AN AUTOMATED DROP SHAPE APPARATUS AND THE SURFACE-TENSION OF PURE WATER

Herein is described the design and operation of an instrument for the determination of surface or interfacial tensions based upon the drop shape technique. In this design, direct observation of the drop image by a sophisticated computer-based image acquisition system eliminates the tedium of manual analysis. High speed drop profile acquisition, obtaining up to 50 profiles per minute, permits the investigation of physio-chemical systems which display aging. For systems of time invariant tension, the use of high speed image analysis makes the statistical reduction of errors practical. A thorough analysis of the effect of error in the determination of each instrument parameter on the determination of the tension is presented, including a brief comparison of edge detection methods. The apparatus is capable of operating at pressures up to 10 000 psig at 250°C, though rarely is it used at conditions in excess of 5000 psig and 100°C. Examples of data obtained at elevated pressures are presented. Finally, the surface tension of pure water is determined at 20 and 25°C and comparison is made to literature data. The accuracy of the instrument is estimated to be approximately ± 0.05% for the determination of the surface tension of water. Furthermore, based upon the data presented, and comparison to the literature, it is concluded that there is insufficient evidence to support the contention that edge corrections are required for the Wilhelmy plate method. © 1990.