Implementation and examination of a new drop shape analysis algorithm to measure contact angle and surface tension from the diameters of two sessile drops

The performance of a new algorithm developed to measure contact angle and s urface tension of sessile drops is examined. To calculate the contact angle and surface tension, the new algorithm (ADSA-TD) requires the radius (cont act or equatorial) and volume of two sessile drops of different sizes that are placed on the same surface. Initially, the algorithm was tested using s ynthetic drops (synthetic or theoretical drops are produced by numerical in tegration of the Laplace equation). The radii and volumes of synthetic drop s were used as ADSA-TD inputs. The calculated contact angle (theta) and sur face tension (gamma) by ADSA-TD matched perfectly the assumed values of the ta and gamma used to produce the synthetic drops, confirming theoretically the validity of the new algorithm. In the next step, the sensitivity of the algorithm to input errors was examined. It was shown experimentally that b oth calculated contact angle and surface tension are affected by the errors in volume and radius. Besides the error in input values, it was shown that the size difference between the paired drops and the differences in their contact angles would affect the output of ADSA-TD. As it turns out, the cal culated surface tension is so sensitive to the above factors that ADSA-TD d oes not appear to be promising as a surface tension measurement technique. However, ADSA-TD produced acceptable contact angle values as compared to me asurements made by other proven techniques such as axisymmetric drop shape analysis-profile. Thus, ADSA-TD may be of interest as a contact angle measu rement technique which does not require the liquid surface tension as input . (C) 2000 Elsevier Science B.V. All rights reserved.