/T(c)-->0], we observe that the wetting layer thickness diverges as t(-beta) with effective critical exponent beta=0.23+/-0.06. This is characteristic of a broad, intermediate scaling regime for the crossover from van der Waals wetting to critical scaling. We predict beta=beta/3 approximately 0.11, with beta the usual bulk-order parameter critical exponent, showing a small but significant difference with experiment.