THE IMBEDDED DISK RETRACTION METHOD FOR MEASUREMENT OF INTERFACIAL-TENSION BETWEEN POLYMER MELTS

A method for measuring interfacial tension of high viscosity polymer m elts a? elevated temperatures is described. The method involves the tr acking of the shape evolution of a disk of one material imbedded in a second one. This makes it possible to determine the interfacial tensio n over a relatively short time period. The technique of preparing the samples makes it possible to measure on practically any combination of polymer melts without restrictions on viscosities and melting tempera ture, as long as one of the materials is transparent in the molten sta te The retraction of the disk is observed by using a microscope with a high resolution video camera. The camera is connected to a video fram e grabber in a personal computer which is programmed to collect images with preselected time intervals. Data of the retraction is acquired b y using an image analysis software, measuring the average radius of th e disk. The driving force for the shape evolution is interfacial tensi on and it is balanced by viscous forces. The analysis of the retractio n process is done analytically with a simplified one-dimensional model . The model has been compared to experiments with the system PS/PMMA a l 210 degrees C, covering viscosity ratios over a range of six decades and five different molecular weight values of PS. It is shown that in terfacial tension can be determined over the whole range and a value o f 1.1 +/- 0.2 mN/m was obtained for all samples.