A technique for the quantitative investigation of the wetting dynamics and droplet deposition or removal on fibres is discussed. The method presented uses light from a laser diode, which is guided down a textile fibre. Light transmission losses are dependent on the type and extent of droplet or particle coverage of the fibre surface. Changes in light transmission can be induced by deposition of droplets of the dispersed phase of an emulsion, by the removal of particles or droplets from the fibre surface, or from changes in the refractive index of the liquid in which the fibre is immersed. These changes in light transmission intensity are monitored in real-time using a lock-in amplifier principle. Experiments on coiled PMMA optical fibers of diameters 250 gm and for straight polyester fibres of diameters 80 pm and 800 pm immersed in a range of oils and in an emulsion system of decane dispersed in 15 mM dodecyltrimethylammonium bromide (DTAB) are presented. For the first time, we show that the light-guiding technique can be applied to straight lengths of textile-type fibers and to smaller fiber diameters of around 50-80 mum. The results show that changes in the wetting of a fiber surface by liquids and droplets of oils can be monitored in real-time. These results are discussed in terms of droplet shape, extent of coverage and droplet kinetics.
|Title of host publication
|Contact angle, wettability and adhesion
|K. L. Mittal
|Place of Publication
|Published - 2002