Assessment of the relative error in the automation task by sessile drop method

Abstract

Assessment of the relative error in the sessile drop method automation. Further development of the sessile drop method is directly related to the development of new techniques and specially developed algorithms enabling automatic computer calculation of surface properties. The sessile drop method mathematical apparatus improvement, drop circuit equation transformation to a form suitable for working, the drop surface calculation method automation, analysis of relative errors in the calculation of surface tension are relevant and are important in experimental determinations. The surface tension measurement relative error, as well as the error caused by the drop ellipsoidness in the plan were determined in the task of the sessile drop automation. It should be noted that if the drop maximum diameter (l) is big or if the ratio of l to the drop height above the equatorial diameter(h) is big, the relative error in the measurement of surface tension by sessile drop method does not depend much on the equatorial diameter of the drop and ellipsoidness of the drop. In this case, the accuracy of determination of the surface tension varies from 1,0 to 0,5%. At lower values the drop ellipsoidness begins to affect the relative error of surface tension (from 1,2 to 0,8%), but in this case the drop ellipsoidness is less. Therefore, in subsequent experiments, we used larger drops. On the basis of the assessment of the relative error in determining the liquid surface tension by sessile drop method caused by drop ellipsoidness in the plan, the tables showing the limits of the drop parameters (h and l) measurement necessary accuracy to get the overall relative error have been made up. Previously, the surface tension used to be calculated with the relative error in the range of 2-3%