Design and performance of a dynamic interfacial tension spinning-drop tensiometer

Two standard spinning-drop tensiometers (SDT) have been modified by the addition of video equipment and an interface to a personal computer. (Since two tensiometers were available in our laboratory, both were modified. There is no reason why the system can't be set up with only one tensiometer). The computer has been fitted with a special video board and a menu-driven image enhancement and analysis program. A date-time generator accurately measures the age of the aqueous-organic interface. The operator can record droplet images for later analysis. Alternatively, the video board can `capture' a droplet image for immediate analysis. Analysis usually consists of measurement of drop length and drop width. However, interesting emulsification and solubilization phenomena can also be recorded for later study. These modifications greatly enhance the capabilities of the SDT. This new system is referred to as the tensiometer image analysis apparatus. Similar procedures can be used with air droplets to determine surface tension values. The operator can determine equilibrium interfacial tension (IFT) values with greater accuracy and in less time than is possible with the conventional SDT. Rapidly changing IFT values can be accurately determined at intervals of as little as one second. These capabilities have been used in studies of detergency, deresination of wood pulp, and deinking of waste paper. The video capture and analysis capabilities of this system are also useful in other applications.