COARSENING OF 3-DIMENSIONAL DROPLETS BY 2-DIMENSIONAL DIFFUSION .1. EXPERIMENT

An experimental study of diffusional coarsening, or Ostwald ripening, in a liquid-liquid two-phase system is described. An experiment perfor med at its isopycnic point, 42-degrees-C, allowed observations for the long times required to investigate coarsening. A holographic techniqu e was instrumental in this work. Holograms taken in situ permit invest igation of details regarding both the influence of local environmental conditions on individual droplet size histories and measurement of gl obal averages. This study utilized a 100 mum pathlength test cell. The discrete phase was nucleated on one wall of the cell. This configurat ion resembles island formation in thin film growth. Observation of Ost wald ripening over a period of 1 x 10(7) s (approximately 4 mo.) revea ls that droplet number decays ast-0.733 and the average radius increas es as t-0.247, in the asymptotic limit. This shows good agreement with theoretical predictions for diffusional growth of spherical caps on a two-dimensional substrate which is a valid approximation for the geom etry of this experiment. Part I of this paper describes the experiment al results. Part II discusses a numerical model for droplet growth in a comparison with the experimental results.