A NON-LINEAR REGRESSION METHOD FOR CALCULATING SURFACE TENSION AND CONTACT ANGLE FROM SHAPE OF A SESSILE DROP

A non-linear regression calculation procedure has been developed which permits calculation of surface tension and contact angle for any sessile drop shape with a contact angle greater than zero. Initial estimates of the drop shape and size parameters (β, b) are needed to start the calculation. Many points on the drop surface are measured, and a minimum sum of squares fit between the measured and calculated coordinates is obtained. No special attention must be given to any one point as is necessary when using the tables of Bashforth and Adams. Accuracy is improved by a factor of two compared to the classical calculation procedure. A computer program has been written to perform all necessary operations. Surface tension and contact angle data for the lead-bismuth eutectic on 316 stainless steel are reported. © 1968.